Affiliations: [a] Centre for Sports Medicine and Human Performance,
Brunel University, Uxbridge, UK
Note: [] Corresponding author: Thomas Korff, PhD, Centre for Sports
Medicine and Human Performance, Brunel University, Uxbridge, UB8 3PH, UK. Tel.:
+44 1895 266 477; Fax: +44 1895 269 769; E-mail: thomas.korff@brunel.ac.uk
Abstract: The mechanisms underlying age-related differences in maximum power
production during multi-joint exercises are not fully understood. One factor
that could contribute to these age-related differences is a differential
development of the ability to generate maximum strength and power across the
involved joints. Therefore, the purpose of this study was to investigate the
age-related changes in knee extensor and plantarflexor strength under isometric
and isokinetic conditions. Ten boys (11.6 ± 0.8 yrs) and
10~male adults (27.7 ± 5 yrs) participated in the study.
Ankle plantarflexion and knee extension strength were measured isometrically
and isokinetically at 30, 75 and 120°/s. Muscle
activity (EMG) from the Gastrocnemius Medialis and Vastus Lateralis was also
recorded. Multivariate analyses of variance identified significant Age by Joint
interactions for isometric peak torque (PT) and isokinetic peak joint powers
for all conditions (p<0.05). Effect sizes revealed that
under isometric conditions, the difference between peak plantarflexor and knee
extensor torques was moderate in children, whilst in adults, this effect was
large. Under isokinetic conditions, the effect sizes describing the differences
between peak joint powers produced at the ankle and knee joints were large for
both children and adults. A MANOVA revealed that the Age by Muscle interaction
for the magnitude of muscle activity was non-significant (p>
0.05). Our results suggest that the development of lower limb isometric
strength is joint-dependent and that this joint dependence is not due to a
muscle-specific development of motor unit recruitment.
