Muscle Strength and Contractile Kinetics of Isometric Elbow Flexion in Girls and Women

Abstract

Ten prepubertal girls and 15 young women were tested for maximal torque, peak rate of torque development, electro-mechanical delay (EMD), and time to peak rate of torque development during isometric elbow flexion. Absolute peak torque (17.0 ± 7.7 vs. 40.5 ± 8.3 Nm) and peak rate of torque development (105.9 ± 58.6 vs. 297.2 ± 113.0 Nm·s −1 ) were lower in the girls (p < .05). Normalized to muscle cross sectional area, torque was similar (8.27 ± 2.74 vs. 8.44 ± 1.65 Nm·cm −2 ), as was peak rate of torque development, normalized to peak torque (6.21 ± 1.94 vs. 7.30 ± 2.26 Nm·s −1 /Nm). Both, time to peak rate of torque development (123.8 ± 36.0 vs. 110.5 ± 52.6 ms) and EMD (73.2 ± 28.6 vs. 51.9 ± 25.6 ms), were longer in the girls, although EMD's difference only approached statistical significance (p = .06). Age-related isometric strength differences in females appear to be mainly muscle-size dependent. However, the time to peak torque and EMD findings suggest differential motor-unit activation which may functionally manifest itself in fast dynamic contractions.Numerous studies have demonstrated that children's maximal muscle strength is lower than that of adults (5,18,42). In males, muscle strength is consistently lower in boys even when normalized for body size (5,42 CIHR Author ManuscriptCIHR Author Manuscript CIHR Author Manuscript some studies report a lower body size-normalized strength in girls compared with women (29), others do not (5,28,31,38,43).Several factors, besides body size may contribute to age-related differences in maximal strength, including differences in muscle activation, fiber composition, and agonistantagonist cocontraction. The scant available literature on muscle fiber composition suggests that the latter is similar in children and adults (12). This is supported by the similar contractile characteristics (contraction time and half-relaxation time) during electrically evoked twitch contraction in children and adults (4,8,9,22,35,39). Although few studies have suggested a lower percentage of type II muscle fibers in boys compared with men (15,34), the difference is too small to account for the age-related muscle strength differences observed between boys and men. No comparison of muscle fiber-type composition has been reported between girls and women.The rate or degree of muscle activation has been suggested to be lower in boys compared with men, based on indirect evidence and varying techniques (1,2,4,5,23,25,33,39,45). However, all these comparisons were made with heterogeneous or male-only samples. There are no comparisons of muscle activation indices or examination of their roles in girl-woman strength differences.Differences in the rate of force development are likely manifestations of the nature of muscle activation or its composition. It too appears to be lower in children than in adults, whether measured during maximal voluntary (1,21), or electrically stimulated twitch contractions (4,22), but has been demonstrated only in males. No age comparisons have been published fo...

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

“…Subgroup analyses of muscle group was conducted to explore potential variance in MF outcomes, attributed to growth, maturation, and peak strength velocity occurring approximately 2 years after peak height velocity in adolescent boys [91,92]. Evidence suggests that children and adolescents have a reduced ability to recruit type 2 muscle fibres, resulting in a lower voluntary muscle strength, speed, and power output [93][94][95]. Interventions conducted in the school environment may provide variance as to when students reach PHV and in turn, PSV.…”

Child—Adult Differences in Muscle Activation — A Review

“…Rate of EMG Rise. The initial slope of the rectified surface-EMG trace has been thought of as reflecting the initial rate of muscle activation (25,34,37,42,44). Greater involvement of type-II motor units is expected to manifest itself by greater EMG activity immediately following neural stimulation.…”

“…their muscles to the extent typical of adults (5,6). Subsequently, in view of more supporting evidence, this view has been fostered by others (4,13,18,34,35,37,48,72).…”

Do neuromuscular adaptations occur in endurance-trained boys and men?

“…The intrasession reliability for maximal strength reliability coefficient (ICC 2,1 ) was 0.95 and 0.93 for boys and men, respectively. A similar protocol was used in previous studies in the pediatric and adult population in our laboratory (Falk et al 2009a(Falk et al , 2009b. To reduce the noise on the recorded torque channel, an EMG-analog signal access interface (Biodex) was used.…”

“…Q 30 was measured over the first 30 ms of electromechanical activity. Q 30 was defined as the area under the linear envelope of the detected EMG signal during the initial 30 ms (Gabriel and Boucher 2000;Gottlieb et al 1989), and has been previously used to reflect rate of increase in muscle activation during a maximal task (Falk et al 2009a(Falk et al , 2009bGabriel and Boucher 2000;Gottlieb et al 1989). The EMG activity onset was defined as the point in time at which the signal first increased 5 SDs above the mean of the baseline and stayed above that point for more than 20 ms.…”