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Thomas Korff and Jody L. Jensen

When performing skillful movement muscular and nonmuscular forces act in concert to produce a resultant force that complies with the goal of the task. Nonmuscular forces are directly dependent on the anthropometry of the performer. The purpose of this study was to determine the effect of age-related changes in relative anthropometric characteristics between 5 and 10 years of age on muscular power production during pedaling. A secondary purpose was to determine the dependence of this effect on movement speed. A torque-driven model of two-legged pedaling was used to track experimental kinematics and forces obtained from 6 experienced adult cyclists pedaling at 60 and 120 rpm. Relative anthropometric characteristics were modified to simulate pedaling for children of 5, 7.5, and 10 years of age. Analyses of variance revealed that age-related differences in anthropometry did not affect the muscular contribution to crank power (p > .05), while they had a significant effect on the muscular contribution to limb power (p < .05). Adjustments by the proximal muscle groups (muscles spanning the hip and knee joints) were necessary to account for anthropometry-driven changes in nonmuscular power. These effects were independent of movement speed. Our results provide researchers with useful information to interpret age-related differences in muscular power production more accurately.

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Christie Powell, Jody Jensen and Samantha Johnson

Context : As sport participation increases globally, so will injury-related risks. The process used to determine return-to-sport following injury is vital to future sport participation and injury prevention. Early specialization along with poor management of sport participation causes an increase in injury risk and potential long-term health consequences for youth athletes. Objectives : Previous injury is a common intrinsic risk factor for new injuries. Identifying functional performance deficits, defined by return-to-sport criteria, minimizes these risk factors and provides athletes with guidelines to return safely to sport. The purposes of this clinical commentary and literature review are to provide a summary of current concepts and clinical practices and to identify functional performance measures as clinical assessment tools for return-to-play criteria in the youth population. Evidence : A literature review was completed using numerous databases, where 154 relevant articles were reviewed and 22 articles were included in this commentary. Of the 22 articles using functional performance measures for return-to-sport criteria, 6 were specific to youth, 12 had mixed populations of adults and youth, and 4 were normative samples for specific youth populations. Acquisition : The gaps in the literature pertaining to functional performance measures in the youth population are addressed, and future research needs for return-to-sport criteria are identified. Evidence Synthesis : This descriptive literature review identifies 22 articles that meet the search criteria for the youth population discussing the use of clinical functional performance measures in order to identify return-to-sport criteria for lower-extremity injuries. Conclusions: Due to the inconsistencies in terminology, definitions, and standardization of clinical assessment tools, it seems necessary to create a comprehensive functional performance test battery for the lower extremity that can be used as return-to-sport criteria.

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Thomas Korff, Ann H. Newstead, Renate van Zandwijk and Jody L. Jensen

The purpose of this study was to examine the interactions between aging, activity levels and maximal power production during cycling. Participants were divided into younger adults (YA), older active adults (OA,) and older sedentary adults (OS). Absolute maximum power was significantly greater in YA compared with OS and OA; no differences were found between OA and OS. The age-related difference in maximum power was accompanied by greater absolute peak knee extension and knee flexion powers. Relative joint power contributions revealed both age- and activity-related differences. YA produced less relative hip extension power than older adults, regardless of activity level. The OS participants produced less relative knee flexion power than active adults, regardless of age. The results show the age-related decline in muscular power production is joint specific and that activity level can be a modifier of intersegmental coordination, which has implications for designing interventions for the aging population.