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Resistance training-induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage - PubMed

  • ️Fri Jan 01 2016

Resistance training-induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage

Felipe Damas et al. J Physiol. 2016.

Abstract

Key points: Skeletal muscle hypertrophy is one of the main outcomes from resistance training (RT), but how it is modulated throughout training is still unknown. We show that changes in myofibrillar protein synthesis (MyoPS) after an initial resistance exercise (RE) bout in the first week of RT (T1) were greater than those seen post-RE at the third (T2) and tenth week (T3) of RT, with values being similar at T2 and T3. Muscle damage (Z-band streaming) was the highest during post-RE recovery at T1, lower at T2 and minimal at T3. When muscle damage was the highest, so was the integrated MyoPS (at T1), but neither were related to hypertrophy; however, integrated MyoPS at T2 and T3 were correlated with hypertrophy. We conclude that muscle hypertrophy is the result of accumulated intermittent increases in MyoPS mainly after a progressive attenuation of muscle damage.

Abstract: Skeletal muscle hypertrophy is one of the main outcomes of resistance training (RT), but how hypertrophy is modulated and the mechanisms regulating it are still unknown. To investigate how muscle hypertrophy is modulated through RT, we measured day-to-day integrated myofibrillar protein synthesis (MyoPS) using deuterium oxide and assessed muscle damage at the beginning (T1), at 3 weeks (T2) and at 10 weeks of RT (T3). Ten young men (27 (1) years, mean (SEM)) had muscle biopsies (vastus lateralis) taken to measure integrated MyoPS and muscle damage (Z-band streaming and indirect parameters) before, and 24 h and 48 h post resistance exercise (post-RE) at T1, T2 and T3. Fibre cross-sectional area (fCSA) was evaluated using biopsies at T1, T2 and T3. Increases in fCSA were observed only at T3 (P = 0.017). Changes in MyoPS post-RE at T1, T2 and T3 were greater at T1 (P < 0.03) than at T2 and T3 (similar values between T2 and T3). Muscle damage was the highest during post-RE recovery at T1, attenuated at T2 and further attenuated at T3. The change in MyoPS post-RE at both T2 and T3, but not at T1, was strongly correlated (r ≈ 0.9, P < 0.04) with muscle hypertrophy. Initial MyoPS response post-RE in an RT programme is not directed to support muscle hypertrophy, coinciding with the greatest muscle damage. However, integrated MyoPS is quickly 'refined' by 3 weeks of RT, and is related to muscle hypertrophy. We conclude that muscle hypertrophy is the result of accumulated intermittent changes in MyoPS post-RE in RT, which coincides with progressive attenuation of muscle damage.

© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.

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Figures

Figure 1
Figure 1. Experimental design

RE: resistance exercise; D2O: deuterated water; MVC: maximal voluntary isometric torque; SOR: muscle soreness; T1: first week of resistance training; T2: third week of resistance training; T3: last week of resistance training.

Figure 2
Figure 2. Muscle damage

Toluidine blue staining of muscle fibres showing (A) a fibre with no Z‐band streaming and (B) a fibre with areas (white arrows) of Z‐band streaming.

Figure 3
Figure 3. Fibre cross‐sectional area (CSA) at the first week (T1), third week (T2) and tenth week (T3) of resistance training

†Significantly different (P < 0.05) from T1 and T2. Values are means (SEM).

Figure 4
Figure 4. Time course of body water enrichment (atom% excess, APE) throughout the experimental period

T1: first week, T2: third week, T3: tenth week of resistance training. Values are means (SEM).

Figure 5
Figure 5. Myofibrillar (Myo) protein fractional synthetic rates expressed as: absolute (A), changes (B), and damage‐corrected (C) rates

A, myofibrillar (Myo) fractional synthetic rate (FSR) at rest, and 24 h and 48 h following a single bout of resistance exercise at the first week (T1), third week (T2) and tenth week (T3) of resistance training. *Significantly different (P < 0.05) from rest at T1. #Main acute time effect (24 h significantly different (P = 0.003) from 48 h independent of training phase). ‡Main training phase effect (T1 significantly different (P < 0.03) from T2 and T3). B, integrated Myo FSR over the first 48 h after a single bout of resistance exercise at T1, T2 and T3. ‡Significantly different (P < 0.05) from T2 and T3. C, integrated Myo FSR over the first 48 h following a single bout of resistance exercise at T1, T2 and T3 normalized for the change (48 h − 0 h) in the amount (% of affected areas) of Z‐band streaming (FSR × (100 − Z‐band streaming)/100) at T1, T2 and T3, respectively. Values are means (SEM).

Figure 6
Figure 6. Muscle damage expressed as Z‐line streaming

A, change from baseline in the percentage of Z‐band streaming areas per total fibre area following a single bout of resistance exercise at the first week (T1), third week (T2) and tenth week (T3) of resistance training. B, change from baseline in the percentage of fibres that showed any sign of Z‐band streaming following a single bout of resistance exercise at T1, T2 and T3. +Significantly different (P < 0.05) from T3. ‡Significantly different (P < 0.05) from T2 and T3. Values are means (SEM).

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