PMID 27900134

Research
All papers

Rethinking the role of fat oxidation: substrate utilisation during high-intensity interval training in well-trained and recreationally trained runners

Hetlelid KJ, Plews DJ, Herold E, Laursen PB, Seiler S

Question

How do well-trained and recreationally trained runners differ in substrate use during a self-paced high-intensity interval running session?

Summary

During one self-paced treadmill HIIT session, well-trained male runners oxidized much more fat than recreationally trained runners while reporting similar effort and lactate responses.

Methodology

  • Male recreationally trained and well-trained runners.
  • 18 participants.
  • Treadmill running.
  • Work intervals: 4 min self-paced highest sustainable speed.
  • Recovery: 2 min recovery.
  • Intensity: About 89-94% VO2max and 93-95% HRmax peak responses.
  • 34 min.
  • Single session.
  • Acute testing.
  • Acute comparative exercise physiology study
  • Fat oxidation, Carbohydrate oxidation, and Perceived exertion were tracked.

Outcomes

Fat oxidation

Well-trained runners had much higher fat oxidation during HIT.

0.57 +/- 0.18 vs 0.20 +/- 0.11 g/min; ES 1.74 +/- 0.93.

Improved

CHO oxidation

Carbohydrate oxidation was similar between groups.

3.61 +/- 0.94 vs 3.79 +/- 1.01 g/min; unclear ES.

No clear change

RPE/lactate

Groups reported similar effort and lactate despite different work rates.

RPE about 16.2 in both groups; lactate similar.

No clear change

Insights

  • The same perceived effort can correspond to very different absolute workloads depending on training status.
  • Fuel-use claims from trained athletes should not be generalized to beginners.

Limitations

  • Acute session only
  • Small male sample
  • Indirect calorimetry equations used above recommended intensity range
  • Diet not controlled beyond instructions

Safety

  • No adverse events were reported.
  • All participants completed the acute laboratory HIIT session; no dropout was reported.
  • Safety context included trained participants familiar with treadmill exercise/HIT, consent and ethics approval, continuous HR/gas monitoring, lactate/RPE checks, and pretest restrictions on hard training, alcohol, tobacco, and caffeine.