Author(s): UCHIMARU, J., SON, D.L., SATO, J., Institution: SENDAI UNIVERSITY, Country: JAPAN, Abstract-ID: 1482

INTRODUCTION:
Electrical muscle stimulation (EMS) also has been proved to be an alternative method or comparable therapy to traditional strength training by voluntary contractions [1]. Furthermore, both training combined with hypoxia increase muscle strength and induce hypertrophy compere to normoxia [2]. These types of training would be similar effects in skeletal muscle function [3] [4], but the fatigue process and/or muscle fibers’ activation seem to be different. Also, hypoxia would be more influence on muscle contractions, muscle fatigue and neuromuscular activations. To our knowledge, there is no research explained why the different mechanisms induce similar effects and what the specific difference is in these exercise modes. We evaluate the effects of voluntary contraction and EMS combined with hypoxia on strength and neuro-muscular activity.
METHODS:
Nine healthy and physically active male people participated in this study. Participants completed the four trials; 1) voluntary contraction with normoxia (N-VOL), 2) EMS with normoxia (N-EMS), 3) voluntary contraction with hypoxia (14.5% O2) (H-VOL) and 4) EMS with hypoxia (H-EMS) separated by one-week wash out period. VOL and EMS trial composed of 50 repetitions of 5 seconds tetanic contraction of the thigh. Also, the stimulation intensity with EMS was set to the maximum intensity that they could tolerate. Voluntary contraction was defined as the participants maximum effort. We measured the following measurements before and after trials: knee extent maximal isometric strength (MVC) and EMG activity of rectus femoris muscle (RF), vastus lateralis muscle (VL) and vastus medialis muscle (VM) during tetanic contraction of the thigh, and at 20%, 40%, 60%, 80% and 100%MVC. The root mean square (RMS) and integral electromyogram (iEMG) were analyzed from the EMG data. Additionally, blood lactate concentrations (BLa) were measured before and after trials. Two-way ANOVA with Tukey’s test were performed to identify any significant (P<0.05).
RESULTS:
MVC did not change after each trial. RMS and iEMG at maximum tetanic contraction decreased in N-EMS and increased in H-VOL and H-EMS. RMS and iEMG of VL and VM muscles at submaximal and maximal strength increased (4-10%) after the N-VOL and H-VOL trials. However, N-EMS trial decreased in RMS and iEMG of all muscles, and no change was observed in H-EMS. BLa was significantly increase after H-VOL (from 1.3 to 1.8 mmol/L), N-EMS (from 1.4 to 2.0 mmol/L) and H-EMS trials (from 1.2 to 2.1 mmol/L) (P<0.05).
CONCLUSION:
From these results, our main findings were as follows: 1) the decrease in EMG activity after EMS may be affected by force production and muscle fatigue with blood lactate accumulation, 2) exercise in a hypoxic environment may induce neuro-muscular activation to maintain force production, regardless of voluntary and involuntary contractions such as EMS.