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.