The measurement of plasma catecholamine and lactate thresholds: a comparison of methods

Plasma lactate and catecholamine thresholds were calculated using three dif ferent variations of linear regression, an algorithmic linear regression me thod, a log-log transformation method and a semi-log method. A group of 18 male sports science students undertook an incremental test to exhaustion on a cycle ergometer. A 5-ml blood sample was drawn at rest, after 4 min of e xercise and every 2 min thereafter until the cessation of the test. Lactate , adrenaline and noradrenaline concentrations were measured. Lactate thresh old (Th-1a), adrenaline threshold (Th-A) and noradrenaline threshold (Th-NA ) were calculated using each of the three methods. The best fits of the met hods were examined by comparing their standard error of estimates (SEEs). T he algorithmic method demonstrated a higher SEE than the other two methods. but only for Th-1a and Th-NA. The power output for which each method calcu lated the thresholds demonstrated a main effect for method. Tukey post hoc tests showed that the algorithmic method produced significantly higher outp uts than the other two methods. which did not differ significantly from one another. Comparison of these power outputs showed that Th-1a and Th-A diff ered significantly, regardless of method, there were no other significant d ifferences. Plasma concentrations of lactate, adrenaline and noradrenaline showed that the values of Th-1a and Th-NA calculated by the algorithmic met hod were significantly higher than those calculated using the other two met hods, which did not differ significantly from one another. The only signifi cant difference for Th-A was between the algorithmic and semi-log methods. Correlations between the power outputs at which each method calculated the thresholds varied greatly between methods, and were at best only moderate ( r = 0.63). It was concluded that the algorithmic method was less powerful t han the other two methods, and that Th-1a, Th-A and Th-NA are not highly co rrelated.