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Yvonne G. Ellis, Dylan P. Cliff, Steven J. Howard and Anthony D. Okely

, this evidence is scarce and inconsistent, especially in cognition and musculoskeletal health ( 6 , 18 , 30 ). The effects of prolonged sitting time on cognitive outcomes have gained more interest ( 37 ). In preschoolers, the relationships of too much sitting on cognition are unclear ( 30 ). A key

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Nathaniel S. Nye, Drew S. Kafer, Cara Olsen, David H. Carnahan and Paul F. Crawford

Background: Abdominal circumference (AC) is superior to body mass index (BMI) as a measure of risk for various health outcomes. Our objective was to compare AC and BMI as predictors of lower extremity overuse injury (LEOI) risk. Methods: Retrospective review of electronic medical records of 79,868 US Air Force personnel over a 7-year period (2005–2011) for incidence of new LEOI. Subjects were stratified by BMI and AC. Injury risk for BMI/AC subgroups was calculated using Kaplan–Meier curves and Cox proportional-hazards regression. Receiver operating characteristic curves with area under the curve were used to compare each model’s predictive value. Results: Cox proportional-hazards regression showed significant risk association between elevated BMI, AC, and all injury types, with hazard ratios ranging 1.230–3.415 for obese versus normal BMI and 1.665–3.893 for high-risk versus low-risk AC (P < .05 for all measures). Receiver operating characteristic curves with area under the curve showed equivalent performance between BMI and AC for predicting all injury types. However, the combined model (AC and BMI) showed improved predictive ability over either model alone for joint injury, overall LEOI, and most strongly for osteoarthritis. Conclusions: Although AC and BMI alone performed similarly well, a combined approach using BMI and AC together improved risk estimation for LEOI.

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Robert J. Kowalsky, Sophy J. Perdomo, John M. Taormina, Christopher E. Kline, Andrea L. Hergenroeder, Jeffrey R. Balzer, John M. Jakicic and Bethany Barone Gibbs

Background: Limited research examines the influence of sit-stand desks on ratings of discomfort, sleepiness, and fatigue. This study evaluated the time course of these outcomes over 1 day. Methods: Adults (N = 25) completed a randomized cross-over study in a laboratory with two 8-hour workday conditions: (1) prolonged sitting (SIT) and (2) alternating sitting and standing every 30 minutes (SIT-STAND). Sleepiness was assessed hourly. Discomfort, physical fatigue, and mental fatigue were measured every other hour. Linear mixed models evaluated whether these measures differed across conditions and the workday. Effect sizes were calculated using Cohen’s d. Results: Participants were primarily white (84%) males (64%), with mean (SD) body mass index of 31.9 (5.0) kg/m2 and age 42 (12) years. SIT-STAND resulted in decreased odds of discomfort (OR = 0.37, P = .01) and lower overall discomfort (β = −0.19, P < .001, d = 0.42) versus SIT. Discomfort during SIT-STAND was lower in the lower and upper back, but higher in the legs (all Ps< .01, d = 0.26–0.42). Sleepiness (β = −0.09, P = .01, d = 0.15) and physical fatigue (β = −0.34, P = .002, d = 0.34) were significantly lower in SIT-STAND. Mental fatigue was similar across conditions. Conclusions: Sit-stand desks may reduce acute levels of sleepiness, physical fatigue, and both overall and back discomfort. However, levels of lower extremity discomfort may be increased with acute exposure.

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Ansku Holstila, Ossi Rahkonen, Eero Lahelma and Jouni Lahti

Background:

The association between changes in physical activity and sickness absence is poorly understood. The aim of this study was to examine the association between changes in leisure-time physical activity and long-term sickness absence due to any cause and musculoskeletal and mental causes.

Methods:

We measured physical activity at baseline in 2000–2002 (response rate 67%) and at follow-up in 2007 (response rate 83%) among middle-aged employees of the City of Helsinki, Finland. The survey data were linked to the Finnish Social Insurance Institute’s register data on sickness benefit periods > 9 days, including diagnoses (ICD-10; International Statistical Classification of Diseases and Related Health Problems, 10th revision) (mean follow-up 2.3 years). We used a negative binomial model to calculate rate ratios. The analyses included 4010 respondents (81% women).

Results:

Those who were persistently vigorously active and those whose physical activity level changed from low to moderate or vigorous, from moderate to vigorous, or from vigorous to moderate were at lower risk for sickness absence than were the persistently low-activity group. For sickness absence due to musculoskeletal causes, vigorous activity showed stronger associations, whereas mental causes showed no such associations.

Conclusions:

To reduce sickness absence due to both musculoskeletal and mental causes, middle-aged and aging employees should be encouraged to engage in physical activity.

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Laura S. Kox, P. Paul F.M. Kuijer, Dagmar A.J. Thijssen, Gino M.M.J. Kerkhoffs, Rick R. van Rijn, Monique H.W. Frings-Dresen and Mario Maas

Background: The benefits and risks of performing popular wrist-loading sports at a young age have not been investigated systematically. We aimed to evaluate positive and negative long-term wrist-related health effects of sports performance requiring repetitive wrist loading during youth. Methods: Six databases were searched for cohort and cross-sectional studies. Three investigators selected studies evaluating quantitatively measured health effects of upper extremities in athletes practicing wrist-loading sports (gymnastics, tennis, volleyball, field hockey, rowing, and judo) for minimally 4 months before the age of 18. Results: A total of 23 studies with 5 outcome measures, nearly all of moderate to good quality, were eligible for inclusion. Bone mineral density and bone mineral content were higher in athletes compared with controls and in tennis players’ dominant arm. Mixed results were found for ulnar variance in gymnasts. Handgrip strength was greater in tennis players’ dominant arm and in experienced gymnasts. Conclusions: Wrist-loading sports performance during youth can promote bone strength in wrists and dominant handgrip strength, but evidence on the lasting of these effects and on prevalence of wrist joint degeneration in former young athletes is limited. For better counseling of young athletes and their parents, future studies with increased comparability are essential, for which recommendations are provided.

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Eric Tsz-Chun Poon, John O’Reilly, Sinead Sheridan, Michelle Mingjing Cai and Stephen Heung-Sang Wong

the musculoskeletal health of this population. Acknowledgments The authors would like to acknowledge the significant role played by the Hong Kong Jockey Club in facilitating this research project to take place, in particular; Mr. Bill Nader and Mr. Steve Railton. Finally, the authors would like to

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David A. Greene, Geraldine A. Naughton, Julie N. Briody, Allan Kemp, Helen Woodhead and Nathalie Farpour-Lambert

This study compared tibial bone and muscle geometry and total body and regional bone mineral content (BMC) in elite female adolescent middle-distance runners (n = 20, age: 16 ± 1.7 years) and age- and sex-matched controls (n = 20, 16 ± 1.8 years) using magnetic resonance imaging and dual-energy X-ray absorptiometry. Significant advantages were found in athletes compared with controls in bone and muscle geometric values for distal tibial cortical, medullary cavity, distal tibial total muscle and dorsi flexor muscle compartment cross-sectional area, and regional BMC. Results imply mechanical loads associated with middle-distance running might be beneficial to musculoskeletal health in adolescent females.

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Ronald F. Zernicke, Grant C. Goulet, Peter R. Cavanagh, Benno M. Nigg, James A. Ashton-Miller, Heather A. McKay and Ton van den Bogert

As a field, biomechanics comprises research from the molecular and cellular levels, to tissues, to organs, to organisms and their movements. In the past 50 years, the impact of biomechanics research on society has been amplified dramatically. Here, we provide five brief summaries of exemplar biomechanics results that have had substantial impact on health and our society, namely 1) spaceflight and microgravitational effects on musculoskeletal health; 2) impact forces, soft tissue vibrations, and skeletal muscle tuning affecting human locomotion; 3) childbirth mechanics, injuries, and pelvic floor dysfunction; 4) prescriptive physical activity in childhood to enhance skeletal growth and development to prevent osteoporotic fractures in adulthood and aging; and 5) creative innovations in technology that have transformed the visual arts and entertainment.

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Jin Qin, Matthieu Trudeau, Bryan Buchholz, Jeffrey N. Katz, Xu Xu and Jack T. Dennerlein

Upper extremity kinematics during keyboard use is associated with musculoskeletal health among computer users; however, specific kinematics patterns are unclear. This study aimed to determine the dynamic roles of the shoulder, elbow, wrist and metacarpophalangeal (MCP) joints during a number entry task. Six subjects typed in phone numbers using their right index finger on a stand-alone numeric keypad. The contribution of each joint of the upper extremity to the fingertip movement during the task was calculated from the joint angle trajectory and the Jacobian matrix of a nine-degree-of-freedom kinematic representation of the finger, hand, forearm and upper arm. The results indicated that in the vertical direction where the greatest fingertip movement occurred, the MCP, wrist, elbow (including forearm) and shoulder joint contributed 10.2%, 55.6%, 27.7% and 6.5%, respectively, to the downward motion of the index finger averaged across subjects. The results demonstrated that the wrist and elbow contribute the most to the fingertip vertical movement, indicating that they play a major role in the keying motion and have a dynamic load beyond maintaining posture.

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Lauren A. Burt, David A. Greene and Geraldine A. Naughton

level. Understanding more about the impact of gymnastics on young males during growth may be important in promoting this sport for musculoskeletal health via the muscle bone unit. There are several different techniques used to assess the material properties and geometric characteristics of bone. The