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Type 1 Muscle Fiber Hypertrophy after Blood Flow–restricted Training in Powerlifters

Bjørnsen, Thomas1; Wernbom, Mathias2; Kirketeig, Alexander3; Paulsen, Gøran4; Samnøy, Lars3; Bækken, Lasse5; Cameron-Smith, David6,7,8; Berntsen, Sveinung1; Raastad, Truls5

doi: 10.1249/MSS.0000000000001775
Original Investigation: PDF Only

PURPOSE To investigate the effects of blood flow restricted resistance exercise (BFRRE) on myofiber areas (MFA), number of myonuclei and satellite cells (SC), muscle size and strength in powerlifters. METHODS

Seventeen national level powerlifters (25±6 yrs [mean±SD], 15 men) were randomly assigned to either a BFRRE group (n=9) performing two blocks (week 1 and 3) of five BFRRE front squat sessions within a 6.5-week training period, or a conventional training group (Con; n=8) performing front squats at ~70% of one-repetition maximum (1RM). The BFRRE consisted of four sets (first and last set to voluntary failure) at ~30% of 1RM. Muscle biopsies were obtained from m. vastus lateralis (VL) and analyzed for MFA, myonuclei, SC and capillaries. Cross sectional areas (CSA) of VL and m. rectus femoris (RF) were measured by ultrasonography. Strength was evaluated by maximal voluntary isokinetic torque (MVIT) in knee extension and 1RM in front squat.

RESULTS BFRRE induced selective type I fiber increases in MFA (BFRRE: 12% vs. Con: 0%, p<0.01) and myonuclear number (BFRRE: 17% vs. Con: 0%, p=0.02). Type II MFA was unaltered in both groups. BFRRE induced greater changes in VL CSA (7.7% vs. 0.5%, p=0.04), which correlated with the increases in MFA of type I fibers (r=0.81, p=0.02). No group differences were observed in SC and strength changes, although MVIT increased with BFRRE (p=0.04), whereas 1RM increased in Con (p=0.02).

CONCLUSION

Two blocks of low-load BFRRE in the front squat exercise resulted in increased quadriceps CSA associated with preferential hypertrophy and myonuclear addition in type 1 fibres of national level powerlifters.

1Department of Public Health, Sport and Nutrition, Faculty of Health and Sport Sciences, University of Agder, Kristiansand, Norway

2Department of Food and Nutrition, and Sport Science, University of Gothenburg, Sweden

3Norwegian Powerlifting Federation, Oslo, Norway

4The Norwegian Olympic federation, Oslo, Norway

5Department of Physical Performance, Norwegian School of Sport Sciences, Oslo, Norway

6Liggins Institute, University of Auckland, New Zealand

7Food & Bio-based Products Group, AgResearch, Palmerston North, New Zealand

8Riddet Institute, Palmerston North, New Zealand

Corresponding author: Thomas Bjørnsen, University of Agder, Faculty of Sports and Health Sciences, PO. Box 422, 4604 Kristiansand, Norway, Tel: +47 986 19 299, E-mail: thomas.bjornsen@uia.no

The study was supported by a grant from the University of Agder, Norwegian School of Sport Sciences, the Norwegian Powerlifting Federation and the Norwegian Olympic Federation. All authors declare no conflict of interest. The results of this study do not constitute endorsement American College of Sport Science, and are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

Submitted for publication May 2018.

Accepted for publication August 2018.

© 2018 American College of Sports Medicine