Co‑contraction of ankle muscle activity during quiet standing in individuals with incomplete spinal cord injury is associated with postural instability

Scientific Reports, 2021 · DOI: 10.1038/s41598-021-99151-w · Published: September 20, 2021

Spinal Cord Injury Physiology Rehabilitation

Simple Explanation

This study investigates the effect of co-contraction between plantar- and dorsiflexors on postural balance in individuals with iSCI (iSCI-group) and able-bodied individuals (AB-group). The iSCI-group exhibited more co-contractions than the AB-group. Furthermore, postural sway was larger during co-contractions than during no co-contraction in the iSCI-group. The study demonstrated that co-contractions may be a compensatory strategy for individuals with iSCI to accommodate for decreased motor function, but co-contractions may result in increased ankle mechanical joint stiffness and consequently postural sway.

Study Duration

Not specified

Participants

13 able-bodied individuals and 13 individuals with iSCI

Evidence Level

Not specified

Key Findings

1
Individuals with iSCI exhibited more co-contractions compared to able-bodied individuals during quiet standing with eyes open and closed.
2
Postural sway was significantly larger during periods of co-contraction compared to periods without co-contraction in the iSCI group, but not in the able-bodied group.
3
Computational simulations showed that increasing mechanical stiffness in the simulated iSCI group resulted in increased postural sway, while no significant difference was observed in the simulated able-bodied group.

Research Summary

The study investigated the role of ankle muscle co-contraction on postural stability in individuals with incomplete spinal cord injury (iSCI) compared to able-bodied (AB) individuals. The iSCI group demonstrated greater co-contraction of ankle muscles and increased postural sway compared to the AB group, suggesting a compensatory strategy for muscle weakness. Computational simulations supported the experimental findings, indicating that increased ankle mechanical joint stiffness due to co-contraction in the iSCI group leads to increased postural sway.

Practical Implications

Rehabilitation Strategies

Rehabilitation programs should focus on improving the coordination of muscle activation to reduce excessive co-contraction and improve standing balance in individuals with iSCI.

Neuroprosthetics Design

Standing balance neuroprosthetics should consider the impact of co-contraction on ankle joint stiffness and postural sway when designing interventions for individuals with iSCI.

Therapeutic Interventions

Therapies that aim to restore appropriate spinal neural circuit connections may lead to better standing balance outcomes for individuals with iSCI.

Study Limitations

1
A potential limitation in the comparison of postural sway between TAon and TAoff periods was the assumption that COPv and COMa are rather stationary signals, and consequently their calculated variabilities should be less depending on their data lengths.
2
The COPv and COMa would have been lower during the TAon periods if the data segment lengths had influenced these results.
3
Participants wore shoes, which may affect postural sway, though efforts were made to ensure similar footwear across participants.

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