It was the purpose of this study to elucidate the difference between endurance runners and normal men in respiratory and circulatory adjustments during prolonged exercise, and to evaluate the relationship between the magnitude of the respiratory and circulatory“drift”and the endurance exercise capacity.
Ten male endurance runners (runner group), aged 19-23 years, and nine normal men (control group), aged 19-28 years, exercised on a bicycle ergometer for 60 min at a constant work load requiring 60% of Vo₂max for each subject.
In the control group, VE increased approximately 20% from 10th to 60th min of prolonged exercise (P<0.05), with a corresponding decrease in PAco₂ (P<0.05), whereas in the runner group VE and PAco₂were remained constant throughout prolonged exercise. The above differences of VE and PAco₂responses between the control and the runner group could not be accounted for by a rising body temperature and lactic acidosis, because it was found that the magnitude of the rise in rectal temperature (Tre) and the behavior in lactic acid (LA) were not different for the two groups. On the other hand, we failed to find the difference of the pattern in HR and SV responses to prolonged exercise in the runner group as compared with the control group. At each comparable time period during prolonged exercise, however, the percentage changes from the values at the 10th min in HR and SV were less in the runner group than in the control group. In addition, Vo₂max (ml/kg/min) correlated significantly with the percentage changes in VE (r=-0.534, P<0.05), HR (r=-0.565, P<0.05), and SV (r=0.588, P<0.01) from 10th to 60th min of prolonged exercise.
The results of this study suggest that the endurance training may improve the magnitude of the respiratory and circulatory “drift”, which appears to become a limiting factor to endurance performance.

A study was conducted to assess the relationship between CO₂ excess due to lactic acid production during exercise and endurance performance in order to clarify the availability of CO₂ excess as an index of endurance capacity. Four healthy males (control group; CON) aged 21-24 years, and six male long-distance runners (LDR) aged 18-22 years, were subjected to incremental maximal testing on a cycle ergometer and 12-min exhaustive track running. The results obtained are summarized as follows.
1) Mean values (±SD) of CO₂ excess (ml) were 3, 442±677 ml for LDR and 2, 667±437 ml for CON, respectively. On the other hand, the mean value of CO₂ excess per unit body weight (CO₂ excess/w) obtained in LDR (59.1±9.07 ml⋅kg^-1) was significantly higher than that in CON (40.3±3.54 ml⋅kg^-1) (p<0.01) .
2) The ratio of CO² excess/w to ΔLA (the difference between blood lactate at 1 min after exercise and that at rest) showed a tendency to be higher in LDR (5.59±1.16 ml⋅kg^-1⋅mmol^-1) than in CON (4.46±0.69 ml⋅kg^-1⋅mmol^-1) . However, there was no significant difference between these two groups in the ratio of CO² excess/w to ΔLA.
3) The CO² excess/w (ml⋅kg^-1) was significantly related to Vo₂max (r=0.813, p<0.01) and Vo₂AT (r=0.892, p<0.001), respectively. Moreover, CO₂ excess/w was significantly correlated with ΔHCO₃- (the difference between blood bicarbonate at l min after exercise and that at rest) (r=0.649, p<0.05) .
4) The CO₂ excess (ml) and CO₂ excess/w (ml⋅kg^-1) were significantly correlated with 12-min exhaustive running performance (r=0.715, p<0.05, r=0.933, p<0.001), as was the ratio of CO₂ excess/w to d LA (r=0.671, p<0.05) .
5) From these results, it was suggested that the CO₂ excess/w and the ratio of CO₂ excess/w to ΔLA could be important factors related to performance of endurance exercise (i. e., 3, 000-5, 000 m running) accompanied by blood lactate accumulation.

Blood lactate disappearance in endurance-trained men (ET) and untrained men (UT) was investigated by application of recovery exercise with high relative intensity. Blood lactate was measured in five male long-distance runners as ET and in seven male relatively active students as UT, using a cycle ergometer (60 rpm) . Two kinds of recovery exercise were performed at intensities of 70% and 40% Vo₂max for 20 min followed by main exercise at 90% Vo₂max for 3 min. The rate of blood lactate removal was calculated by linear regression of time (min) against blood lactate (mmol·l^-1) at 5, 10, 15 and 20 min during recovery exercise. Values of blood lactate at 10, 15 and 20 min during recovery exercise at 70% Vo₂max were significantly more reduced in ET than in UT (P<0.05, P<0.01) . There was, however, no significant difference between ET and UT during recovery exercise at 40% Vo₂max. The rate A of blood lactate removal during 70% recovery exercise was significantly greater in ET (0.2730±0.0920mmol·l^-1.min^-1) than in UT (0.0520±0.1010mmol·l^-1·min^-1) (P<0.01), but there was no significant difference in the rate between ET and UT during 40% recovery exercise. The rate B of blood lactate removal during 70% recovery exercise was significantly higher in ET (0.3770±0.08000 mmol·l^-1· min^-1) than in UT (0.1163±0.14416 mmol·l^-1·min^-1) (P<0.01), but there was no significant difference in the rate between ET and UT during 40% recovery exercise.
In conclusion, the present data indicate that endurance-trained men possess more pronounced capability for blood lactate removal during recovery exercise at high relative intensity.

The purpose of this study was to investigate the kinetics of Vco₂during incremental exercise. The subjects were 7 males, age 21-28 years, exercised at two steady state work loads (540 kpm/min, 810 kpm/min) and incremental work load which was increased stepwise by every 1 min from 180 kpm/min to exhaustion. The Vo₂and Vco₂during steady state exercise (4 to 5 min) were determined by the Douglas bag method and arterialized blood samples were taken for lactate (LA) analysis and blood gas analysis. The Vo₂, Vco₂, and blood lactate were also determined throughout the incremental exercise. At exhaustion, mixed venous Pco₂ (PVco₂) was determined by the CO₂rebreathing method.
1) The Vco₂values at rest and during steady state exercise were linearly related to the Vo₂values. When the regression line was compared with Vco₂during the incremental exercise on the same Vo₂, the Vco₂during the incremental exercise below the anaerobic threshold showed lower values.
2) The total sum of the difference in Vco₂between steady state and incremental exercise was defined as CO₂store. The calculated CO₂store and CO₂store per body weight were significantly related to PVco₂at exhaustion in incremental exercise, respectively (r=0.954, r=0.954) .
3) At work load below the anaerobic threshold, Vco₂was linearly related to Vo₂. If the Vco₂above the anaerobic threshold is estimated from Vo₂using the regression line obtained at work load below the anaerobic threshold, the estimated Vco₂will be lower than the measured Vco₂. The total sum of the difference in the Vco₂was defined as CO₂excess. The CO₂excess and the CO₂excess per body weight were significantly related to ΔLAmax (the difference between LA at 3rd min after exhastion and LA at exercise below the anaerobic threshold), respectively (r=0.870, r=0.930) .
4) HCO₃^-calculated from blood gases (pH and Pco₂) was significantly related to LA (r=-0.902) . The increase of 1 mM/1 in LA was corresponding to the decrease of 0.843 mEq/l in HCO₃^-.
5) From these results, it appeared that the expired Vco₂during the incremental exercise consisted of the stored Vco₂, the exceeded Vco₂, and the produced Vco₂ (Vco₂metabolically produced from Vo₂) .