Relationship between the lactate and ventilatory thresholds during prolonged exercise.
The anaerobic threshold is commonly measured by either blood lactate (lactate threshold) or ventilatory gases (ventilatory threshold); however, the relationship between these 2 methods is not conclusive. The lactate threshold has been characterised at either a fixed or variable blood lactate concentration (BLa). Recent studies have indicated a specific blood lactate concentration for each individual which considers the interindividual variations in lactate kinetics (individual anaerobic threshold), following either a continuous, exponential pattern or a discontinuous, threshold-like response. The ventilatory threshold is assessed using a variety of ventilatory parameters, many of which exhibit a threshold-like response during progressive exercise. Despite the apparent causal relationship between the stimulation of the ventilatory chemoreceptors and ultimately the ventilatory response and the accumulation of protons in the circulating blood, evidence does exist which refutes such a connection. Such evidence supporting a coincidental relationship examines no significant change in ventilation with significant increases in blood lactate concentration. Conversely, evidence from patients with McArdle's disease indicates that although no lactic acid is produced, these individuals do experience a threshold-like ventilatory response during incremental exercise. The ability to perform at the anaerobic threshold is now recognised as an integral component of endurance events. Several studies have concluded that the ventilatory threshold is highly correlated with endurance performance, in distances ranging from 26 miles (41.6 km) [r = -0.94] to 5 and 10 km (r = -0.945). The lactate threshold, in particular the individual anaerobic threshold, has been examined from a performance standpoint. Much of the literature supports the individual anaerobic threshold as the exercise intensity at which performance is maximal and able to be sustained for at least 50 minutes. With the variety of techniques utilised in assessing the anaerobic threshold, caution should be taken in interpretation of the results as the different protocols may elicit a variety of responses during incremental exercise. Furthermore, it is essential to account for the individual's unique response to such exercise.