Effects of motor-level transcutaneous electrical nerve stimulation on ipsilateral and un-stimulated contralateral quadriceps femoris.

Purpose: There is a paucity of data on effects of motor-level stimulation using Transcutaneous Electrical Nerve Stimulator (TENS) on ipsilateral quadriceps femoris group of muscles. The effect is also unknown on the untrained contralateral quadriceps femoris. The primary purpose of this study was to determine the effect of TENS on quadriceps muscle strength at the stimulated ipsilateral and un-stimulated contra-lateral extremities.

Methods: Participants were 50 apparently healthy undergraduate. They were recruited using sample of convenience. The right quadriceps group of muscles were stimulated for 15 minutes twice a week for 8 weeks using motor-level stimulation parameters (frequency of 85 Hz and pulse width of 100 microseconds) while the left lower limbs (control) were not stimulated. The right and left quadriceps muscle strengths were quantified using tensiometer; at onset and after 8 weeks. The data were analysed using the descriptive and inferential statistics (paired t-test and ANOVA). Alpha level was set at 0.05.

Results: The initial and final left strengths of the un-stimulated quadriceps muscles were 311.46 ± 58.84N and 395.60 ± 100.71N at onset and after 8 weeks respectively. After 8 weeks the un-stimulated left quadriceps strength was significantly greater than the initial value (t=-7.63, p < 0.001). Similarly, the initial and final right quadriceps strength (stimulated limb) were 351.51 ± 117.68N and 471.31 ± 112.19N; at onset and after 8 weeks respectively. The post stimulation strength of the right quadriceps was also significantly higher than the pre-intervention strength (t=-10.25, p < 0.001). However, the increment in quadriceps strength between right and left extremities after 8 weeks was insignificant (t =-1.35, p=0.18). There was also significant increase in the girth of the right quadriceps (t= -6.08, p=0.001) after 8 weeks.

Conclusion: We concluded that there were increments in both strength and muscle size of the stimulated right quadriceps using motor level stimulation parameters of TENS modality. The un-stimulated contralateral quadriceps strength also increased after 8 weeks. This implied that there was cross-training effect at the contralateral quadriceps group of muscles.