Upper Limb Effort Does Not Increase Maximal Voluntary Muscle Activation in Individuals with Incomplete Spinal Cord Injury

Clin Neurophysiol, 2009 · DOI: 10.1016/j.clinph.2009.07.038 · Published: September 1, 2009

Spinal Cord Injury Physiology Rehabilitation

Simple Explanation

This study investigated how using your arms to push and pull during leg exercises affects leg muscle activity in people with incomplete spinal cord injury. The researchers found that when people were already using their leg muscles as hard as they could, adding arm effort didn't make the leg muscles work any harder. However, when the legs were relaxed, using the arms did increase activity in the leg muscles, and vice versa.

Study Duration

Not specified

Participants

15 individuals with incomplete spinal cord injury

Evidence Level

Not specified

Key Findings

1
Upper limb effort did not increase lower limb muscle activation during active lower limb effort in individuals with incomplete spinal cord injury during recumbent stepping.
2
Active upper limb effort resulted in greater passive lower limb muscle activation.
3
Active lower limb effort resulted in greater passive upper limb muscle activation.

Research Summary

The study aimed to determine if upper limb effort could enhance maximal lower limb muscle activation in individuals with incomplete spinal cord injury during recumbent stepping. The results showed that upper limb effort did not increase lower limb muscle activation during active lower limb effort. However, upper limb effort increased passive lower limb muscle activation, and vice versa. The researchers concluded that individuals with incomplete spinal cord injury cannot recruit additional lower limb motor units using maximal volitional effort of their upper limbs during active lower limb exercise.

Practical Implications

Rehabilitation Strategies

The findings suggest that simply adding maximal upper limb effort to lower limb exercises might not increase maximal lower limb muscle activation in individuals with incomplete spinal cord injury.

Submaximal Effort

Further research is needed to explore if upper limb effort at submaximal levels can improve lower limb muscle activation and coordination during rehabilitation.

Interlimb Neural Connections

The study highlights the complex interplay between interlimb neural connections and muscle activation during exercise, suggesting a neural limit on muscle recruitment during maximal effort.

Study Limitations

1
A limitation of this study was that we had to rely on the subjects’ confirmation of their effort for each stepping condition.
2
Another limitation was that we did not examine any submaximal levels of recumbent stepping.
3
Providing feedback such as a display of the subject’s force production would alter the task and involve more voluntary and supraspinal processes.

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