Neuromuscular adaptations in endurance-trained boys and men

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 health-related 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.;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, normalized for peak EMG amplitude, was consistently higher in the endurance-trained 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 normalized 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 normalized 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 suggest a higher relative involvement of type I muscle fibres in the endurance-trained athletes.;In children and adults, resistance training can enhance strength and increase 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 (RTD), along with the pattern of muscle activation during elbow and knee flexion and extension in muscle-endurance-trained and untrained men and boys.;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. Furthermore, training intervention studies could reveal the effects of endurance training during different developmental stages, as well as In different muscle groups.