Predicting Cardiorespiratory Fitness Using the 20-m Shuttle Run Test: New Insights Using Nonlinear Allometry.

PURPOSE Recently, doubts have been raised concerning the validity of the 20-m shuttle run test (20mSRT) to predict cardiorespiratory fitness (CRF) in youth. Despite these doubts, authors continue to provide powerful evidence that CRF can be predicted reliably using the 20mSRT albeit using contrasting models. Therefore, we aimed to compare a new linear model with an alternative allometric model to predict CRF (peak oxygen uptake, V˙O2peak) using 20mSRT. METHODS The study included 148 adolescents (43% girls), aged 13.37 ± 1.84 years. Adolescents were randomly assigned to validation (n = 91) and cross-validation (n = 57) groups. V˙O2peak was measured using a gas analyser in both maximal exercise tests in the laboratory as well as 20mSRT. Multiple linear regression methods were applied to develop the linear models using 20mSRT (laps), BMI and body fat percentage. Alternative allometric models were also proposed/fitted using 20mSRT (laps), height and body mass. RESULTS The criterion validity of both the linear and the allomeric models were found to be acceptable R2=82.5% and 82.7% respectively, providing reassuring evidence that the 20mSRT can be used with confidence to predict CRF. However, the allometric model identified a height-to-mass ratio, not dissimilar to the inverse BMI (known to be a measure of leanness), to be associated with CRF. The allometric model also revealed that the rise in energy cost (V˙O2peak) with increasing laps was exponential. This will more accurately reflect the non-linear rise in energy demand of shuttle running as the test progresses to exhaustion. CONCLUSIONS These observations provided powerful evidence that allometric models are more than satisfactory in terms of both criterion AND construct validity when predicting CRF (V˙O2peak) using the 20mSRT.