Impact of blood flow restriction on bone markers during resistance training

December 17, 2020
Bob Kronemyer

Freelance writer for Contemporary OB/GYN

A 12-week course of low-intensity resistance training in postmenopausal women with osteoporosis or osteopenia was found safe and an effective method to improve muscle strength, bone formation markers and balance, according to a study in the Journal of Exercise Science and Fitness.

Neither hormone therapy nor medication are considered suitable first-line treatments for osteoporosis, according to the authors. “On the other hand, exercise intervention positively influences both bone strength and balance to prevent falls,” wrote the authors.1

Of the 26 study participants (average age 56 and a T-score of -2.5), 12 had osteopenia and 14 had osteoporosis.

The women were randomly assigned to one of four groups: moderate-to-high intensity resistance training (MHIRT, n = 7); blood flow restriction (BFR) combined with low-intensity resistance training (LIBFR, n = 7); low-intensity resistance training (LIRT, n = 6); and an unspecified control group (n = 6).

Note that BFR training works by occluding venous flow yet allowing partial arterial inflow with manual or pneumatically inflated cuff on the most proximal site of limb during exercise. A number of studies reported low-intensity resistance training with BFR (LIBFR) increased both muscle size, and strength in healthy adult.

The three exercise groups performed leg press, leg extension, biceps curl and triceps extension three times a week for 12 weeks. Training intensity were set at 60% of 1-repetition maximum.

This is the maximum amount of weight that a person can possibly lift for a single repetition. Repetition maximums were reset every 4 weeks for increasing intensity.

With 1-repetition maximum, both the lower and upper limb increased strength in the MHIRT group by 65% (P < 0.001) and in the LIBFR group by 40% (P < 0.05) groups, whereas LIRT only showed 28% incremental strength on the lower limb with 1-repetition maximum (P < 0.05).

All exercise groups showed significant incremental increases in blood lactate concentration after the training sessions (P < 0.001).

However, LIBFR achieved a 2.7-fold higher incremental concentration than LIRT (P < 0.001).

“Theoretically, blood lactate response after training should be similar between LIBFR and LIRT, because of identical training intensity and volume,” wrote the authors. “However, due to the occlusion of venous flow in LIBFR, lactate was accumulated on the training site, and resulted in higher lactate concentration.”

The blood lactate concentration of LIBFR (8.8 mmol/L) was comparable to MHIRT (8.99 mmol/L) after one training session. “Thus, it proved not only occlusion pressure used in this study was enough to induce the metabolic accumulation, but also LIBFR can induce chemical stimulus analogous with MHIRT,” wrote the authors.“Lactate response is important, because higher lactate concentration, and intramuscular acidity stimulates secretion of growth hormone.”

No changes were observed in bone mineral density (BMD) in the three exercise groups, but the control group showed a significant decrease in BMD (P < 0.05).

In addition, while LIRT demonstrated no responses on bone turnover markers, LIBFR significantly increased bone formation markers by roughly 7.05 ng/ml (P < 0.05).

The study also found a balance improvement in MHIRT and LIBFR (P < 0.05), with LIBFR showing improvement in static balance (both open and closed eyes), but not for dynamic balance. Static eye open balance test showed a significant increase in both MHIRT and LIBFR compared to baseline. But on eye closed static balance, only LIBFR resulted in longer time compared to baseline (P < 0.05). For dynamic balance test, significant improvement was limited to MHIRT (P < 0.05). Combined, MHIRT and LIBFR showed greater improvement only on static balance with eyes open.

The authors assume that dynamic balance is more associated with muscle strength and/or speed, while static balance seems more strongly linked to neuromuscular connections because there is no movement, only maintaining the equilibrium.

“Since balance has complex factors, it is difficult to determine which factors were stimulated in this study,” the authors wrote. “Of particular interest, LIBFR showed improvement in static balance, both open and closed eyes (P < 0.05), but not on dynamic balance. It appears to be the strengthening of the major muscle groups, such as knee flexor and knee extensor for postural stability, because muscle mass and muscle strength were positively correlated to balance.”

Although MHIRT showed the greatest improvement in muscle strength and bone turnover markers, the higher risk of injury in this group cannot be neglected, according to the authors.

__

Reference

  1. Linero C, Choi S-J.Effect of blood flow restriction during low-intensity resistance training on bone markers and physical functions in postmenopausal women. J Exerc Sci Fit. 2021 Jan;19(1):57-65. doi:10.1016/j.jesf.2020.09.001