Background: Neuromuscular electrical stimulation (NMES) has long been used to strengthen skeletal muscles. Voluntary muscle contraction (VMC) obeys the size principle, whereas NMES does not. Thus, the therapeutic effects of VMC vs. NMES on muscle strength may be different, which may in turn impact on balance and proprioception. Objects: To examine the effects of NMES training on muscle strength, balance and proprioception in young adults. Methods: Thirty healthy young adults were randomly assigned to VMC or NMES+ group. All participants performed one-leg standing on a force plate to measure balance, and sat on Biodex for ankle strength and proprioception measures before and after muscle strengthening training, which involved a 4-week resistance exercise training with a theraband for the VMC group, and electrical stimulation of the tibialis anterior, gastrocnemius, and soleus muscles along with VMC for the NMES+ group. Outcome variables included mean distance, root mean square distance, total excursion (TOTEX), mean velocity (MVELO), and 95% confidence circle area acquired from the force plate during single-leg standing; absolute error and strength of ankle dorsiflexion/plantarflexion as measured by Biodex. Results: There were no significant differences between groups in dorsiflexion strength, balance, and proprioception (p > 0.051). However, all outcome variables were associated with time (p < 0.05), and when compared to pre-intervention, the TOTEX and MVELO were 5.6% and 6.5% lower, respectively, in the NMES+ group, and 7.5% and 7.4% lower, respectively, in the VMC group in post-intervention. However, there were no interactions between the group and time for all outcome variables (p > 0.05). Conclusion: A 4-week ankle muscle strengthening training with NMES+ has improved ankle muscle strength, proprioception, and static balance. However, when compared to conventional strengthening exercise, the NMES did not provide additional benefits.

INTRODUCTION
MATERIALS AND METHODS
    1. Participants
    2. Experimental Protocols
    3. Statistical Analysis
RESULTS
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• Jeongwoo Je(Injury Prevention and Biomechanics Laboratory, Department of Physical Therapy, Yonsei University)
• Woochol Joseph Choi(Injury Prevention and Biomechanics Laboratory, Department of Physical Therapy, Yonsei University) Corresponding author
• Chunghwi Yi(Department of Physical Therapy, Yonsei University, Wonju, Korea,)
• Hye-Seon Jeon(Department of Physical Therapy, Yonsei University, Wonju, Korea,)
• Marco Y. C. Pang(Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom)
• Yijian Yang(Department of Sports Science and Physical Education, The Chinese University of Hong Kong, N.T., Hong Kong, China)