Bone turnover marker responses to 12 weeks of walking with and without blood flow restriction

Abstract

Neuromuscular adaptations to blood flow restricted (BFR) exercise have been well documented. Few studies have investigated the effects of BFR exercise on bone metabolism and none in women.PURPOSE: To investigate the effects of 12 weeks walking with and without BFR on bone turnover markers in college-aged women.METHODS: Thirty-one women (20.9 ± 2.1 yrs) were randomly assigned to a low-intensity treadmill walking (WALK, n=10), a low-intensity treadmill walking with BFR (BFR, n=11), or a non-exercise control group (CON, n=10). BFR and WALK groups walked on a treadmill at 45% VO2peak for up to 20 minutes four days per week for 12 weeks. The BFR group wore 5 cm wide electronically monitored elastic pressure cuffs (Kaatsu-Mini, Tokyo, Japan) around their upper thighs during walk training. BFR cuffs were inflated to an initial pressure of 140 mmHg for the first four weeks, increased by 20 mmHg at week five (160 mmHg), and again at the start of week nine (180 mmHg). The CON group was asked not to change their normal physical activity levels or dietary habits during the study. Fasted morning blood samples at baseline and post-training were assayed for bone-specific alkaline phosphatase (Bone ALP, U/L) and tartrate-resistant acid phosphatase isoform 5b (TRAP5b, U/L).RESULTS: Serum bone marker levels were not different between groups at baseline. Significant time (p=0.002) and group x time interaction (p=0.02) effects were detected for Bone ALP. Bone ALP was reduced in both BFR (pre: 29.6 ± 2.8, post: 27.6 ± 2.4) and CON (pre: 34.7 ± 3.4, post: 31.1 ± 3.2) groups post-training. No significant main or interaction effects were found for TRAP5b or Bone ALP/TRAP5b ratio.CONCLUSIONS: Bone ALP, a serum marker of bone formation, decreased following 12 weeks of BFR walking in college-aged women with no change in bone resorption. These findings are in contrast to past studies of BFR exercise in young and older men who reported either an increase in bone formation markers or a decrease in resorption markers. The discrepancy in findings between studies may be related to factors other than BFR exercise known to affect bone metabolism including energy availability, participant age, and seasonal effects.