Muscle activation during low-intensity muscle contractions with varying levels of external limb compression

Abstract

The purpose was to investigate muscle activation during low- intensity muscle contractions with various levels of external limb compression to reduce muscle perfusion/outflow. A series of unilateral elbow flexion muscle contractions (30 repetitive contractions followed by 3 sets x 15 contractions) was performed at 20% of 1RM with varying levels of external compression (0 (without compression), 98, 121, and 147 mmHg external compression) around the upper arm. Electromyography (EMG) signals were recorded from surface electrodes placed on the biceps brachii muscle and analyzed for integrated EMG (iEMG). Maximal voluntary isometric contraction (MVC) decreased similarly during the control (0 mmHg) and 98 mmHg external compression bout (~18%); the decline in MVC with 121 and 147 mmHg external compression was significantly greater (~37%). Muscle activation increased progressively throughout the contraction bout with each level of external compression, but iEMG was significantly greater during 147 mmHg external compression. In conclusion, low-intensity muscle contractions performed with external compression of 147 mmHg appears to alter muscle perfusion/outflow leading to increased muscle activation without decrements in work performed during the contraction bout. Key pointsLow-intensity muscle contractions with external compression are maintained by greater neural activation.It appears there is optimal external compression pressure for increased muscle activation without exaggerated fatigue.External compression per arm circumference was related to the neuromuscular response and fatigue.

Keywords: EMG; Neuromuscular function; biceps brachii; cuff pressure; ischemia.

Figure 1.

Experimental timeline. Pre is resting data collected 5 min prior to the start of the experiment, Post-1 is immediately following the contraction bout, and Post-2 is 1-min following removal of the cuff. MVC=maximal voluntary isometric contraction, RPE=ratings of perceived exertion.

Figure 2.

Illustrations showing the MVC measurement (A) and the contraction bout (B). (A): The upper arm was maintained in the horizontal plane (at 90°) while the hand grasped the Biodex lever in the pronated position. (B): Elbow flexion contractions were performed with a dumbbell at a contraction intensity of 20% of the 1RM.

Figure 3.

Mean integrated EMG during muscle contractions (n = 10). One plot was five muscle activations during low-intensity muscle contractions. Each iEMG value was normalized to those five actions before muscle contractions. Data are means ± SE. ○-control, unimpaired blood flow; -cuff pressure at 98 (3) mmHg; -cuff pressure at 121 (4) mmHg, -cuff pressure at 147 (4) mmHg. * = different from control, p ¼ 0.05.

Figure 4.

Maximal voluntary isometric contraction (MVC; Panel A) and integrated EMG (iEMG; Panel B) at MVC in experiment (n = 10). Data are means ± SE. ○-control, unimpaired blood flow; -cuff pressure at 98 (3) mmHg; -cuff pressure at 121 (4) mmHg, -cuff pressure at 147 (4) mmHg. *=different from control, p¼0.05.

Figure 5.

Relationships between external compression/arm circumference and decrease in MVC at Post-1 (A) or peak iEMG during contraction bout (B).