Cross-Validation of Predictive Equation for Cardiorespiratory Fitness by Modified Shuttle Walk Test in Adults with Schizophrenia: A Secondary Analysis of the CORTEX-SP Study

Cardiorespiratory fitness (CRF) can be direct or estimated from different field tests. The Modified Shuttle Walk Test (MSWT) is suitable for all levels of function, allowing a peak response to be elicited. Therefore, we aimed (1) to validate the equation presented in the original study by Singh et al. for evaluating the relationship between MSWT with peak oxygen uptake (VO(2peak)) in adults with schizophrenia (SZ), (2) to develop a new equation for the MSWT to predict VO(2peak), and (3) to validate the new equation. Participants (N = 144, 41.3 ± 10.2 years old) with SZ performed a direct measurement of VO(2peak) through a cardiopulmonary exercise test and the MSWT. A new equation incorporating resting heart rate, body mass index, and distance from MSWT (R(2) = 0.617; adjusted R(2) = 0.60; p < 0.001) performs better than the Singh et al. equation (R(2) = 0.57; adjusted R(2) = 0.57; p < 0.001) to estimate VO(2peak) for the studied population. The posteriori cross-validation method confirmed the model’s stability (R(2) = 0.617 vs. 0.626). The findings of the current study support the validity of the new regression equation incorporating resting heart rate, body mass index, and distance from MSWT to predict VO(2peak) for assessment of CRF in people with SZ.