Are fixed-rate step tests medically safe for assessing physical fitness?

Maximal oxygen uptake (VO_2max) can be predicted by fixed-rate step tests. However, it remains to be analyzed as to what exercise intensities are reached during such tests to address medical safety. In this study, we compared the physiological response to a standardized fixed-rate step test with maximal cardiopulmonary exercise testing (CPET). One hundred and thirteen healthy adults executed a maximal CPET on bike, followed by a standardized fixed-rate step test 1 week later. During these tests, heart rate (HR) and VO₂ were monitored continuously. From the maximal CPET, the ventilatory threshold (VT) was calculated. Next, the physiological response between maximal CPET and step testing was compared. The step test intensity was 85 ± 24% CPET VO_2max and 88 ± 11% CPET HR_max (VO_2max and HR_max were significantly different between CPET and step testing; p < 0.01). In 41% of the subjects, step test exercise intensities >95% CPET VO_2max were noted. A greater step testing exercise intensity (%CPET VO_2max) was independently related to higher body mass index, and lower body height, exercise capacity (p < 0.05). Standardized fixed-rate step tests elicit vigorous exercise intensities, especially in small, obese, and/or physically deconditioned subjects. Medical supervision might therefore be required during these tests.