|dc.description.abstract||Competitive sports participation in youth is becoming increasingly more common in the
Western world. It is widely accepted that sports participation, specifically endurance
training, is beneficial for physical, psychomotor, and social development of children. The
research on the effect of endurance training in children has focused mainly on healthrelated
benefits and physiological adaptations, particularly on maximal oxygen uptake.
However, corresponding research on neuromuscular adaptations to endurance training
and the latter's possible effects on muscle strength in youth is lacking.
In children and adults, resistance training can enhance strength and mcrease
muscle activation. However, data on the effect of endurance training on strength and
neuromuscular adaptations are limited. While some evidence exists demonstrating
increased muscle activation and possibly increased strength in endurance athletes
compared with untrained adults, the neuromuscular adaptations to endurance training in
children have not been examined. Thus, the purpose of this study was to examine
maximal isometric torque and rate of torque development (RID), along with the pattern
of muscle activation during elbow and knee flexion and extension in muscle-endurancetrained
and untrained men and boys.
Subjects included 65 males: untrained boys (n=18), endurance-trained boys
(n=12), untrained men (n=20) and endurance-trained men (n=15). Maximal isometric
torque and rate of torque development were measured using an isokinetic dynamometer
(Biodex III), and neuromuscular activation was assessed using surface electromyography
(SEMG). Muscle strength and activation were assessed in the dominant arm and leg, in a
cross-balanced fashion during elbow and knee flexion and extension. The main variables
included peak torque (T), RTD, rate of muscle activation (Q30), Electro-mechanical delay
(EMD), time to peak RTD and co-activation index.
Age differences in T, RTD, electro-mechanical delay (EMD) and rate of muscle
activation (Q30) were consistently observed in the four contractions tested. Additionally,
Q30, nonnalized for peak EMG amplitude, was consistently higher in the endurancetrained
men compared with untrained men. Co-activation index was generally low in all
contractions. For example, during maximal voluntary isometric knee extension, men were
stronger, had higher RTD and Q30, whether absolute or nonnalized values were used.
Moreover, boys exhibited longer EMD (64.8 ± 18.5 ms vs. 56.6 ± 15.3 ms, for boys and
men respectively) and time to peak RTD (112.4 ± 33.4 ms vs. 100.8 ± 39.1 ms for boys
and men, respectively). In addition, endurance-trained men had lower T compared with
untrained men, yet they also exhibited significantly higher nonnalized Q30 (1.9 ± 1.2 vs.
1.1 ± 0.7 for endurance-trained men and untrained men, respectively). No training effect
was apparent in the boys.
In conclusion, the findings demonstrate muscle strength and activation to be lower
in children compared with adults, regardless of training status. The higher Q30 of the
endurance-trained men suggests neural adaptations, similar to those expected in response
to resistance training. The lower peak torque may su9gest a higher relative involvement
oftype I muscle fibres in the endurance-trained athletes.
Future research is required to better understand the effect of growth and
development on muscle strength and activation patterns during dynamic and sub-maximal
isometric contractions. Furthennore, training intervention studies could reveal the effects
of endurance training during different developmental stages, as well as in different