Myogenic and proteolytic mRNA expression following blood flow restricted exercise

Abstract

Aim: Resistance exercise performed at low loads (20-30% of maximal strength) with blood flow restriction (BFR) acutely increases protein synthesis and induces hypertrophy when performed chronically. We investigated myogenic and proteolytic mRNA expression 8 h following an acute bout of knee extension exercise.

Methods: Fifteen subjects (22.8 ± 3.7 years, eight men and seven women) were randomized to two exercise conditions: BFR or control exercise. All participants performed four sets of exercise (30, 15, 15 and 15 repetitions) at 20% of maximal strength. Persons in the BFR group had a cuff placed on the upper thigh inflated to 1.5 times brachial systolic blood pressure (cuff pressure range: 135-186 mmHg). Muscle biopsies from the vastus lateralis were excised 24 h before and 8 h following the exercise.

Results: RT-PCR analysis demonstrated no change in myogenic gene expression (insulin-like growth factor-1, MyoD, myogenin, myostatin - a negative regulator) with either exercise condition (P > 0.123). However, BFR exercise downregulated mRNA expression in transcripts associated with proteolytic pathways (FOXO3A, Atrogin-1 and MuRF-1) with no change in the control exercise condition. Specifically, median mRNA expression of FOXO3A decreased by 1.92-fold (P = 0.01), Atrogin-1 by 2.10-fold (P = 0.01) and MuRF-1 by 2.44-fold (P = 0.01).

Conclusion: These data are consistent with the downregulation of proteolytic transcripts observed following high-load resistance exercise. In summary, myogenic genes are unchanged and proteolytic genes associated with muscle remodelling are reduced 8 h following low-load BFR exercise.

Figure 1

Schematic of experimental design. (EX = exercise condition and PA = physical activity).

Figure 2

Normalized electromyographic activity changes over subsequent sets of exercise for randomized experimental groups. Subjects performing blood flow restricted (BFR) knee extension exercise showed an increase in normalized electromyographic activity with additional sets of exercise (p = 0.002). No change was observed in the control group (p = 0.084). Note: asterisk (*) group difference at set 4. Note: electromyographic data were normalized to a maximal voluntary contraction prior to the exercise bout. Values are means (SEM).

Figure 3

Relative changes (post – pre values) in mRNA expression for subjects performing blood flow restricted (BFR) (grey symbols) and control knee extension exercise (black symbols). The line represents the median change in relative expression.

Figure 3

Relative changes (post – pre values) in mRNA expression for subjects performing blood flow restricted (BFR) (grey symbols) and control knee extension exercise (black symbols). The line represents the median change in relative expression.

Figure 3

Relative changes (post – pre values) in mRNA expression for subjects performing blood flow restricted (BFR) (grey symbols) and control knee extension exercise (black symbols). The line represents the median change in relative expression.