title: Blood flow restriction prevents muscle damage but not protein synthesis signaling following eccentric contractions.
abstract: There is a growing body of evidence to suggest that resistance training exercise combined with blood flow restriction (BFR) increases muscle size and strength in humans. Eccentric contraction (ECC) frequently induces severe muscle damage. However, it is not known whether and to what extent muscle damage occurs following ECC + BFR due to the difficulty of conducting definitive invasive studies. The purpose of this study was to examine muscle fiber damage following ECC + BFR at the cellular level. High-intensity ECC was purposefully selected to maximize the opportunity for muscle damage and hypertrophic signaling in our novel in vivo animal model. Male Wistar rats were assigned randomly to the following groups: ECC and ECC + BFR at varying levels of occlusion pressure (140, 160, and 200 Torr). In all conditions, electrical stimulation was applied to the dorsiflexor muscles simultaneously with electromotor-induced plantar flexion. We observed severe histochemical muscle fiber damage (area of damaged fibers/total fiber area analyzed) following ECC (26.4 ± 4.0%). Surprisingly, however, muscle damage was negligible following ECC + BFR140 (2.6 ± 1.2%), ECC+BFR160 (3.0 ± 0.5%), and ECC + BFR200 (0.2 ± 0.1%). Ribosomal S6 kinase 1 (S6K1) phosphorylation, a downstream target of rapamycin (mTOR)-phosphorylation kinase, increased following ECC + BFR200 as well as ECC. In contrast, S6K1 phosphorylation was not altered by BFR alone. The present findings suggest that ECC combined with BFR, even at high exercise intensities, may enhance muscle protein synthesis without appreciable muscle fiber damage.
authors.affiliation: Department of Engineering Science, Bioscience and Technology Program, University of Electro-communications, Chofu Tokyo, Japan Physical Fitness Research Institute Meiji Yasuda Life Foundation of Health and Welfare, Tokyo, Japan.
authors.forename: Mizuki
authors.initials: M
authors.lastname: Sudo
authors.affiliation: Department of Mechanical Engineering and Intelligent Systems, Control Systems Program, University of Electro-communications, Chofu Tokyo, Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Ando
authors.affiliation: Departments of Anatomy & Physiology and Kinesiology, Kansas State University, Manhattan, Kansas.
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
authors.affiliation: Department of Engineering Science, Bioscience and Technology Program, University of Electro-communications, Chofu Tokyo, Japan kano@pc.uec.ac.jp.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kano
keywords: Blood flow restriction; S6K1; eccentric contraction; muscle damage