The Acute Physiological Responses to a University Step Aerobics Session

The Sport and Recreation Service of Glasgow University has introduced a step aerobics class called "Uni-Step" to its range of exercise classes. It has been suggested that step aerobics is a suitable exercise modality for developing cardiovascular fitness and for promoting weight loss in healthy adults. These assumptions are based on the specific step heights and choreography utilised in previous studies. Exercise intensity is commonly estimated using heart rate (HR) or Ratings of Perceived Exertion (RPE); however, neither may accurately predict intensity during step aerobic exercise. The aim of this study was to provide cardiovascular and metabolic data for Uni-Step at three different step heights, and to evaluate the use of heart rate (%HR max), %Heart Rate Reserve (%HRR) and RPE for the estimation of exercise intensity during this mode. Ten healthy females (22 +/- 2.2 years) (mean +/- S.D.), who were regular participants in step aerobics, performed a 40 minute Uni-Step routine as demonstrated on a TV monitor, on a 6" (15.2 cm), 8" (20.3 cm) and 10" (25.4 cm) step (STEP6, STEP8 and STEP10) on separate occasions. The order of testing was randomised. Oxygen uptake (VO2), HR and RPE were recorded throughout each test. Expired air was collected continuously in Douglas bags (12 samples). Heart rate was recorded every 15 s using a Polar 4000 portable heart rate monitor. RPE was measured 30 s before the end of each sample of expired air using the Borg 6 - 20 scale. Total energy expenditure was estimated using the Weir formula (Weir, 1949). Maximum oxygen uptake and maximum heart rate were determined using a continuous treadmill protocol. All four tests took place within a three week period. Repeated measures analysis of variance showed a significant increase (P < 0.001) in mean VO2, mean HR, mean RPE and total energy expenditure with each increase in step height. These results are summarised in Table 1. Correlations indicated a strong positive relationship between %VO2max and HR (r = 0.90 at STEP6, 0.94 at STEPS and 0.96 at STEP10 for both %HR max and %HRR) and a less good relationship between %VO2max and RPE (r = 0.61 at STEP6, 0.66 at STEP8 and 0.79 at STEP10) (r values are median correlation coefficients for all ten subjects). Table 1. Oxygen uptake (VO2), heart rate (HR), ratings of perceived exertion (RPE) and total energy expenditure (means and standard deviations) at each step height. According to the American College of Sports Medicine recommendations (A.C.S.M., 1990), Uni-Step, when performed on STEP8 and STEP10, is of a sufficient relative intensity to maintain or improve cardiovascular fitness. STEP6 could perhaps be of value to participants of a low fitness level. Heart rate exhibited a strong positive correlation with VO2, however, the mean heart rate responses suggested an overestimation of the actual metabolic cost of exercise at all three step heights during this mode (McArdle et al, 1994), and therefore caution would be advised if used as a predictor of intensity. The low correlations between %VO2max and RPE at STEP6 and STEP8 indicate that the use of RPE to prescribe intensity may have limitations. Uni-Step meets well recognised guidelines (A.C.S.M., 1990; Haskell, 1985; Haskell et al, 1985) for promoting changes in body composition when performed at STEP8 and STEP10.