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Variations in the ventilatory and lactate thresholds with prolonged aerobic exercise Mavrogiannis, Apostolos


The purpose of this study was to examine the changes in the ventilatory (VT) and lactate (LT) thresholds and VO₂max following prolonged aerobic exercise. Six well-trained distance runners (T:age=25.2 yrs, Ht=170.0 cm, Wt=65.0 kg, VO₂max=59.6 ml •kg⁻¹•min⁻¹) and six untrained (UT:age=25.3 yrs, Ht=180.3 cm, Wt=79.2 kg, VO₂max=46.8 ml•kg⁻¹•min⁻¹) males were studied on two occasions seven days apart. The initial evaluation involved a continuous horizontal treadmill test with a starting velocity of 2.22 m•s⁻¹, which was increased by 0.22 m•s⁻¹ each minute until fatigue. Expired gases were continuously sampled and analyzed by a Beckman Metabolic Measurement Cart. Measurements were processed by a data acquisition system (HP 3052A), which determined respiratory gas exchange variables every 15 seconds. Blood lactate measurements were taken via an indwelling catheter during the last 10 sec of each minute of work. VT and LT were determined by visual inspection of the excess CO₂ elimination and lactate curves, respectively. Seven days later the subjects repeated the treadmill test preceded by a 60 minute treadmill run at a heart rate corresponding to their LT. The physiological measurements recorded during the first session were repeated. There were significant (p<0.10) reductions in VO₂max, LT, VT, and total treadmill time on the VO₂max test (TTT) in the T group (59.6 to 56.9 ml •kg⁻¹•min⁻¹, 9.6 to 9.3 mph , 8.9 to 8.2 mph , and 925.0 to 882.5 sec, respectively). VO₂max, LT, VT, and TTT were reduced in the UT group (46.8 to 45.0 ml•kg⁻¹•min⁻¹ 7.7 to 7.6 mph, 8.0 to 7.2 mph, and 730.0 to 652.5 sec, respectively), however, only VT and TTT were reduced significantly (p<0.10). Although the groups were significantly different (p<0.05) in the initial physiological measures due to training status, there was no change in the rate of decline in VO₂max, LT, VT, or TTT when the UT group was compared to T. As LT and VT are affected by prolonged aerobic exercise it is questionable whether these thresholds can be used with confidence to predict endurance performance in events up to 60 min duration for well-trained and recreational athletes.

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