PMID 39330519

Research
All papers

Metabolic Predictors of Cardiorespiratory Fitness Responsiveness to Continuous Endurance and High-Intensity Interval Training Programs: The TIMES Study-A Randomized Controlled Trial

Castro A, Ferreira AG, Catai AM, Amaral MAB, Cavaglieri CR, Chacon-Mikahil MPT

Question

Can baseline serum and intramuscular metabolites classify cardiorespiratory fitness responders and non-responders after 8 weeks of continuous endurance training or HIIT?

Summary

In sedentary young men, an 8-week supervised cycling HIIT program and a matched endurance program both improved cardiorespiratory fitness, with wide individual variation. The paper mainly examined baseline serum and muscle metabolites that might predict who responds to training; it found candidate markers, but the authors warned that the models had limited specificity and need replication.

Methodology

  • Healthy sedentary young Caucasian men in Campinas, Brazil who completed the TIMES study.
  • 70 participants.
  • Cycle ergometer.
  • Work intervals: 4 min at 90% heart-rate reserve.
  • Recovery: 3 min at 50-60% heart-rate reserve.
  • Intensity: HR reserve prescribed, cadence 70-80 rpm.
  • 40 min.
  • 3-4 days/week.
  • 8 weeks.
  • Randomized controlled clinical trial with ET, HIIT, and non-exercise control arms
  • Cardiorespiratory fitness response, Serum metabolite predictor, and Intramuscular metabolite predictor were tracked.

Outcomes

CRF response

CRF responses ranged from 1.1 to 4.7 METs after HIIT and 0.9 to 3.9 METs after ET, compared with -0.9 to 0.2 METs in controls.

Improved

Responder rate

Responder/non-responder frequency was 90.0%/10.0% for HIIT and 76.7%/23.3% for ET, with no significant between-program difference.

p=0.166

No clear change

Serum predictor

Higher serum O-acetylcarnitine helped classify responders versus non-responders regardless of training program.

OR 4.72, p=0.012; model accuracy 78.0%, p=0.006

Improved

Muscle predictor

Intramuscular creatinine helped classify responders versus non-responders regardless of training program.

OR 4.53, p=0.0137; model accuracy 72.3%, p=0.028

Improved

Insights

  • The reproducible HIIT template is 5 x 4 min hard cycling at 90% heart-rate reserve with 3 min easier cycling at 50-60% heart-rate reserve.
  • Fitness retesting and intensity recalibration after 4 weeks may help maintain the intended stimulus.
  • Metabolite predictor findings are mechanistic and should not be translated into user-facing prediction.

Limitations

  • Only healthy sedentary young Caucasian men were studied.
  • Intervention lasted 8 weeks.
  • Small non-responder count, especially in HIIT.
  • Dietary control over the intervention was limited.
  • Models had low specificity and require replication.
  • No adverse event detail was reported.

Safety

  • Participants were medically screened and sessions were supervised.
  • No adverse events were reported in the the paper.