Metabolic response and muscle glycogen depletion pattern during prolonged electrically induced dynamic exercise in man

Abstract

Muscle glycogen depletion pattern and metabolic responses during voluntary (VOL) and functional electrical stimulated (FES) dynamic knee-extensor exercise with one leg were evaluated. Seven healthy men exercised for 60 minutes at 30 W with an pulmonary oxygen uptake of 0.8 and 1.01 min-1, and respiratory exchange ratios of 0.90 and 0.95 in VOL and FES, respectively. Heart rate reached a level around 90 beats min-1 (VOL) and up to 110 beats min-1 (FES). Muscle glycogen decreased in FES with 260 and 290 mmol kg-1 d.w. in vastus lateralis and m. rectus femoris, respectively, compared with 45 and 160 mmol kg-1 d.w. in VOL (p < 0.05). In FES the percentage of empty and almost empty fibres determined by periodic acid-Schiff staining in vastus lateralis and rectus femoris was 50 and 77% of type I, 63 and 90% of type IIa, and 59 and 84% of type IIb fibres, respectively, whereas in VOL it was 24 and 26% of type I, 7 and 19% of type IIa, and 2 and 3% of type IIb fibres. Muscle lactate reached 30 mmol kg-1 d.w. in FES and was 9 mmol kg-1 d.w. lower in VOL. The changes in blood lactate and NH3 during the exercise were slightly higher in FES than in VOL, whereas the alterations in glucose, FFA, and K+ were small in both exercise modes. The pressure in the two muscle portions at different locations (proximal-distal) and depths was always higher (~ 50%) in FES than in VOL, reaching levels around 55 mmHg. It is concluded that with FES the entire quadriceps muscle was engaged and all fibre types were recruited, resulting in a quite significant energy turnover and a more pronounced metabolic response compared to VOL. Furthermore, FES can be used for prolonged dynamic exercise.