PMID 37589512

Research
All papers

Proteolytic markers associated with a gain and loss of leg muscle mass with resistance training followed by high-intensity interval training

Michel JM, Godwin JS, Plotkin DL, Mesquita PHC, McIntosh MC, Ruple BA, Libardi CA, Mobley CB, Kavazis AN, Roberts MD

Question

Do proteolytic markers increase when resistance-training-induced vastus lateralis hypertrophy is lost after a subsequent 7-week treadmill HIIT block?

Summary

This secondary mechanistic analysis studied muscle biopsies from 11 untrained young men before training, after 7 weeks of resistance training, and after a subsequent 7 weeks of treadmill HIIT. The authors found that the previously observed loss of resistance-training-induced vastus lateralis size after HIIT coincided with higher proteolysis-related markers, but the paper provides limited HIIT protocol detail and does not report exercise safety or adherence outcomes.

Methodology

  • Untrained college-aged men with complete vastus lateralis biopsies at PRE, MID, and POST.
  • 11 participants.
  • Resistance training, then treadmill HIIT.
  • Intensity: High-intensity; exact HIIT target not reported.
  • RT 2 days/week, then HIIT 3 days/week.
  • 7 weeks RT plus 7 weeks HIIT.
  • Secondary mechanistic pre-mid-post analysis of a single exercise sequence
  • Proteolysis markers, Vastus lateralis size, and In vitro myotube response were tracked.

Outcomes

Atrogene mRNA

TRIM63, FBXO32, and FOXO3A were higher after HIIT than both baseline and post-RT.

POST vs PRE and MID p<0.05.

Safety concern

Proteasome markers

20S proteasome core abundance increased after HIIT; activity increased after RT and remained higher after HIIT.

20S core POST vs PRE p=0.031; POST vs MID p=0.049; activity MID and POST vs PRE p<0.05.

Safety concern

Calpain/autophagy

Calpain-2 and Beclin-1 increased at MID and POST, but interpretation as breakdown versus turnover was uncertain.

MID and POST vs PRE p<0.05 for calpain-2 and Beclin-1 protein levels.

Mixed

In vitro MPS

IGF1+AICAR blunted IGF1-related myotube growth and had lower MPS proxy than IGF1 alone.

Myotube diameter p=0.017; puromycin/MPS proxy p<0.001.

Safety concern

Insights

  • Do not use this paper as a direct HIIT workout template because interval details and safety outcomes are missing.
  • For users focused on hypertrophy, this paper raises a hypothesis that switching from RT to HIIT may not maintain RT-induced muscle size in untrained men.
  • The evidence is mechanistic and should not be framed as proof that HIIT alone causes muscle loss.

Limitations

  • Small sample of 11 men
  • Secondary analysis
  • No control or comparator exercise group
  • No nontraining post-RT control
  • No in vivo muscle protein synthesis or breakdown measures
  • Exact HIIT protocol not reported in this article
  • No adverse-event or adherence reporting

Safety

  • The article did not report adverse events, injuries, symptoms, adherence, or tolerability for the training intervention.
  • Participants were screened to exclude cardiometabolic disease and conditions contraindicating exercise training or muscle biopsy.
  • Hydration was checked before testing sessions using urine specific gravity <=1.020 as a threshold to continue testing.
  • Repeated vastus lateralis biopsies were part of the study procedures, but biopsy complications were not reported.