EFFECTS OF ENDURANCE TRAINING ABOVE THE ANAEROBIC THRESHOLD ON ISOCAPNIC BUFFERING PHASE DURING INCREMENTAL EXERCISE IN MIDDLE-DISTANCE RUNNERS

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.