Effects of NMES-elicited versus voluntary low-level conditioning contractions on explosive knee extensions

Journal of Musculoskeletal and Neuronal Interactions, 2022 · DOI: · Published: July 7, 2022

Simple Explanation

This study explores how different types of muscle contractions performed before a voluntary explosive movement affect the explosiveness of that movement. The conditioning contractions (CC) were either electrically induced using neuromuscular electrical stimulation (NMES) or performed voluntarily. The key finding is that NMES-elicited conditioning contractions can enhance the early phase of explosive muscle contractions compared to voluntary conditioning contractions. This suggests NMES may help overcome central fatigue. This research has implications for training and rehabilitation, suggesting NMES conditioning contractions may be a valuable tool for improving muscle explosiveness, particularly in populations where central fatigue may be a limiting factor.

Study Duration

Not specified

Participants

20 subjects (15 males and 5 females)

Evidence Level

Not specified

Key Findings

1
Time to Peak Torque was significantly lower when preceded by NMES (11.1%, p=0.019), indicating a faster rise to peak force.
2
The Rate of Torque Development (RTD) in the 0-50 ms window was 37.3% higher after NMES compared to the voluntary conditioning contraction protocol, indicating enhanced early explosiveness.
3
Explosive contractions performed during both protocols generated similar Mean Torque_EC, Peak Torque_EC and TTI_EC (p>0.05).

Research Summary

The study compared the effects of neuromuscular electrical stimulation (NMES) versus voluntary conditioning contractions (CC) on subsequent explosive contractions (EC) of the knee extensors. Results indicated that while most muscle output parameters were similar between the NMES and voluntary CC protocols, Time to Peak Torque was lower and Rate of Torque Development (RTD 0-50ms) was higher following NMES. The conclusion is that NMES-elicited CC potentiated explosive contraction better than voluntary CC, possibly due to a reduction in descending drive following voluntary efforts.

Practical Implications

Training Paradigms

The findings can be important for training paradigms where athletes need to generate high levels of muscle force quickly.

Rehabilitation Strategies

An exercise strategy that enhances muscle explosive performance and promotes higher muscle work could be useful for training in the elderly population, reducing fall risk and improving mobility.

Conditioning Contraction Methods

NMES conditioning contractions may offer advantages over voluntary contractions for improving muscle explosiveness, potentially by mitigating central fatigue.

Study Limitations

1
Muscle fatigue occurrence was inferred without direct evaluation; future studies should evaluate voluntary activation and cortical activation.
2
The source of enhanced explosiveness during the NMES CC protocol could not be precisely identified; further research is needed to investigate afferent activation patterns.
3
The non-randomized order of the two experimental protocols might be a limit of this study.

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