Health, Exercise, and Sports Sciences ETDs

Publication Date

6-26-2015

Abstract

Fatigue is a task dependent multifactorial phenomenon, and the most common tool to analyze it is the VO2max test. The purpose of this study was to investigate if muscle is exhaustively taxed at the end of a VO2max test. This was based on data from sEMG, heart rate, and force applied to the pedals during and immediately after a VO2max test compared to an intense anaerobic test. Methods. 12 male participants (mean ± SD age = 28.09 ± 6.55 years, height = 176.7 ± 2.97 cm, weight = 73.31 ± 8.44 kg, and VO2max = 60.93 ± 9.75 mL/kg/min) were recruited for the study to perform a VO2max test and an intense anaerobic test (the control), to compare the level of muscle fatigue at the end of the VO2max test. Following a load determining VO2max cycling trial, exercise trials were performed in a randomized order separated by at least seven days. For the VO2max tests, the participants performed a graded exercise protocol at 60 rpm on a mechanically braked cycle ergometer; the power output was set according to each subjects fitness level to complete the test in 8 to 10 minutes. The intense anaerobic test consisted of cycling on the same ergometer at 60 rpm and 100% of the initial Wattspeak. In both tests, the participants were encouraged to pedal constantly until reaching volitional exhaustion. The root mean square (RMS), mean power frequency (MPF), and median frequency (MF) were extracted and normalized using the maximal voluntary contraction (MVC) from the selected sEMG samples. MATLAB was used in order to observe the tendencies over time for the left and right rectus femoris, vastus medialis and vastus lateralis. Force production applied to the pedals was measured using four flexiforce load sensors (Teskan, Inc. Boston, MA. USA) installed within each pedal. Heart rate (HR) was monitored during the tests via a commercial clinical electrocardiogram (GE Medical Systems, Milwaukee, WI, USA). Bilateral MVCs were measured before and immediately after each test with the knee positioned at 60 degrees of flexion prior to the MVCs. A paired t-test was used to compare means from sEMG, heart rate and force production pre-test and post-test between both group trials with significance set at p<0.05. Results. The percentage change in mean sEMG from baseline MVC values was significantly larger for the intense anaerobic tests at the end compared to the VO2max test for two of the six muscles monitored. For the left rectus femoris the remaining percentage of baseline MVC was 84.53 ± 15.01% and 89.9 ± 16.74, respectively, for the intense anaerobic and the VO2max trial; F(1,5)= 8.124, p = 0.036. Also, a significantly lower remaining percentage of baseline MVC was found for the anaerobic intense trial compared to the VO2max test for right vastus lateralis, 81.92 ± 8.0% and 93.12 ± 4.21% respectively; F(1,6)= 11.47, p = 0.015. There was a significant remaining difference in the median sEMG frequency for three of the six muscles monitored. A lower remaining percentage was found for the intense anaerobic test for the right vastus lateralis than for the VO2max test (80.54 ± 13.1% and 93.46 ± 8.78% respectively; F(1,6)= 7.58, p = 0.03. respectively). Similarly, the right rectus femoris showed a smaller remaining percentage for the anaerobic test than for the VO2max (82.5 ± 10.51% and 92.9 ± 8.85%; F(1,5)= 12.60, p = 0.016). The only muscle that showed a smaller remaining percentage for the VO2max compared to the intense anaerobic test was the left vastus medialis (79.39 ± 11.26% and 88.28 ± 9.6%, respectively; F(1,6)= 8.51, p = 0.027). No statistically significant differences were found for the post-test heart rate, force production and MVC. Conclusion. Mean and median frequency sEMG data provided the best way to analyze muscle fatigue at the end of a maximal test. From these signals muscle fatigue at the end of a VO2max test seems not to be maximal; there is a reserve of muscle fiber recruitment mainly from the slow-twitch fiber type.'

Keywords

VO2max, Anaerobic Test, sEMG, Muscle fatigue

Document Type

Dissertation

Language

English

Degree Name

Physical Education, Sports and Exercise Science

Level of Degree

Doctoral

Department Name

Health, Exercise, and Sports Sciences

First Advisor

Gibson, Ann

First Committee Member (Chair)

Mermier, Christine

Second Committee Member

Kravitz, Leonard

Third Committee Member

Nazeran, Homer

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