Exercise-induced fluid shifts are distinct to exercise mode and intensity: a comparison of blood flow-restricted and free-flow resistance exercise

Abstract

Aim: MRI can provide fundamental tools in decoding physiological stressors stimulated by training paradigms. Acute physiological changes induced by three diverse exercise protocols known to elicit similar levels of muscle hypertrophy were evaluated using muscle functional magnetic resonance imaging (mfMRI). Methods: The study was a cross-over study with participants (n=10) performing three acute unilateral knee extensor exercise protocols to failure and a work matched control exercise protocol. Participants were scanned after each exercise protocol; 70% 1 repetition maximum (RM) (FF70); 20% 1RM (FF20); 20% 1RM with blood flow restriction (BFR20); free-flow (FF) control work matched to BFR20 (FF20WM). Post exercise mfMRI scans were used to obtain interleaved measures of muscle R2 (indicator of edema), R2' (indicator of deoxyhemoglobin), muscle cross sectional area (CSA) blood flow and diffusion. Results: Both BFR20 and FF20 exercise resulted in a larger acute decrease in R2, decrease in R2', and expansion of the extracellular compartment with slower rates of recovery. BFR20 caused greater acute increases in muscle CSA than FF20WM and FF70. Only BFR20 caused acute increases in intracellular volume. Post-exercise muscle blood flow was higher after FF70 and FF20 exercise than BFR20. Acute changes in mean diffusivity were similar across all exercise protocols. Conclusion: This study was able to differentiate the acute physiological responses between anabolic exercise protocols. Low-load exercise protocols, known to have relatively higher energy contributions from glycolysis at task failure, elicited a higher mfMRI response. Noninvasive mfMRI represents a promising tool for decoding mechanisms of anabolic adaptation in muscle.

Muscle thickness and inflammation during a 50km ultramarathon in recreational runners

“…We also report declines in knee extensor torque and elevations in CK concentrations that appear to remain at the 24-hr post-race timepoint, and acute increases in leukocyte number, plasma IL-6, and calprotectin concentrations that return to pre-race levels within 24 hrs. While prolonged low-load exercise protocols contribute to muscular swelling or edema [28], this was not observed as greater resting rectus femoris MT following the 50km in our study. Elevation changes, especially elevation loss, can increase muscle swelling and inflammation due to the repeat eccentric contractions that occur during a race with large elevation loss [29].…”

Effects of low load exercise with and without blood‐flow restriction on microvascular oxygenation, muscle excitability and perceived pain

“…However, at 80‐100% of exercise time, this effect seems to be equalled out by the effect of BFR. Interestingly, the changes in Δ[HHb] in VL was not replicated in VM, possibly due to intermuscular differences in muscle excitability or degree of BFR (Haddock et al, 2021).…”

Safety and efficacy of blood flow restriction exercise in individuals with neurological disorders: A systematic review

“…[12][13][14] Blood flow restriction (BFR) is achieved by applying an external pneumatic tourniquet at the proximal end of the upper or lower extremity, applying an occlusion pressure promoting ischemia and blood pooling in the capillary beds of the musculature distal to the tourniquet. 15 The combination of ischemia and mechanical tension during exercise creates an environment of mechanotransductive and metabolic stress in the exercising myofibers 16,17 promoting hypertrophic and strength adaptations. 16,18 Previous meta-analyses have concluded that LL-BFRE may be less effective than HL-RE 19 in increasing maximal muscle strength, but superior to LL-RE without BFR for increasing muscle size and strength.…”