Chronic Bone Adaptations To Bike Interval Training With Or Without Blood Flow Restriction

PURPOSE: This counterbalance study aimed to compare the effects of two different bike interval training (IT) protocols, one with blood flow restriction (BFR) and the other without, on whole and regional bone mineral content (BMC) in sedentary young adult males with a body mass index greater than 24.9 kg/m2. METHODS: Twenty-four male subjects (age = 23.1 ± 3.6 yr) were randomly assigned to one of two training groups (high-intensity interval training (HIIT), n = 12, BMI = 33.2 ± 8.0 kg/m2; BFR, n = 12, BMI = 32.5 ± 3.7 kg/m2) to perform IT 2x/wk for 8 weeks. The HIIT group performed at 80-100% of their average anaerobic power output (Wavg), completing 16 × 30-sec leg cycling, with each bout followed by 45 sec of passive rest. In contrast, the BFR group performed IT at 40-60% of Wavg for 8 × 60-sec leg cycling with 60 sec of passive rest in between. Following their respective bike IT, both groups completed 3 circuits of 4 upper-body resistance band exercises at a light-to-moderate intensity, performing 10-20 repetitions for each exercise without the use of BFR. Under fasted and hydrated conditions, the subjects' pre- and post-training whole and regional BMC values were assessed using dual-energy X-ray absorptiometry. RESULTS: No significant differences were noted between the groups at baseline. However, significant time main effects were observed in total BMC (p < 0.01), leg BMC (p < 0.05), and trunk BMC (p < 0.05) within the HIIT group. Additionally, the HIIT group exhibited a trending effect towards increased gynoid BMC (p = 0.07). In contrast, the BFR group did not demonstrate any significant main effects over time for whole and regional BMC (p > 0.05). CONCLUSION: The observed effects of HIIT on BMC could be due to the high-intensity nature of the exercise. HIIT may stimulate bone remodeling processes, leading to increased bone density, especially in regions subjected to more mechanical load. The forces generated by the contractions of skeletal muscles during short, intense cycling bouts interspersed by brief rest periods could stimulate bone growth by activating osteoblasts and increasing bone formation markers. Increasing the intensity of cycling intervals may be necessary to achieve significant improvements in BMC through combined bike IT with BFR.