Training-Induced Muscle Fatigue with a Powered Lower-Limb Exoskeleton: A Preliminary Study on Healthy Subjects

Med. Sci., 2022 · DOI: https://doi.org/10.3390/medsci10040055 · Published: September 26, 2022

Assistive Technology Rehabilitation Musculoskeletal Medicine

Simple Explanation

Powered lower-limb exoskeletons are a promising technology for helping people with lower-body paralysis or severe paresis from spinal cord injury to stand upright and walk. This technology can reduce lower-limb muscular fatigue, a risk factor for spasticity. This study involved thirty healthy subjects who performed three motor tasks: walking overground, treadmill walking, and standing and sitting. Each task was performed in separate 60-minute exoskeleton-based training sessions. The study assessed changes in lower-limb muscle strength before and after these sessions. The study found that muscle strength decreased after the training sessions, except for ankle dorsiflexion. This suggests that the exoskeleton-based training led to muscle fatigue, particularly in the knee flexor muscles during overground and treadmill walking tasks.

Study Duration

Not specified

Participants

30 healthy subjects (age 23.2 ± 2.7 years)

Evidence Level

Not specified

Key Findings

1
MVIC forces decreased significantly after the three trained motor tasks except for the ankle dorsiflexion.
2
Significant fatigue was induced by WO and WT trained motor tasks in knee flexion.
3
The STS task leads to a lower level of muscular fatigue, especially for the knee flexor muscles.

Research Summary

This study assessed lower-limb muscle fatigue induced by prolonged training using a powered lower-limb exoskeleton during walking overground (WO), treadmill walking (WT), and standing and sitting (STS). Maximum voluntary isometric contraction (MVIC) was used to assess muscle fatigue across four different lower-limb muscle groups depending on the trained motor task. The study concludes that walking overground and on a treadmill with a powered lower-limb exoskeleton induce muscle fatigue in the knee flexors (e.g., hamstrings).

Practical Implications

Training Considerations

Particular attention should be paid while training patients at risk of developing spasticity in the lower limb muscles when using a powered lower-limb exoskeleton due to potential fatigue.

Motor Task Selection

Standing and sitting exoskeleton-based training may be preferred as it is less fatiguing for the knee flexors compared to exoskeleton-based gait training.

Exercise Planning

When administering exoskeleton-based walking training, avoid or closely monitor for fatigue development, particularly when combined with knee flexor exercises.

Study Limitations

1
The study was conducted on a non-clinical population.
2
Fatigue was measured only via force data.
3
Further studies with neurological populations and sEMG are needed to deepen the understanding of muscular fatigue.

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