RESUMO
This study was undertaken to investigate the relationship between blood lactate concentration ([La]) and heart rate (HR) values obtained during treadmill and field tests at fixed velocities with respect to interchangeability of results to be used in exercise prescription. A total of 22 male soccer players participated in the study. Each player performed exercise tests on a motorized treadmill and in the field with 3-min runs and 30 s allowed for blood sampling. During both tests, velocities at the first, second, and third stages were 8, 10, and 12 km x hr(-1), respectively. Velocity was then increased by 1 km x hr(-1) every 3 min until exhaustion. During the field test, players ran on artificial turf on a 120-m hexagonal track marked with cones placed 20 m apart. Running velocity was controlled by means of audio signals. Blood samples were analyzed immediately with an automated lactate analyzer. HR was monitored continuously at 5-s intervals. Data were analyzed with Student's paired t tests to look for differences between treadmill and field data. Coefficients of variation and Blan-Altman plots assessed agreement of HR and blood [La] values between the 2 tests. Although running velocities corresponding to a fixed blood [La] of 4 mmol L-1 showed significant differences between treadmill and field tests (15.9+/-0.9 vs 14.1+/-0.7 km x h(-1), respectively) (P<.01), no significant difference between HR values was noted (190+/-7 vs 187+/-7, field vs laboratory, respectively). Overall, the mean intermeasurement coefficient of variation was 4.8% (+/-0.9%) for HR. Although the lowest coefficient of variation (2.4%) was found, fairly wide differences between individual field and laboratory HR values at velocities corresponding to fixed blood [La] of 4 mmol.L(-1) cast doubt on the interchangeability of tests.
