Pre-training Skeletal Muscle Fiber Size and Predominant Fiber Type Best Predict Hypertrophic Responses to 6 Weeks of Resistance Training in Previously Trained Young Men.

Haun CT, Vann CG, Mobley CB, Osburn SC, Mumford PW, Roberson PA, Romero MA, Fox CD, Parry HA, Kavazis AN, Moon JR, Young KC, Roberts MD

Frontiers in physiology26 Mar 2019Cited by 52 (Europe PMC)

PMID30971942PMCIDPMC6445136DOI10.3389/fphys.2019.00297PepBankPUB-30971942

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Summary

Limited evidence exists regarding differentially expressed biomarkers between previously-trained low versus high hypertrophic responders in response to resistance training. Herein, 30 college-aged males (training age 5 ± 3 years; mean ± SD) partook in 6 weeks of high-volume resistance training. Body composition, right leg vastus lateralis (VL) biopsies, and blood were obtained prior to training (PRE) and at the 3-week (W3) and 6-week time points (W6). The 10 lowest (LOW) and 10 highest (HIGH) hypertrophic responders were clustered based upon a composite hypertrophy score of PRE-to-W6 changes in right leg VL mean muscle fiber cross-sectional area (fCSA), VL thickness assessed via ultrasound, upper right leg lean soft tissue mass assessed via dual x-ray absorptiometry (DXA), and mid-thigh circumference. Two-way ANOVAs were used to compare biomarker differences between the LOW and HIGH clusters over time, and stepwise linear regression was performed to elucidate biomarkers that explained significant variation in the composite hypertrophy score from PRE to W3, W3 to W6, and PRE to W6 in all 30 participants. PRE-to-W6 HIGH and LOW responders exhibited a composite hypertrophy change of +10.7 ± 3.2 and -2.1 ± 1.6%, respectively (p p = 0.022). Time effects (p W3 > PRE), phospho (p)-4EBP1 (PRE > W3&W6), pan-mTOR (PRE > W3 W3 W3 W3), muscle ubiquitin-labeled proteins (PRE > W6), mechano growth factor mRNA (W6 > W3&PRE), 45S rRNA (PRE > W6), and muscle citrate synthase activity (PRE > W3&W6). No interactions existed for the aforementioned biomarkers and/or other assayed targets (muscle 20S proteasome activity, serum total testosterone, muscle androgen receptor protein levels, muscle glycogen, or serum creatine kinase). Regression analysis indicated PRE type II fiber percentage (R ² = 0.152, β = 0.390, p = 0.033) and PRE type II fCSA (R ² = 0.207, β = -0.455, p = 0.019) best predicted the PRE-to-W6 change in the composite hypertrophy score. While our sample size is limited, these data suggest: (a) HIGH responders may exhibit more growth potential given that they possessed lower PRE type II fCSA values and (b) possessing a greater type II fiber percentage as a trained individual may be advantageous for hypertrophy in response to resistance training.

CC BYText from Europe PMC. Highlighted sentences are the source of results.

Results from this study2

No result from this study comes from a test of the peptide.

Natural levels measured2

These results measure the body's own peptide. Nobody was given the peptide. They are not evidence about taking it. They are left out of key results, evidence counts and charts.

01HumanEndogenous levelNon-randomized trialMechanism
In trained young men, muscle mechano growth factor mRNA was higher at week 6 than at week 3 and before training.
In plain wordsIn trained young men, six weeks of resistance training raised the body's own mechano growth factor gene activity in muscle.
Peptide
MGF / PEG-MGF
Outcome
IncreaseMuscle MGF mRNA over 6 weeks of resistance training
Study
n = 30
Comparator
Pre-training and week 3
Outcome group
Endogenous peptide levels · Musculoskeletal
Source sentences
Summary
mechano growth factor mRNA (W6 > W3&PRE)
2 context sentences(design, population, supporting numbers)
Summary · context
Herein, 30 college-aged males (training age 5 ± 3 years; mean ± SD) partook in 6 weeks of high-volume resistance training.
Summary · context
Body composition, right leg vastus lateralis (VL) biopsies, and blood were obtained prior to training (PRE) and at the 3-week (W3) and 6-week time points (W6).
This result measures the body's own MGF / PEG-MGF. Nobody was given the peptide. It is not evidence about taking it.
Show in the study text Report a problemFND-3097194201
02HumanEndogenous levelNon-randomized trialMechanism
In trained young men, the change in muscle mechano growth factor mRNA over training did not differ between high and low hypertrophic responders.
In plain wordsIn trained young men, the body's own mechano growth factor gene activity changed alike in high and low muscle-growth responders.
Peptide
MGF / PEG-MGF
Outcome
No significant changeMuscle MGF mRNA, high versus low hypertrophic responders
Study
n = 20
Comparator
Low hypertrophic responders
Outcome group
Endogenous peptide levels · Musculoskeletal
Source sentences
Summary
No interactions existed for the aforementioned biomarkers and/or other assayed targets (muscle 20S proteasome activity, serum total testosterone, muscle androgen receptor protein levels, muscle glycogen, or serum creatine kinase).
3 context sentences(design, population, supporting numbers)
Summary · context
mechano growth factor mRNA (W6 > W3&PRE)
Summary · context
Herein, 30 college-aged males (training age 5 ± 3 years; mean ± SD) partook in 6 weeks of high-volume resistance training.
Summary · context
Body composition, right leg vastus lateralis (VL) biopsies, and blood were obtained prior to training (PRE) and at the 3-week (W3) and 6-week time points (W6).
This result measures the body's own MGF / PEG-MGF. Nobody was given the peptide. It is not evidence about taking it.
Show in the study text Report a problemFND-3097194202

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Version 2Current
13 Oct 2026, 21:44 UTC
Study results updated
Version 1
13 Oct 2026, 16:31 UTC
First added · source update from Europe PMC

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