Abstract
The present study examined if high intensity training (HIT) could increase the expression of oxidative enzymes in fast-twitch muscle fibers causing a faster oxygen uptake () response during intense (INT), but not moderate (MOD), exercise and reduce the slow component and muscle metabolic perturbation during INT. Pulmonary kinetics was determined in eight trained male cyclists (-max: 59 ± 4 (means ± SD) mL min−1 kg−1) during MOD (205 ± 12 W ∼65% -max) and INT (286 ± 17 W ∼85% -max) exercise before and after a 7-week HIT period (30-sec sprints and 4-min intervals) with a 50% reduction in volume. Both before and after HIT the content in fast-twitch fibers of CS (P < 0.05) and COX-4 (P < 0.01) was lower, whereas PFK was higher (P < 0.001) than in slow-twitch fibers. Content of CS, COX-4, and PFK in homogenate and fast-twitch fibers was unchanged with HIT. Maximal activity (μmol g DW−1 min−1) of CS (56 ± 8 post-HIT vs. 59 ± 10 pre-HIT), HAD (27 ± 6 vs. 29 ± 3) and PFK (340 ± 69 vs. 318 ± 105) and the capillary to fiber ratio (2.30 ± 0.16 vs. 2.38 ± 0.20) was unaltered following HIT. kinetics was unchanged with HIT and the speed of the primary response did not differ between MOD and INT. Muscle creatine phosphate was lower (42 ± 15 vs. 66 ± 17 mmol kg DW−1) and muscle lactate was higher (40 ± 18 vs. 14 ± 5 mmol kg DW−1) at 6 min of INT (P < 0.05) after compared to before HIT. A period of intensified training with a volume reduction did not increase the content of oxidative enzymes in fast-twitch fibers, and did not change kinetics.
Highlights
It has been known for decades that endurance training results in a faster increase in the pulmonary oxygen uptake (V_ O2) response in the initial phase of exercise (Hickson et al 1978)
Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society
An overall effect was found for fiber type for citrate synthase (CS) (P = 0.01), complex 4 (COX-4) (P = 0.007) and PFK (P < 0.001) since protein content in ST fibers was higher than FT fibers for CS (P = 0.016 pre-high intensity training (HIT) and P = 0.007 post-HIT) and COX-4 (P = 0.012 pre-HIT and P = 0.01 post-HIT) and lower for PFK (P < 0.001 pre and post-HIT)
Summary
It has been known for decades that endurance training results in a faster increase in the pulmonary oxygen uptake (V_ O2) response in the initial phase of exercise (Hickson et al 1978). During constant load exercise at intensities above the gas exchange threshold (GET) V_ O2 continues to rise at a slow rate, with training reported to reduce the magnitude of this ‘V_ O2 slow component’ (Jones et al 2011) These alterations may be due to elevated muscle oxidative enzyme capacity and greater oxygen delivery (Jones and Poole 2005) as have been found in training studies using untrained subjects with a maximal V_ O2 (V_ O2-max) of ~50 mL minÀ1 kgÀ1 (Saltin et al 1976; Phillips et al 1995; Shoemaker et al 1996; Krustrup et al 2004a).
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