Effects of arm cranking exercise on muscle oxygenation between active and inactive muscles in people with spinal cord injury

The Journal of Spinal Cord Medicine, 2021 · DOI: 10.1080/10790268.2020.1754649 · Published: January 1, 2021

Spinal Cord Injury Physiology Rehabilitation

Simple Explanation

This study investigates how arm exercises affect oxygen levels in active (biceps) and inactive (thigh) muscles in people with spinal cord injuries (SCI). It compares individuals with complete SCI, incomplete SCI, and able-bodied individuals. The research aims to understand if differences in muscle oxygenation during arm exercises exist between these groups, particularly focusing on the role of sympathetic nerve activity, which controls blood vessel constriction. The study also explores the relationship between peak oxygen uptake (VO2peak) and changes in oxygen levels in inactive muscles to see if reduced oxygenation contributes to aerobic capacity.

Study Duration

Not specified

Participants

8 complete SCI, 8 incomplete SCI, and 8 able-bodied individuals

Evidence Level

Observational study

Key Findings

1
Muscle oxygenation in the lower limbs of complete SCI participants remained unchanged during arm-crank exercise, while it decreased in incomplete SCI and able-bodied participants.
2
No significant relationship was found between VO2peak and decreases in StO2 in inactive muscles, suggesting sympathetic vasoconstriction in inactive muscles may not contribute to peak aerobic capacity.
3
Heart rate at peak exercise was significantly higher in both SCI groups compared to the able-bodied group, while peak oxygen uptake (VO2peak) and muscle oxygen extraction in active muscles were similar across all groups.

Research Summary

The study examined the effects of incremental arm-cranking exercise on tissue oxygen saturation (StO2) in active (biceps brachii) and inactive (vastus lateralis) muscles among individuals with complete SCI, incomplete SCI, and able-bodied controls. Results showed that StO2 in inactive muscles decreased in able-bodied and incomplete SCI groups during exercise, suggesting sympathetic vasoconstriction, while StO2 remained unchanged in complete SCI participants, likely due to reduced sympathetic nerve activity. Contrary to the hypothesis, no significant relationship was found between VO2peak and changes in StO2 in inactive muscles, indicating that sympathetic vasoconstriction in inactive muscles may not contribute to peak aerobic capacity in the studied population.

Practical Implications

Rehabilitation Strategies

Exercise programs for individuals with complete SCI may need to focus on alternative mechanisms to improve aerobic capacity, as sympathetic vasoconstriction in inactive muscles is not contributing to VO2peak.

Understanding Autonomic Dysfunction

The study highlights the importance of considering autonomic dysfunction in SCI when evaluating physiological responses to exercise, especially regarding blood flow redistribution and heart rate responses.

Muscle Oxygenation Monitoring

Muscle oxygenation, measured by NIRS, may serve as a valuable tool for assessing physiological responses to exercise in SCI populations, particularly in the context of limited heart rate variability.

Study Limitations

1
The study included SCI participants with only low thoracic and lumbar motor complete SCI, not cervical or upper thoracic SCI.
2
The effects of skin and adipose tissue thickness on NIRS signals could not be completely ruled out, despite efforts to minimize their impact.
3
Sympathetic nerve activity was not directly measured due to device and technical limitations.

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