Author ORCID Identifier

https://orcid.org/0009-0003-8617-2611

Date Available

4-22-2023

Year of Publication

2023

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Education

Department/School/Program

Kinesiology and Health Promotion

First Advisor

Dr. Haley C. Bergstrom

Abstract

The purposes of this study were to: 1) Examine the patterns of force responses relative to critical force (CF) during submaximal, fatiguing, isometric handgrip exercise anchored to different rating of perceived exertion (RPE) levels (RPE=3, 5, and 7); 2) assess the loss of force during the task and the level of performance fatigability after each RPE hold; 3) examine the time course of changes and patterns of neuromuscular [electromyography (EMG) amplitude (AMP), mean power frequency (MPF), mechanomyography (MMG) AMP and MPF, and neuromuscular efficiency (NME) (i.e. force/EMG AMP)] and muscle oxygen saturation (% SmO2) responses during each RPE hold; 4) examine which theory (i.e. corollary discharge, afferent feedback, sensory tolerance limit) best explains the regulation of exercise during each RPE hold. Twelve, healthy men between 18 and 35 years performed submaximal, continuous, isometric contractions to task failure at one of four randomly determined percentages of maximal voluntary isometric contraction (MVIC) (30, 40, 50, and 60%) on separate days. The amount of work performed (Wlim) was obtained by multiplying the force by the corresponding time to task failure (Tlim). The four Wlim values were plotted as a linear function of the Tlim values, and the CF was defined as the slope coefficient of Wlim versus Tlim relationship. Subjects performed constant RPE handgrip holds at one of the three randomly ordered RPE levels (RPE= 3, 5, and 7). EMG and MMG, AMP and MPF were calculated in standardized segments of 5% Tlim (0-100% Tlim) during each hold and normalized to the respective values at the pre-MVIC. SmO2 response was recorded in standardized segments of 5% Tlim (5-100% Tlim). For the Tlim and performance fatigability, 2(Time: pre- vs post-hold) x 3(RPE: 3, 5, and 7) repeated measure ANOVAs and post-hoc t-tests with a Bonferroni corrected alpha level (plim) repeated measures ANOVAs, with follow up one-way repeated measures ANOVAs and post-hoc t-tests with Bonferroni for comparisons across time (p2 responses, a 3(RPE: 3, 5, and 7) x 20(time: 5-100% MVIC) repeated measures ANOVA, with a follow up one-way ANOVA and post-hoc t-tests with Bonferroni for comparisons across time (plim between RPE 3, 5, and 7 (p=0.569-0.744). There were decreases in force, relative to the initial value (0% Tlim), from 20% to 100% Tlim for RPE 3, from 45% to 100% Tlim for RPE 5, and from 15% to 100% Tlim for RPE 7. Based on the force profiles for each RPE, the patterns of responses were examined according to three phases, phase 1 (initial force to 15% Tlim), phase 2, (20-85% Tlim), and phase 3 (90-100% Tlim). For the performance fatigability, there were no difference in pre-MVIC (p=0.494-0.894) among RPE 3, 5, and 7, but the post-MVIC value of RPE 3 was greater than RPE 5 (p=0.008), but not RPE 7 (p=0.024), and there was no difference in RPE 5 and 7 (p=0.924). For EMG AMP, there were decreases, relative to 0% Tlim, at 20% and 25%, and from 35% to 100% Tlim at RPE 3, at 30%, 55%, 60%, and 100% Tlim at RPE 5, and at 30% and from 40% to 100% Tlim at RPE 7. For EMG MPF, there were decreases, relative to 0% Tlim, at 15%, 25%, 30%, and from 45% to 95% Tlim, collapsed across RPE. For MMG AMP, there were no significant changes, relative to 0% Tlim, at any time points (p=0.005-0.036), collapsed across RPE, and RPE 7 was greater than RPE 3 (p=0.013) and RPE 5 (p=0.001), collapsed across time. For MMG MPF, there were no significant changes, relative to 0% Tlim, at any time points (p=0.027-0.920). For NME, there were no differences, relative to 0% Tlim, at any time points (p=0.004-0.780) for RPE 3 but decreases from 50% to 65% and from 80% to 100% for RPE 5, and a decrease at the last time point (100% Tlim) for RPE 7. For SmO2, there was no significant differences, relative to the initial value (5% Tlim), at any time point for RPE 3,5, and 7 (p=0.017-0.774). Overall, during phase 1 (0-15% Tlim), the integrated process of anticipatory (i.e., feedforward) regulation and group III afferent neurons (i.e., inhibitory feedback) was likely primarily responsible for the decrease in force. However, afferent feedback primarily from group IV neurons may also have led to force reductions in the later stages of phase 1 and carried over into phase 2 (20-85% Tlim). During phase 2 and 3 (90-100% Tlim), a combination of afferent feedback and the feedforward pathway via corollary discharges likely contributed to the continuous, voluntary reduction in force to maintain the predetermined RPEs. In phase 3, the sensory tolerance limit (i.e., sum of afferent feedback and feedforward signals) may explain the force reduction to task failure at a similar time across each RPE. This study suggested that force alterations, the accompanying metabolic and/or neuromuscular responses, and performance fatigability were affected by different mechanisms depending on phases (1 vs. 2 and 3) and/or RPE (3 vs. 5 vs. 7), which may provide insights when prescribing continuous or repetitive handgrip tasks in occupational or industrial settings.

Digital Object Identifier (DOI)

https://doi.org/10.13023.etd.2023.064

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