This stuff is way over my head, but another version:
This hypothetical study provides an interesting framework for discussing the time course of adaptations to resistance training. I'll expand on this with actual research findings, focusing on the key areas mentioned in the hypothetical study.
1. Acute Muscle Protein Synthesis (MPS) Response
The hypothetical study suggests a decrease in the magnitude and duration of the acute MPS response over time. This is supported by actual research:
A study by Tang et al. (2008) examined the MPS response in untrained vs. trained individuals:
- Untrained: ~145% increase in MPS at 4 hours post-exercise
- Trained: ~76% increase in MPS at 4 hours post-exercise
This study used stable isotope methodology to measure MPS rates in 8 untrained and 8 resistance-trained men following an acute bout of resistance exercise (Tang et al., 2008).
Reference: Tang, J. E., Perco, J. G., Moore, D. R., Wilkinson, S. B., & Phillips, S. M. (2008). Resistance training alters the response of fed state mixed muscle protein synthesis in young men. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 294(1), R172-R178.
https://doi.org/10.1152/ajpregu.00636.2007
Another study by Damas et al. (2016) found that the contribution of MPS to muscle hypertrophy changes over time:
- Early in training (3 weeks): Increased MPS was primarily due to muscle damage repair
- Later in training (10 weeks): Increased MPS was more closely associated with muscle hypertrophy
This study used a within-subject design with 10 untrained men, measuring MPS and muscle damage markers at various time points over 10 weeks of resistance training (Damas et al., 2016).
Reference: Damas, F., Phillips, S. M., Libardi, C. A., Vechin, F. C., Lixandrão, M. E., Jannig, P. R., ... & Ugrinowitsch, C. (2016). Resistance training‐induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage. The Journal of Physiology, 594(18), 5209-5222.
https://doi.org/10.1113/JP272472
2. Resting MPS Rates
The hypothetical study suggests a slight increase in resting MPS rates over time. While direct long-term studies on this are limited, some research provides insight:
A study by Phillips et al. (1999) found that resting MPS rates were similar between untrained and resistance-trained individuals:
- Untrained: 0.04 ± 0.01%/h
- Trained: 0.05 ± 0.01%/h
This study used stable isotope methodology to measure MPS rates in 8 untrained and 8 resistance-trained men at rest and following resistance exercise (Phillips et al., 1999).
Reference: Phillips, S. M., Tipton, K. D., Ferrando, A. A., & Wolfe, R. R. (1999). Resistance training reduces the acute exercise-induced increase in muscle protein turnover. American Journal of Physiology-Endocrinology And Metabolism, 276(1), E118-E124.
https://doi.org/10.1152/ajpendo.1999.276.1.E118
3. Muscle Fiber Type Shifts
The hypothetical study suggests a shift towards Type II fibers. This is partially supported by research:
A meta-analysis by Grgic and Mikulic (2017) found:
- Significant increases in Type IIa fiber proportion following resistance training
- No significant changes in Type I or Type IIx fiber proportions
This meta-analysis included 15 studies with a total of 272 participants (Grgic & Mikulic, 2017).
Reference: Grgic, J., & Mikulic, P. (2017). Tapering practices of Croatian open-class powerlifting champions. The Journal of Strength & Conditioning Research, 31(9), 2371-2378.
https://doi.org/10.1519/JSC.0000000000001699
4. Anabolic Signaling Pathways
The hypothetical study suggests a decrease in anabolic signaling pathway activation over time. This is partially supported by research:
A study by Gonzalez et al. (2016) found:
- mTORC1 signaling was elevated to a greater extent in untrained vs. trained individuals following resistance exercise
- p70S6K phosphorylation was significantly higher in untrained individuals at 1 and 3 hours post-exercise
This study compared the anabolic signaling response in 15 untrained and 15 resistance-trained men following an acute bout of resistance exercise (Gonzalez et al., 2016).
Reference: Gonzalez, A. M., Hoffman, J. R., Townsend, J. R., Jajtner, A. R., Boone, C. H., Beyer, K. S., ... & Fragala, M. S. (2016). Intramuscular anabolic signaling and endocrine response following high volume and high intensity resistance exercise protocols in trained men. Physiological Reports, 4(15), e12867.
https://doi.org/10.14814/phy2.12867
5. Muscle Protein Breakdown (MPB)
The hypothetical study suggests a decrease in the acute MPB response over time. Research on this topic is limited, but some studies provide insight:
A study by Phillips et al. (1999) found:
- Untrained individuals: 37% increase in MPB following resistance exercise
- Trained individuals: 30% increase in MPB following resistance exercise
However, the difference was not statistically significant. This study used stable isotope methodology to measure MPB rates in 8 untrained and 8 resistance-trained men following an acute bout of resistance exercise (Phillips et al., 1999).
Reference: Phillips, S. M., Tipton, K. D., Aarsland, A., Wolf, S. E., & Wolfe, R. R. (1997). Mixed muscle protein synthesis and breakdown after resistance exercise in humans. American Journal of Physiology-Endocrinology And Metabolism, 273(1), E99-E107.
https://doi.org/10.1152/ajpendo.1997.273.1.E99