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, 577 (Pt 3), 985-96

Prior Heavy Exercise Elevates Pyruvate Dehydrogenase Activity and Speeds O2 Uptake Kinetics During Subsequent Moderate-Intensity Exercise in Healthy Young Adults

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Prior Heavy Exercise Elevates Pyruvate Dehydrogenase Activity and Speeds O2 Uptake Kinetics During Subsequent Moderate-Intensity Exercise in Healthy Young Adults

B J Gurd et al. J Physiol.

Abstract

The adaptation of pulmonary oxygen uptake (.VO2) during the transition to moderate-intensity exercise (Mod) is faster following a prior bout of heavy-intensity exercise. In the present study we examined the activation of pyruvate dehydrogenase (PDHa) during Mod both with and without prior heavy-intensity exercise. Subjects (n = 9) performed a Mod(1)-heavy-intensity-Mod(2) exercise protocol preceded by 20 W baseline. Breath-by-breath .VO2 kinetics and near-infrared spectroscopy-derived muscle oxygenation were measured continuously, and muscle biopsy samples were taken at specific times during the transition to Mod. In Mod(1), PDHa increased from baseline (1.08 +/- 0.2 mmol min(-1) (kg wet wt)(-1)) to 30 s (2.05 +/- 0.2 mmol min(-1) (kg wet wt)(-1)), with no additional change at 6 min exercise (2.07 +/- 0.3 mmol min(-1) (kg wet wt)(-1)). In Mod(2), PDHa was already elevated at baseline (1.88 +/- 0.3 mmol min(-1) (kg wet wt)(-1)) and was greater than in Mod(1), and did not change at 30 s (1.96 +/- 0.2 mmol min(-1) (kg wet wt)(-1)) but increased at 6 min exercise (2.70 +/- 0.3 mmol min(-1) (kg wet wt)(-1)). The time constant of .VO2 was lower in Mod(2) (19 +/- 2 s) than Mod(1) (24 +/- 3 s). Phosphocreatine (PCr) breakdown from baseline to 30 s was greater (P < 0.05) in Mod(1) (13.6 +/- 6.7 mmol (kg dry wt)(-1)) than Mod(2) (6.5 +/- 6.2 mmol (kg dry wt)(-1)) but total PCr breakdown was similar between conditions (Mod(1), 14.8 +/- 7.4 mmol (kg dry wt)(-1); Mod(2), 20.1 +/- 8.0 mmol (kg dry wt)(-1)). Both oxyhaemoglobin and total haemoglobin were elevated prior to and throughout Mod(2) compared with Mod(1). In conclusion, the greater PDHa at baseline prior to Mod(2) compared with Mod(1) may have contributed in part to the faster .VO2 kinetics in Mod(2). That oxyhaemoglobin and total haemoglobin were elevated prior to Mod(2) suggests that greater muscle perfusion may also have contributed to the observed faster .VO2 kinetics. These findings are consistent with metabolic inertia, via delayed activation of PDH, in part limiting the adaptation of pulmonary .VO2 and muscle O2 consumption during the normal transition to exercise.

Figures

Figure 1
Figure 1. AbsoluteV˙O2 response of a representative subject (τMod1= 30 s; τMod2= 21 s)
Line of best fit and residuals for Mod1 (•, and black line of best fit and residuals) and Mod2 (○, and grey line of best fit and residuals) with ΔV˙O2 (0–100% end-exercise) with line of best fit inset.
Figure 2
Figure 2. Pyruvate dehydrogenase activity of the active form (PDHa) at rest and at 30 s and 6 min of moderate-intensity exercise during Mod1 (•) and Mod2 (○)
Values are means ±s.d.*P < 0.05 versus Mod1. †P < 0.05 versus baseline. ‡P < 0.05 versus 30 s.
Figure 3
Figure 3. Muscle lactate and phosphocreatine at baseline and at 30 s and 6 min of moderate-intensity exercise during Mod1 (•) and Mod2 (○)
Values are means ±s.d. (n = 9) in mmol/kg dry wt. *P < 0.05 versus Mod1. †P < 0.05 versus baseline.
Figure 4
Figure 4. Relationship between τMod1 and the change (Δ) in V˙O2 time constant (τV˙O2) between Mod1 and Mod2

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