Hetelid, K. J., Herold, E., & Seiler, S. (2009). Comparison of metabolic responses to high intensity interval training in trained and well-trained males. ACSM 56th Annual Meeting, Seattle, Washington, Presentation Number 2915.

"During steady state exercise, well-trained endurance (WT) athletes oxidize more fat at the same relative intensity compared to recreationally trained people (RT). However, less is known about substrate oxidation during high intensity intermittent exercise. We have compared total energy expenditure (TEE) and fat oxidation during a fixed duration, high-intensity, self-paced interval training prescription in WT and RT subjects".

Well-trained (N = 9) and recreationally-trained (N = 9) runners performed preliminary testing followed by a 34-minute interval-training session consisting of six, 4-minute work bouts separated by 2-minute recovery periods on a motorized treadmill (constant 5 % incline). The high-intensity workout goal was to achieve the highest possible average running speed for the work bouts. Energy expenditure and fat oxidation were calculated from continuous measurements of VO2 consumption and CO2 production. [Due to some net CO2 contribution from bicarbonate buffering during intermittent high intensity exercise, fat oxidation rates are presumably underestimated and should be considered minimum estimates.]

Blood lactate and ratings of perceived effort responses throughout the interval session were similar for both groups. However, VO2 during the last three minutes of each work bout was higher in the well-trained group when compared to the recreationally-trained group. Mean respiratory exchange ratio for the entire session was higher in the recreationally-trained group. Total energy expenditure and fat oxidation during the interval session were higher in the well-trained group when compared to the recreationally-trained group.

Implication. Well-trained and recreationally-trained runners perform the same program with similar levels of effort and perceived intensity. However, well-trained runners responded differently in a number of indices generally indicating that they oxidize more fat despite higher relative oxygen consumption rates. This is but one index of the differences that exist between well-trained and moderately-trained athletes. Those differences warrant a careful attribution of response features and characteristics in exercise in the two levels of activity involvement. It is unwise to think that well-trained individuals will respond similarly to research findings on groups of a recreational-fitness standard.

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