Muscle Strength Cutoff Points for Functional Independence and Wheelchair Ability in Men With Spinal Cord Injury

Objective: Determine trunk and shoulder muscle strength cutoff points for functional independence and wheelchair skills, and verify the predictive capacity of relative and absolute peak torque in men with spinal cord injury (SCI).

Design: Cross-sectional study.

Setting: Rehabilitation hospital setting.

Participants: Men (N=54) with SCI were recruited and stratified into high and low paraplegia groups.

Interventions: All participants performed maximum strength tests for shoulder abduction or adduction (isokinetic) and trunk flexion or extension (isometric) to determine relative and absolute peak torque cutoff points for the Spinal Cord Independence Measure version III (SCIM-III) and Adapted Manual Wheelchair Circuit (AMWC).

Main Outcome Measures: The primary outcome measures were SCIM-III, AMWC-Brazil test, and strength variables (peak torques). Demographic characteristics obtained from participants' electronic medical records were the secondary outcomes used as predictor variables of functional independence.

Results: The best predictive model for SCIM-III (R=0.78, P≤.05) used the sum of trunk flexion and extension relative peak torque values to determine the cutoff points (1.42 N·m/kg for a score of 70). Relative shoulder abduction peak torque was used in the predictive models for AMWC outcomes: performance score (R=0.77, P≤.05, cutoff points of 0.97 N·m/kg for 300.0m) and 3-minute overground wheeling (R=0.72, P≤.05, cutoff points of 0.96 N·m/kg for 18.5s).

Conclusions: Relative peak torque showed better predictive capacity compared to absolute peak torque. Cutoff points were established for relative muscle strength and could help health professionals set appropriate goals for individuals with SCI to achieve high functional independence and wheelchair ability.