Muscle Metabolism During Multiple Muscle Stimulation Using an Affordable Equipment

Abstract

Background/Objectives: Previous studies have shown that neuromuscular electrical stimulation (NMES), while expensive, can provide some of the health benefits of exercise to people who cannot exercise their legs normally. The aim of this study was to quantify the increases in muscle metabolism in four muscles of the legs of able-bodied individuals with NMES. Methods: Healthy college-aged students were tested. NMES of four muscle groups was performed with inexpensive stimulators and reusable tin foil electrodes. The biceps femoris, vastus lateralis, medial gastrocnemius, and tibialis anterior muscles on one leg were stimulated for ten minutes with twitch stimulations at the highest comfortable stimulation current. Muscle metabolism was measured using the slope of oxygen consumption measured with near-infrared spectroscopy (NIRS) during 5 s of cuff ischemia. Results: Initial studies found fold increases in muscle metabolism above rest of 8.9 ± 8.6 for the vastus lateralis, 7.9 ± 11.9 for the biceps femoris, 6.6 ± 7.8 for the medial gastrocnemius, and 4.9 ± 3.9 for the tibialis anterior. Some participants were able to obtain large increases in muscle metabolism, while other participants had lower increases. Conclusions: The ability to produce large increases in metabolism has the potential to allow NMES to replace or augment exercise to improve health in people who cannot otherwise exercise. The devices used were inexpensive and could be adapted for easy use by a wide range of individuals.

Keywords: human subjects; near-infrared spectroscopy (NIRS); neuromuscular electrical stimulation; oxidative metabolism; skeletal muscle.

Figure 1

The experimental setup for measurements on the four muscles using near-infrared spectroscopy (NIRS). Aluminum foil electrodes were placed proximally and distally. The black sleeve is an inflatable blood pressure cuff, placed on the upper thigh, for rapid cuff inflation. The participant’s foot rests on the pedal and receives support from a thin pillow placed below the knee.

Figure 2

Representative example of the vastus lateralis muscle oxygen saturation during rest, resting arterial occlusions, 5 min neuromuscular electrical stimulation exercises, and end-exercise recovery. A 5 s arterial occlusion is performed after each period of electrical stimulation to determine the relative oxygen levels.

Figure 3

(a) Average muscle oxygen saturation for all four muscles throughout the procedure. Values are means (STDEV). Statistical differences were found for all comparisons to rest in this figure; (b) average metabolic rates for all four muscles during the different conditions. The normalized value is calculated as a ratio of the resting slope and the stimulation slope. Values are means (STDEV). * p < 0.05.

Figure 4

A histogram of average increases in mVO2 for 5 and 10 min for the four muscle groups. The target goal of an 8–12-fold increase is shown by the yellow shaded area.