Substrate metabolism during exercise in the spinal cord injured

The primary aim of the study was to examine substrate metabolism during combined passive and active exercise in individuals with spinal cord injury (SCI). Nine men and women with SCI (mean age 40.6 ± 3.4 years) completed two trials of submaximal exercise 1 week apart. Two maintained a complete injury and seven had an incomplete injury. Level of injury ranged from thoracic (T4–T6 and T10) to cervical (four C5–C6 and three C6–C7 injuries). During two bouts separated by 1 week, subjects completed two 30 min sessions of active lower-body and passive upper-body exercise, during which heart rate (HR) and gas exchange data were continuously assessed. One-way analysis of variance with repeated measures was used to examine differences in all variables over time. Results demonstrated significant increases (P < 0.05) in HR and oxygen uptake (VO₂) from rest to exercise. Respiratory exchange ratio (RER) significantly increased (P < 0.05) during exercise from 0.85 ± 0.02 at rest to 0.95 ± 0.01 at the highest cadence, reflecting increasing reliance on carbohydrate from 50.0 to 83.0% of energy metabolism. Data demonstrate a large reliance on carbohydrate utilization during 30 min of exercise in persons with SCI, with reduced contribution of lipid as exercise intensity was increased. Strategies to reduce carbohydrate utilization and increase lipid oxidation in this population should be addressed.