Date of Award

Fall 2019

Document Type

Open Access Thesis

Department

Exercise Science

First Advisor

Raymond Thompson

Abstract

Background: The Endurance Index (EI%) is a method to objectively assess a muscle’s ability to resist fatigue. The purpose of these studies was to determine the reproducibility of the EI% and determine the influence of muscular fatigue on the EI%. Methods Study 1: sixteen apparently healthy participants (18-30yrs) completed three nonconsecutive visits each with 3 bouts of 5-minute electrical muscle stimulations (EMS) and accelerometer-based mechanomyography (aMMG) of the vastus lateralis at 4 Hz and low amperage (25-35mA) on the hamstrings of the dominant leg; peak torque was measured at each visit. Study 2: fifteen apparently healthy participants (ages 18-30yrs) completed 3 bouts of 5-minute bouts of EMS and aMMG of the vastus lateralis at 4 Hz and low amperage (25-35mA) on both limbs to determine the effect of exercise on the EI%. Next the participants performed 50 maximal voluntary contractions (MVCs) with one limb and the contralateral limb serving as a control; peak torque was assessed for each limb. EMS and aMMG were repeated immediately following the second peak torque assessment. MVCs (60 degrees/sec) were collected via isokinetic dynamometry.The EI was calculated from aMMG data as a percent change from peak acceleration for each period. One-, Two-, and Three-way Repeated Measures ANOVA’s assessed main effects and interactions (p≤0.05) and Intraclass Correlations were used to determine reproducibility. Results: Study 1: The EI% was not different between Trials 1, 2 and 3 (p>0.05), however the EI% changed significantly over time.Post hoc analysis revealed D0 was different from D1, D2, and D3 (100±0.0, 61.3±3.1,61.8±3.1 60.3±3.1; p<001) but no other differences were found. Moderate reliability coefficients were computed for D1 (.445), D2 (.410), and D3 (.534) across trials for the EI% while strong reliability coefficients were computed for the strength data (0.96). Study 2: A significant Treatment by Trial interaction for peak torque (p=0.0003) followed by post hoc analysis revealed no difference in peak torque between control and exercise limb at baseline. Peak torque was significantly lower only in the exercise limb after 50 MVCs (p<0.0001) (Ex Pre 109.8±9.2, Ex Post 67.6±4.4, Con pre 105.9±11.5,Con Post 104.7±10.7 Nm). Treatment by Trial interaction followed by post-hoc analysis revealed that the EI% was significantly lower in the exercise limb after 50. Conclusion: The EI% appears to be moderately reliable, however it was sufficiently sensitive to detect local muscular fatigue indicating that the EI% is a valid measure of skeletal muscle endurance.

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