Efficacy of high- versus moderate-intensity spatially distributed sequential stimulation in subjects with spinal cord injury: an isometric study

Journal of NeuroEngineering and Rehabilitation, 2025 · DOI: https://doi.org/10.1186/s12984-025-01567-2 · Published: January 30, 2025

Spinal Cord Injury Rehabilitation Biomedical

Simple Explanation

This study investigates how different intensities of electrical stimulation affect muscle fatigue in people with spinal cord injuries when using a technique called spatially distributed sequential stimulation (SDSS). SDSS involves using multiple electrodes to stimulate muscles. The research compares high-intensity SDSS to moderate-intensity SDSS, using traditional single electrode stimulation (SES) as a baseline. The aim is to determine if the benefits of SDSS in reducing muscle fatigue are affected by the intensity of the stimulation. Two experiments were conducted, one focusing on the quadriceps and the other on the vastus lateralis muscle. The results suggest that the advantages of SDSS over SES are less pronounced at high stimulation intensities compared to moderate intensities.

Study Duration

Not specified

Participants

Seven adult male subjects with lower-limb motor-complete spinal cord injuries

Evidence Level

Not specified

Key Findings

1
The advantages of SDSS over SES in reducing muscle fatigue and enhancing force generation were significantly diminished at high intensity compared to moderate intensity.
2
For the quadriceps muscle group, the percentage increase in time to fatigue (TTF) was 2.80-fold greater during moderate-intensity stimulation compared to high-intensity stimulation.
3
Experiment 2, focusing on the vastus lateralis muscle, did not show a significant difference between moderate and high-intensity modalities in terms of %TTFDifference, %MPFDifference, and %APFDifference.

Research Summary

The study assessed the efficacy of SDSS compared to SES at moderate and high electrical stimulation intensities, focusing on time to fatigue (TTF), maximum produced force (MPF), and average produced force until fatigue (APF). The research found that the superior performance of SDSS over SES is considerably compromised for the quadriceps muscle group under high-intensity modality due to overlapping motor unit activation. In contrast, results from the vastus lateralis muscle did not exhibit a significant difference between moderate and high-intensity modalities, possibly due to the relatively high value of moderate intensity used.

Practical Implications

Optimizing Stimulation Intensity

The findings suggest the importance of carefully selecting stimulation intensity to maximize the benefits of SDSS, with moderate intensities potentially being more effective for fatigue reduction.

Targeted Muscle Stimulation

The differences observed between the quadriceps and vastus lateralis muscles highlight the need for tailored stimulation strategies based on the specific muscle group being targeted.

Application in FES-based Exercises

The study's insights can inform the design and implementation of FES-based exercises, particularly in tasks requiring sustained force output over extended durations.

Study Limitations

1
The randomization method used in Experiment 1 resulted in an unequal number of subjects assigned to high-intensity and moderate-intensity stimulation in Session 1.
2
The study focused on continuous isometric stimulation, which has a distinct fatigue profile, and further investigation is needed to confirm the extent to which the spillover effect impacts performance in FES-based exercises.
3
The sample size was relatively small, which may limit the generalizability of the findings.

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