Ventilatory threshold: a useful method to determine aerobic fitness in children?
The objective of this study was to assess intra- and inter-evaluator reliability and validity of ventilatory threshold (VT) determination in children. At the age of 6-12 yr, 35 children born prematurely and 20 controls born at term performed an incremental continuous cycling task until volitional fatigue. Fifteen-second averages of VE/VO2, VE/VCO2, and respiratory exchange ratio were plotted 1) over time (X-time) and 2) over VO2 (X-VO2). VCO2 was plotted over VO2 only (X-VO2). Two experienced evaluators, blind to the identity of plots, independently assessed VT from X-time and X-VO2 plots on two occasions, 6 wk apart. Thus, for each of the 55 subjects, four VT values were expected from X-time plots and four from X-VO2 plots (2 evaluators, 2 occasions). VT expressed as VO2 in mL x min(-1) could be determined by both evaluators on both occasions in 40/55 children from X-time and in 45/55 children from X-VO2. VT was significantly different between evaluators for X-time plots. Using X-time plots, intraevaluator ICC were 0.88 and 0.98 and interevaluator ICC were 0.82 and 0.79. The respective values for X-VO2 plots were 0.94 and 0.95, and 0.96 and 0.92. Intra- and inter-evaluator reliability of VT determinations tended to be slightly lower in children born prematurely compared with those born at term. There was a close association between VT and VO2peak (r = 0.92). Plotting gas exchange data over VO2 is likely to be the method of choice for determining VT. Although a minority of children have uninterpretable X-VO, plots, VT can be reliably interpreted in the remainder. Furthermore, VT is a valid marker of aerobic capacity. Thus, VT is a useful measure of aerobic fitness in children.