Abstract
BackgroundIt has been believed that the contribution of fat oxidation to total energy expenditure is becoming negligible at higher exercise intensities (about 85% VO2max). The aim of the present study was to examine the changes in substrate oxidation during high-intensity interval exercise in young adult men.MethodsA total of 18 healthy well-trained (aged 19.60 ± 0.54 years, BMI = 22.19 ± 0.64 kg/m2, n = 10) and untrained (aged 20.25 ± 0.41 years, BMI = 22.78 ± 0.38 kg/m2, n = 8) young men volunteered to participate in this study. After an overnight fast, subjects were tested on a cycle ergometer and completed six 4-min bouts of cycling (at ∼80% VO2max) with 2 min of rests between intervals. Energy expenditure and the substrate oxidation rate were measured during the experiment by using indirect calorimetry. The blood lactate concentration was collected immediately after each interval workout.ResultsThe fat oxidation rate during each workout was significantly different between the untrained and the athlete groups (p < 0.05), and the carbohydrate (CHO) oxidation rate during the experiment was similar between groups (p > 0.05). Moreover, lactate concentration significantly increased in the untrained group (p < 0.05), whereas it did not significantly change in the athlete group during the workouts (p > 0.05). Fat contribution to energy expenditure was significantly higher in the athlete group (∼25%) than in the untrained group (∼2%).ConclusionsThe present study indicates that 17 times more fat oxidation was measured in the athlete group compared to the untrained group. However, the athletes had the same CHO oxidation rate as the recreationally active subjects during high-intensity intermittent exercise. Higher fat oxidation rate despite the same CHO oxidation rate may be related to higher performance in the trained group.
Highlights
The main sources of energy for skeletal muscles are carbohydrate (CHO) and fat
Fatty acids are oxidized as the main source of energy during low-intensity exercise, mobilization of fatty acids decreases when exercise intensity increases (Hodgetts et al, 1991; Sidossis et al, 1997)
It was noted that the activity of carnitine palmitoyltransferase (CPT), which is responsible for the transfer of fatty acids to mitochondria, decreases during high-intensity exercise, and sufficient CHOs in the cell lead to a decrease in fat oxidation (Ockner, 1990)
Summary
The main sources of energy for skeletal muscles are carbohydrate (CHO) and fat. While CHO is utilized in aerobic and anaerobic systems, fat is utilized only in the aerobic system (McArdle, Katch & Katch, 2010). It was noted that the activity of carnitine palmitoyltransferase (CPT), which is responsible for the transfer of fatty acids to mitochondria, decreases during high-intensity exercise, and sufficient CHOs in the cell lead to a decrease in fat oxidation (Ockner, 1990). Glycogen breakdown and CHO oxidation are the main sources of energy, at 85% of VO2max In this situation, lactate increase in muscle and blood (Coyle, 1995) is reported to lead to decrease in fat mobilization (Maughan & Gleeson, 2010). It has been believed that the contribution of fat oxidation to total energy expenditure is becoming negligible at higher exercise intensities (about 85% VO2max). The athletes had the same CHO oxidation rate as the recreationally active subjects during high-intensity intermittent exercise. Higher fat oxidation rate despite the same CHO oxidation rate may be related to higher performance in the trained group
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