Muscle fatigue and metabolic responses following three different antagonist pre-load resistance exercises

Purpose: Preload of antagonist muscles can be achieved by reciprocal actions (RAs) or by opposing muscle actions. However, evidence concerning neuromuscular and fatigue responses are scarce. Objective: To compare the effects of different knee flexor (KF) preload methods on knee extension (KE) vastus medialis muscle fatigue, based on EMG-spectral index (FI), load range (LR), total work (TW), blood lactate (LAC) and biceps femoris co-activation (BFc) during resistance exercise. Methods: Twenty-four healthy men (23.5±3.6yrs) performed three antagonist pre-load isokinetic exercises (4 sets, 10 repetitions, 60°s^-1, 1min rest between sets): RA (KF contraction immediately followed by KE); Superset (SS; one KF set immediately followed by one KE set); Multiple Set (MS; four KF sets followed by four KE sets). Results: Total work was significantly greater in RA. There was no significant decrease in LR between sets in RA. The BFc did not differ between protocols (p=0.063). However, RA presented greater biceps femoriscoactivation. The FI was greater during SS compared to RA and MS (p<0.05). The SS had greater LAC when compared to MS and RA (p=0.005 and p=0.007, respectively). Conclusion: It is suggested that the RA protocol is more neuromuscular and metabolic efficient during the performance of knee extension resistance exercise.