We examine the influence of the cytosolic and membrane-bound contents of carbonic anhydrase (CA; CAII, CAIII, CAIV, and CAXIV) and the muscle content of proteins involved in lactate and proton transport [monocarboxylate transporter (MCT) 1, MCT4, and Na⁺/H⁺exchanger 1 (NHE1)] on work capacity during supramaximal exercise. Eight healthy, sedentary subjects performed exercises at 120% of the work rate corresponding to maximal oxygen uptake (Ẇ_max) until exhaustion in placebo (Con) and metabolic alkalosis (Alk) conditions. The total (W_tot) and supramaximal work performed (W_sup) was measured. Muscle biopsies were obtained before and immediately after standardized exercises (se) at 120% Ẇ_maxin both conditions to determine the content of the targeted proteins, the decrease in muscle pH (ΔpH_m), and the muscle lactate accumulation ([Lac]_m) per joule of W_sup(ΔpH_m/W_sup-seand Δ[Lac]_m/W_sup-se, respectively) and the dynamic buffer capacity. In Con, W_supwas negatively correlated with ΔpH_m/W_sup-se, positively correlated with Δ[Lac]_m/W_sup-seand MCT1, and tended to be positively correlated with MCT4 and NHE1. CAII + CAIII were correlated positively with ΔpH_m/W_sup-seand negatively with Δ[Lac]_m/W_sup-se, while CAIV was positively related to W_tot. The changes in W_supwith Alk were correlated positively with those in dynamic buffer capacity and negatively with W_supin Con. Performance improvement with Alk was greater in subjects having a low content of proteins involved in pH regulation and lactate/proton transport. These results show the importance of pH regulating mechanisms and lactate/proton transport on work capacity and the role of the CA to delay decrease in pH_mand accumulation in [Lac]_mduring supramaximal exercise in humans.

The influence of sickle cell trait and/or α-thalassemia on skeletal muscle microvascular network characteristics was assessed and compared with control subjects [hemoglobin (Hb) AA] in 30 Cameroonian residents [10 HbAA, 5 HbAA α-thalassemia (α-t), 6 HbAS, and 9 HbASα-t] matched for maximal work capacity and daily energy expenditure. Subjects performed an incremental exercise to exhaustion and underwent a muscle biopsy. Muscle fiber type and surface area were not different among groups. However, sickle cell trait (SCT) was associated with lower capillary density (P < 0.05), lower capillary tortuosity (P < 0.001), and enlarged microvessels (P < 0.01). SCT carriers had reduced counts of microvessels 10 μm (P < 0.05). α-Thalassemia seemed to be characterized by a higher capillary tortuosity and unchanged capillary density and diameter. Thus, while SCT is a priori clinically benign, we demonstrate for the first time that significant remodeling of the microvasculature occurs in SCT carriers. These modifications may possibly reflect protective adaptations against hemorheological and microcirculatory dysfunction induced by the presence of HbS. The remodeling of the microvascular network occurs to a lesser extent in α-thalassemia. In α-thalassemic subjects, increased capillary tortuosity would promote oxygen supply to muscle tissues and might compensate for the lower Hb content often reported in those subjects.

Lactate is known to play a central role in the link between glycolytic and mitochondrial oxidative metabolism, as well as to serve as a primary gluconeogenic precursor. Blood lactate concentration is sensitive to the metabolic state of tissues and organs as lactate rates of appearance and disposal/disappearance in the circulation rise and fall in response to physical exercise and other metabolic disturbances. The highest lactate flux rates have been measured during moderate intensity exercise in endurance-trained individuals who exhibit muscular and metabolic adaptations lending to superior oxidative capacity. In contrast, a diminished ability to utilize lactate is associated with poor metabolic fitness. Given these widespread implications in exercise performance and health, we discuss the concept of lactate metabolic clearance rate, which increases at the onset of exercise and, unlike flux rates, reaches a peak just below the power output associated with the maximal lactate steady state. The metabolic clearance rate is determined by both disposal rate and blood concentration, two parameters that are mutually interdependent and thus difficult to parse during steady state exercise studies. We review the evolution of the in vivo lactate clamp methodology to control blood lactate concentration and discuss its application in the investigation of whole-body lactate disposal capacities. In conclusion, we assert that the lactate clamp is a useful research methodology for examining lactate flux, in particular the factors that drive metabolic clearance rate.

The purpose of the present study was to relate the training-induced alterations in lactate kinetics parameters to the concomitant changes in time to exhaustion (T_lim) at a work rate corresponding to maximal oxygen uptake (Pa_peak). Eight subjects performed before and after training i) an incremental exercise up to exhaustion to determine Pa_peak, ii) a 5-min 90 % Pa_peak exercise followed by a 90-min passive recovery to determine an individual blood lactate recovery curve fitted to the bi-exponential time function: La(t) = La(0) + A₁(1 - e^{-γ1 · t}) + A₂(1 - e^{-γ2 · t}), and iii) a time to exhaustion at Pa_peak to determine T_lim. A biopsy of the vastus lateralis muscle was made before and after training. The training programme consisted in pedalling on a cycle ergometer 2 h a day, 6 days a week, for 4 weeks. Training-induced increases (p < 0.05) in Pa_peak, muscle capillary density, citrate synthase activity, γ₂ that denotes the lactate removal ability (from 0.0547 ± 0.0038 to 0.0822 ± 0.0071 min^-1) and T_lim (from 299 ± 23 to 486 ± 63 s), decreases (p < 0.05) in activities of lactate dehydrogenase (LDH) and muscle type of LDH, the phosphofructokinase/citrate synthase activities ratio and the estimated net amount of lactate released (NALR) during exercise recovery (from 66.5 ± 8.6 to 47.2 ± 11.1 mmol) were also observed. The improvement of T_lim with training was related to the increase in γ₂ (r = 0.74, p = 0.0367) and to the decrease in NALR (r = 0.77, p = 0.0250). These results suggest that the post-training greater ability to remove lactate from the organism and reduced muscle lactate accumulation during exercise account for the concomitant improvement of the time to exhaustion during high-intensity exercise performed at the same relative work rate.

The present study investigated morphological and physiological factors of rowing ergometer performance over 2000 m (P_2000, W) in 70 national and international level [27 lightweight (LW) and 43 heavyweight (HW)] female rowers. Maximal oxygen uptake (V̇O_2max, L.min⁻¹), maximal aerobic power (Pa_max, W), power output corresponding to 4 mmol.L⁻¹ blood lactate concentration expressed in absolute (PLa₄, W) and relative to Pa_max (PLa₄%, %) values, peak power output (P_peak, W), and rowing gross efficiency (RGE, %) were determined during an incremental rowing test. In the whole group, P_peak was the best predictor of P₂₀₀₀ (r=0.89, p<0.001), as it was shown in men. PLa₄ (r=0.87), V̇O_2max (r=0.83), body mass (r=0.65), and height (r=0.64) were also significantly correlated with P₂₀₀₀ (p<0.001 for all). P_peak was also the best predictor of P₂₀₀₀ when the two sub-groups LW and HW were considered separately. It was concluded that P_peak is an overall index of physiological rowing capacity in groups of high-level LW and HW female rowers. The predictive value of P_peak is similar to that of PLa₄, but P_peak presents the advantage of being obtained with a simple ergometer test without biological measurements.