Sarcolemmal permeability and muscle damage as hypertrophic stimuli in blood flow restricted resistance exercise (Reply to Loenneke and Abe)

Abstract

Dear Editor,We welcome the letter by Loenneke and Abe (2011)relating to our recent publication (Wernbom et al. 2011), aswe feel that the topics are of importance and deserve fur-ther discussion.1. Regarding their first point, we were interested instudying the recovery of maximal voluntary contraction(MVC) during maintained partial blood flow restriction(BFR) in order to document the acute effects of our BFRmodel on muscle function during and after exercise, whileblood flow was still restricted. We were also aiming tostudy later recovery, hence our choice of time points.2. Regarding their second point, we acknowledge thatthere were no significant differences in MVC after the BFRwas released. However, there was a trend for MVC of theBFR leg to still be reduced at 72 h post-exercise(p\0.10), the nonsignificance possibly reflecting a type IIerror. Nevertheless, some signs of membrane permeabilitywere present also in the free-flow leg, see below.Concerning signs of damage in the BFR leg, Umbelet al. (2009) demonstrated greater reductions in MVC(-14.1 vs. -1.5%) in the BFR leg than in the free-flowtrained leg at 24 h post-exercise. Interestingly, inspectionof their figures on vastus lateralis cross-sectional area(CSA) reveals a muscle swelling of *5.5% at 24 h post-exercise (vs. *2% in the free-flow leg), and the swelling at24 h was significant when the CSA data for both legs werecombined. The moderate torque decrements, muscleswelling and delayed onset muscle soreness (DOMS) areconsistent with the suggestion of mild muscle damage, asproposed by Umbel et al. (2009). The torque decrements,the signs of increased membrane permeability, the pro-longed increase in resting tension, and DOMS in our study(Wernbom et al. 2011) are also consistent with thisproposal.There are other reports that signs of muscle damage canbe induced by low-to-moderate load resistance exerciseduring ischemic conditions (see point 3), and also a casereport on rhabdomyolysis after BFR-resistance exercise(Iversen and Rostad 2010). These findings suggest that thepotential for muscle damage with strenuous acute BFR-resistance exercise needs to be taken seriously.However, it should also be emphasised that this was thefirst time that our subjects performed strenuous BFR-resistance exercise. It is our experience that the symptomsof muscle damage are much less evident with subsequentbouts, suggesting a protective ‘‘repeated-bout effect’’similar to that for eccentric exercise.3. Concerning Loenneke and Abe’s third point, it shouldbe noted that the exercise was performed without relaxa-tion between repetitions. Signs of ischemia with continuousdynamic knee-extensions have been noted at loads as lowas 10% of MVC (Shoemaker et al. 1994), and isometricknee-extensions at 25–35% of MVC elicited a similar