Effects Of Electrical Muscle Stimulation In Hypoxia On Skeletal Muscle Morphology And Strength

Resistance training in hypoxia has also been reported to be more effective than resistance training in normoxia. Interestingly, it is well known that electrical muscle stimulation (EMS) training improves muscle functions and used as an alternative or comparable therapy to resistance training. However, the effect of EMS training in hypoxia has not been clarified. PURPOSE: To examine the effects of EMS training in normobaric hypoxia for 8 weeks on the muscles morphology and strength. METHODS: Twenty-seven college-age male students participated in this study. They were randomly divided into three groups; EMS training in normoxia (20.9%O2) group; (N, n = 9), in normobaric hypoxia (14.5%O2) group (H, n = 8) and control group (C, n = 10). They completed EMS training for 8 weeks (two times per weeks). EMS training consisted of 60 repetitions of 5 seconds electrical tetanic contraction of the thigh while a relax seated position with their legs extended. The stimulator current waveform was set at a frequency of 80 Hz with a pulse width of 250 μs for both groups. Also, the stimulation intensity was set to the maximum intensity that they could tolerate for each session. We measured knee extension isometric strength, rectus femoris (RF) and vastus lateralis (VL) muscle thickness and thigh circumference before, after 4 and 8 weeks of training. Each parameter was statistical analyzed by two-way ANOVA with Dunnett were completed to identify any significant. RESULTS: Knee extension maximal isometric strength of both groups were significantly increase at 4 weeks (H group; 15%, N group; 10%, p < 0.05) and 8 weeks training period (H group; 22%, N group; 14%, p < 0.05). Furthermore, strength of the H group was significantly higher than that of the N group (p < 0.05). RF muscle thickness significantly increased from 26.5 ± 2.3 to 28.6 ± 2.6 mm in the N group, while the H group further increased from 24.6 ± 1.7 to 28.4 ± 3.7 mm (p < 0.05). VL muscle thickness did not change after training. CONCLUSIONS: 8 weeks of EMS training in hypoxia would be induce increased isometric muscle strength and induce muscle hypertrophy. The increase in muscle strength is considered to be greatly influenced by the improvement of neurological factors.