Date of this Version
Smith CM. Time Course of Changes in Neuromuscular Parameters during Fatiguing High-Load and Low-Load Concentric Dynamic Constant External Resistance Leg Extension Muscle Actions. (MS Thesis, University of Nebraska-Lincoln) 2016
The purpose of this study was to simultaneously assess electromyographic (EMG) and mechanomyographic (MMG) signals to examine the time course of changes in EMG amplitude, EMG frequency, MMG amplitude, and MMG frequency from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles during high-load (70%1 repetitions maximum; 1-RM) and low-load (30% 1-RM) concentric, dynamic constant external resistance (DCER) leg extension muscle actions to failure. Twelve men performed two randomized visits consisting of either 30 or 70% 1-RM DCER leg extension muscle actions to failure. Maximal voluntary isometric contractions (MVIC) and 1-RM measurements were performed before and after each protocol. Electromyographic amplitude, EMG frequency, MMG amplitude, and MMG frequency were measured from the VL, VM, and RF. The results indicated mode- (DCER versus isometric) and intensity-specific (30 versus 70% 1-RM) differences in the 1-RM and MVIC measurements. There were increases in EMG amplitude and MMG amplitude, but decreases in EMG frequency and MMG frequency during both the 30 and 70% 1-RM protocols. The time course of changes in neuromuscular responses, however, were unique to each protocol and muscle. The 30% 1-RM protocol had three unique phases (1 to 30, 30 to 60, and 60 to 100% of the repetitions to failure), but the 70% 1-RM protocol had only one phase (1 to 100% of the repetitions to failure). These time course of changes in neuromuscular responses during both the 30 and 70% 1-RM protocols could be explained by Muscle Wisdom and the Onion Skin Scheme, but not the After-Hyperpolarization theory. The findings of the current study suggested that the time course of changes in neuromuscular responses can provide insight in muscle- and intensity- specific differences in the motor unit activation strategies used to maintain force production and allow for a greater understanding of the fatiguing process by identifying the time-points at which these neuromuscular parameters changed.
Advisor: Terry J. Housh