Peripheral alterations after two different concentric power protocols

Abstract

The aims of the present study were to assess the ability of explosive concentric contractions to induce high-frequency fatigue, and to determine what effects the number of repetitions and number of sets have upon peripheral fatigue. Nine male students performed two protocols (6 sets, 5 min and 1 week rest between sets and protocols, respectively) with a different number of concentric jumps in a set on the sledge (10 vs. 20 jumps in the first (S10) and the second protocol (S20), respectively). Isometric twitch torque, torque during low-frequency (20 Hz) and high-frequency (100 Hz) electrical stimulation of the vastus lateralis were measured (before protocols and 30 s after sets). Peak twitch torque increased, while contraction and half-relaxation times shortened during the S10 protocol (P<0.05). The increase in peak twitch torque was accompanied by non-significant reductions in contraction time and half-relaxation time in the S20 protocol. High- and low-frequency torques did not change significantly in either protocol. The high- to low-frequency torque ratio increased significantly (P<0.05) after the fourth set in the S10 protocol. Post-activation potentiation was the main reason for enhanced contractile response after both protocols. There were no alterations in high-frequency torque or reductions in the high- to low-frequency torque ratio, even with increased sets and repetitions. Explosive concentric contractions showed no potential to induce high-frequency fatigue, when separated with long periods of rest.

Keywords:

• High-frequency fatigue
• explosive concentric contraction
• vastus lateralis
• sledge jumps