The relationship between lactate and ventilatory thresholds: coincidental or cause and effect?

To determine if blood lactate (LA) is the stimulus responsible for ‘breakaway’ ventilation (V_E), the lactate (LT) and ventilation (VT) thresholds were monitored during one-legged cycling exercise. Ten healthy volunteer male subjects (Mean 2-legged \(\dot V_{O_{2\max } } \) =4.27 l·min⁻¹) performed prior exercise (PE) to reduce muscle glycogen stores by cycling at 75–85% of maximal heart rate (HR max) for 60–75 min, followed by a 30 h low carbohydrate diet. Pre- and post- LT and VT tests were performed on a cycle ergometer employing a continuous protocol with increments of 16 W every 3 min. Muscle biopsies were taken from the vastus lateralis muscle before the PE ride, prior to the threshold test 24 h later, and before testing the non-exercised (NE) leg. An I.V. catheter placed in the antecubital vein was used for serial blood samples taken at rest, and during the final 30 s of each progressive load. Gas analysis was calculated every 30 s (Beckman Metabolic Measurement Cart). Biopsies (N=3) showed that the exercise and diet regimen elicited glycogen reduction which significantly (p<0.05) reduced R and the blood LA concentration in both the PE (2.62 to 1.99 mmol·l⁻¹) and NE (2.87 to 2.26 mmol·l⁻¹) legs at LT. At VT, LA concentrations were also significantly reduced in the PE (3.35 to 2.56 mmol·l⁻¹) and NE (3.59 to 2.74 mmol·⁻¹) legs. \(\dot V_{O_2 } \) and V_E, however, were similar between pre- and post- tests. Results of this study suggest that plasma LA accumulation is not responsible for ‘breakaway’ ventilation during progressive exercise and that LT and VT are not a cause and effect relationship.