Elbow Flexor Strength, Muscle Size, and Moment Arms in Prepubertal Boys and Girls

Abstract

The aim of this study was to examine elbow fl exion torque, muscle cross-sectional area (CSA), and leverage in boys and girls. Thirty-eight prepubertal children (9.6 ± 0.3 years) volunteered to participate. All performed isometric fl exion actions at 10°, 50°, and 90° of elbow fl exion. Magnetic resonance imaging was used to assess elbow fl exor (EF) muscle CSA and brachialis moment arm lengths. No signifi cant gender differences were observed for any of the variables studied. EF CSA was directly proportional to isometric torque at 50° and 90°. CSA explained between 47% and 57% of torque variance. Moment arm estimates explained 19% of the variance in isometric torque at 90°. These baseline data contribute to our understanding of factors infl uencing strength variation during childhood.Upper-extremity strength differences between boys and girls are of particular interest, given that by adulthood, males outperform females in practically all upper-body sport events involving a strength component (10). Examination of the factors contributing to strength variation will aid our understanding of differences in upper-body performance, but initial baseline data on prepubertal children are required in order to put observations during growth and maturation into context.The majority of studies have focused on the ability of intrinsic muscle properties to explain strength variation (4); relatively few have examined extrinsic factors, which include the role of anatomy and biomechanics (5). However, unless muscle force is measured directly at the tendon or at the point of application of a load, leverage (an extrinsic factor) will infl uence measurements of strength. When strength is expressed as joint torque, it represents the product of all the muscle forces and their moment arms contributing to a specifi ed joint action. Given that muscle force is also infl uenced by moment arm length via its effect on musculotendinous length changes and velocity, it is important to understand the role of variation in moment arm lengths, across a joint range of motion and between individuals, in torque development (15).

Sex differences in time to task failure during early pubertal development

“…Our findings indicate that boys and girls at prepubertal stage T1 had similar MVC torques and times to task failure. This finding is in agreement with others who reported no sex difference in arm muscle strength and upper body muscular endurance in prepubertal boys and girls.…”

Can Achilles tendon moment arm be predicted from anthropometric measures in pre-pubescent children?

“…The mechanisms underpinning the development of age-related gains in muscular strength include neuro-maturation (Savelsbergh, 2003), increases in muscle size (Kanehisa et al, 1995;Morse et al, 2008), changes in muscle architecture (Binzoni et al, 2001) and increases in moment arm length (Wood et al, 2006;Morse et al, 2008;O'Brien et al, 2009).…”

“…Its measurement is vital for quantifying changes in muscle force production (Wood et al, 2006), where the changing moment arm impacts on joint moment magnitude. In addition, to moment arm length is both an essential parameter in many musculoskeletal models (Delp et al, 1990) and is also used in the calculation of other important parameters such as tendon stiffness and Young's modulus (O'Brien et al, 2010).…”

Efficacy of School-Based Interventions for Improving Muscular Fitness Outcomes in Adolescent Boys: A Systematic Review and Meta-analysis

“…Furthermore, existing evidence supports the role of MF interventions for improving physiological and psychological health [6,8,47]. However, research suggests that the development of MF in upper and lower limbs is not homogeneous, and may vary throughout growth and maturation [48][49][50]. The heterogeneous nature of MF development in adolescent boys may not be accounted for when prescribing RT on a large scale.…”