PMID 41462026

Research
All papers

Cardiorespiratory and metabolic stress responses to acute high-intensity interval training anchored to critical power or maximal heart rate

Bone J, Richards DL, Gibala MJ

Question

Does critical-power-based HIIT reduce variability in blood lactate response compared with HRmax-based HIIT, and how do cardiorespiratory stress responses differ?

Summary

Nineteen active adults completed two acute cycling HIIT trials, one anchored just above critical power and one adjusted to elicit 80-90% HRmax. Critical-power anchoring did not reduce lactate-response variability, but it produced higher workload, oxygen uptake, heart rate, ventilation, and perceived exertion. All 19 completed both trials.

Methodology

  • Nineteen apparently healthy active young adults
  • 19 participants.
  • Stationary cycling.
  • Work intervals: 4 minutes.
  • Recovery: 3 minutes at 25 W.
  • Intensity: CP + workload to deplete 10% W-prime in 4 minutes.
  • 4 x 4-min bouts plus warm-up/recovery/cool-down.
  • Single acute trial.
  • Acute crossover.
  • Randomized counterbalanced crossover acute exercise study
  • Blood lactate variability, Oxygen uptake, Heart rate, and Perceived exertion were tracked.

Outcomes

Lactate

CP anchoring did not reduce lactate-response variability.

Variability comparison p=0.75; net lactate p=0.10.

No clear change

Workload

CP_HIIT used a higher workload than HR_HIIT.

192 +/- 39 W vs 180 +/- 43 W; p=0.0013.

Improved

VO2/HR

CP_HIIT produced higher oxygen uptake, ventilation, and heart-rate responses.

Final 30 s VO2 p=0.0019; HRmean and HRpeak higher in CP_HIIT.

Improved

RPE

CP_HIIT felt harder than HR_HIIT.

Mean RPE 14 +/- 2 vs 13 +/- 2; p=0.0034.

Safety concern

Insights

  • HR-based HIIT can place users in different metabolic domains even at similar HR targets.
  • Threshold-based prescriptions may increase workload and stress but require more testing.
  • A familiarization/verification session can help ensure HR-based sessions hit intended responses.

Limitations

  • Acute-only study.
  • Small active young adult sample.
  • CP + 10% W-prime may have been conservative.
  • Critical power estimates had possible error in some participants.
  • Point-of-care lactate devices have mixed validity.
  • One author reported a relevant exercise-related commercial relationship.

Safety

  • Adverse events were not explicitly reported.
  • One enrolled participant was lost to follow-up; all 19 analyzed participants completed both CP_HIIT and HR_HIIT trials.
  • The CP workload was conservatively set at CP + 10% W-prime depletion to ensure trial completion.
  • Sessions were supervised with HR, lactate, metabolic, and RPE monitoring.