Impact of wear time criteria upon physical activity estimates in children

Paper presented at 14th meeting of the International Society of Behavioral Nutrition and Physical Activity: Advancing Behavior Change Science, June 2015, EdinburghPurpose: Lack of compliance with accelerometer wear time requirements can potentially lead to selection bias within a study. In an attempt to maximize participant numbers researchers may be tempted to employ more lenient wear time criteria. However, this may lead to misclassification of physical activity (PA) and sedentary time (ST), both through reducing the monitoring period and through failure to capture distinct periods of the day, resulting in inaccurate estimates of PA and ST and masking of true relationships between PA, ST and health. The present study aimed to explore the misclassification that may occur using three distinct 10 hour periods across the day in comparison to 24 hour continuous wear in children. Methods: 149 children were asked to wear a GENEActiv accelerometer on their left wrist for 24 hours a day, for a period of 7 days. Including only children who complied with the full wear time protocol (n = 78), weekly average estimates of ST and time spent in light, moderate and vigorous PA were created for the full 24 hour criteria and for three 10 hour periods (8am – 6pm, 10am – 8pm, 12pm – 10pm) . Repeated Measures ANOVA were used to assess for significant differences across monitoring periods. Results: In comparison to complete observation (24hours), the 10 hour periods across the day resulted in an underestimation of time spend sedentary and in each activity intensity (ps < 0.05). ST was underestimated by an average of 269 minutes, whilst Moderate to Vigorous PA (MVPA) was underestimated by 30 minutes. Between the 10 hour periods, higher rates of ST were accumulated in the latest period (12pm – 10pm), whilst higher estimates of MVPA were apparent between 8am and 6pm. Conclusions: Time in PA and ST was underestimated with the use of shorter wear periods and researchers may be unknowingly misclassifying PA and ST by not accounting for which period of the day was measured. Future studies should use longer monitoring periods to gain accurate assessment of PA and to establish relationships with health variables

The relationship between the raw acceleration signal from a commercially available accelerometer and ground reaction force

PublishedPoster presentation. 2nd International Congress on Ambulatory Monitoring of Physical Activity and Movement Hosted by Glasgow Caledonian University May 2011Accelerometers are increasingly employed to assess relationships between physical activity and health. Output is in proprietary counts, hindering between model comparisons, and translated into time spent at activity intensities based on energy expenditure. Bone mineral density (BMD) is improved by mechanical overload. Thus, in order to use accelerometers to assess activity beneficial to bone, accelerometer output needs to be calibrated against mechanical loading, e.g. ground reaction force (GRF). The purpose of this study was to examine the relationship between the raw acceleration signal (vertical and resultant over three axes) from a new commercially available accelerometer and mechanical loading

Prolonged Unilateral Disuse Osteopenia 14 Years Post External Fixator Removal: A Case History and Critical Review

Disuse osteopenia is a complication of immobilisation, with reversal generally noted upon remobilisation. This case report focuses on a patient who was seen 18 years following a road traffic collision when multiple fractures were sustained. The patient had an external fixator fitted for a tibia and fibula fracture, which remained in situ for a period of 4 years. Following removal, the patient was mobilised but, still required a single crutch to aid walking. Fourteen years post removal of the fixator, the patient had a DXA scan which, demonstrated a T-score 2.5 SD lower on the affected hip. This places the patient at an increased risk of hip fracture on this side, which requires monitoring. There appear to be no current studies investigating prolonged disuse-osteopenia in patients following removal of long-term external fixators. Further research is required to quantify unilateral long-term effects to bone health and fracture risk in this population

Validation of the GENEA accelerometer

Purpose: The study aims were: 1) to assess the technical reliability and validity of the GENEA using a mechanical shaker; 2) to perform a GENEA value calibration to develop thresholds for sedentary and light-, moderate-, and vigorous-intensity physical activity; and 3) to compare the intensity classification of the GENEA with two widely used accelerometers. Methods: A total of 47 GENEA accelerometers were attached to a shaker and vertically accelerated, generating 15 conditions of varying acceleration and/or frequency. Reliability was calculated using SD and intrainstrument and interinstrument coefficients of variation, whereas validity was assessed using Pearson correlation with the shaker acceleration as the criterion. Next, 60 adults wore a GENEA on each wrist and on the waist (alongside an ActiGraph and RT3 accelerometer) while completing 10-12 activity tasks. A portable metabolic gas analyzer provided the criterion measure of physical activity. Analyses involved the use of Pearson correlations to establish criterion and concurrent validity and receiver operating characteristic curves to establish intensity cut points. Results: The GENEA demonstrated excellent technical reliability (CVintra = 1.4%, CVinter = 2.1%) and validity (r = 0.98, P < 0.001) using the mechanical shaker. The GENEA demonstrated excellent criterion validity using V̇O as the criterion (left wrist, r = 0.86; right wrist, r = 0.83; waist, r = 0.87), on par with the waist-worn ActiGraph and RT3. The GENEA demonstrated excellent concurrent validity compared with the ActiGraph (r = 0.92) and the RT3 (r = 0.97). The waist-worn GENEA had the greatest classification accuracy (area under the receiver operating characteristic curve (AUC) = 0.95), followed by the left (AUC = 0.93) and then the right wrist (AUC = 0.90). The accuracy of the waist-worn GENEA was virtually identical with that of the ActiGraph (AUC = 0.94) and RT3 (AUC = 0.95). CONCLUSION:: The GENEA is a reliable and valid measurement tool capable of classifying the intensity of physical activity in adults. © 2011 by the American College of Sports Medicine

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

The effects of exercise-induced muscle damage on the human response to dynamic exercise

Exercise-induced muscle damage (EIMD) is a commonly experienced phenomenon, yet its effect on the human response to dynamic exercise is poorly understood. Therefore the intention of this thesis was to provide empirical evidence to advance the scientific knowledge and understanding of the phenomenon of EIMD; principally by investigating the physiological, perceived exertion and metabolic responses to the performance of dynamic exercise with EIMD. The eccentric, muscle-damaging exercise protocol employed for all four studies involved participants completing 100 squats performed as 10 sets of 10 repetitions with the load on the bar corresponding to 70% of the individual’s body mass. Measures of markers of muscle damage were taken before and after the eccentric exercise protocol in each of the four studies. The markers used were plasma creatine kinase activity, isokinetic peak torque and perceived muscle soreness. Cycling rather than running was used as the dynamic exercise mode in studies 1, 2 and 4 in order to avoid the confounding influence of alterations in gait subsequent to EIMD. The dynamic exercise in study 3 was performed inside a whole body scanner and was therefore limited to knee extension and flexion. These four studies have provided novel insights into the influence of eccentric, muscle-damaging exercise on the human response to the performance of dynamic exercise. We have demonstrated for the first time that following EIMD, the enhanced ventilatory response to dynamic exercise is provoked by stimuli unrelated to the blood lactate response, and that this enhanced ventilation may provide an important cue to inform the perception of effort. Furthermore, we have shown that the reduced time to exhaustion observed following EIMD is associated with an elevated perception of exertion and increases in [Pi] during dynamic exercise. Finally, we have demonstrated that the kinetic response is unaltered during the transition to high intensity dynamic exercise. Changes in [HHb] kinetics indicate that compensatory mechanisms act to preserve blood-myocyte O2 flux in the face of microvascular dysfunction, resulting in the unaltered observed across the rest-to-exercise transition.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

THE MEASUREMENT AND INTERPRETATION OF CHILDREN'S PHYSICAL ACTIVITY

The accurate and reliable assessment of physical activity is necessary for any research study where physical activity is either an outcome measure or an intervention. The aim of this review is to examine the use of objective measurement techniques for the assessment and interpretation of children's physical activity. Accurate measurement of children's activity is challenging, as the activity is characteristically sporadic and intermittent, consisting of frequent, short bouts. Objective measures of physical activity include heart rate telemetry, pedometry and accelerometry, and each of these methods has strengths and limitations. Heart rate is suited to the measurement of sustained periods of moderate and vigorous activity, pedometry provides a valid measure of total activity, and accelerometry provides a valid measure of total activity as well as the pattern and intensity of activity. As the weaknesses of heart rate and accelerometry for the assessment of activity are not inter-correlated, a combination of the two methods may be more accurate than either method alone. Recent evidence suggests that the Actiheart, an integrated accelerometer and heart rate unit, provides a more accurate prediction of children's energy expenditure than either heart rate or accelerometry alone. However, the cost of the Actiheart is prohibitive for large-scale studies. The pedometer is recommended when only the total amount of physical activity is of interest. When the intensity or the pattern of activity is of interest, accelerometry is the recommended measurement too

Intermonitor variability of the RT3 accelerometer during typical physical activities

Purpose To evaluate the reliability and variability of eight RT3 accelerometers.Methods The RT3 were subjected to two repeated trials of six activities: rest, walking (4 and 6 km·h−1), running (8 and 10 km·h−1), and sit-stand position (20 min). One person performed all trials (female: age 24 yr, height 158.0 cm, mass 48.2 kg). Each activity lasted 12 min. The middle 10 min were taken from each 12-min trial and used as the output measure (cts·min−1). Data were analyzed for activity (6), monitor (8), and trial (2) effects using four three-way ANOVA: vector magnitude, X (vertical), Y (anterioposterior), and Z (mediolateral) axes.Results Intermonitor coefficient of variation was <6% during locomotive activities, however, increased to 8–25% during sit-stand. A three-way interaction was found for vector magnitude (F35,315=88945.7, P < 0.001) and Y (F35,315=978435.6, P < 0.001) and Z axes (F35,315=103802.8, P < 0.001). A two-way activity × monitor interaction was found for the X axis (F35,315=1037787.0, P < 0.001). Follow-up tests revealed no differences between trials 1 and 2 for vector magnitude, X and Z axes. One monitor recorded significantly lower activity counts in trial 1 compared with trial 2 along the Y axis. Intermonitor differences were evident at 4, 6, 8, and 10 km·h−1 for the Y and Z axes, and at 6, 8, and 10 km·h−1 for the vector magnitude and X axis. Variability between monitors at each activity increased as intensity increased.Conclusion Reliability of the RT3 is good; however, intermonitor variability exists. The vertical axis of the RT3 accelerometer showed the least variability and was the most reliable. It is recommended that intermonitor variability and reliability of RT3 on each axis be assessed before use