Early structural remodeling and deuterium oxide-derived protein metabolic responses to eccentric and concentric loading in human skeletal muscle.

Martino V Franchi,Neil D Reeves,William K Mitchell,Philip J Atherton,John P Williams,Daniel J Wilkinson,Marco V Narici,Jonathan I Quinlan,Jonathan N Lund,Kenneth Smith

doi:10.14814/phy2.12593

Martino V Franchi, Neil D Reeves + Show 8 more

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https://doi.org/10.14814/phy2.12593

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Abstract

We recently reported that the greatest distinguishing feature between eccentric (ECC) and concentric (CON) muscle loading lays in architectural adaptations: ECC favors increases in fascicle length (Lf), associated with distal vastus lateralis muscle (VL) hypertrophy, and CON increases in pennation angle (PA). Here, we explored the interactions between structural and morphological remodeling, assessed by ultrasound and dual x-ray absorptiometry (DXA), and long-term muscle protein synthesis (MPS), evaluated by deuterium oxide (D2O) tracing technique. Ten young males (23 ± 4 years) performed unilateral resistance exercise training (RET) three times/week for 4 weeks; thus, one-leg trained concentrically while the contralateral performed ECC exercise only at 80% of either CON or ECC one repetition maximum (1RM). Subjects consumed an initial bolus of D2O (150 mL), while a 25-mL dose was thereafter provided every 8 days. Muscle biopsies from VL midbelly (MID) and distal myotendinous junction (MTJ) were collected at 0 and 4-weeks. MPS was then quantified via GC–pyrolysis–IRMS over the 4-week training period. Expectedly, ECC and CON RET resulted in similar increases in VL muscle thickness (MT) (7.5% vs. 8.4%, respectively) and thigh lean mass (DXA) (2.3% vs. 3%, respectively), albeit through distinct remodeling: Lf increasing more after ECC (5%) versus CON (2%) and PA increasing after CON (7% vs. 3%). MPS did not differ between contractile modes or biopsy sites (MID-ECC: 1.42 vs. MID-CON: 1.4% day−1; MTJ-ECC: 1.38 vs. MTJ-CON: 1.39% day−1). Muscle thickness at MID site increased similarly following ECC and CON RET, reflecting a tendency for a contractile mode-independent correlation between MPS and MT (P = 0.07; R2 = 0.18). We conclude that, unlike MT, distinct structural remodeling responses to ECC or CON are not reflected in MPS; the molecular mechanisms of distinct protein deposition, and/or the role of protein breakdown in mediating these responses remain to be defined.

Highlights

The most characteristic physiological adaptation to resistance exercise training (RET) is muscle hypertrophy
Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society
By using recently developed D2O tracers approaches (Previs et al 2004; Gasier et al 2010; Robinson et al 2011; Wilkinson et al 2014), the aim of the present study was to investigate whether the different patterns of skeletal muscle remodeling with ECC versus CON training were associated with differences in muscle protein synthesis (MPS), and through a novel biopsy approach at midbelly and in proximity to the myotendinous junction of the vastus lateralis (VL) muscle, if the previously reported heterogeneity in muscle hypertrophy along the muscle was reflected by regional differences in MPS

Summary

Introduction

The most characteristic physiological adaptation to resistance exercise training (RET) is muscle hypertrophy. RET involves raising and lowering of weights via “concentric” (CON), shortening, and “eccentric” (ECC), lengthening, actions. ECC contractions are more efficient than CON, that is, the same absolute work is achieved at a lower a 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

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