Although the efficacy of low-load training with BFR is particularly relevant for patients and healthy untrained or aged individuals, for whom heavy-load strength training may be problematic and contraindicated ( 6–8,11,12), such training may be insufficient in well-trained athletes who require high level of strength or power ( 13).Īlthough increases in maximal strength are due to both muscle and neural adaptations, the purpose of our article is not to provide an in-depth review of the molecular mechanisms underlying muscle hypertrophy or to discuss the numerous neural adaptations induced by strength training. We also explore the utility of the approach of combining moderate to high loads (mechanical stress) and brief rest intervals between sets (metabolic stress) to maximize muscle hypertrophy and strength gains in untrained and trained individuals. As one of the objectives was to examine the possible contribution of metabolic stress on muscle hypertrophy, we chose to compare low-load exercise with BFR to high-load strength training, as the former method produces more metabolic stress and needs fewer repetitions to reach failure ( i.e., greater efficacy) than low-load training performed under normal blood circulation ( 5). The current Perspective for Progress article compares training programs performed with high loads to those involving low loads under BFR and the adaptations elicited by each approach. These studies suggested that the accumulation of fatigue-related metabolites ( i.e., metabolic stress) may play a role in the exercise stimulus, leading to an increased accretion of muscle mass and strength ( 9,10). More recently, however, studies using training loads of less than 50% of 1RM performed until failure ( 5) or with blood flow restriction (BFR) (ischemic/hypoxic condition) have reported gains in maximal strength and comparable levels of muscle hypertrophy to that observed with conventional heavy-load strength training (for recent reviews, see ( 6–8)). Based on this concept, moderate to high mechanical loading of the muscle (≥60%–70% of the one repetition maximum ) has long been considered as the main stimulus ( i.e., mechanical tension) for muscle hypertrophy and thereby an increase in muscle strength ( 2–4). This principle, which states that a minimal load/contraction intensity must be exceeded during the training sessions to increase muscle strength, is used in sport training and in clinical and rehabilitation settings. The increase in muscle strength is classically based on the “overload” principle ( 1). One training option is to combine different levels of mechanical tension and metabolic stress that are optimized to the training status of the individual.As the magnitude of the neural adaptations after low-load exercise with blood flow restriction is less than that elicited by high-load strength training and this method is difficult for some individuals and insufficient for well-trained athletes, we suggest there is a need for new strength training protocols.Mechanical tension and metabolic stress contribute to training-related muscle hypertrophy and increase in maximal strength.
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