Slow component of V̇O2 kinetics: the effect of training status, fibre type, UCP3 mRNA and citrate synthase activity

Abstract

OBJECTIVE:In healthy individuals performing constant-load exercise at intensities above the lactate threshold a secondary rise in pulmonary oxygen uptake (V O 2 ) occurs. V O 2 reaches a maximum and exhaustion rapidly prevails for a range of work rates lower than the maximal work rate achieved during a conventional rapid-incremental test. This phenomenon is called the slow component (SC) of V O 2 kinetics and represents an increase in V O 2 without an increase in work rate. Although still under debate, the magnitude of the SC is believed to be associated with the percentage of type II muscle fibres and their recruitment. In this study we investigated the relationship between the magnitude of the relative SC, citrate synthase activity, UCP2 and UCP3 mRNA levels and muscle fibre composition in both endurance-trained and recreationally active subjects. METHOD: The magnitude of the relative SC was measured in 12 endurance-trained (Tr) and 15 recreationally active (RA) male subjects. The magnitude of the relative SC was determined as the difference between the end-exercise V O 2 and 3 min V O 2 divided by the difference between end-exercise V O 2 and baseline V O 2 . UCP2 and UCP3 mRNA expression in the vastus lateralis was measured by RT-PCR with b-actin mRNA used as an internal control. These values were also normalized against cytochromeb mRNA to control for training induced changes in mitochondria when comparing the Tr and RA groups. Type I, IIa and IIx skeletal muscle fibre composition was determined using a routine myosin ATPase histochemical staining technique. Citrate synthase (CS) activity was measured using spectrophotometric detection. RESULTS:The magnitude of the relative SC of the Tr group had the highest correlation with citrate synthase activity (r ¼ 7 0.90, P < 0.001) and that of the RA group with V O 2 peak (r ¼ 7 0.68, P < 0.01). For the Tr group other correlations with the magnitude of the relative SC included UCP3 mRNA levels (r ¼ 0.69, P < 0.05) and the percentage of type I fibres (r ¼ 7 0.58, P < 0.05), while for the RA group they included UCP3 mRNA (r ¼ 0.58, P < 0.05) and the percentage of type IIa muscle fibres (r ¼ 0.59, P < 0.05). The Tr subjects had a lower relative SC (P ¼ 0.04) and a lower expression of UCP2 (P ¼ 0.04), and UCP3 mRNA (P ¼ 0.01) than the RA subjects. When the groups were combined the magnitude of the relative SC correlated with UCP3 mRNA (r ¼ 0.70, P < 0.01), percentage of type IIa muscle fibres (r ¼ 0.60, P < 0.01) and V O 2 peak (r ¼ 7 0.73, P < 0.01). Additionally UCP3 mRNA correlated with the percentage of type IIa muscle fibres (r ¼ 0.63, P < 0.001). CONCLUSION: Citrate synthase activity and V O 2 peak are indicators of aerobic fitness. The high negative correlations between the magnitude of the relative SC and citrate synthase activity and V O 2 peak, of the Tr and RA subjects, respectively, suggests that the magnitude of the relative SC is inversely correlated with aerobic fitness. Additionally the correlations between UCP3 mRNA and the magnitude of the relative SC...

Endurance Training in Humans Leads to Fiber Type-Specific Increases in Levels of Peroxisome Proliferator-Activated Receptor-γ Coactivator-1 and Peroxisome Proliferator-Activated Receptor-α in Skeletal Muscle

“…RNA extraction and real-time quantitative PCR. Total RNA was extracted, and oligo-dT primed first-strand cDNA was synthesized as reported previously (23). Real-time PCR was performed using a Lightcycler rapid thermal cycler system; a Lightcycler-DNA Fast-Start Master SYBR Green I mix for the quantification of PGC-1, PPAR-␤/␦, Tn1-slow, COX4, GLUT4, and CPT-1; and a Lightcycler-DNA Master SYBR Green I mix for the quantification of PPAR-␣, PPAR-␥, and ␤-actin (Roche Diagnostics, Rotkreuz, Switzerland), according to the manufacturers' instructions.…”

Lipotoxicity: the obese and endurance-trained paradox

“…10,11 Additionally, ETr, unlike obesity, also results in an increase in CPT-I, citrate synthase and cytochrome c oxidase gene expression and their respective enzyme activities. [12][13][14][15][16][17] Therefore, the mechanisms regulating IMTG storage in ETr subjects appear to differ to those from obese subjects. Endurance exercise has been shown to use both carbohydrate and lipids as a fuel source.…”

Pulmonary oxygen uptake and muscle deoxygenation kinetics during recovery in trained and untrained male adolescents

“…In the adult population, training has been shown to result in both faster muscle phosphocreatine (Forbes et al 2008;Takahashi et al 1995;Yoshida 2002) and pulmonary oxygen uptake (Fukuoka et al 2002;Fukuoka et al 2006) kinetics during recovery from moderate-intensity exercise, suggestive of enhanced oxidative capacity of the exercising muscle (Barker et al 2008;Paganini et al 1997;Rossiter et al 2002). The favourable adaptations to oxygen delivery, mitochondrial density and oxidative enzyme activity and thus aerobic fitness that appropriate training permits (Holloszy and Coyle 1984;Murias et al 2010;Phillips et al 1995;Russell et al 2002) are likely to explain the faster recovery kinetics relative to the untrained state. However, to our knowledge no previous study has examined the effect of training status on pulmonary oxygen uptake kinetics during recovery from exercise in adolescents.…”