The American College of Sports Medicine (ACSM) recommended that, optimising muscular strength and hypertrophy training can be achieved through moderate to high intensities of resistance exercise that utilise 8∼10 upper and lower body exercises. These exercises should target major muscle group’s 2∼3 day a week at a training intensity of more than 65% of the subject’s one-repetition maximum. (Donnelly 2009) During resistance training the load should exceed 70% of the one repetition maximum to achieve maximum hypertrophy. Unfortunately, the elderly or people rehabilitating from injury may not be able to tolerate these loads, which can limit their ability to have an adequate strength and hypertrophy response. 

Blood flow restriction (BFR) training in which a tourniquet is used on a proximal limb to limit arterial inflow while blocking venous outflow has consistently demonstrated strength and hypertrophy gains and comparable to heavy load lifting. 

From this large body of evidence it becomes apparent that the combination of vascular occlusion with low-level exercise can induce a strength and hypertrophy response. In fact, the strength and hypertrophy responses from BFR are so predictable that scientists now use it as a model to study muscle physiology. The exact mechanism for these adaptations to BFR and exercise are not fully understood. One likely mechanism is the metabolite theory of muscle strength and hypertrophy, which researchers are just recently beginning to understand. The increase in metabolic byproducts from anaerobic metabolism seems to play as powerful a role in muscle physiology as mechanical load. In an invited editorial on BFR in the Journal of Applied Physiology Dr. Meyer’s states “the recommendation that hypertrophy requires a load 70% of one repetition maximum might just as well be recast as a recommendation that the training must result in substantial anaerobic metabolism”. He concludes his editorial by stating that the responses seen from BFR “deserves serious consideration from those interested in the molecular biology of hypertrophy”. (Meyers 2006) Dr. Schoenfeld’s recent review on the subject is an excellent source for further background on the metabolic adaptations to hypertrophy. (Schoenfeld 2013) 

What we do know is that BFR and low-level exercise has an effect on strength and hypertrophy. What we don’t know is the exact mechanism. Current theories behind the proposed mechanisms of BFR include increased fibre type recruitment, metabolic accumulation, activation of muscle protein synthesis, and cell swelling, although it is likely that many of the aforementioned mechanisms work together. 

Understanding two of the prevailing mechanisms, metabolite accumulation and cellular swelling, can aide the rehabilitation professional to develop personalised protocols for a wide range of injuries. We will begin with metabolite accumulation.

Bibliography 

Donnelly JE, Blair SN, Jakicic JM, Manore MM, Rankin JW, Smith BK; American College of Sports Medicine. American College of Sports Medicine Position Stand. Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults. Med Sci Sports Exerc. 2009;41:459-471. 

Kraemer WJ, Adams K, Cafarelli E, et al. American College of Sports Medicine position stand:progression models in resistance training for healthy adults. Med Sci Sports Exerc. 2002;34(2): 364–80. 

Loenneke, J. P., Wilson, J. M., Marin, P. J., Zourdos, M. C., & Bemben, M. G. (2012). Low intensity blood flow restriction training: a meta-analysis. Eur J Appl Physiol, 112(5), 1849-1859. doi: 10.1007/s00421-011-2167-x 

Meyer, R. A. (2006). Does blood flow restriction enhance hypertrophic signaling in skeletal muscle? J Appl Physiol (1985), 100(5), 1443-1444. 

Schoenfeld, B. J. (2013). Potential mechanisms for a role of metabolic stress in hypertrophic adaptations to resistance training. Sports Med, 43(3), 179-194. doi: 10.1007/s40279-013-0017-1 

Takarada, Y., Tsuruta, T., & Ishii, N. (2004). Cooperative effects of exercise and occlusive stimuli on muscular function in low-intensity resistance exercise with moderate vascular occlusion. Jpn J. Physiol, 54(6), 585-592. 

Takarada, Y., Takazawa, H., Sato, Y., Takebayashi, S., Tanaka, Y., & Ishii, N. (2000). Effects of resistance exercise combined with moderate vascular occlusion on muscular function in humans. J Appl Physiol (1985), 88(6), 2097-2106.