Unchanged content of oxidative enzymes in fast-twitch muscle fibers and V˙O₂ kinetics after intensified training in trained cyclists

TY - JOUR

T1 - Unchanged content of oxidative enzymes in fast-twitch muscle fibers and V˙O2 kinetics after intensified training in trained cyclists

AU - Christensen, Peter Møller

AU - Gunnarsson, Thomas Gunnar Petursson

AU - Thomassen, Martin

AU - Wilkerson, Daryl P

AU - Nielsen, Jens Jung

AU - Bangsbo, Jens

N1 - CURIS 2015 NEXS 262

PY - 2015

Y1 - 2015

N2 - 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 (VO2) response during intense (INT), but not moderate (MOD), exercise and reduce the VO2 slow component and muscle metabolic perturbation during INT. Pulmonary VO2 kinetics was determined in eight trained male cyclists (VO2-max: 59 ± 4 (means SD) mL min–1 kg–1) during MOD (205 ± 12 W ~65% VO2-max) and INT (286 ± 17 W ~85% VO2- 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 (lmol 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. VO2 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 VO2 kinetics.

AB - 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 (VO2) response during intense (INT), but not moderate (MOD), exercise and reduce the VO2 slow component and muscle metabolic perturbation during INT. Pulmonary VO2 kinetics was determined in eight trained male cyclists (VO2-max: 59 ± 4 (means SD) mL min–1 kg–1) during MOD (205 ± 12 W ~65% VO2-max) and INT (286 ± 17 W ~85% VO2- 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 (lmol 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. VO2 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 VO2 kinetics.

U2 - 10.14814/phy2.12428

DO - 10.14814/phy2.12428

M3 - Journal article

C2 - 26152692

SN - 2051-817X

VL - 3

JO - Physiological Reports

JF - Physiological Reports

IS - 7

M1 - e12428

ER -