The Influence Of Limb Blood Flow On Muscle Growth With Different Resistance Training Protocols

Abstract

Exercise-induced muscle growth may be dependent upon the baseline vascular network or the ability to increase this network through training. Given the cost of protein synthesis, the delivery of nutrients to the muscle could serve as a physiologic limiter to exercise-induced growth. PURPOSE: To determine if baseline resting blood flow or the change in resting blood flow moderates the change in muscle thickness throughout different resistance training protocols. METHODS: Forty individuals were included for analysis. Four distinct training conditions were compared throughout the upper and lower body before and after eight weeks of training: 1) 15% 1RM with no blood flow restriction (Low Load); 2) 15% 1RM with 40% of resting arterial occlusion pressure (Low Load+40%); 3) 15% 1RM with 80% of resting arterial occlusion pressure (Low Load+80%); and 4) traditional resistance training at 70% 1RM (High Load). Each limb of the participant was randomly assigned to a training condition. Blood flow was quantified by strain gauge plethysmography and muscle size was measured via ultrasound at 11 separate sites (3 in the biceps and 8 in the thighs). To examine if limb blood flow moderated the changes in muscle thickness between groups, while accounting for our within/between subject design, two-factor (condition x limb blood flow) analysis of variance was used. RESULTS: Muscle thickness increased in all conditions. Resting blood flow changed the greatest for the Low Load +80% and High Load conditions in both the upper and lower body (~0.5 ml·min·100 ml-1). There was no evidence for moderation for baseline resting limb blood flow. However, there was for the change in blood flow at the 70% site for the biceps. Those with smaller changes in resting blood flow had greater changes in muscle size following high load resistance training compared to the Low Load (β = 0.26, p = 0.0024), Low Load+40% (β = 0.21, p = 0.0022), and the Low Load+80% (β = 0.17, p = 0.038) conditions. CONCLUSIONS: The baseline vascular network seems sufficient for young individuals to mount an anabolic response. Participants who had the smallest change in blood flow in the high load condition had the greatest changes in muscle thickness compared to the other exercise conditions. The lack of moderation at other sites indicates that this finding should be interpreted with caution.