•  
  •  
 

TIME COURSE OF MECHANOMYOGRAPHIC AMPLITUDE RESPONSES DURING MOTOR UNIT ACTIVATION AND DEACTIVATION WITH FATIGUING EXERCISE

Abstract

PURPOSE: To examine the effects of fatiguing exercise on mechanomyographic amplitude (MMGRMS)-torque relationships of the vastus lateralis (VL) in resistance-trained males. METHODS: Seventeen lower-body resistance trained males (24 ± 4 yrs, 178.44 ± 8.97 cm, 87.17 ± 9.91 kg) performed maximal voluntary contractions (MVCs) of the knee extensors, followed by 3 sets (S#) of 50% MVC isometric trapezoidal contractions to failure with 5 minutes of rest between sets. MMG was recorded from the VL. The first and the last completed repetition (REP) from S1 and S3 were analyzed. Individual a (gain) and b (slope) terms were calculated from the log-transformed MMGRMS-torque relationship for the linearly increasing (LI) and linearly decreasing (LD) segments. MMGRMS during steady torque was normalized (N-MMGRMS) to MVC MMGRMS. Separate 3-way repeated measures ANOVAs (set [S1 vs. S3] x rep [FIRST vs. LAST] x segment [LI vs. LD]) examined the a and b terms. A 2-way repeated measures ANOVA (set [S1 vs. S3] x rep [FIRST vs. LAST]) examined N-MMGRMS. Alpha was ≤ 0.05. RESULTS: For the b terms, there was a 3-way interaction (p = 0.015). For the a terms, there was no (p > 0.05) 3-way interaction or main effect for rep. There was a main effect for segment (p = 0.018). For the mean, SDs, and follow-up tests for the a and b terms, refer to table 1. For N-MMGRMS, there was no (p > 0.05) 3-way interaction or main effects for rep and segment. CONCLUSION: Regardless of set and rep, the a term (gain) was greater during the LD segment. For the b term (slope), there were numerous set-, rep-, and muscle-action related differences that indicated a downward deceleration in MMGRMS relative to torque as the fatiguing protocol progressed. It is possible that accumulating fatigue required greater excitation to the motor unit pool, resulting in greater firing rates and increased active stiffness of the VL. Nonetheless, the b terms were sensitive to changes in the mechanical behavior of the VL during an intermittent fatiguing task.

This document is currently not available here.

Share

COinS