Venous Blood Changes with Low-Intensity Muscle Contractions and Blood Flow Restriction

Abstract

Work output during repetitive low-intensity muscle contractions is presumably maintained by increased motor unit recruitment (increased EMG activity) during restricted blood flow. Interestingly, the increased muscle activation is associated with an increased oxygen uptake (Vo2); an unexpected finding given the same external work and reduced muscle blood flow. PURPOSE: To investigate changes in venous blood metabolites and gases during repetitive muscle contractions with restricted blood flow. METHODS: Six male volunteers performed 3 trials (separated by 1-week) of unilateral elbow flexion muscle contractions (20% of 1-RM; 30 repetitive contractions then 3 sets of 15 contractions, 30 sec rest between sets). Contractions were performed with unrestricted blood flow (C) or two levels of blood flow restriction using a KAATSU belt; a specially designed elastic cuff placed at the most proximal position of the upper arm and inflated to either 100 (K100) or 160 (K160) mmHg to restrict blood flow. Venous blood was collected prior to contractions and following the 30 repetitive contractions and the last set of 15 contractions; (an indwelling catheter inserted in the brachial vein below the cuff). Venous blood was analyzed using a blood gas analyzer (Instrumentation Laboratory, Japan). RESULTS: Oxygen saturation decreased with contractions in all trials (P<0.05) with K160 (33% and 34%, respectively) being greater than K100 (41% and 42%, respectively) and both greater than C (67% and 56%, respectively). Changes in venous blood pH and PCO2 were greater in K160 than K100 and C. Venous PO2 decreased similarly in K160 and K100, significantly less than C. Hematocrit and [glucose] were similar in all trials while [lactate] was greater (P<0.05) in K160 (4.4 and 5.6 mmol/L, respectively) than K100 (3.2 and 3.6 mmol/L, respectively) and C (2.5 and 2.9 mmol/L, respectively). CONCLUSION: The significant reduction in oxygen saturation supports the previously observed increase in VO2 during blood flow restriction. The basis for the greater lactate concentration is unknown; either increased production or reduced removal. These data appear to support the conclusion that energy supply is paradoxically increased during low-intensity muscle contractions with restricted blood flow, likely associated with increased muscle activation.