A study was performed to clarify the relationships between oxygen uptake (VO₂) kinetics on recovery from incremental maximal exercise and blood lactate, glucose and alanine metabolism. Eight healthy males aged 21.6±3.3 years were studied. The incremental exercise test was performed using a modified version of Bruce's protocol until 30 min after exhaustion. The VO₂ responses on recovery were fitted by a two-component exponential model. Blood lactate concentration in the recovery phase was fitted by a bi-exponential time function to assess the velocity constant of the slowly decreasing component (γ2) expressing the rate of blood lactate removal. Both blood lactate and plasma alanine concentration were significantly increased from rest to maximal exercise, and were significantly decreased thereafter, but remained above resting values for 30 min after the maximal stage. Blood glucose concentration was significantly decreased following maximal exercise and returned to the pre-exercise value by 30 min after the maximal stage. Concentrations of plasma branched-chain amino acids (valine, leucine and isoleucine) were significantly decreased from the maximal stage until 30 min after exhaustion. The time constant of the slow component on recovery VO₂ [τVO₂ (s) ] was correlated with neither γ2 nor the degree of change in blood lactate from the maximal stage until 30 min after exhaustion (Δlactate) . However, τVO₂ (s) was significantly correlated with both Δ blood glucose and Δ alanine. In addition, Δ alanine was significantly correlated with Δ blood glucose. From these results, we conclude that oxygen uptake kinetics after exhaustive maximal exercise is related to glucose resynthesis through alanine metabolism, as compared with that from lactate metabolism.

A study was performed to clarify the effects of endurance training above the anaerobic threshold (AT) on the isocapnic buffering phase during incremental exercise in athletes. Eight middle-distance runners aged 19.6±1.2 years performed incremental exercise testing with a modified version of Bruce's protocol. After a 6-month high-intensity interval and paced running training at levels above AT, maximal oxygen uptake (VO₂max) (ml⋅ kg^-1⋅min^-1) was significantly increased from 60.1±5.7 to 64.7±5.5 (p<0.05) . AT (m⋅lkg^-1⋅min^-1) was slightly but significantly increased from 28.2±3.5 to 29.6±4.3 (p<0.05) . The respiratory compensation point (RC) (ml⋅ kg^-1⋅min^-1) was markedly increased from 53.0±8.3 to 57.7±8.2 (p<0.05) . Although neither the slope of the first regression line below AT (S1) nor that of the second line above AT (S2) calculated by V-slope analysis was altered, the range of isocapnic buffering (ml⋅kg^-1⋅min^-1) from AT to RC was significantly extended from 24.8±5.9 to 28.1±6.0 after the 6-months of training (p<0.05) . In addition, the amount of change in VO₂max after the 6-month of training period (ΔVO₂max) was correlated with Δisocapnic buffering (R=0.72, p<0.05) . We conclude that the degree of increased respiratory compensation point is larger than that of AT after high-intensity endurance training at levels above AT, and that the range of isocapnic buffering may be an important factor in relation to the increase in the maximal aerobic capacity of athletes.