Proceedings of the Third American Conference on Human Vibration, June 1-4

McDowell, T. W.

Warren, C

Welcome, D. E.

Dong, R. G.

LABORATORY MEASUREMENT OF RIVETING HAMMER VIBRATION    TW McDowell, C Warren, DE Welcome, RG Dong  Health Effects Laboratory Division, National Institute for Occupational Safety and Health (NIOSH), Morgantown, WV, USA  Introduction  As part of a collaboration with the United States Air Force (USAF) 72nd Aerospace Medicine Squadron (72 AMDS), Bioenvironmental Engineering Flight at Tinker Air Force Base (AFB) in Oklahoma, the Physical Effects Research Team (PERT) of the National Institute for Occupational Safety & Health (NIOSH) is studying vibration emissions of riveting hammers used in aircraft assembly and maintenance. The PERT team is involved with the ongoing systematic development of new methodologies for evaluating hand-transmitted vibration exposures and effects. Among those efforts, PERT has completed studies on chipping hammers,1 impact wrenches,2 and other powered hand tools. Therefore, an examination of riveting hammer vibrations fits in well with PERT’s mission.  In this initial study, ten riveting hammers were evaluated in the NIOSH laboratory. Weighted and unweighted vibration data were collected at the tool handles and at the tool operators’ ring fingers. The tools were rank-ordered by vibration magnitude for each measurement method. The rank orders generated by the different vibration measurement criteria were then compared.      Methods  The percussive tool test setup used in this study was that specified in the ISO standard for the measurement of vibrations at the handles of chipping hammers and riveting hammers (ISO 8662-2, 1992).3  The test apparatus features an energy absorber that comprises a steel tube filled with hardened steel balls. (See Fig. 1.) When the percussive tool operates, the energy absorber provides a dynamic reaction force which enables stable and reproducible tool action.     Ten brand-new riveting hammers were evaluated in this study.  Piezoelectric triaxial accelerometers were used to measure the vibrations.  Accelerometers were installed on mounting blocks and secured to the tool handles with hose clamps. An adapter-mounted accelerometer was also secured to the operator’s ring finger with a Velcro strap.  The accelerometer mounts are depicted in Fig. 1. Six healthy males served as tool operators. Each operator stood on a force measurement plate/platform and applied a downward push force on the Fig.  1. Tools were operated against the energy absorber specified in ISO 8662-2.  Vibration data were collected at the tool handle and at the operator’s ring finger. 3rd ACHV     Iowa City, Iowa     1-4 June 2010 47tool handle. The tool operators were instructed to apply a feed force of 100 ± 20 N. A computer monitor displayed a full-screen force strip chart so that the tool operator could monitor and control the feed force during tool operation. The tool operators completed five consecutive 10-second trials with each tool. Tool order was randomized among the operators. Tool handle and finger vibration data were collected simultaneously. The vibration data were expressed as the root-mean-square (r.m.s.) values of the accelerations in the 1/3-octave frequency bands, with center frequencies from 10 to 1,250 Hz.  The ‘total’ values of the r.m.s. accelerations were computed with and without frequency weighting per the ISO 5349-1 standard.4    Results, Discussion, and Conclusions  The rank-orders of the ten tools for each of the four vibration measurement criteria are presented in Table 1. The rankings are based on the averages of the six tool operators. Tools E and A were consistently ranked with the lowest vibration regardless of tool operator, measurement location (tool or finger), or acceleration weighting (ISO-weighted or unweighted), and Tools H and D were among the highest vibration. The rankings of the other tools were somewhat inconsistent among the ranking criteria. However, it appears that any of the four ranking criteria would be acceptable for initial tool screening. Particularly, the rankings based on weighted accelerations measured on the tool and finger were fairly consistent. Tool selection should not be based solely on laboratory vibration measurements. Field studies should be conducted to verify or refine tool selection. Other criteria such as productivity, tool versatility, worker acceptance, initial cost, and maintenance costs should also be considered during tool selection. It is emphasized that ISO 8662 laboratory tool tests are designed for screening tools; these standards are not designed to measure the acceleration values for risk assessment. Therefore, acceleration values obtained via such laboratory testing should not be used for assessing workplace vibration exposures.   References 1. Dong, R.G., McDowell, T.W., Welcome, D.E., Warren, C. and Schopper, A.W. (2004). An evaluation of the standardized chipping hammer test specified in ISO 8662-2, 1992. Ann Occup Hyg. 48, 39-49. 2. McDowell, T.W., Marcotte, P., Warren, C., Welcome, D.E. and Dong, R.G. (2009). Comparing three methods for evaluating impact wrench vibration emissions. Ann Occup Hyg. 53, 617-626. 3. ISO. (1992). ISO 8662-2, 1992: Hand-held portable power tools -- measurement of vibrations at the handle -- part 2: Chipping hammers and riveting hammers. International Organization for Standardization, Geneva, Switzerland. 4. ISO. (2001). ISO 5349-1: Mechanical vibration -- measurement and evaluation of human exposure to hand-transmitted vibration -- part 1: General requirements. International Organization for Standardization, Geneva, Switzerland. Table 1.  The rank orders of the ten tools from 1 (lowest) to 10 (highest) vibration by each of the four ranking criteria.                  RankISO-Weighted Tool Vib.Unweighted Tool Vib.ISO-Weighted Finger Vib.Unweighted Finger Vib.1 E E E A2 A A A E3 F B F B4 J F J F5 C J C J6 B I G G7 I C B C8 D G I H9 G D D D10 H H H IRanking Criteria3rd ACHV     Iowa City, Iowa     1-4 June 2010 48

English

Laboratory Measurement of Riveting Hammer Vibration

Johannsing, Eckardt

DIFFERENTIAL DIAGNOSIS OF WHOLE-BODY VIBRATION RELATED DISORDERS Dr. med. ECKARDT JOHANNING MD, MSc. Occupational and Environmental Life Science, Albany, N.Y.  Introduction  Occupational whole-body vibration (WBV) exposure can lead to multiple, often non-specific health complaints and to physical disorders in vehicle operators. Primarily musculoskeletal or neurological disorders of the spine are generally recognized adverse health outcomes of intense and prolonged exposures due to strong epidemiological evidence. In some countries these types of "mechanical" repetitive back injuries are compensable if certain criteria are met.1 2 Less frequently organ damage has been reported including the prostate, the intestinal organs (stomach, bladder and kidneys), female reproductive organs, peripheral veins, hemorrhoids,  or the cochlear vestibular system.3 4 The medical diagnosis, treatment and prevention of occupational low back disorders has been reviewed in a clinical consensus protocol. 5 A prototype health surveillance scheme for WBV has been proposed.6 However, many physicians and occupational safety and health experts seem not to be familiar with the wide spectrum of health complaints and the proper diagnostic evaluation of WBV-exposed patients.7 The aim of this study is to review the current medical knowledge and  differential diagnostic evaluation methodology.  Methods  Review of peer-reviewed clinical reports and scientific journal publications of whole-body vibration related health effects and the medical differential diagnostic evaluation protocols and recommendations. Review of the evidence and differential diagnosis. Results  There is general recognition that the diagnostic approach for the medical evaluation of cases with suspected vibration-induced disorders should include a comprehensive work history, a list of hobbies that may include vibration exposure, a complete medical -, family- and social history, review of systems (smoking habits), medications, prior injury and trauma, followed by a complete physical examination. In addition, some special diagnostic laboratory and imaging studies may be indicated to rule out "red flag" conditions. WBV is frequently associated with symptoms such as acute or chronic low back pain, peripheral neuropathy and progressive degenerative changes of the spine, including lumbar inter-vertebral disc disorders. Typically, significant symptoms and signs are severe and chronic pain, paresthesia and neurological dysfunction. To a lesser degree WBV exposure may also lead to neck-shoulder problems, digestive disorders, circulatory disorders, auditory effects, and reproductive problems. The health 3rd ACHV     Iowa City, Iowa     1-4 June 2010 65complaints are typically discomfort, pain or organ related dysfunction.  The differential diagnosis includes pathologies principally related to acute trauma (fractures), infections (i.e., tuberculosis), cancer, systemic and chronic diseases (i.e., osteoporosis, auto-immune diseases, inflammatory rheumatologic problems, metabolic diseases (diabetes, thyroid), bone, prostate, renal or psychiatric disorders. Diagnostic tests include blood and urine laboratory studies, radiological imaging and electrophysiological studies. Symptoms, pathology, and radiologic appearances may be only weakly correlated. The prevalence of a prolapsed intervertebral disk among persons with low back pain in primary care is estimated to be 1 to 3 percent. About 4 percent of patients with low back pain in primary care settings have a compression fracture, and about 1 percent have a tumor. Inflammatory rheumatologic conditions (ankylosing spondylitis) and spinal infections are typically less common. The causal diagnosis is based on the medical findings, the differential diagnostic methodology and supportive work exposure data (WBV vibration measurements according to national or international (i.e., ISO 2631-1,  ACGIH) guidelines and supportive literature.    Discussion  A proper WBV-related injury diagnosis includes a critical review of  the work history, exposure data assessment and the clinical differential diagnostic evaluation. Many health care providers receive little or no training in occupational medicine and recognition of WBV related injuries. The aims of improved WBV health surveillance are to assess health status and improve the diagnosis of vibration-induced disorders at an early stage, to inform the workers on the potential risk associated with vibration exposure, to give preventive advice to employers and employees. Customized occupational and clinical health questionnaires and examination protocols may be useful in the systematic medical monitoring of WBV exposed workers and should me more utilized in the medical evaluation.    Reference List  1.  C. T. Hulshof et al. The fate of Mrs. Robinson: Criteria for recognition of whole-body vibration injury as an occupational disease, 253 J SOUND VIBRATION.185,  185-194  (2002).  2.  K. TESCHKE et al. Whole body vibration and back disorders among motor vehicle drivers and heavy equipment operators - A review of the Scientific evidence. (1999).  http://www.cher.ubc.ca/PDFs/WBV_Report.pdf  3.  H. Seidel & R. Heide,. Long-term effects of whole-body vibration: a critical survey of the literature, 58 INT.ARCH.OCCUP.ENVIRON.HEALTH.1,  1-26  (1986).  4.  M. Bovenzi,. Criteria for case definitions for upper limb and lower back disorders caused by mechanical vibration, 98 MED.LAV.98,  98-110  (2007).  5.  E. Johanning,. Evaluation and management of occupational low back disorders 2, 37 AM.J.IND.MED.94,  94-111  (2000).  6.  M. Bovenzi & C. T. Hulshof. Risk of occupational vibration exposure (VIBRISKS) ANNEX 21 TO FINAL TECHNICAL REPORT. (2007). http://www.vibrisks.soton.ac.uk/body_reports.htm  7.  A. R. Last & K. Hulbert,. Chronic low back pain: evaluation and management, 79 AM.FAM.PHYSICIAN.1067,  1067-1074  (2009). 3rd ACHV     Iowa City, Iowa     1-4 June 2010 66

Differential Diagnosis of Whole-Body Vibration Related Disorders

Dornela, Juliana Gonçalves

Duarte, Maria Lúcia Machado

 WHY CAN WHOLE BODY VIBRATION (WBV) CAUSE REDNESS ON VOLUNTEERS? THE EFFECT OF MECHANICAL VIBRATION AND ANXIETY ON PERIPHERAL BLOOD FLOW  Juliana Gonçalves Dornela and Maria Lúcia Machado Duarte*  PPGMEC/UFMG: Post-Graduation Program in Mechanical Eng., Universidade Federal de Minas Gerais; GRAVIHB: Group of Acoustics and Vibration in Human Beings, BRAZIL mlduarte@dedalus.lcc.ufmg.br  Introduction Mechanical vibrations are physical stimuli that are present in various occupational or even leisure environments, as well as in the daily lives of the population in general. Although the majority of the studies investigate the damaging effects associated to vibration, nothing much is found on the effects of vibration on the peripheral circulation, being that the main objective of this article.  The peripheral circulation can be considered as one whose flow is directed to the muscular system (muscles) and the integumentary system (epidermis and dermis)1. The substance responsible to promote the vasodilatation in blood flow is nitric oxide (NO). The NO plays a role in modeling the diameter and vascular resistance of the blood vessels by its ability to relax their sleek muscles5.  In an experiment conducted by the Group of Acoustics and Vibration in Human Beings - GRAVIHB/UFMG, to investigate the effects of whole body vibration (WBV) on human hearing, it was observed that one of the volunteers apparently anxious by the stimulation, presented in the neck and upper limbs redness in some points. However, soon after the stimulus (at 5 Hz, 2.45 m/s2 in the Z-axis vibration, during approximately 8 minutes), these signs disappeared. Faced with this fact, this article aims at discussing about an updated review on the subject in order to understand what would be the effect of mechanical vibration and anxiety/stress in the peripheral blood flow so to justify the results found in the GRAVIHB/UFMG research.     Methods Papers were reviewed2, without limitation of initial time until 2010, which related anxiety and/or mechanical vibration (both local and whole body) with their effects on the peripheral blood flow, in order to justify the results found during the GRAVIHB/UFMG research. The survey was conducted in libraries and databases such as Medline, Lilacs, BIREME, Pubmed, Wiley Interscience and Science Direct. Results and Discussions In total, only 10 studies were found on the effects of mechanical vibration on peripheral blood flow2. All these studies found that vibration leads to increased shear stress on the walls of blood vessels. This increase in the mechanical forces has an effect on the DNA. That is because the nitric oxide (NO) is synthesized from the information originating in the DNA of the cells which transcribes this information to the mRNA for the production of nitric oxide (NO), sending it to the tissues of blood vessels (endothelium) where the enzymes nitric oxides (NOs) are present and receive it for the synthesis of NO. Consequently, there is vasodilatation, causing increase in the blood flow, making the skin redness turns visible.  3rd ACHV     Iowa City, Iowa     1-4 June 2010 30Only seven studies used humans as sample2. Moreover, it was observed a great variation between the studies regarding both the types of vibrations used (3 used local vibration and 7 whole body vibration), as well as in relation to both the frequency ranged (0.23 to 2000 Hz) and vibration amplitudes (displacement from 2 to 6 mm and/or acceleration from 2.22 to 46m/s2) employed. There was no standard on how the vibration information was presented, making the interpretation and comparison of the findings more difficult, as in some cases, not all the necessary information was even reported. One study3 in dogs and 2 studies4,6 in humans used similar amplitude and frequency to that used in the experimental study by GRAVIHB/UFMG, arriving to the same conclusions, corroborating to the hypothesis of the study.  Therefore, although the region investigated was different, similar conclusion may be drawn.  About the influence of anxiety on peripheral blood flow, 7 studies were found2 and all these studies corroborate to the occurrence of increased blood flow in the forearm of humans when they are subjected to situations of anxiety / mental or emotional stress. It was not found any study about the combined factors (vibration/anxiety). Conclusions There are few studies in the literature reporting about the effects of the vibrations on peripheral blood flow. Nevertheless, from the studies found, it may be concluded that in the study by GRAVIHB/UFMG an increase in the shear forces on the blood vessels walls had caused peripheral vasodilatation and redness in certain parts of the upper limbs and cervical region of the volunteer. Furthermore, the anxiety, as seen in the literature, also causes peripheral vasodilatation and contributed to the appearance of such signals in the volunteer. However, no study was found about the combined effect, vibration/anxiety, being that a suggestion for future work. Moreover, one important point is the urgent need to standardize the information relative to the vibration parameters, with all the relevant information reported, in order to easier the comparison and interpretation of the findings.  Acknowledgment The authors would like to thanks the financial support given to this work by FAPEMIG and CNPq.  References 1. Berne, R.M. and Levy M.N. (2000). Principles of Physiology, Third Edition. Mosby,Inc., St. Louis, MO. 256–64 apud Lohman III, E.B., Petrofsky, J.S., Maloney-Hinds,C., Betts-Schwab, H. and  Thorpe D. (2007). The effect of whole body vibration on lower extremity skin blood flow in normal subjects. Med Sci Monit.13(2), pp 71-76, 2. Dornela, J.G. and Duarte, M.L.M. (2010). Effects of Mechanical Vibration and Anxiety on Peripheral Blood Circulation: Review of Literature to Explain Redness Caused by the Presence of Whole Body Vibration (WBV). Internal Report. GRAVIHB/UFMG.  3. Hood, W.B. and Higgins, L.S., (1965). Circulatory and respiratory effects of whole-body vibration in anesthetized dogs.  Appl Physiol 20, pp 1157-1162. 4. Lythgo, N., Eser,P., Groot,P. and Galea, M. (2009). Whole-body vibration dosage alters leg blood flow. Clin Physiol Funct Imaging 29, pp 53–59. 5. Wong, G.K.T. and Marsden, P.A. (1996). Nitric oxide synthases: regulation in disease.  Nefrol Dial Transplant 11, 215-20. 6. Zhang, Q., Ericson, K.. and Styf, J. (2003). Blood flow in the tibialis anterior muscle by photoplethysmography during foot-transmitted vibration. Eur J Appl Physiol 90, pp 464–469.  3rd ACHV     Iowa City, Iowa     1-4 June 2010 31

Why Can Whole Body Vibration (WBV) Cause Redness on Volunteers? The Effect of Mechanical Vibration and Anxiety on Peripheral Blood Flow

Oliver, Michele

Conrad, Leanne

Jack, Robert J.

Dickey, James P.

Eger, Tammy

COMFORT BASED SEAT SELECTION TO MINIMIZE 6 DOF WHOLE-BODY VIBRATION IN INTEGRATED STEEL MANUFACTURING MOBILE MACHINERY  *Michele Oliver1, Leanne Conrad1, Robert J. Jack1,3, James P. Dickey2,      Tammy Eger3 1. University of Guelph, Guelph, Ontario, Canada                                                  2. University of Western Ontario, London Ontario, Canada 3. Laurentian University, Sudbury, Ontario, Canada  Introduction Operators of heavy machinery are often exposed to complex whole-body vibration (WBV) involving simultaneous motion along three translational and three rotational axes (6-DOF).  When companies retrofit machines, seats are usually selected and implemented without testing using machine and/or terrain specific vibration inputs to assess seat efficacy. The purpose of this project was to provide the steel industry and others with information which would allow them to more efficiently retrofit existing machines. Methods Six-DOF chassis acceleration data were recorded for various mobile machines from the steel making industry.1 Six, 20 second representative profiles (Table 1) were assembled from the ‘worst’ WBV machine for use in this seat selection study.  Profiles were implemented while subjects sat on one of three heavy equipment seats (BeGe7150, Grammar MSG 95G1721, and a 6801 Isringhausen in which the seat pan cushion was retrofitted with Skydex™ seating material) mounted on a 6 DOF Parallel Robotics System Corporation (PRSCO) robot.  Three randomized trials of each combination of seat and profile were conducted using 8 male (22.3±2.0 yrs) and 8 female (23.5±1.8 yrs) inexperienced operators as well as 4 male (47.3±12.3 yrs) experienced operators from a participating steel making company.  All subjects provided informed consent and all laboratory procedures were approved by the Research Ethics Board at the University of Guelph. Assessment variables included operator reported normalized (to the operator’s mean response) comfort (ORC) which was verbally reported by subjects following each vibration exposure according to methods reported in Dickey et al.2  The other assessment variable was 6 DOF VTV Weighted Comfort (VTVC) which was assessed using a 6-DOF seat pad transducer according to ISO 2631-1 standards. 3 Results For inexperienced operators, factorial ANOVA procedures revealed no significant (p≤0.01) differences between seats, sex or trials for ORC; however, Bonferroni post-hoc procedures showed that all of the profiles were different from one another (p≤0.01). For the VTVC, a significant difference was observed between seats with the 3rd ACHV     Iowa City, Iowa     1-4 June 2010 91BeGe7150 resulting in the lowest VTVC value followed by the Grammar MSG 95G1721 and finally the 6801 Isringhausen. Unlike results for ORC, the VTVC for profile 1 was not significantly different than profile 3. A significant interaction between profile and seat was obtained, indicating that VTVC values were different for various combinations of profile and seat.  For experienced subjects, results were the same as inexperienced subjects for ORC with the exception that profiles 5 and 6 were not different from one another. Unlike the inexperienced subjects, for VTVC, there were no significant differences between seats, but all profiles were found to be different from one another with the exception of profiles 4 and 6.  Profile  ProfileTask/Condition 6-DOF Unweighted Chassis Vibration Total Value (m/s2) 1 Driving Loaded 2.122 2 Driving Loaded 1.247 3 Driving Unloaded 2.168 4 Driving Unloaded  1.442 5 Slag Pot Pickup 1.028 6 Pot Banging 1.816 Table 1. 6-DOF Vibration total value (VTV) and corresponding field tasks for each of the six vibration profiles. Profiles were developed from a Pot Hauler1. Discussion In the inexperienced operators, the best seat was found to be the BeGe7150 (from VTVC); however, in the small number of experienced subjects, neither ORC nor VTVC resulted in a ‘clear cut’ seat selection. One of the potential reasons for this is that all three tested seats were considered to be higher end seats and were much better than the seats currently used by the operators in their jobs. The significant interaction effect found between profile and seat in both the inexperienced and experienced operators shows clearly that from a comfort perspective, there may not be one best seat for all of the different vibration profiles encountered in an operator’s daily routine.  References  1. Oliver, M, Jack, J., Eger, T., Dickey, J., Conrad, L., and Harnish, C. 2009 Quantification and characterization of 6-degree-of-freedom whole-body vibration exposure spectra from the chassis of selected mobile machines used in the steel making industry. Proceedings of the 4th International Conference on Whole-body Vibration Injuries, Montreal, Quebec. 2. Dickey, J.P., Eger, T.R., Oliver, M.L., Boileau, P.E., Trick, L.M., & Edwards, A.M. 2007. Multi-axis sinusoidal whole-body vibrations: Part II - Relationship between Vibration Total Value and discomfort varies between vibration axes. Journal of Low Frequency Noise Vibration and Active Control, 26, (3) 195-204. 3. ISO 2631/1 1997, Mechanical vibration and shock - Evaluation of human exposure to whole-body vibration - Part 1: General requirements, International Standards Organization, Geneva, Switzerland.  3rd ACHV     Iowa City, Iowa     1-4 June 2010 92

Comfort Based Seat Selection to Minimize 6 DOF Wholebody Vibration in Integrated Steel Manufacturing Mobile Machinery

Reddy, Vinay A.H.

Channamallu, Raghu R.

Wilson, Sara E.

NEUROMOTOR TRANSMISSIBILITY OF HORIZONTAL SEATPAN VIBRATION AND A MATHEMATICAL MODEL  Vinay A.H. Reddy*, Raghu R. Channamallu, Sara E. Wilson Mechanical Engineering, University of Kansas  Introduction Recent studies of whole body vibration in seated postures have suggested that the neuromotor system may play a role in the etiology of low back disorders1-4.  A number of researchers have modeled whole body vibration transmission to the low back, spine and head5.  However, no model to our knowledge has examined the transmission of mechanical vibration to muscle shortening/lengthening, the neuromotor system and reflex muscle activation.  In addition, only a few studies have examined biodynamic vibration transmission in the fore-aft (anterior-posterior) direction. In this work, transmission of fore-aft vibration to the spine rotation and erector spinae muscle activation was assessed and a model of the motion was created.  Methods Ten healthy young subjects (5 male, 5 female, age 24±3 years, height 1.6 ± 0.04 m, weight 69 ± 4 kg) were assessed. Subjects were screened for low back pain and other neuromuscular disorders. The KU-L Human Subjects Committee approved this study and all subjects gave informed consent. A Ling 1512 electro-dynamic shaker was used to create fore-aft vibration. Data from tri-axial accelerometers on the seatpan and attached to the skin at the T10 spinous process, an electrogoniometer across the lumbar spine, electromyography (EMG) on the erector spinae (ES) muscles at L2/L3 was collected during vibration.  EMG data was filtered, rectified, integrated and normalized to a maximum obtained prior to vibration exposure.  A running average method was used to analyze and obtain a single ensemble average of the processed data for a vibration period.  Responses to fore-aft seatpan vibration (3 Hz to 14 Hz, 1 m/s^2 RMS and 2 m/s^2  RMS) both with and without a backrest were measured.  From the ensemble averages, trunk acceleration transmissibility (seatpan acceleration to T10 accelerometer), vibration transmitted to lumbar rotations (seatpan acceleration to electrogoniometer), vibration-induced muscle activity (seatpan acceleration to ES EMG) and muscle activity relative to lumbar rotation (electrogoniometer to ES EMG) were calculated.  A lumped parameter model was created with two lumped masses representing head-arm-trunk (HAT) and the pelvis-legs connected with linear and rotational dampers and springs (Figure 1).  The parameters for the model were based on weights of the experimental subjects and anthropometric data from literature6.  Using Lagrangian dynamics, a linearized state-space model was created.  This model was used to compare the model to the experimental data.  In addition, using Simulink in MATLAB, the vibration experiment was simulated.   Results The fore-aft trunk acceleration transmissibility declined with increasing frequency consistent with previous research5 and increased with the presence of a backrest. Transmissibility was found to be greater at 2 m/s^2 RMS compared to 1 m/s^2 RMS. It was observed that the vibration induced lumbar rotations declined with frequency similar 3rd ACHV     Iowa City, Iowa     1-4 June 2010 105to trunk acceleration transmissibility but with little change in the presence of a backrest. Examining the relationship between muscle activity and lumbar rotation, the magnitude of muscle activity was found to be mostly linearly related to the magnitude of lumbar rotation, suggesting that lumbar rotation is eliciting the muscle response (Figure 2).  The peak muscle activity was delayed relative to peak trunk acceleration, with delays of 390ms at 3Hz to 43ms at 14Hz, suggesting a transition from voluntary to reflex muscle activation.  The model was found to exhibit a similar pattern of fore-aft vibration transmissibility and lumbar rotation as found experimentally.  It was also found to exhibit similar patterns of both fore-aft and vertical vibration transmissibility and lumbar rotation as previously reported in the literature5,7.    Discussion In this work, transmissibility of fore-aft vibration to the low back was found to be consistent with previous literature.  Muscle activity in fore-aft vibration was found to correspond to lumbar rotation with delays that suggest a transition from voluntary to reflex-modulated erector spinae muscle response.  A mechanical model of trunk dynamics has been created and found to have similar transmissibility and lumbar rotations as were observed experimentally.  Future work will be to modify this model to incorporate a Hill type model of muscle dynamics and a model of neuromotor response and to assess the model behavior relative to the muscle activity results found in this fore-aft vibration study and previous studies of vertical vibration7.              Figure 1 A 2-D model of                           Figure 2 The ratio of muscle activity (fraction  vibration transmission                               of max) to lumbar rotation (deg) was mostly         constant with frequency.                                                                                                             References 1. Wilder, D. G., et al. (1996). Muscular response to sudden load. A tool to evaluate fatigue and rehabilitation. Spine, 21(22), pp. 2628-39. 2. Li, L., et al. (2008). Whole body vibration alters proprioception in the trunk. International Journal of Industrial Engineering, 38(9-10), pp. 792-800. 3. Solomonow, M., et al., (2000). Biexponential recovery model of lumbar viscoelastic laxity and reflexive muscular activity after prolonged cyclic loading. Clinical Biomechanics, 15(3), pp. 167-75. 4. Bluthner, R., et al., (2002). Myoelectric response of back muscles to vertical random whole-body vibration with different magnitudes at different postures. Journal of Sound and Vibration, 253(1), 37-56. 5. Griffin, M. J. (1990). Handbook of Human Vibration, Academic Press Limited, London, England. 6. Winter, D. A. (1990). Biomechanics and Motor Control of Human Movement, Wiley-Interscience, N.Y. 7. Abraham, P. M., and Wilson, S. E. (2006). Whole Body Vibration and Neuromuscular Response. ASME Summer Bioengineering Conference, Amelie Island, Florida. 00.010.020.030.040.050.063 4 5 6 7 8 9 10 11 12 13 14Frequency (Hz)ES EMG/Lumbar Rotation (1/deg)1 rms w/ back rest 2 rms w/ back rest1 rms w/o back rest 2 rms w/o back rest3rd ACHV     Iowa City, Iowa     1-4 June 2010 106

Neuromotor Transmissibility of Horizontal Seatpan Vibration and a Mathematical Model

Plewa, Katherine

ARE COMFORT PREDICTIONS FROM ISO 2631-1 AND SELF-REPORTED COMFORT VALUES DURING OCCUPATIONAL EXPOSURE TO WHOLE-BODY VEHICULAR VIBRATION RELATED?  Katherine Plewa1, James P. Dickey1*, Tammy Eger2, Michele Oliver3 1. University of Western Ontario, London Ontario, Canada 2. Laurentian University, Sudbury, Ontario, Canada  3. University of Guelph. Guelph, Ontario, Canada Introduction Exposure to whole-body vibration is strongly associated with health and comfort problems. The way in which workplace vibration exposure affects comfort is an important factor in worker activity levels and performance. International standards (ISO 2631-1) predict comfort based on vibration magnitudes, frequencies and durations. The objective of this study was to determine whether the ISO 2631-1 prediction method produces similar results to self-reported field comfort levels during occupational exposure to whole-body vehicular vibration.  Methods 6 degree of freedom seatpan acceleration data were recorded in various industrial machines in forestry2, mining4, and construction1 industries. Following an audio tone at 5-minute intervals, operators reported their comfort level on a ten point scale3 based on the preceding minute of vibration exposure.   The one minute profiles of raw acceleration data were processed using the appropriate filtering and multiplying factors5. Frequency weighted RMS accelerations and point vibration total values were then calculated for each axis and combined as a vector sum. Comfort was predicted from the overall vibration total value for each acceleration profile. Overall vibration total, normalized overall vibration total, and total vibration dose values were compared to self-reported comfort for each of the three industries.  Results We collected 45 matched sets of comfort and vibration data from 10 mining LHD vehicles, 18 sets of data from 6 forestry skidders and 60 sets of data from 15 construction scrapers. Each industry showed consistent trends for each predicted value; however, there were different relationships between the industries (Figure 1). The data from the construction industry showed weak positive relationships between predicted and self-reported comfort values, whereas the data for the forestry and mining industries showed no relationship or a weak negative relationship between predicted and self-reported comfort.    3rd ACHV     Iowa City, Iowa     1-4 June 2010 95 Figure 1. Total Vibration Dose Value (VDVT) versus Self-Reported Comfort for vehicles in the mining, construction and forestry industries. Discussion It is difficult to capture the relationship between comfort and vibration using mathematical equations because comfort is a subjective reflection of many factors. The predicted comfort levels did not accurately represent self-reported comfort. This may be due to limitations of the prediction equations or perhaps that the operators were incorporating additional factors such as temperature, noise and fatigue into their self-reported comfort ratings. In order to improve our understanding of the relationship between multi-axis vibration and comfort, a more controlled study should be done in the laboratory where workplace vibrations are simulated and subjects rate their comfort given a certain acceleration profile.  References  1. Cann, A.P., Salmoni, A.W., Vi, P., & Eger, T.R. 2003. An exploratory study of whole-body vibration exposure and dose while operating heavy equipment in the construction industry. Applied Occupational and Environmental Hygiene, 18, (12) 999-1005. 2. Cation, S., Jack, R., Oliver, M., Dickey, J.P., & Lee Shee, N.M. 2008. Six degree of freedom whole-body vibration during forestry skidder operations. International Journal of Industrial Ergonomics, 38, (9-10) 739-757 3. Dickey, J.P., Eger, T.R., Oliver, M.L., Boileau, P.E., Trick, L.M., & Edwards, A.M. 2007. Multi-axis sinusoidal whole-body vibrations: Part II - Relationship between Vibration Total Value and discomfort varies between vibration axes. Journal of Low Frequency Noise Vibration and Active Control, 26, (3) 195-204 4. Eger, T., Stevenson, J., Boileau, P.E., & Salmoni, A. 2008. Predictions of health risks associated with the operation of load-haul-dump mining vehicles: Part 1 - Analysis of whole-body vibration exposure using ISO 2631-1 and ISO-2631-5 standards. International Journal of Industrial Ergonomics, 38, (9-10) 726-738 5. ISO 2631/1 1997, Mechanical vibration and shock - Evaluation of human exposure to whole-body vibration - Part 1: General requirements, International Standards Organization, Geneva, Switzerland. 0.01.02.03.04.05.06.07.08.00 2 4 6 8VDVT(m/s1.75)Self-Reported Comfort (0-9)MiningForestryConstruction3rd ACHV     Iowa City, Iowa     1-4 June 2010 96

Are Comfort Predictions From ISO 2631-1 and Self-Reported Comfort Values During Occupational Exposure to Whole-Body Vehicular Vibration Related?

Wimer, Bryan

McDowell, Thomas W.

Xu, Xueyan S.

Welcome, Daniel E.

Warren, Christopher

Dong, Ren G.

Effects of Gloves on the Grip Strength Applied to Cylindrical Handles           Bryan Wimer, Thomas W. McDowell, Xueyan S. Xu,  Daniel E. Welcome, Christopher Warren, and Ren G. Dong,   Engineering and Control Technology Branch, Health Effects Laboratory Division, National Institute for Occupational Safety & Health, Morgantown, WV, USA  INTRODUCTION Anti-vibration (AV) gloves have been used to reduce hand-transmitted vibration exposure. However, some workers have complained of increased hand and arm fatigue when they use these gloves. This is likely because some of the AV gloves could greatly reduce the grip strength or require workers to exert more grip effort in the operation of a vibrating tool. Although this has been generally understood, it is unknown exactly how much the AV gloves could reduce the grip strength applied to cylindrical handles used on many powered hand tools. It is also unclear whether the AV gloves could reduce grip strength more than regular work gloves. To answer these questions, this study measured the total grip strength applied on two cylindrical handles with, and without, wearing different gloves.     METHOD The grip strength on a cylindrical handle was computed by quantifying the total contact force normal to the handle surface1.  Two instrumented cylindrical handles (30 mm and 40 mm diam.) were used to measure the contact force.  The 30 mm handle was comprised of an aluminum cylinder equipped with a Tekscan pressure mat1.  The 40 mm handle was a six-piece handle developed in an earlier study2, which measured the contact force by means of shear strain gauges installed on each of the six arms. As shown in Fig. 1, four types of AV gloves and two types of standard work gloves were used in the experiment. Ten healthy male adult subjects participated in the experiment. The test setup and subject posture are shown in Fig.2. Each subject was asked to apply his maximum grip for 5 seconds. The sampling rate was 5 Hz. The middle 3 seconds of data were used to calculate the grip strength. Two test segments were carried out; one set of trials used the 40 mm handle and the other utilized the 30 mm handle.  During each segment, the subject completed three maximum grip efforts on the handle with each of the six gloves as well as in the bare-handed condition for a total of 21 trials (7 hand conditions × 3 trials).  The test sequence in each segment was randomized among the subjects. The thickness of each glove was also measured. Fig.2.  Test setup and subject posture used in the measurement. Fig. 1. The six gloves used in the study: (1) Mechanix Wear automotive (2) leather/cotton construction (3) Decade gel padded, anti-vibration (4) Impacto leather, air pocket, anti-vibration (5) Impacto mesh, air pocket, anti-vibration (6) ErgoAir pump, air pocket, anti-vibration 3rd ACHV     Iowa City, Iowa     1-4 June 2010 45RESULTS AND DISCUSSION As shown in Fig. 3, Glove 1 reduced the grip strength on both handles by less than 10% when compared with the bare hand grip strength. Each of the four anti-vibration gloves (Gloves 3-6) reduced the grip strength by more than 29%, regardless of handle size. One of the standard work gloves (Glove 2) also largely reduced the grip strength (≥25%).   The major underlying cause of the observed strength reduction is likely associated with the mechanics of the glove in the gripping action. A glove is usually bowed and compressed at the palm side, and stretched at the back side. The forces required to generate these deformations must be the result of the hand grip effort. Therefore, part of the hand energy or grip effort must be absorbed by the glove. This mechanism suggests that the stiffness of a glove is likely to play an essential role in the reduction of the measured grip strength. The glove stiffness generally increases with the thickness in the glove material. This explains why the grip strength was reliably correlated with the measured glove thickness.  Glove use also increases the effective handle diameter, as confirmed from the glove influence on the grip force distribution around the circumference of the cylindrical handle. The changed handle size could also positively or negatively affect grip strength, depending on the original handle size. The increase of the handle size from 30 mm using gloves should theoretically increase the grip strength, but instead it was reduced. It is likely that the increased grip effort required to generate more deformation of the glove on a smaller handle counteracts the positive effect of the increased handle diameter.  These observations suggest that it is not the type of glove but the actual stiffness of the glove that primarily determines the reduction in grip strength. Because some AV gloves are thicker or stiffer than most standard working gloves, their reduction effect could be greater than that of the regular gloves. How to lessen the stiffness of AV gloves or to have less influence on the grip strength remains an interesting and useful research topic.  REFERENCES 1. Dong, R.G., Wu, J.Z., Welcome, D.E., and McDowell, T.W., 2008. A New Approach to Characterize Grip Force Applied to a Cylindrical Handle. Medical Engineering & Physics, 30(1): 20-33. 2. Wimer, B.M., Dong, R.G., Welcome, D.E., Warren, C., and McDowell, T.W., 2009. Development of a New Dynamometer for Measuring Grip Strength Applied on a Cylindrical Handle. Medical Engineering & Physics, 31(6): 695-704. Figure 3.  Mean grip strength percent reduction for the six gloves used in testing.  (Y-error bars indicate the 95% confidence intervals for each mean).  051015202530354045Glove 1 Glove 2 Glove 3 Glove 4 Glove 5 Glove 6Mean Strength Reduction (%)40mm handle30mm handle3rd ACHV     Iowa City, Iowa     1-4 June 2010 46

Effects of Gloves on the Grip Strength Applied to Cylindrical Handles

Zheng, Guangtai

Qiu, Yi

Griffin, Michael J.

MULTIBODY MODELLING OF THE VERTICAL APPARENT MASS AND FORE-AND-AFT CROSS-AXIS APPARENT MASS OF THE SEATED HUMAN BODY WITH A BACKREST  Guangtai Zheng, Yi Qiu and Michael J Griffin Human Factors Research Unit, Institute of Sound and Vibration Research, University of Southampton, United Kingdom  Introduction  Backrests affect the biodynamic responses of the body to whole-body vibration.1-2 Models of the seated human body exposed to whole-body vibration should therefore take into account the effects of backrests. The purpose of this study was to identify the characteristics of a model needed to reflect both the vertical in-line apparent mass and the fore-and-aft cross-axis apparent mass measured at both the seat and backrest and consider the contribution of each body segment to the dynamic response.  Methods  The human body was represented by five rigid bodies: upper-body, middle-body, pelvis, thighs, and legs (Figure 1). The rigid bodies were inter-connected by pin joints with rotational stiffness and damping. The normal and shear deformation of the pelvis, thigh and back tissues at the seat-occupant interfaces were simulated using linear springs and dampers. The equations of motion of the model were derived using the Lagrange formulation. The geometric and inertial properties were derived from the literature.3 The mechanical properties were obtained by minimizing the error functions between the computed and measured moduli of the median apparent masses over the frequency range 0.3 to 20 Hz.            (i)                    (ii)  Figure 1 A two-dimensional multi-body biomechanical model in the normal upright posture: (i) model structure; (ii) motion description. 3rd ACHV     Iowa City, Iowa     1-4 June 2010 107Results  The predicted moduli and phases of the vertical apparent mass and fore-and-aft apparent mass at the seat and back are compared with experimental data in Figure 2.2,4   (i) Modulus  (ii) Phase   Figure 2 Predicted and measured vertical and fore-and-aft cross-axis apparent mass of the human body with backrest: (i) modulus, (ii) phase.  ——— predicted (with backrest contact point at the upper lumbar spine); ―○― measured 2,4; (a) vertical apparent mass on the seat; (b) fore-and-aft cross-axis apparent mass on the seat; (c) vertical apparent mass on the back; (d) fore-and-aft cross-axis apparent mass on the back.                                                                                Discussion  The model is capable of predicting apparent masses in reasonable agreement with the measured data. A parameter sensitivity analysis indicated that the apparent masses at the seat and back in the vertical and fore-and-aft directions were mainly influenced by the vertical pelvis stiffness and the rotational motion of the lumbar spine and pelvis.   Contact with a backrest affects the apparent mass and so backrest contact should be taken into account in biodynamic models of human responses to vibration.  References               1. Fairley, T.E. and Griffin, M.J. (1989). The apparent mass of the seated human body: vertical              vibration. Journal of Biomechanics, 22, 81-94.  2. Nawayseh, N. and Griffin, M.J. (2003). Non-linear dual-axis biodynamic response to vertical whole-body vibration. Journal of Sound and Vibration, 268, 503-523. 3. National Aeronautical and Space Administration (1978). NASA Reference Publication 1024. Anthropometric source book, volume1: anthropometry for designers. 4. Qiu, Y. and Griffin, M.J. (2009). Biodynamic responses of the seated human body to single-axis and dual-axis vibration, Proceedings of 4th International Conference on Whole-Body Vibration Injuries, June 2 to 4, 2009, Montreal, Canada. 3rd ACHV     Iowa City, Iowa     1-4 June 2010 108

Multibody Modelling of the Vertical Apparent Mass and Fore-And-Aft Cross-Axis Apparent Mass of the Seated Human Body With a Backrest

Peterson, Donald R.

Asaki, Takafumi

Brammer, Anthony J.

Cherniack, Martin G.

NOISE AND VIBRATION EXPOSURES TO DENTAL HYGIENISTS  Donald R. Peterson*, Takafumi Asaki, Anthony J. Brammer, Martin G. Cherniack Biodynamics Laboratory, Univ. of Conn. Health Ctr., Farmington, CT 06030-2017  Introduction  The association of hand paresthesias and auditory damage to exposures of high-frequency sound and vibration from dental instrumentation remains unclear.  Auditory threshold studies have shown dental practitioners to have significant hearing loss at 3 kHz, 4 kHz, and 6 kHz 1,2.  Experienced hygienists were observed to have elevated Vibration Perception Thresholds (VPTs) at the FAII mechanoreceptors3 even though daily vibration exposures are below the limit value of the ISO 5349-based European Union Directive4.  These studies suggest that years of high-frequency exposures may lead to symptoms of Hand-Arm Vibration Syndrome (HAVS) and hearing loss.  This paper explores these exposure-response relationships using data from questionnaires, vibrotactile testing, and laboratory measurements of high-frequency dental instruments.  Methods  Two populations of dental hygienists (hygiene students (n=66), and experienced hygienists (n=94) with at least five years of experience) were recruited to investigate the relationships between multiple exposures and symptoms, as well as the early onset of symptoms in previously unexposed students3.  Job information was obtained by questionnaire and vibrotactile perception thresholds were measured for the FAII (125 Hz), FAI (32 Hz), and SAI (4 Hz) mechanoreceptors on both hands using a tactometer.  (Auditory thresholds were not collected.)  The most commonly used vibratory dental instruments were identified from the questionnaire data and the weighted and un-weighted 1/3 octave band frequency spectra of sound and vibration up to 63 kHz were measured using a 1/4-inch free-field microphone (4939, B&K, Denmark) coupled with an ultra high-frequency Scanning Laser Vibrometer (PSV-300, Polytec GmbH, Germany).  Instruments were operated without load (i.e., no tip contact) at recommended operating pressures and were evaluated using two mounting positions (tool base and typical grip position) using a simulated pinch grip with a similar biodynamic response to a human three-finger grip for grip forces between 30 and 45 N 3.  Results and Discussion Table 1: Questionnaire Results3  STUDENTS (n=66, 98.5% Female) EXPERIENCED (n=94, 97.9% Female) Age (SD) 26.1 (6.4) 45.5 (8.8)  Years in Practice (SD) 3.0 (4.3) 21.8 (8.3) Vibration Exposure (years (SD)) 1.0 (1.9) 17.1 (8.7) Manual Tool Use (hours/week (SD)) 5.2 (5.5) 12.0 (7.3) Vibratory Tool Use (hours/week (SD)) 3.0 (3.9) 5.1 (5.4) Est. Lifetime Ave. Weekly Vib. Exp. (hrs*1000 (SD)) 0.3 (0.6) 10.8 (11.5) Presence of Musculoskeletal Pain (number (%)) 27 (40.9) 81 (86.7) Presence of Carpal Tunnel Syndrome (number (%)) 3 (4.6) 17 (18.1) Use of Hearing Protection (number (%)) 2 (3.0) 2 (2.1)   Questionnaire results (Table 1) showed significant differences between mean age, years in practice, and self-reported vibration exposures.  Experienced hygienists were shown to be four times more likely to suffer from musculoskeletal pain and carpal tunnel 3rd ACHV     Iowa City, Iowa     1-4 June 2010 49syndrome and only four hygienists (two students and two experienced) reported the use of hearing protection.  Average VPTs (Table 2) for the FAII mechanoreceptors of the third and fifth digits of both hands were observed to be slightly higher for the experienced hygienists, while FAI and SAI results showed no differences and there was no association with age for any of the threshold measurements.  The sound and vibration levels of the dental instruments varied and the spectra indicated small differences in frequency components between mounting conditions.  Table 3 shows the measured unweighted and weighed total band powers for the SPL and the VL.  While the weighted results suggest minimal effects on health, the unweighted results, self-reported exposures, and VPTs suggest that accumulated exposures over time may cause musculoskeletal discomfort, HAVS, and possibly hearing loss.  Table 2: Average Vibration Perception Threshold Results3 in dB (re 1x10-6 m/s2) HAND AND DIGIT MECHNORECEPTOR STUDENTS EXPERIENCED Dominant Hand, 3rd Digit FAII – 125 Hz 103.0 (7.5) 107.0 (8.8) (Median Nerve) FAI – 32 Hz 102.7 (6.8) 104.4 (6.3)  SAI – 4 Hz 83.4 (4.5) 83.6 (5.1) Dominant Hand, 5th Digit FAII – 125 Hz 100.6 (6.2) 104.3 (8.8) (Ulnar Nerve) FAI – 32 Hz 104.0 (5.7) 104.5 (11.8)  SAI – 4 Hz 83.8 (3.6) 84.2 (4.5) Non-Dominant Hand, 3rd Digit FAII – 125 Hz 101.3 (7.8) 105.2 (9.0) (Median Nerve) FAI – 32 Hz 102.5 (6.0) 103.8 (6.5)  SAI – 4 Hz 83.3 (4.3) 83.2 (4.8) Non-Dominant Hand, 5th Digit FAII – 125 Hz 98.9 (5.5) 103.2 (9.3) (Ulnar Nerve) FAI – 32 Hz 102.9 (7.2) 104.2 (7.2)  SAI – 4 Hz 83.4 (4.0) 84.6 (5.1)      Table 3: Sound Pressure Level (SPL) and Vibration Level (VL) Measurements           TYPE MODEL MOUNT OP. FREQ. SPL (re 2x10-5 Pa) VL (re 1x10-6 m/s2)    (kHz) dB dB(A) dB dB(Weighted) Rotary 5k GRIP 4.4 69.2 65.9 169.2 97.6 Polisher RDH GRIP 4.4 77.4 72.5 168.7 98.1  Hygiene GRIP 5.0 72.7 68.9 171.8 101.0  Titan GRIP 4.6 70.2 67.7 165.9 94.9 Sonic Quixonic BASE 6.5 73.8 73.0 199.0 46.4 Scaler  GRIP 6.5 77.6 77.2 198.7 46.1  Pirouette BASE 6.3 80.2 75.4 176.4 51.9   GRIP 6.3 81.8 79.7 171.4 54.2 Ultrasonic Cavitron BASE 29.0 102.0 75.6 192.3 78.3 Scaler  GRIP 29.0 99.6 75.2 198.0 76.6  Advantage BASE 27.8 99.3 48.5 201.4 83.0   GRIP 27.8 94.7 46.9 197.2 65.1  References 1. Taylor W., Pearson J., Mair A. (1965). The hearing threshold levels of dental practitioners exposed to air turbine drill noise. Br. Dental J. 118, 206–210. 2. Wilson J.D., Darby M.L., Tolle S.L., Sever J.C. (2002). Effects of occupational ultrasonic noise exposure on hearing of dental hygienists: A pilot study. J. Dental Hyg. 76 (4), 262–269. 3. Cherniack M., Brammer A.J., Nilsson T., Lundstrom R., Meyer J.D., Morse T., Neely G., Peterson D., et al. (2006). Nerve conduction and sensorineural function in dental hygienists using high frequency ultrasound handpieces. Am. J. Ind. Med. 49, 313–326. 4. Mansfield, N.J. (2005). The European vibration directive—how will it affect the dental profession? Br. Dental J. 199, 575–577. 3rd ACHV     Iowa City, Iowa     1-4 June 2010 50

Noise and Vibration Exposures to Dental Hygienists

Kim, Heon-Jeong

Martin, Bernard J.

WHOLE-BODY VIBRATION RESPONSE THROUGH THE UPPER LIMBS ASSOCIATED WITH REACHING MOVEMENTS AND POSTURE  Heon-Jeong Kim*,1) and Bernard J. Martin2) 1) Department of Mechanical Engineering, University of Michigan 2) Department of Industrial and Operations Engineering, University of Michigan  Introduction   Exposure of human operators to whole-body vibration may induce health risks, interfere with manual operation, and compromise tasks performed in a vehicle [Griffin 1990], [Okunribido et al 2007]. For operator’s safety and performance enhancement, numerous investigations have attempted to identify the characteristics of WBV responses of seated individuals. WBV responses are functions of vibration variables [Griffin 1990] and postures [Lim et al 2004], [Kim and Bernard 2008]. As opposed to earlier studies involving limited static postures, the present work analyzes human responses for a large range of arm postures including two elbow flexion constraints in reaching movements.  Methods   Twenty-one participants performed a reaching task on the ride motion simulator of the U.S Army TARDEC, and maintained pointing posture at the end of the reaches for the estimation of WBV transmission. The task consisted of reaching with the right hand seven targets distributed in the right hemisphere of the workspace: upward [TG1], forward-upward [TG2], forward [TG3], forward-lateral [TG4], diagonal-upward [TG5], lateral near [TG6], and lateral far [TG7]. To investigate effects of movement direction and posture on vibration responses of the seated human, all reaches were performed with two postures such as elbow fully extended or flexed (Figure 1). Three vertical vibration conditions with a frequency of 2, 4, and 6 Hz were selected. Reaching movements and cab perturbations were measured by a VICON motion tracking system and tri-axial accelerometers, respectively.        Figure 1:  Elbow fully extended and flexed postures used during reaching tasks  Results and Discussion   WBV responses through the human multi-segment system vary as functions of vibration condition (p ≈ 0), target direction/location (p ‹ 0.01), and elbow joint constraint (p ‹ 0.01). Vibration frequency is the dominant factor affecting WBV responses. The interaction between the movement direction and the vibration direction influences WBV responses for specific vibration frequencies. Furthermore, the full extension of the elbow 3rd ACHV     Iowa City, Iowa     1-4 June 2010 78produces small elbow oscillations but contributes an amplification of the finger displacement relative to the elbow, while the elbow flexed posture produces large elbow perturbations but contributes to an attenuation of finger perturbation. In this study, transmission propagated through the upper limb was investigated for vertical sinusoidal vibrations with the selected frequencies only as they correspond to the largest effects. For realistic human motion simulation in vibratory environments, biodynamic characteristics of the seated human under multi-directional vibration inputs may be required to provide a more complete description of whole-body vibration transmissibility and facilitate the implementation of a 3-dimensional biomechanical model development.            (a) 2 Hz vertical vibration           (b) 4 Hz vertical vibration           (c) 6 Hz vertical vibration Figure 2:  Vibration responses through the upper limb with elbow extended and flexed postures during forward-lateral reach [TG 4]: superscripts S: shoulder, E: elbow, F: fingertip              (a) 2 Hz vertical vibration           (b) 4 Hz vertical vibration           (c) 6 Hz vertical vibration Figure 3:  Vibration responses through the upper limb with elbow extended and flexed postures during diagonal-upward reach [TG 5]: superscripts S: shoulder, E: elbow, F: fingertip  References  1. Griffin, M.J. (1990). Handbook of human vibration. San Diego, Academic press. 2. Okunribido, O,O., Shimbles, S.J., Magnusson, M., and Pope, M. (2007). City bus driving and low back pain: A study of the exposure to posture demands, manual materials handling and whole-body vibration. Applied Ergonomics 38, 29-38. 3. Lim, S.H., Martin, B.J., and Chung, M.K., (2004). The effects of target location on temporal coordination of the upper body during 3D seated reaches considering the range of motion. International J. Industrial Ergonomics 34, 395-405. 4. Kim, H.J., and Martin, B.J. (2008). Three-dimensional joint kinematics of the upper exteremity in reach movements under whole-body vibraiton exposure. Human Factors and Ergonomic Society 52nd Annual Meeting. 52(15), 1000-1004. 3rd ACHV     Iowa City, Iowa     1-4 June 2010 79

Whole-Body Vibration Response Through the Upper Limbs Associated With Reaching Movements and Posture

Heartland Center for Occupational Safety and Health

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