Abstract
The purpose of this study was to test if the lactate exchange (γ1) and removal (γ2) abilities during recovery following short all-out supramaximal exercise correlate with the muscle content of MCT1 and MCT4, the two isoforms of the monocarboxylate transporters family involved in lactate and H+ co-transport in skeletal muscle. Eighteen lightweight rowers completed a 3-min all-out exercise on rowing ergometer. Blood lactate samples were collected during the subsequent passive recovery to assess an individual blood lactate curve (IBLC). IBLC were fitted to the bi-exponential time function: La(t) = [La](0) + A1(1 − ) + A2(1 − ) where [La](0) is the blood lactate concentration at exercise completion and the velocity constants γ1 and γ2 denote the lactate exchange and removal abilities, respectively. An application of the bi-compartmental model of lactate distribution space allowed estimation of the lactate removal rate at exercise completion [LRR(0)]. Biopsy of the right vastus lateralis was taken at rest to measure muscle MCT1 and MCT4 content. Fiber type distribution, activity of key enzymes and capillary density (CD) were also assessed. γ1 was correlated with [La](0) (r = −0.54, P < 0.05) but not with MCT1, MCT4 or CD. γ2 and LRR(0) were correlated with MCT4 (r = 0.63, P < 0.01 and r = 0.73, P < 0.001, respectively) but not with MCT1 or cytochrome c oxidase activity. These findings suggest that the lactate exchange ability is highly dependent on the milieu so that the importance of the muscle MCT1 and MCT4 content in γ1 was hidden in the present study. Our results also suggest that during recovery following all-out supramaximal exercise in well-trained rowers, MCT4 might play a significant role in the distribution and delivery of lactate for its subsequent removal.
Highlights
During recovery following short high-intensity exercises, the blood lactate curve displays a bi-phasic pattern: the concentrations increase during the first minutes of recovery, reach a peak value, and decrease to return to near resting levels after 60–90 min of passive recovery (Freund and Gendry, 1978; Messonnier et al, 1997, 2001)
Previous studies have reported correlation between the muscle MCT1 content and the net lactate release rate during exercise (Dubouchaud et al, 2000) or post exercise blood lactate concentrations (Bonen et al, 1998; Messonnier et al, 2007). These results suggested that MCT1 could facilitate lactate release from myocytes during heavy exercise i.e., when the gradients of concentrations are favorable for the efflux of lactate from the muscle cells (Bonen et al, 1998; Messonnier et al, 2007)
The first important finding of the present study was the lack of correlation between γ1 and the muscle content of MCT1 and MCT4
Summary
During recovery following short high-intensity exercises, the blood lactate curve displays a bi-phasic pattern: the concentrations increase during the first minutes of recovery, reach a peak value (between the first to the ninth minute of recovery depending on duration and intensity of exercise as well as on the training status of the subject), and decrease (first rapidly slowly) to return to near resting levels after 60–90 min of passive recovery (Freund and Gendry, 1978; Messonnier et al, 1997, 2001). The net lactate release rate from the previously active muscles decreases rapidly to become almost nil after a few minutes into recovery (Juel et al, 1990; Bangsbo et al, 1991), so that the lactate removal rate surpasses rapidly the appearance rate and blood lactate concentrations decrease progressively. This particular pattern of blood lactate concentrations during recovery can be well-described by a bi-exponential time function (Equation 1) referring to a bi-compartmental model of lactate distribution space (Freund and Zouloumian, 1981a,b; Zouloumian and Freund, 1981a,b): La(t) = [La](0) + A1(1 − e−γ1t) + A2(1 − e−γ2t) (1)
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