Post by John A. Casler on Jul 31, 2009 6:56:15 GMT -8
This is from Jamie Carruthers as posted to SuperTraining
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Strength athletes are capable to produce greater muscle activation and neural fatigue during high-intensity resistance exercise than nonathletes.Strength Cond Res. 2009 Jul;23(4):1129-34. Links
Ahtiainen JP, Häkkinen K.
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.
Further comments:
A unique finding in the present study was that neural fatigue occurs during the loading in SAs, and it can be observed as decreased EMG activity during fatiguing high-intensity dynamic resistance exercise. There might be several explanations why especially strength-trained men were able to produce greater muscle activation during voluntary command than nonathletes and achieved neural fatigue during the present FR exercise. Strength training may cause adaptive changes within the nervous system that allow a trainee to more fully activate prime mover muscles in specific movements and to better coordinate the activation of all relevant muscles. Training-related neural adaptations that occur during long-term strength training include increased neural drive to agonist muscles, resulting in higher discharge rates of motor units (22,25,23,19). Also, improved intermuscular coordination between agonist, antagonist, and synergist muscles, which can be observed, for example, as a reduction in antagonist coactivation due to resistance training, would allow increased expression of agonist muscle force during the dynamic muscle actions and consequently greater neuromuscular fatigue (15,7). Bilateral limb deficit (i.e., the maximum force generated during simultaneous bilateral contraction is less than the sum of the forces produced by unilaterally, separately) can decrease or reverse due to resistance training, allowing greater force production during bilateral exercise movements (17,24,18). Strength-trained men may be able to activate a greater proportion of muscle tissue and to perform resistance exercise very intensively, which is associated with greater excitatory input and recruitment of fast-twitch fibers (1,6,20,8). Furthermore, it can be speculated that the changes in afferent input and the sensory receptors (i.e., Golgi tendon organs) in SAs may lead to disinhibition and an increased ability of the nervous system to appropriately activate the muscles (9,2). Some of these factors may explain the greater neural fatigue observed during the FR loading in SAs.
To visit SUPERTRAINING FORUM
health.groups.yahoo.com/group/Supertraining/?yguid=44276758
Strength athletes are capable to produce greater muscle activation and neural fatigue during high-intensity resistance exercise than nonathletes.Strength Cond Res. 2009 Jul;23(4):1129-34. Links
Ahtiainen JP, Häkkinen K.
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.
Further comments:
A unique finding in the present study was that neural fatigue occurs during the loading in SAs, and it can be observed as decreased EMG activity during fatiguing high-intensity dynamic resistance exercise. There might be several explanations why especially strength-trained men were able to produce greater muscle activation during voluntary command than nonathletes and achieved neural fatigue during the present FR exercise. Strength training may cause adaptive changes within the nervous system that allow a trainee to more fully activate prime mover muscles in specific movements and to better coordinate the activation of all relevant muscles. Training-related neural adaptations that occur during long-term strength training include increased neural drive to agonist muscles, resulting in higher discharge rates of motor units (22,25,23,19). Also, improved intermuscular coordination between agonist, antagonist, and synergist muscles, which can be observed, for example, as a reduction in antagonist coactivation due to resistance training, would allow increased expression of agonist muscle force during the dynamic muscle actions and consequently greater neuromuscular fatigue (15,7). Bilateral limb deficit (i.e., the maximum force generated during simultaneous bilateral contraction is less than the sum of the forces produced by unilaterally, separately) can decrease or reverse due to resistance training, allowing greater force production during bilateral exercise movements (17,24,18). Strength-trained men may be able to activate a greater proportion of muscle tissue and to perform resistance exercise very intensively, which is associated with greater excitatory input and recruitment of fast-twitch fibers (1,6,20,8). Furthermore, it can be speculated that the changes in afferent input and the sensory receptors (i.e., Golgi tendon organs) in SAs may lead to disinhibition and an increased ability of the nervous system to appropriately activate the muscles (9,2). Some of these factors may explain the greater neural fatigue observed during the FR loading in SAs.