PMID 30356659

Research
All papers

The effect of fitness level on cardiac autonomic regulation, IL-6, total antioxidant capacity, and muscle damage responses to a single bout of high-intensity interval training

Cipryan L

Question

Does baseline fitness level modify cardiac autonomic, inflammatory, antioxidant, and muscle-damage responses to one HIIT session?

Summary

Young healthy participants with different fitness levels completed one treadmill HIIT bout. All groups completed the protocol; better-trained participants showed faster cardiac autonomic recovery and less muscle-damage signal, while inflammatory and antioxidant responses also differed by fitness level.

Methodology

  • Young healthy individuals in well-trained, moderately trained, and untrained groups.
  • 30 participants.
  • Treadmill running.
  • Work intervals: 2 min at 100% vVO2max.
  • Recovery: 2 min passive recovery.
  • Intensity: 100% vVO2max; mean HR about 83-85% HRmax.
  • 30 min.
  • Single session.
  • Acute.
  • Acute exercise study with fitness-level groups and randomized exercise/control visit order
  • HRV recovery, IL-6, Antioxidant capacity, and Muscle damage were tracked.

Outcomes

HRV recovery

Untrained participants had the most pronounced transient HRV suppression.

rMSSD decrease persisted most clearly at 1 h in untrained participants.

Mixed

IL-6/TAC

Well-trained participants showed larger IL-6 and antioxidant-capacity responses.

Mixed

Muscle damage

Muscle-damage markers rose more in less-trained groups.

Myoglobin changes were more noticeable in moderately trained and untrained groups.

Safety concern

Completion

All participants completed the prescribed HIIT.

30/30 completed.

Improved

Insights

  • Baseline fitness may affect how quickly users recover from hard intervals.
  • A 6 x 2-min treadmill protocol is feasible in screened young adults but physiologically demanding.

Limitations

  • Acute-only study.
  • Small fitness subgroups.
  • Fitness group assignment was not randomized.
  • Young healthy participants limit generalizability.

Safety

  • No adverse events were reported.
  • The session produced high lactate, high RPE, transient HRV suppression, and increases in muscle-damage biomarkers, especially in less-trained participants.