Why the study?
The mechanisms by which blood flow restricted exercise limits muscular endurance are not well understood, and the impact of increasing restriction pressure during already occlusive contractions was unknown.
Does increasing blood flow restriction pressure to 150% of arterial occlusion reduce time to task failure compared to 100% in individuals performing isometric contractions?
Does increasing blood flow restriction pressure to 150% of arterial occlusion reduce time to task failure compared to 100% in individuals performing isometric contractions?
Increasing blood flow restriction pressure beyond arterial occlusion reduces local muscle endurance without affecting discomfort or force steadiness.
Higher pressures may hasten fatigue even during occlusive contractions without raising discomfort; leaves open neural mechanisms beyond blood flow.
CONTEXT: Blood flow restricted exercise involves the use of external pressure to enhance fatigue and augment exercise adaptations. The mechanisms by which blood flow restricted exercise limits muscular endurance are not well understood. OBJECTIVE: To determine how increasing blood flow restriction pressure impacts local muscular endurance, discomfort, and force steadiness when the contractions are already occlusive. DESIGN: Within-participant, repeated-measures crossover design. SETTING: University laboratory. PATIENTS: A total of 22 individuals (13 males and 9 females). INTERVENTION: Individuals performed a contraction at 30% of maximal isometric elbow flexion force for as long as possible. One arm completed the contraction with 100% of arterial occlusion pressure applied, while the other arm had 150% of arterial occlusion pressure applied. At the end of the protocol, individuals were asked to rate their perceived discomfort. MAIN OUTCOME MEASURES: Time to task failure, discomfort, and force steadiness. RESULTS: Individuals had a longer time to task failure when performing the 100% arterial occlusion condition compared with the 150% arterial occlusion pressure condition (time to task failure = 82.4 vs 70.8 s; Bayes factors = 5.77). There were no differences in discomfort between the 100% and 150% conditions (median discomfort = 5.5 vs 6; Bayes factors = 0.375) nor were there differences in force steadiness (SD of force output 3.16 vs 3.31 N; Bayes factors = 0.282). CONCLUSION: The results of the present study suggest that, even when contractions are already occlusive, increasing the restriction pressure reduces local muscle endurance but does not impact discomfort or force steadiness. This provides an indication that mechanisms other than the direct alteration of blood flow are contributing to the increased fatigue with added restrictive pressure. Future studies are needed to examine neural mechanisms that may explain this finding.
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Nucci et al. (2021) studied this question.
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