RELATION BETWEEN INITIAL MUSCLE LENGTH AND ELECTROMECHANICAL D

INTRODUCTION: The exact knowledge of electromechanical delay (EMD) can provide important conclusions concerning the mechanical effectiveness of a particular muscle, which becomes evident via the corresponding EMG. Recent results show an EMD of 24ms for the hamstrings (HS) in an optimal muscle length (OML). Therefore these values are distinctly shorter than those ever determined for the hip flexors (32-118ms). However athletic movement normally starts in an initial muscle length (IML) which is not necessarily identical with OML. Previous publications comparing 3 IML at the most show both positive and negative relations to EMD. Because existing results are not very satisfactory it was the aim of the present study to elucidate the relation between IML and EMD more exact. METHODS: For this purpose 18 male subjects performed four explosive maximal isometric voluntary contractions with their HS in six different length positions. EMG- and force-time-curves were digitally recorded with a sampling rate of 2 kHz. EMD was estimated by means of a specially designed computer program as the delay between the onset of EMG and force. RESULTS: The results showed a dependence of EMD on IML. While OML showed the shortest EMD (37-40ms) an increment of EMD was to be seen in direction of both stretched (45-48ms) and unstretched (42-46ms) IML. The results in OML were greater than in a recent study (24ms, JÖLLENBECK, 1997) for the same muscle group but in good accordance with the shortest values reported for the hip flexors (32ms, SYMONS et al., 1988). CONCLUSIONS: Maximum differences of about 8ms or 20% of EMD in different IML are not negligible in exact motion analysis. Furthermore the EMD-lengthcurve in course seems to correspond with the inverse force-length-curve. It must be supposed that EMD is not directly dependent on IML but on the maximum force and the rate of force development which depends on the grade of overlapping of the sarcomeres in different length positions. These results and the enormous differences in existing EMD values underline the importance of further investigation of the EMD and suggest to redefine the EMD in different IML for all muscles involved in athletic motions. REFERENCES: Cavanagh, P. R., Komi, P. V. (1979). Electromechanical Delay in Human Skeletal Muscle under Concentric and Eccentric Contractions. Eur. J. Appl. Phys. 42, 159- 163. Jöllenbeck, T. (1997). Electromechanical Delay of the Hamstrings and its Significance for the Analysis and Optimization of Sprint Running. Congress: Sport Kinetics ’97, Magdeburg. In Press. Symons, J. D. et al. (1988). Electromechanical Response Times and Muscle Strength after Sleep Deprivation. Canadian Journal of Sport Science 13, 225-230

IS ELECTROMECHANICAL DELAY MISINTERPRETED?

INTRODUCTION: In all publications on this subject the major portion of electromechanical delay (EMD), with direct or indirect references to Cavanagh/ Komi (1979), is referred to as the time it takes to stretch the series elastic elements (SE) by the contractile elements (CE). This seems to be confirmed by investigations showing shorter EMD in stretched muscle (SM) than in unstretched muscle (UM), whereby there are also contrary examples. In physiological positions a permanent tension exists in SE comparable with a stretched rubber band, and they do not slacken. A force generated by the CE at one end of the SE can only have a stretching effect if the other end of the SE is held back by the same amount of counter-force. It is of decisive importance that this happens at the same time without any delay. It was the aim of the present study to show experimentally that EMD cannot be determined by the time for stretching the SE. METHODS: For this purpose 18 male subjects performed four explosive maximal isometric voluntary contractions with their hamstrings in six different length positions from stretched to unstretched. EMG- and force-time-curves were digitally recorded with a sampling rate of 2 kHz. EMD was estimated by means of a specially computer program as the delay between the onset of EMG and force. RESULTS: The results showed that the shortest EMD, 38ms, occurred in an optimal muscle length (OML), and longer EMDs, 47ms for SM and 44ms for UM respectively, were seen. The results in OML were in good accordance with the shortest values reported for the hip flexors (32ms, SYMONS et al. 1988). Comparing the resulting EMDs in a stretched with those in an unstretched position, the investigation showed contrary results as those reported in most of the previous studies. Adding the four intermediate positions this trend was continued. CONCLUSIONS: Comparison of all six length positions showed the shortest EMD in OML and not in SM, as should be expected on the basis of earlier results. In contrast to previous results and assumptions, the EMD-length-curve showed the same, but inverse, course as the force-length curve. This latter phenomena could be attributed to the rate of force development, which depends on the grade of overlapping of the sarcomeres in different length positions. Both results impressively underlined the assumption that EMD cannot be determined by the time for stretching the SE, and it may be necessary to redefine EMD. REFERENCES: Cavanagh, P. R., Komi, P. V. (1979). Electromechanical Delay in Human Skeletal Muscle under Concentric and Eccentric Contractions. Eur. J. Appl. Phys. 42, 159- 163. Symons, J. D. et al. (1988). Electromechanical Response Times and Muscle Strength after Sleep Deprivation. Canadian Journal of Sport Science 13, 225-230

CORRELATION BETWEEN MUSCULAR FUNCTION AND POSTURE - LOWERING THE DEGREE OF PELVIC INCLINATION WITH EXERCISE

Muscular balance is one of the most widely discussed topics in sport science over the past years. The publications show a significant discrepancy between the accuracy of the numerous published statements on the theory of muscular balance and the small number of empirical studies. In the present investigation the authors examined both the logical and the empirical extent of the theory of muscular balance. Examination of the plausibility and the stringency of the argument showed that the theory of muscular balance lacks a scientific basis. However the empirical section disclosed a number of correlations between muscle function and body posture. Within a ten week training period the students´ average pelvic tilt was lowered significantly by a suitable program

SURFACE-ELECTROMYOGRAPHY: SKIN AND SUBCUTANEOUS FAT TISSUE ATTENUATE AMPLITUDE AND FREQUENCY PARAMETERS

The purpose of this study was to identify the attenuating influence on surface-EMG amplitude (IEMG) and mean power frequency (MPF) by skin and subcutaneous fat tissue. The electrode-muscle-distance (ΔEM) of the left m. biceps brachii is determined by tissue thickness. This was established by ultrasound in 12 females and 15 males six times each during a 43-week period (n=162). IEMG and MPF were measured during isometric maximum voluntary contractions (MVC). ΔEM explained up to 31 % of the variance of EMG-amplitude during MVC, which corresponds to previous studies on submaximum and maximum contractions. MPF variation was explained by ΔEM with up to 16 % and requires further validation. These results are important for the assessment of long-term training studies and neuromuscular fatigue measurements

Der Cross-Shaper: ein neues Sportgerät zum gesunden und effektiven Ganzkörpertraining – Ergebnisse einer biomechanischen Feldstudie

ZusammenfassungDer Cross-Shaper wurde entwickelt, um in den Bewegungsablauf des Walkens den Oberkörper effektiver einbeziehen zu können. Diese Feldstudie konnte deutlich positive gesundheitliche Effekte des Cross-Shapers zeigen, die umfassender ausgeprägt sind als beim Walking und Nordic Walking. Der Bewegungsverlauf ist harmonisch. Der stoßreduzierte Abdruck ist effektiver als beim Nordic Walking. Der Oberkörper wird vermehrt aufgerichtet und die Wirbelsäule effektiv entlastet und mobilisiert. Weite Teile der Muskulatur werden physiologisch gleichermaßen trainiert. Positive Effekte auf das Herz-Kreislauf-System sind gegenüber Walking und Nordic Walking deutlich erhöht.SummaryThe Cross-Shaper was developed to include the upper body more effectively in the motion sequence of walking. Results of this field study clearly show positive health effects from cross-shaper, which are pronounced more extensive than in walking and nordic walking. The path of movement is harmonious. The shock reduced push off is considerably more effective than in nordic walking. The upper body is increasingly erected and the spine is relieved and mobilized effectively. Large parts of muscles were physiologically trained equally effective. Positive effects on the cardiovascular system are increased considerably compared to walking and nordic walking

CROSS-SHAPING – THE MORE EFFECTIVE NORDIC WALKING? RESULTS OF A BIOMECHANICAL FIELD STUDY

Cross-shaping is a new developed kind of nordic walking. The main difference between nordic walking and cross-shaping is the use of special sticks with forearm shells and wheels. The purpose of this study was to analyze the health effects of cross-shaping and to compare the results with own previous studies of nordic walking. Results clearly show positive health effects from cross-shaping, which are more extensive than in walking and nordic walking. Cross-shaping is harmonious similar to cross-country skiing in classic style. Push off is more effective than in nordic walking. Upper body is more erected and spine is relieved and mobilized effectively. Large parts of muscles of the upper and lower extremities were physiologically trained effective. Positive effects on the cardiovascular system are increased considerably compared to walking and nordic walking

HIP- AND BACK-PROTECTORS IN SPORTS AND EVERYDAY LIFE - EFFECTIVE PROTECTION?

Hip and back protectors are recommended to reduce impact forces when falling in sports or everyday life. This study analyzed the shock-reducing effect of 29 different hip and back protectors using a drop test and a Kistler force plate. Our results showed large differences between the single protectors. Measured peak forces often and quickly exceeded the supposed limit of bone fracture strength. Therefore sufficient safety does not seem to exist yet and protectors must not be overestimated in their protection potential. In our opinion protectors should have a certain thickness preferably a combination of hardshell and viscoelastic material. Hip protectors for sports still show large deficits. Back protectors only protect against direct contusion but not against axial compressions or cervical spine

BIOMECHANICAL LOADING OF THE LOWER EXTREMITIES DURING NORDIC WALKING – A FIELD STUDY

The purpose of this study was to analyse under field conditions the loading of the lower extremities during nordic walking compared to walking. For that purpose 14 experienced, middle aged nordic walkers and 6 nordic walking instructors have been asked to walk a 1575m field track in randomised sequence, once with and once without poles. The mean vertical ground reaction forces are not different between nordic walking and walking. The present results are showing that the common opinion of a load reduction of the lower extremities by 30-50 % during Nordic Walking has to be rejected

A multicomponent exercise intervention to improve physical functioning, cognition and psychosocial well-being in elderly nursing home residents: a study protocol of a randomized controlled trial in the PROCARE (prevention and occupational health in long-term care) project

Background Older adults, who are living in nursing homes that provide a high level of long-term nursing care, are characterized by multimorbidity and a high prevalence of dependency in activities of daily living. Results of recent studies indicate positive effects of structured exercise programs during long-term care for physical functioning, cognition, and psychosocial well-being. However, for frail elderly the evidence remains inconsistent. There are no evidence-based guidelines for exercises for nursing home residents that consider their individual deficits and capacities. Therefore, high-quality studies are required to examine the efficacy of exercise interventions for this multimorbid target group. The purpose of this study is to determine the feasibility and efficacy of a multicomponent exercise intervention for nursing home residents that aims to improve physical and cognitive functioning as well as quality of life. Methods A two-arm single-blinded multicenter randomized controlled trial will be conducted, including 48 nursing homes in eight regions of Germany with an estimated sample size of 1120 individuals. Participants will be randomly assigned to either a training or a waiting time control group. For a period of 16 weeks the training group will meet twice a week for group-based sessions (45–60 min each), which will contain exercises to improve physical functioning (strength, endurance, balance, flexibility) and cognitive-motor skills (dual-task). The intervention is organized as a progressive challenge which is successively adapted to the residents’ capacities. Physical functioning, cognitive performance, and quality of life will be assessed in both study groups at baseline (pre-test), after 16-weeks (post-treatment), and after 32-weeks (retention test, intervention group only). Discussion This study will provide information about the efficacy of a multicomponent exercise program in nursing homes (performance, recruitment). Results from this trial will contribute to the evidence of multicomponent exercises, which specifically focus on cognitive-motor approaches in the maintenance of mental and physical functioning. In addition, it will help to encourage older adults to actively engage in social life. Furthermore, the findings will lead to recommendations for health promotion interventions for frail nursing home residents. Trial registration The trial was prospectively registered at DRKS.de with the registration number DRKS00014957 on October 9, 2018

Physical activity and health promotion for nursing staff in elderly care: a study protocol for a randomised controlled trial

Introduction Nursing staff is burdened by high workload and stress. Furthermore, heavy lifting, as well as transferring nursing home residents, cause lumbar tissue damage and back pain. Exercise intervention studies to reduce work-related problems are rare and the evidence for efficacy of studies among nurses is limited. Studies including targeted analysis of requirements are necessary to generate effective recommendations and tailored interventions for health promotion programmes. The purpose of this multicentred intervention study is to identify work-related problems, to implement health promotion programmes and to evaluate their effectiveness. Methods and analysis A randomised controlled trial will be conducted, including a total of 48 nursing home facilities in eight regions of Germany with an estimated sample size of 700 nurses. Standardised ergonomics and posture training (10 weeks, once a week for 20–30 min) and subsequently, back-fitness training (12 weeks, once a week for 45–60 min) will be administered. Following the implementation of standardised health promotion programmes, further demand-oriented interventions can be implemented. The perceived exposure to work-related demands, work-related pain in different parts of the body, health-related quality of life, perceived stress, work-related patterns of behaviour and experience, presentism behaviour, work environment as well as general needs and barriers to health promotion, will be assessed at baseline (pre-test), at 10 weeks (post-test, after ergonomics training), at 22 weeks (post-test, after back-fitness training) and at 34 weeks of the programme (follow-up). Ethics and dissemination The study was reviewed and approved by the local ethics committee of the University of Hamburg (AZ: 2018_168). The results of the study will be published in open-access and international journals. Furthermore, the results will be presented in the participating nursing homes and at national and international conferences