Experimental studies on the effects of exercise on the lactate and ventilatory threshold
Date
1984
Authors
Neary, Patrick J.
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
In order for an athlete to perform exercise for a prolonged period of time, the cardiovascular, respiratory and muscular systems must function together in an efficient manner. The most widely used method to measure these endurance parameters has been maximal oxygen consumption VO2 max) (Astrand and Rodahl, 1977). An individuals ability to consume and utilize large quantities of 02 reflect an efficient system. Research suggests that as the exercise duration increases, aerobic capacity becomes increasingly more important (MacDougall, 1977).
Recent research however, has also demonstrated that the 'anaerobic threshold' (AT) is an important aerobic parameter (Sjodin et al., 1982). The ability of an athlete to sustain exercise at a higher percentage of VO2 max, without accumulating metabolites, may be as important as VO2 max values (Thoden et al., 1983; Weltman et al., 1978). The concept of AT was originally used to describe the metabolic events associated with the production of lactic acid during progressive exercise. However, in this at tempt researchers have encountered a number of problems associated with the anaerobic threshold. These include: an appropriate definition or terminology (Kindermann et al., 1979; Skinner and McLellan, 1980), validation and determination of a threshold measurement (Yeh et al., 1983), and problems associated with its use (Jones and Ehrsam, 1982).
The anaerobic threshold has been defined as the intensity of exercise where blood lactate begins to accumulate in blood (MacDougall, 1977). It has been suggested that this metabolic phenomenon is due to an imbalance between pyruvate production and utilization in the Krebs cycle (Holloszy, 1975). Pyruvate is converted to lactate in the presence of lactate dehydrogenase (LDH) and reduced nicotinamide adenine dinucleotide (NADH), in an attempt to regenerate NAD+ to maintain production of ATP via glycolysis. During lactate product ion, hydrogen ions (H+) are formed in an equimolar concentration, creating a metabolic acidosis which then must be buffered. The bicarbonate buffering system in blood controls pH levels when H+ and HCO3- combine, and the excess CO2 produced (Hughson and Green, 1982) then stimulates ventilation (VE). As exercise intensity increases, an equivalent fall in bicarbonate concentration continues as lactate levels rise (Jones, 1980). This results in further hypernea due to the stimulation of respiratory chemoreceptors by increases in Pco2 and H+. Therefore, it has been suggested that noninvasive gas measures can be used to reflect lactate and H+ formation, and consequently metabolic acidosis (Davis et al., 1976; Wasserman et al., 1973). Thus, a ventilation threshold (VE vs VO2 or VE/VO2 vs VO2) has been used to reflect the lactate threshold (LA vs VO2). It is this event which can then limit endurance performance.
Recent research however, suggests that it is unreliable to use a respiratory event to reflect a metabolic phenomenon (Green et al., 1983). These authors conclude that this relationship between ventilation and metabolism was only coincidental. Some researchers have explored the physiological bases of the anaerobic threshold in an attempt to determine what factors effect the lactate (LT) and ventilation (VT) thresholds. Hughes et al. (1982) studied the effects of glycogen depletion exercise on LT and VT and found these thresholds could be manipulated independently of each other. This suggests that the relationship is not one of cause and effect. Stamford et al. (1978a) discussed the anaerobic threshold and cardiovascular responses during oneĀ-versus two-legged cycling and suggested that AT was similar between leg protocols. They did not however, discuss to what extent peripheral and central (circulatory) factors play on the exercise responses at the LT and VT. This may help to shed light on the nature of the training stimulus. There 1s limited research on the effects of different protocols on the measurement of LT and VT (McLellan, 1983). Documenting these effects may provide greater insights into the nature of lactate efflux from muscle during resting periods when using an intermittent protocol.
With this background information, the purpose of the present studies were:
1. to examine the effects of a continuous and discontinuous exercise protocol on the lactate and ventilation thresholds.
2. to determine the differences between 1- versus 2-legged cycling on the lactate and ventilation thresholds and on selected variables at V02 max.
3. to determine both the reliability of the lactate and ventilation thresholds and the effects of prior exercise on these threshold points.
4. to determine whether the relationship between the lactate and ventilation threshold is coincidental or cause and effect.