It has been postulated that skeletal muscle fibers innervated by high threshold motor neurons possess the greatest potential for hypertrophy. Traditionally, stimulation of high threshold motor units was thought to require high intensity training loads. Recent research has demonstrated that similar levels of hypertrophy may be induced from a resistance training protocol utilizing low loads if sets are performed until exhaustion.
PURPOSE: The purpose of this study was to compare surface electromyographic (EMG) amplitude under two conditions: 1) low-torque muscle contractions performed until exhaustion and 2) high-torque muscle contractions in a non-fatigued state.
METHODS: Nine untrained males (ages 18-35 years, BMI < 30) performed unilateral, isometric knee extensor testing at 80% of maximum voluntary contraction (MVC) torque, as well as 30% MVC until exhaustion. Bipolar surface EMG signals were detected from the right vastus lateralis. The 30% MVC trial for each subject was normalized for time, and data were analyzed at the beginning, middle, and end of the protocol. The root-mean-squared value (µV) for EMG amplitude from two-second epochs was the dependent variable. RESULTS: Increases in EMG amplitude were demonstrated during the 30% MVC trial (beginning < middle < end). EMG amplitude at the end of the 30% MVC trial was similar to that for 80% MVC (p = .140), with a small/medium effect size (Cohen’s d = 0.40).
CONCLUSION: Although hypertrophic potential should not be inferred from surface EMG studies, our data suggest that similar levels of EMG amplitude may be found when performing low-torque contractions performed until exhaustion and when performing non-fatiguing, high-torque contractions.
Hamilton, Adam S.; Bartek, Frank; and Johnson, Brent D., "Surface Electromyographic Amplitude During Low-torque, Fatiguing Muscle Actions Versus High-torque, Non-fatiguing Muscle Actions" (2018). UCF DPT Research Capstone. 3.