Effect Of Electrically Stimulated And Voluntary Plantarflexion Contractions On Mitochondrial Function Using Near-infrared Spectroscopy

PURPOSE: To compare the recovery rate of mitochondria following electrically stimulated (ES) and voluntary (VOL) skeletal muscle contractions. METHODS: Ten recreationally active men and women (27 ± 3.3 years; 171.7 ± 5.5 cm; 77.2 ± 12.6 kg; 0.93 ± 0.46 cm lower limb adipose tissue thickness) volunteered to participate in this investigation. Participants were seated in a recumbent position with the right knee fully extended and ankle supported at 90o. The foot was attached to a force transducer and a blood pressure cuff was applied above the knee joint. A near-infrared spectroscopy (NIRS) device was placed on the posterior mid-line of the tibia at the largest circumference of the gastrocnemius. ES pads were placed directly superior and inferior to the NIRS device. Participants performed fifteen seconds of ES plantar flexion (2 Hz with 60amps at a pulse duration of 500 μs). Immediately after exercise six repeated arterial occlusions were performed. Each occlusion lasted 5 seconds(s) and was followed by 5 s of recovery. After five minutes of rest the procedure was repeated with VOL contractions with real time feedback so they could match forces produced during ES. Recovery slopes and rate constants were calculated to determine the proficiency of the mitochondria to return the rate of oxygen consumption to baseline. A maximum ischemic calibration and blood volume correction was performed. RESULTS: No significant differences were observed between ES (2.11 ± 1.01) and VOL (1.47 ± 1.22) rate constants. There was a significant interaction (f = 13.85, p < 0.001), main effect of condition (f = 28.72, p < 0.001) and main effect of time (f = 24.11, p < 0.001). Post-hoc testing revealed significant differences in slope recovery between ES and VOL contractions at all time points: Immediately (4.05 ± 2.07 v. 0.83 ± 0.35; p < 0.001), 10s (2.29 ± 1.06 v. 0.58 ± 0.33; p = 0.001), 20s (1.8 ± 0.95 v. 0.53 ± 0.32; p = 0.002), 30s (1.32 ± 0.79 v. 0.40 ± 0.21; p = 0.004), 40s (1.14 ± 0.52 v. 0.45 ± 0.22; p = 0.002) and 50s (1.01 ± 0.30 v. 0.41 ± 0.22; p < 0.001) after cessation of contractions. CONCLUSION: No significant differences were observed in the rate of recovery. However, ES contractions evoked a larger magnitude of recovery due to a greater rate of oxygen consumption.