Effects of low-load resistance training with blood flow restriction on muscle fiber myofibrillar and extracellular area

Cleiton A Libardi; Joshua S Godwin; Tanner M Reece; Carlos Ugrinowitsch; Trent J Herda; Michael D Roberts

doi:10.3389/fphys.2024.1368646

Effects of low-load resistance training with blood flow restriction on muscle fiber myofibrillar and extracellular area

Front Physiol. 2024 Feb 20:15:1368646. doi: 10.3389/fphys.2024.1368646. eCollection 2024.

Authors

Cleiton A Libardi¹, Joshua S Godwin², Tanner M Reece³, Carlos Ugrinowitsch^{4

5}, Trent J Herda⁶, Michael D Roberts²

Affiliations

¹ MUSCULAB-Laboratory of Neuromuscular Adaptations to Resistance Training, Department of Physical Education, Federal University of Sao Carlos, Sao Carlos, Brazil.
² School of Kinesiology, Auburn University, Auburn, AL, United States.
³ Program in Physical Therapy, Washington University School of Medicine, St. Louis, MO, United States.
⁴ School of Physical Education and Sport, University of Sao Paulo, Sao Paulo, Brazil.
⁵ Department of Health Sciences and Human Performance, The University of Tampa, Tampa, FL, United States.
⁶ Department of Health, Sport, and Exercise Sciences, University of Kansas, Lawrence, KS, United States.

Abstract

Blood flow restriction applied during low-load resistance training (LL-BFR) induces a similar increase in the cross-sectional area of muscle fibers (fCSA) compared to traditional high-load resistance training (HL-RT). However, it is unclear whether LL-BFR leads to differential changes in myofibrillar spacing in muscle fibers and/or extracellular area compared to HL-RT. Therefore, this study aimed to investigate whether the hypertrophy of type I and II fibers induced by LL-BFR or HL-RT is accompanied by differential changes in myofibrillar and non-myofibrillar areas. In addition, we examined if extracellular spacing was differentially affected between these two training protocols. Twenty recreationally active participants were assigned to LL-BFR or HL-RT groups and underwent a 6-week training program. Muscle biopsies were taken before and after the training period. The fCSA of type I and II fibers, the area occupied by myofibrillar and non-myofibrillar components, and extracellular spacing were analyzed using immunohistochemistry techniques. Despite the significant increase in type II and mean (type I + II) fCSA (p < 0.05), there were no significant changes in the proportionality of the myofibrillar and non-myofibrillar areas [∼86% and ∼14%, respectively (p > 0.05)], indicating that initial adaptations to LL-BFR are primarily characterized by conventional hypertrophy rather than disproportionate non-myofibrillar expansion. Additionally, extracellular spacing was not significantly altered between protocols. In summary, our study reveals that LL-BFR, like HL-RT, induces skeletal muscle hypertrophy with proportional changes in the areas occupied by myofibrillar, non-myofibrillar, and extracellular components.

Keywords: exercise; extracellular matrix; myofibers; myofibrils; vascular occlusion.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was made possible by a Master’s Level Graduate Research Grant from the National Strength and Conditioning Association (Grant ID: 1002814). Additionally, this work was supported by an NIH-funded predoctoral fellowship to TR (NIH T32007434), the São Paulo Research Foundation (#2020/13613–4 to CL), and the National Council for Scientific and Technological Development (CL Grant no. 302801/2018-9; and CU Grant no. 303085/2015-0). Article publishing charges were provided through the Auburn University School of Kinesiology.