Physiological responses to moderate intensity continuous and high-intensity interval exercise in persons with paraplegia

Study design: Randomized crossover. Objectives: To test differences in the duration and magnitude of physiological response to isocaloric moderate intensity continuous (MICE) and high-intensity interval exercise (HIIE) sessions in persons with spinal cord injury (SCI). Setting: Academic medical center in Miami, FL, USA. Methods: Ten adult men (mean ± s.d.; 39 ± 10 year old) with chronic (13.2 ± 8.8 year) paraplegia (T2–T10) completed a graded exercise test. Then, in a randomized order, participants completed MICE and HIIE for a cost of 120 kcal. MICE was performed at 24.6% PO _peak. During HIIE, exercise was completed in 2 min work and recovery phases at 70%:10% PO _peak. Results: MICE and HIIE were isocaloric (115.9 ± 21.8 and 116.6 ± 35.0 kcal, respectively; p = 0.903), but differed in duration (39.8 ± 4.6 vs 32.2 ± 6.2 min; p < 0.001) and average respiratory exchange ratio (RER; 0.90 ± 0.08 vs 1.01 ± 0.07; p = 0.002). During MICE, a workrate of 24.6 ± 6.7% PO _peak elicited a V̇O ₂ of 53.1 ± 6.5% V̇O _2peak (10.1 ± 2.2 ml kg ⁻¹ min ⁻¹). During HIIE, a workrate at 70% PO _peak elicited 88.3 ± 6.7% V̇O _2peak (16.9 ± 4.2 ml kg ⁻¹ min ⁻¹), and 29.4 ± 7.7% of the session was spent at or above 80% V̇O _2peak. During HIIE working phase, RER declined from the first to last interval (1.08 ± 0.07 vs 0.98 ± 0.09; p < 0.001), reflecting an initially high but declining glycolytic rate. Conclusions: Compared with MICE, HIIE imposed a greater physiological stimulus while requiring less time to achieve a target caloric expenditure. Thus, exercise intensity might be an important consideration in the tailoring of exercise prescription to address the cardiometabolic comorbidities of SCI.