Abstract
PURPOSE: The Incremental Shuttle Walk Test (ISWT) is an important functional and prognostic marker in chronic disease. Aging has a detrimental effect on exercise performance. The objective of this study was to produce normal age-specific values for the ISWT in a healthy British population and to explore whether additional variables improve the accuracy of a predictive equation.
METHODS: Healthy subjects (N = 152), aged 40 to 90 years, were recruited. Data collection occurred over 2 study visits. Anthropometric and demographic data were collected, and lung function and quadriceps maximal voluntary contraction were measured. An accelerometer was worn for 2 consecutive days at home. The Duke Activity Status Index was completed, and the greatest distance from 2 ISWTs was recorded.
RESULTS: One hundred forty subjects (56 men) with mean age (SD) of 59.4 (11.0) years completed 2 ISWTs. Forced expiratory volume in 1 second (FEV1) was 109.1% (14.56%) predicted and ISWT distance was 737 m (183 m). Age-specific normal values for the ISWT were observed: mean (lower limit of normal)-40 to 49 years, 824 m (765 m); 50 to 59 years, 788 m (730 m); 60 to 69 years, 699 m (649 m); and 70 years and older, 633 m (562 m). A predictive equation was developed from 114 subjects. Age, body mass index, FEV1, quadriceps maximal voluntary contraction, and Duke Activity Status Index contributed to ISWT distance predicting 50.4% of the variation in performance.
CONCLUSION: We have developed age-specific normal values for performance on the ISWT in a healthy British population. However, even using practical, clinically relevant variables, it is not possible to accurately predict exercise capacity from a regression equation.