Physiological variables at lactate threshold under-represent cycling time-trial intensity.

BACKGROUND: The importance of lactate threshold (LT) as a determinant of performance in endurance sports has been established. In addition, it has been shown that during running and selected other endurance competitions, athletes perform at a velocity and VO2 slightly above LT for the duration of the event. Prior work indicates however, that this may not be true during a cycling time-trial (TT). This investigation sought to compare physiological variables during a 20-k TT with those corresponding to the athlete's LT.

METHODS: Thirteen male cyclists (22.7+/-0.8 yrs; 180.6+/-8.0 cm; 77.1+/-10.0 kg; 8.3+/-2.5% fat; 4.9+/-2.2 l x min(-1), VO2max) participated in the study. Subjects performed a graded protocol starting at 150 Watts (W) to determine LT (2 mmol x L(-1) above baseline) which consisted of 20 W increases every 4-min. Following an 8 min-recovery, subjects cycled at the wattage corresponding to LT-20 W for 1 min and then workload increased 20 W every minute until volitional exhaustion to determine VO2max x On a separate occasion a self-paced, 20-k TT was completed.

RESULTS: Mean values of blood lactate, HR and % HRmax, VO2 and % VO2max, and power output throughout the 20-k TT were greater (p<0.01) than those at LT. During the TT these cyclists performed at an intensity well above LT (blood lactate=252.0+/-0.1%, HR=9.4+/-0.03%, %HRmax=9.2+/-0.15%, VO2=26.5+/-0.7%, %VO2max=17.2+/-0.08% and power out-put=14.8+/-0.14% above LT) for over 30 min.

CONCLUSIONS: Therefore, while LT may be highly correlated to performance, it may not be representative of race pace for a cycling TT, and may be questionable as a benchmark used to prescribe training intensity for competitive TT-cycling.