EFFECTS OF EXPERIMENTAL ACID-BASE DISTURBANCE ON BLOOD LACTATE KINETICS DURING INCREMENTAL EXERCISE

The present study was conducted to investigate the effect of acid-base disturbance on blood lactate concentration (bLA) and OBLA (Onset of Blood Lactate Accumulation) during an incremental bicycle test. Nine healthy male subjects underwent the incremental test at 60 min after the oral administration of NH4C1 (acidotic-treatment ; Acid) , NaHC03 (alkalotic-treatment ; Alk) and NaCI (control ; Cont) at 1.87 mM • kg-1 body weight. Exercise was started at a load of 80W, which was subsequently increased by lOW every minute until exhaustion. During exercise, 02 intake (VO2), ventilatory volume (VE) and heart rate (HR) were monitored continuously. Venous blood samples were obtained before administration and every 2 min during exercise. No change could be detected in resting V02, VE and HR following oral administration of NH4C1, NaHCO3 and/or NaCI. At 60 min after oral administration venous blood pH (pH) and bicarbonate ion concentration (v [HCO3-]) were significantly lower in Acid (7.265 f 0.033 ; p <0.001, 23.6 ± 1.8 mM ;p<0.01) ;and significantly higher in Alk (7.370 ± 0.045 ; p < 0.01, 29.7 ± 1.6 mM • 1-' ; p < 0.01) compared to Cont (7.318•}0.041, 26.6•}2.1 mM • 1-1) . Changes in VO2, VE and HR dur ing exercise were essentially the same in all cases. No differences were observed in exercise time. During exercise, vpH and [HCO3-] gradually decreased, but remained significantly lower in Acid and higher in Alk compared to Cont. Blood lactate concentration (bLA) increased during exercise. Peak values were observed at exhaustion, but it was lower in Acid (8.03•}1.18mM • 1-1) and higher in Alk (10.73•}1.48) compared to Cont (9.49•}1.79) in all subjects. The Onset of Blood Lactate Accumulation (OBLA) was determined for each subject. OBLA was significantly higher in Acid (71.9 f 9.1% VO2max) than Cont (62.5•}9.9% VO2max) and Alk (62.2•}8.0%V02max) . Changes in acid-base balance were found to cause differences in bLA responses to the same exercise load and possibly change OBLA. Care must be taken when using OBLA or LT as an index of aerobic capacity in some patients with acid-bace disorders ; hemodialitic , obese or diabetic patient. (Jpn. J. Phys. Fitness Med. 1995, 44: 297 -306) key words : lactate, acid-base balance, bicarbonate buffering system, OBLA

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