Idiosyncratic bone responses to blood flow restriction exercise: new insights and future directions

Abstract

Applying blood flow restriction (BFR) during low load exercise induces beneficial adaptations of the myotendinous and neuromuscular system. Despite the low mechanical tension, BFR exercise facilitates a localized hypoxic environment and increase in metabolic stress, widely regarded as the primary stimulus for tissue adaptations. First evidence indicates that low load BFR exercise is effective in promoting an osteogenic response in bone, although this has previously been postulated to adapt primarily during high-impact weight-bearing exercise. Besides studies investigating the acute response of bone biomarkers following BFR exercise, first long-term trials demonstrate beneficial adaptations in bone in both healthy and clinical populations. Despite the increasing number of studies, the physiological mechanisms are largely unknown. Moreover, heterogeneity in methodological approaches such as biomarkers of bone metabolism measured, participant and study characteristics, and time-course of measurement render it difficult to formulate accurate conclusions. Furthermore, incongruity in the methods of BFR application (e.g., cuff pressure) limits the comparability of datasets and thus hinders generalizability of study findings. Appropriate use of biomarkers, effective BFR application and befitting study design has the potential to progress knowledge on the acute and chronic response of bone to BFR exercise and contribute toward the development of a novel strategy to protect or enhance bone health. Therefore, the purpose of the present synthesis review is to: i) evaluate current mechanistic evidence; ii) discuss and offer explanations for similar and contrasting data findings; and iii) create a methodological framework for future mechanistic and applied research.

How to Suppress Mineral Loss and Stimulate Anabolism in Postmenopausal Bones with Appropriate Timing of Exercise and Nutrients

“…The prevailing view in the field of bone research is that a substantial supra-threshold mechanical stimulus is a necessary condition for any anabolic bone remodeling [ 35 , 36 ]. Yet in several protocols that manipulate the timing of nutrients and exercise, anabolic changes in bone can be triggered at sub-threshold mechanical loading either by a meal in the absence of the second mechanical stimulus [ 27 ], or after delayed access to food [ 37 ], and by timed blood-flow restriction (BFR) [ 38 ].…”

“…A final illustration of the ability of bone to generate an osteogenic response at subthreshold mechanical loads features application of a blood-flow restriction (BFR) procedure during exercise training [ 38 ]. The BFR or KAATSU practice was invented in Japan, but is now more widely practiced in both joint-reaction [ 39 ], and ground-reaction [ 40 ] training.…”

“…During muscle contractions, blood flow and access to these needed substances is intermittently reduced. The main attraction of BFR is that muscle hypertrophy, and some increases in BMC, can be achieved at sub-threshold resistance loads [ 38 ]. The practice attracts not only young and healthy individuals who desire to produce maximal muscle hypertrophy, but also older or disabled individuals who cannot, or do not wish to, engage in heavy-loading exercise.…”

“… Blood-flow restriction (BFR) or KAATSU is practiced by individuals who seek to increase muscle mass and strength [ 39 , 40 ] by training at subthreshold training effort. In addition to facilitating hypertrophy, this practice has also been found to increase BMD [ 38 ]. The practice has spread from Japan across the globe, but is not without some clotting risks.…”