Skeletal Muscle Adaptation in Cardiac Rehabilitation Patients Undertaking Traditional or Higher Intensity Stair-climbing Exercise

Exercise-based cardiac rehabilitation is associated with reduced secondary events in coronary artery disease (CAD) patients. Despite this evidence, the rate of participation in cardiac rehabilitation exercise is low. There is a lack of information evaluating how both traditional and time-reduced higher intensity protocols affect muscle metabolism in this population, even though CAD exacerbates skeletal muscle defects that contribute to the poor metabolic phenotype. PURPOSE: To determine the effect of a traditional cardiac rehabilitation exercise program and an alternative stair climbing-based high-intensity interval training program on the skeletal muscle phenotype in CAD patients. METHODS: 16 participants (15M, 1F) were randomly assigned to either traditional moderate-intensity exercise (7M, TRAD) or brief but higher-intensity interval stair climbing exercise (8M, 1F, STAIR). Both programs were 12 weeks (3d/w) in duration, each TRAD exercise session consisted of 45 minutes of moderate-intensity aerobic exercise, and each STAIR session consisted of 3 bouts x 6 flights of high-intensity stair climbing. Muscle biopsies were collected from the vastus lateralis at baseline and after 12 weeks of training. Immunofluorescent staining of muscle cross sections was completed to determine fiber size, capillarization, satellite cell (SC) and myonuclear content. RESULTS: There were no differences in the cross-sectional area and myonuclear domain of type I or II fibers following 12 weeks of either TRAD or STAIR training (p>0.05). Following 12 weeks, both exercise programs resulted in increases in, myonuclear content (type I: TRAD Δ0.4±0.5, STAIR Δ0.3±0.6, p=0.012; type II: TRAD Δ0.8±0.7, STAIR Δ0.4±0.7, p=0.006), capillary contacts (type I: TRAD Δ0.5±0.5, STAIR Δ0.2±0.7, p=0.038; type II: TRAD Δ1.2±0.6, STAIR Δ0.7±0.4, p<0.001), capillary-to-fiber perimeter exchange index (type I: TRAD Δ1.6±1.8, STAIR Δ0.4±0.8, p=0.011; type II: TRAD Δ1.8±1.7, STAIR Δ0.7±0.8, p=0.002), and capillary to fiber ratio (type II: TRAD Δ0.5±0.3, STAIR: Δ0.3±0.2, p<0.001). CONCLUSION: Both brief stair climbing-based high-intensity interval training and traditional cardiac rehabilitation exercise result in improvements in variables associated with skeletal muscle health in CAD patients.