Blood flow-restricted strength training displays high functional and biological efficacy in women: a within-subject comparison with high-load strength training

Abstract

Limited data exist on the efficacy of low-load blood flow-restricted strength training (BFR), as compared directly to heavy-load strength training (HST). Here, we show that 12 wk of twice-a-week unilateral BFR [30% of one repetition maximum (1RM) to exhaustion] and HST (6-10RM) of knee extensors provide similar increases in 1RM knee extension and cross-sectional area of distal parts of musculus quadriceps femoris in nine untrained women (age 22 ± 1 yr). The two protocols resulted in similar acute increases in serum levels of human growth hormone. On the cellular level, 12 wk of BFR and HST resulted in similar shifts in muscle fiber composition in musculus vastus lateralis, evident as increased MyHC2A proportions and decreased MyHC2X proportions. They also resulted in similar changes of the expression of 29 genes involved in skeletal muscle function, measured both in a rested state following 12 wk of training and subsequent to singular training sessions. Training had no effect on myonuclei proportions. Of particular interest, 1) gross adaptations to BFR and HST were greater in individuals with higher proportions of type 2 fibers, 2) both BFR and HST resulted in approximately four-fold increases in the expression of the novel exercise-responsive gene Syndecan-4, and 3) BFR provided lesser hypertrophy than HST in the proximal half of musculus quadriceps femoris and also in CSApeak, potentially being a consequence of pressure from the tourniquet utilized to achieve blood flow restriction. In conclusion, BFR and HST of knee extensors resulted in similar adaptations in functional, physiological, and cell biological parameters in untrained women.

Keywords: gene expression; heavy-load strength training; low-load blood flow-restricted training; muscle fiber; muscle strength and mass.

Fig. 1.

Overview of the strength-training intervention. BFR, blood flow-restricted strength training; HST, heavy-load strength training; 1RM, 1 repetition maximum; MR, magnetic resonance imaging.

Fig. 2.

Representative immunohistochemical staining of myosin heavy chains (A) in serial sections of human skeletal muscle using antibodies toward MyHC1 (1; A4.840), MyHC2A (2A; EPR5280), and MyHC2X [2(A)X; 6H1] and dystrophin (B) with hematoxylin staining of nuclei. Arrows indicate myonuclei.

Fig. 3.

The effect of 12-wk blood flow-restricted strength training (BFR, left) and heavy-load strength training (HST, right) on 1RM knee extension in previously untrained women (n = 12). Each individual performed the two protocols in a contralateral manner. Data are expressed as means ± SD (⧫ with error bars) and individual values (black lines). *Significant effects of HST and BFR on 1RM performance (P < 0.05). No difference was found between HST and BFR.

Fig. 4.

A: effect of 12-wk BFR (○) and HST (●) on cross-sectional area (CSA) of distal and proximal parts of musculus quadriceps femoris (QUAD, left) and musculus vastus lateralis (VL, right) in previously untrained women (n = 12). Each individual performed the two protocols in a contralateral manner. The border between distal and proximal parts of muscles were defined using images showing the highest cross-sectional area. Data are expressed as means ± SD. #Significant effects of BFR on muscle (P < 0.05). *Significant effects of HST on muscle CSA (P < 0.05). £Significant differential effects of HST and BFR, measured as the difference in relative change of CSA from baseline (P < 0.05). B: representative MR image of the thigh from one subject taken before (PRE) and after (POST) 12 wk of BFR. The four muscle bellies of QUAD is highlighted in green: VL; VI, musculus vastus intermedius; VM, musculus vastus medialis; RF, musculus rectus femoris. This particular individual exhibited a 6.8% increase in the CSA of QUAD and a 9.4% increase in the CSA of VL.

Fig. 5.

A: correlation between changes in peak cross-sectional area (CSA_peak) of musculus quadriceps femoris (QUAD) and 1RM knee extension performance following 12 wk of BFR and HST in previously untrained women (n = 12). CSA_peak was defined by the part of QUAD showing the largest CSA in postintervention images, assessed using magnetic resonance imaging. Data are individual values. Straight lines illustrate trend lines, while dotted lines indicate a perfect 1:1 slope. CI denotes the 95% confidence interval of Pearson r. B: correlation between changes in CSA in QUAD following 12 wk of HST and BFR.

Fig. 6.

The effect of 12 wk of BFR (left) and HST (right) on immunohistochemistry (Immuno)-determined muscle fiber proportions (A and B) and qRT-PCR-determined myosin heavy chain (MyHC) composition (C and D) in musculus vastus lateralis of previously untrained women (n = 8). Data appear as proportions of overall My.HC expression. Data are back-transformed means (◇) with 95% confidence intervals and back-transformed individual values (black lines). *Significant effects of BFR and HST on MyHC proportions (P < 0.05). No difference was found between HST and BFR.

Fig. 7.

Correlation between baseline MyHC1 and MyHC2 proportions in musculus vastus lateralis and changes in 1RM performance (A) and CSApeak (B) in musculus quadriceps femoris (QUAD) following 12 wk of BFR (○) and HST (●) in previously untrained women (n = 9). Values are individual. MyHC proportions are presented as combined IMMUNO- and qPCR-data, calculated as described in methods. CI denotes the 95% confidence interval of Pearson r. Straight lines illustrate trend lines.

Fig. 8.

The effect of 12 wk of BFR and HST on myonuclei numbers, measured per muscle fiber, in musculus vastus lateralis of previously untrained women (n = 7). Data are expressed as means ± SD. No effect was found of HST or BFR. No difference was found between HST and BFR.

Fig. 9.

Serum concentrations of human growth hormone (sHGH) (A) and cortisol (sCOR) (B) measured before (PRE), directly after (POST_1min), and 30 min after (POST_{30 min}) bouts of unilateral knee extension exercise of BFR (○) and HST (●) in previously untrained women (n = 7 at 0 WKS and n = 9 at 12 WKS). Each individual performed each of the two training protocols in a contralateral manner, with acute HST and BFR sessions being performed both before (week 0) and after (week 12) 12 wk of twice weekly HST and BFR, in each case on different days, separated by 4–6 days. mIU/l, milli-international units per liter. Data are expressed as means ± SD. #Significant changes caused by BFR (P < 0.05). *Significant changes caused by HST (P < 0.05). No difference was found between HST and BFR.

Fig. 10.

Log2-fold changes in expression of 29 genes involved in muscle function and plasticity in musculus vastus lateralis of previously untrained women (n = 9) following 12 wk of BFR (○) and HST (●) (left), and 1 h after acute bouts of BFR and HST at 0 wk (Pre, middle), and 12 wk (Post, right). Each individual performed each training protocol in a contralateral manner. Values are expressed as means ± 95% CI. *Significant changes in expression caused by BFR or HST (P < 0.05). No differences were found between HST and BFR.

Fig. 11.

Correlation between log2-fold changes in gene expression in musculus vastus lateralis following acute bouts of BFR and HST (A), or 12 wk of HST and BFR (assessed as rested-state expression) in previously untrained women (n = 9) (B). Each individual performed each of the two training protocols in a contralateral manner, with sessions of HST and BFR being performed both before (week 0) and after (week 12) the strength training intervention, in each case on different days, separated by 4–6 days. One particular symbol represents the average GeNorm-normalized log2-fold change in expression of one particular gene (n = 32 genes). CI denotes the 95% confidence interval of Pearson r. Straight lines illustrate trend lines, while dotted lines indicate the perfect 1:1 slope. For detailed information on the expression of singular genes, see Fig. 10.