| Abstract: | This study examined the effects of prior exercise on the lactate (Tlac) and ventilatory (Tvent) thresholds. Ten healthy male subjects volunteered to perform one-legged cycling. Muscle glycogen reduction was achieved by cycling at 75-85% of maximal heart rate for 60-75 min, and by a low carbohydrate diet. Pre- and post-exercise tests for measuring the thresholds employed a 3-min continuous protocol in 16 W increments. Muscle biopsies (n = 3) were taken from the vastus lateralis before the 'prior exercise' (PE) ride, the post-PE threshold test, and before testing the non-exercised (NE) leg. An i.v. catheter was used for serial blood lactate concentration determination during rest and the final 30 s of each progressive load. Ventilatory gas analyses were performed every 30 s. Biopsies showed that the PE and diet regimen reduced muscle glycogen in the PE leg (46.7%) and NE leg (36.4%). Venous blood lactate and respiratory exchange ratio (R) were reduced at Tlac and Tvent in both the PE and NE leg. The VO2 at a blood lactate concentration of 4 mmol l-1 was elevated in the PE leg at Tlac (2.89 versus 2.46 1 min-1), but not in the NE leg at Tlac. These results suggest that lactate concentration at Tlac and Tvent is reduced by endurance exercise performed 24 h prior to testing, and that the central circulation plays a major role in this response. Furthermore, since blood lactate is reduced at the thresholds by prior exercise, the use of a lactate level of 4 mmol l-1 as a criterion for Tlac should be interpreted cautiously. |
