The weight of available evidence suggests that endurance performance is better predicted by the lactate threshold (LT) than by maximal oxygen uptake (VO2max). However, it is not clear whether exercise intensity at the LT is equal to the maximal exercise intensity able to be sustained during a time-trial (TT), nor whether exercise at either of these work rates elicits a `maximal lactate steady state`. The purpose of the present investigation was to examine the relationships between the LT, constant-load exercise at the LT and TT performance in running and cycling. Methods: Ten highly-trained male triathletes (age 27.5 ± 4.4 years, cycle VO2max 61.5 ± 3.8 mmol/l, run VO2max 59.9 ± 6.8 mmol/l) completed three trials for both cycling and running: 1) incremental tests to determine their LT; 2) 30 min constant-load (cycle) or speed (run) tests at their LT intensity; and 3) TT (40 km cycling and 10 km running). Results: Strongest predictors of TT performance for running were LT speed (r = -0.92; p < 0.01) and VO2max (r = -0.89; p < 0.01), while for cycling, LT power output was the only significant predictor (r = -0.68; p < 0.05). Only four out of nine participants were able to run for 30 minutes at their LT speed; in contrast, all 10 participants were able to maintain their LT cycle power output for the same duration. During the running constant load trial, the average plasma [La] between 10 and 30 minutes was not in steady state; in contrast, during the cycle constant load trial, plasma [La] was in steady state between minutes 10 and 30. In the running trials, the LT speed (15.6 ± 1.2 km/h) was significantly greater than the average TT speed (14.8 ± 2.0 km/h) (p < 0.05) whereas in cycling, there was no difference between power output at LT (243.5 ± 35.2 W) and average TT power output (251.6 ± 33.5 W). Discussion: The present data demonstrate that the run LT predicts 10 km TT performance yet over-predicts the highest sustainable running speed over a 30 minute duration. In contrast, the cycle protocol more accurately predicts the highest sustainable cycling workload over 30 minutes, in addition to predicting 40 km TT performance. The cycling LT protocol is more useful than the running protocol since it predicts a sustainable workload over 30 minutes in addition to the workload and performance time during a TT.
© Copyright 2012 17th Annual Congress of the European College of Sport Science (ECSS), Bruges, 4. -7. July 2012. Veröffentlicht von Vrije Universiteit Brussel. Alle Rechte vorbehalten.