Ventilatory threshold: a useful method to determine aerobic fitness in children?

Purpose: The objective of this study was to assess intra-and inter-evaluato r reliability and validity of ventilatory threshold (VT) determination in c hildren. Methods: At the ape of 6-12 yr, 35 children born prematurely and 2 0 controls born at term performed an incremental continuous cycling task un til volitional fatigue. Fifteen-second averages of (V) over dotE/(V) over d ot O-2, (V) over dotE/(V) over dot CO2, and respiratory exchange ratio were plotted 1) over time (X-time) and 2) over (V) over dot O-2 (X-(V) over dot O-2) (V) over dot CO2 was plotted over (V) over dot O-2 only (X-(V) over d ot O-2). Two experienced evaluators, blind to thr identity of plots, indepe ndently assessed VT from X-time and X-(V) over dot O-2 plots on two occasio ns, 6 wk apart. Thus, for each of the 55 subjects, four VT values were expe cted from X-time plots and four from X-(V) over dot O-2 plots (2 evaluators , 2 occasions). Results: VT expressed as (V) over dot O-2 in mL.min(-1) cou ld be determined by both evaluators on both occasions in 40/55 children fro m X-time and in 45/55 children from X-(V) over dot O-2. VT was significantl y different between evaluators for X-time plots. Using X-time plots, intrae valuator ICC were 0.88 and 0.98 and interevaluator ICC were 0.82 and 0.79. The respective values for X-(V) over dot O-2 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 tho se born at term. There was a close association between VT and (V) over dot O-2peak (r = 0.92). Conclusion: Plotting gas exchange data over (V) over do t O-2 is likely to be the method of choice for determining VT. Although a m inority of children have uninterpretable X-(V) over dot O-2 plots. VT can b e reliably interpreted in the remainder. Furthermore, VT is a valid marker of aerobic capacity. Thus, VT is a useful measure of aerobic fitness in chi ldren.