Background: Neuromuscular electrical stimulation (NMES) is a physical modality used to activate skeletal muscles for strengthening. While voluntary muscle contraction (VMC) follows the progressive recruitment of motor units in order of size from small to large, NMES-induced muscle contraction occurs in a nonselective and synchronous pattern. Therefore, the outcome of muscle strengthening training using NMES-induced versus voluntary contraction might be different, which might affect balance performance.
Objects: We examined how the NMES training affected balance and proprioception.
Methods: Forty-four young adults were randomly assigned to NMES and VMC group. All participants performed one-leg standing on a force plate and sat on the Biodex (Biodex R Corp.) to measure balance and ankle proprioception, respectively. All measures were conducted before and after a training session. In NMES group, electric pads were placed on the tibialis anterior, gastrocnemius, and soleus muscles for 20 minutes. In VMC group, co-contraction of the three muscles was conducted. Outcome variables included mean distance, root mean square distance, total excursion, mean velocity, 95% confidence circle area acquired from the center of pressure data, and absolute error of dorsi/plantarflexion.
Results: None of outcome variables were associated with group (p > 0.35). However, all but plantarflexion error was associated with time (p < 0.02), and the area and mean velocity were 37.0% and 18.6% lower in post than pre in NMES group, respectively, and 48.9% and 16.7% lower in post than pre in VMC group, respectively.
Conclusion: Despite different physiology underlying the NMES-induced versus VMC, both training methods improved balance and ankle joint proprioception.

INTRODUCTION
MATERIALS AND METHODS
    1. Subjects
    2. Experimental Equipment
    3. Experimental Protocol
    4. Data 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, Wonju, Korea)
• Woochol Joseph Choi(Injury Prevention and Biomechanics Laboratory, Department of Physical Therapy, Yonsei University, Wonju, Korea) Corresponding Author