Validity of the step test for exercise prescription: no extension to a larger age range

Do assessments of cardiorespiratory and muscular fitness influence subsequent reported physical activity? A randomized controlled trial

BACKGROUND

Regular physical activity and exercise provide many health benefits. These health benefits are mediated in large part through cardiorespiratory fitness and muscular strength. As most individuals have not had an assessment of their personal cardiorespiratory fitness or muscular strength we investigated if measurements of cardiorespiratory fitness and muscular strength would influence an individual's subsequent self-reported exercise and physical activity.

METHODS

Volunteer subjects at a State Fair were randomized in 1:1 parallel fashion to control and intervention groups. The baseline Exercise Vital Sign (EVS) and type of physical activity were obtained from all subjects. The intervention group received estimated maximum oxygen uptake (VO2max) using a step test and muscular strength using a hand grip dynamometer along with age-specific norms for both measurements. All subjects were provided exercise recommendations. Follow up surveys were conducted at 3, 6 and 12 months regarding their EVS and physical activity.

RESULTS

One thousand three hundred fifteen individuals (656 intervention, 659 control) were randomized with 1 year follow up data obtained from 823 subjects (62.5%). Baseline mean EVS was 213 min/week. No change in EVS was found in either group at follow-up (p = 0.99). Subjects who were less active at baseline (EVS < 150) did show an increase in EVS (86 to 146) at 6 months (p < 0.05). At 3 months the intervention group increased resistance training (29.1 to 42.8%) compared to controls (26.3 to 31.4%) (p < 0.05). Lifestyle physical activity increased in the intervention group at 3 months (27.7 to 29.1%) and 6 months (25%) whereas it declined in the control group at 3 months (24.4 to 20.1%) and 6 months (18.7%) (p < 0.05).

CONCLUSION

Providing VO2max estimates and grip strength did not produce an increase in overall physical activity. The EVS and exercise recommendations did however produce an increase in physical activity in less active individuals. In a very active population the VO2max estimate and measured grip strength did increase lifestyle activity and resistance training. Wider adoption of these measures could be effective in promoting physical activity and resistance training.

TRIAL REGISTRATION

clinicaltrials.gov NCT03518931 Registered 05/08/2018 -retrospectively registered.

Validation of a single-stage fixed-rate step test for the prediction of maximal oxygen uptake in healthy adults

Healthcare professionals with limited access to ergospirometry remain in need of valid and simple submaximal exercise tests to predict maximal oxygen uptake (VO2max ). Despite previous validation studies concerning fixed-rate step tests, accurate equations for the estimation of VO2max remain to be formulated from a large sample of healthy adults between age 18-75 years (n > 100). The aim of this study was to develop a valid equation to estimate VO2max from a fixed-rate step test in a larger sample of healthy adults. A maximal ergospirometry test, with assessment of cardiopulmonary parameters and VO2max , and a 5-min fixed-rate single-stage step test were executed in 112 healthy adults (age 18-75 years). During the step test and subsequent recovery, heart rate was monitored continuously. By linear regression analysis, an equation to predict VO2max from the step test was formulated. This equation was assessed for level of agreement by displaying Bland-Altman plots and calculation of intraclass correlations with measured VO2max . Validity further was assessed by employing a Jackknife procedure. The linear regression analysis generated the following equation to predict VO2max (l min(-1) ) from the step test: 0·054(BMI)+0·612(gender)+3·359(body height in m)+0·019(fitness index)-0·012(HRmax)-0·011(age)-3·475. This equation explained 78% of the variance in measured VO2max (F = 66·15, P<0·001). The level of agreement and intraclass correlation was high (ICC = 0·94, P<0·001) between measured and predicted VO2max . From this study, a valid fixed-rate single-stage step test equation has been developed to estimate VO2max in healthy adults. This tool could be employed by healthcare professionals with limited access to ergospirometry.

Evaluating Variables as Unbiased Proxies for Other Measures: Assessing the Step Test Exercise Prescription as a Proxy for the Maximal, High-intensity Peak Oxygen Consumption in Older Adults

To assess validity of a low-intensity measure of fitness (X) in a population of older adults as a proxy measure for the original, high-intensity measure (Y), we used ordinary least square regression with the new, potential proxy measure (X) as the sole explanatory variable for Y. A perfect proxy measure would be unbiased (i.e., result in a regression line with a y-intercept of zero and a slope of one) with no error (variance equal to zero). We evaluated the properties of potential biases of proxy measures. A two degree-of-freedom approach using a contrast matrix in the setting of simple linear ordinary least squares regression was compared to a one degree-of-freedom paired t test alternative approach. We found that substantial improvements in power could be gained through use of the two degree-of-freedom approach in many settings, while scenarios where no linear bias was present there could be modest gains from the paired t test approach. In general, the advantages of the two degree-of-freedom approach outweighed the benefits of the one degree-of-freedom approach. Using the two degree-of-freedom approach, we assessed the data from our motivating example and found that the low-intensity fitness measure was biased, and thus was not a good proxy for the original, high-intensity measure of fitness in older adults.