A biomechanical analysis of exercise in standing, supine, and seated positions: Implications for individuals with spinal cord injury

The Journal of Spinal Cord Medicine, 2012 · DOI: 10.1179/2045772312Y.0000000011 · Published: May 1, 2012

Spinal Cord Injury Rehabilitation Biomechanics

Simple Explanation

This study uses a mathematical model to compare forces at the distal femur (a common fracture site) during quadriceps stimulation in standing, supine, and seated positions for people with spinal cord injury (SCI). The aim is to understand which exercise positions are safest and most effective for preventing bone loss after SCI, by minimizing shear forces (dangerous) and maximizing compressive forces (beneficial). The study suggests that standing exercises may be more beneficial due to higher compressive loads and lower shear forces, while seated exercises might be the riskiest due to high shear forces.

Study Duration

Not specified

Participants

Hypothetical subject, biomechanical model

Evidence Level

Level 5, Biomechanical Model

Key Findings

1
Standing generates the highest compressive force (240% body weight) and lowest shear force (24% body weight) at the distal femur compared to supine and seated positions.
2
The seated position yields the lowest compressive force (139% body weight) and the highest shear force (215% body weight).
3
The supine model had shear forces of 17–62% across the same quadriceps force range.

Research Summary

This study mathematically compared compression and shear forces at the distal femur during quadriceps stimulation in standing, supine, and seated positions to inform exercise recommendations for individuals with SCI. The standing model estimated the highest compressive force and the lowest shear force at the distal femur compared with the supine and seated models, suggesting it may be the most effective for preventing bone loss. The seated position yielded the lowest compressive force and the highest shear force, indicating it may be the least safe position for exercises involving quadriceps stimulation in individuals with SCI.

Practical Implications

Exercise Prescription

When prescribing exercise for individuals with SCI, prioritize exercises that maximize compressive forces and minimize shear forces at the distal femur, such as active resistive standing.

Alternative Positions

If standing is not feasible, supine exercises could be a temporary alternative, but seated exercises with high quadriceps forces should be approached with caution due to the potential for high shear forces.

NMES Parameter Optimization

When using NMES during seated exercises, consider alternative stimulation frequency parameters to limit deleteriously high shear forces.

Study Limitations

1
Anthropometric values used in the model were determined from a non-SCI cohort.
2
The models do not account for contractures, spasticity, or anatomical variants in insertion angles of skeletal muscle.
3
The supine and seated models were not validated in humans with SCI.

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