Resumen de Strength Athletes Are Capable to Produce Greater Muscle Activation and Neural Fatigue During High-Intensity Resistance Exercise Than Nonathletes

Juha P. Ahtiainen, Keijo Häkkinen

• Acute neuromuscular responses to maximum versus forced repetition (FR) knee extension resistance exercises (4 sets of 12 repetitions [reps] with a 2-minute recovery between the sets) were examined in 4 male strength athletes (SAs) and 4 nonathletes. Maximum repetition (MR) sets were performed to voluntary exhaustion (12 repetition maximum [RM]), whereas in the FR sets, the load was greater (8RM) and the set was continued after voluntary fatigue with 4 additional assisted reps. Maximal isometric force and electromyogram (EMG) activity of the knee extensors were measured before and after the exercise, as well as 2 recovery days after the exercise. Electromyogram activity was also measured during the actual concentric phases of the knee extensions. Both loading protocols in both groups led to decreases in isometric force, but no significant changes were observed in EMG activity during isometric actions at any time points. However, the difference between the 2 loading protocols and experimental groups was observed in muscle activity during the concentric phases of the knee extensions. As expected, EMG activity increased in both groups throughout the MR sets when compared with the first repetitions of the sets. Only in SAs, EMG activity decreased significantly at the end of the FR sets. The results suggest that experienced SAs were capable to activate their muscles to a greater extent than their non-strength-trained counterparts indicated by neural fatigue during the FR exercise. Greater motor unit activation in SAs than in nonathletes may be due to training-induced neural adaptation, which manifested during fatiguing exercise. The present study suggests that FRs are an efficient training protocol to overload the neuromuscular system especially in SAs.