The Impact Of Increasing Blood Flow Restriction Pressure During Already Occlusive Contractions.

Abstract

Restricting blood flow during resistance exercise reduces the number of repetitions required to see adaptations, with higher blood flow restriction pressures resulting in greater muscle fatigue when sub-occlusive pressures are applied. The augmented fatigue is thought to be related to alterations in blood flow, but the impact of increasing the restriction pressure during completely occlusive contractions remains unknown and may provide information on alternative mechanisms responsible for fatigue. PURPOSE: To determine whether increasing the blood flow restriction pressure reduces local muscular endurance and increases discomfort when the contractions are already occlusive. We also the examined potential changes in force steadiness. METHODS: Twenty-two 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. A Bayesian paired samples t-test was used to compare differences in time to task failure, average force output, and force steadiness and a Wilcoxon signed rank test was performed to compare differences in discomfort between high and low pressure conditions. RESULTS: Individuals had a longer time to task failure when performing the 100% arterial occlusion condition as compared to the 150% arterial occlusion pressure condition (time to task failure = 82.4 vs. 70.8 seconds; BF10 = 5.77). There were no differences in discomfort between the 100% and 150% conditions (median discomfort = 5.5 vs. 6; p = 0.243) nor were there differences in force steadiness (standard deviation of force output 1.09 vs. 1.06 %; BF10 = 0.29). CONCLUSIONS: 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.