We did not find that estimates of CRF and MF increased total physical activity over the subsequent year as measured by the EVS. We did find a significant increase in both lifestyle exercise and resistance type exercise in an already very physically active population. Having a below norm grip strength was associated with a significant increase in resistance training throughout the subsequent year. We found that individuals not meeting current recommended physical activity recommendations (EVS < 150 minutes/week) showed a significant increase in their EVS at 6 months of follow up. This study indicates that recording EVS, providing exercise recommendations and estimating CRF and MF could provide both a useful incentive to stimulate greater interest in exercise, lifestyle physical activity and resistance training. To our knowledge no other study has investigated the effect on subsequent physical activity of VO2max estimates or grip strength.
Recognizing the importance of exercise and physical activity to good health, the Surgeon General and others have called for regular assessments of an individual’s physical activity. The National Physical Activity Plan asks healthcare systems to prioritize physical activity assessment, advice, and promotion and regularly assess physical activity as a "vital sign" . The EVS has been advocated as a tool to help accomplish this goal. We used the EVS to quantify the exercise activity in our subjects. It is easily calculated with just two questions and corresponds to current exercise guidelines recommending 150 minutes of moderately vigorous physical activity per week. The EVS has been shown to under-report physical activity measured by accelerometer and may best be employed to identify individuals not meeting current physical activity guidelines. Other limitations of using the EVS are the absence of a specific time frame and the inability to differentiate exercise intensity.
Our study population was done in random self-selected volunteers. These volunteers were already very physically active as indicated by the mean EVS of 223.2 with a median value of 180, significantly exceeding current exercise recommendations. The high level of pre-existing physical activity likely attenuated the impact of the fitness measurements on their future physical activity and limited the utility of the EVS as a measurement tool. We did find, however, that the subjects not meeting current physical activity guidelines did exhibit a significant increase in their reported EVS at 6 months. Both the control and intervention groups exhibited this increase indicating that recording the EVS and providing information on current exercise recommendations likely influenced this change. This observation validates calls for recording exercise as a vital sign. It has previously been reported that systematically recording the EVS during outpatient visits was associated with significant changes in exercise-related clinical counseling and documentation (30).
In addition to obtaining the EVS we recorded the types of physical activity both initially and in follow up. We found that the intervention group significantly increased their reported resistance training and lifestyle physical activity relative to controls at 3-months follow-up, despite the much less favorable climate for these activities during winter. The increase in lifestyle activity was sustained at 6 months follow up. A significant increase in resistance training was observed throughout the following year in those individuals with a reported grip strength less than the reported norm. Below norm grip strength appears to stimulate interest in strength training activities in this already very active population. At baseline, 88% of our study population reported participating in some form of cardiovascular exercise but only 28% reported participation in resistance type exercise. This lower level of resistance training is consistent with prior surveys showing only 21.9% of Americans meet muscle strengthening guidelines. This provides greater potential for our assessments and recommendations to have an impact on resistance exercise activity. We did not observe that those subjects with grip strength below the norm increased their EVS even though they did increase their resistance training.
Cardiorespiratory Fitness as measured by VO2max is an important indicator of overall health and has significant prognostic implications. Recognizing the significance of CRF the American Heart Association has called for the inclusion of CRF measurement or estimation in routine clinical practice. Despite its importance it is not typically measured in a clinical encounter. This relates to the difficulty of formal VO2max measurements. Other forms of estimating VO2max such as maximal or sub-maximal treadmill or bicycle exercise testing are also not suited to routine use. VO2max can easily be estimated by several formulas based on demographics and reported exercise habits . Estimating CRF from one of these formulas has been associated with CVD and all-cause mortality independent of other risk factors. The estimated CRF from formulas however are significantly influenced by the subjective reporting of exercise activity. We elected to use a step test that had been previously validated in a geriatric population. This test in younger individuals and other populations has been found to be less accurate in the measured VO2max yet still felt to be useful in classifying CRF. When this step test has been used to measure CRF to aid in exercise prescription a significant improvement in VO2max at 12 months was found compared with baseline measures.
We felt that providing a CRF estimate requiring actual physical activity using the step test would positively influence future exercise behavior relative to no measurement. We did not observe significant changes in the EVS in either the control group or the intervention group over one year of follow up. The fitness assessments did not appear to influence this very active population’s physical activity as measured by the EVS. We also did not observe an increase in follow up EVS in those individuals who were reported to have an estimated VO2max below the provided norm even when the norm was increased from “good” to “superior”.
We used a hand-grip dynamometer to estimate muscular strength. This test is inexpensive, convenient and previously demonstrated in multiple studies to be a clinically significant marker of sarcopenia and correlate with lower extremity muscle power and mobility (20). In a large longitudinal population study, measurement of grip strength was found to be a simple, inexpensive risk-stratifying method for all-cause death, cardiovascular death, and CVD (21). Grip strength is predictive of mortality in both young adults and middle age. Low grip strength has been documented to correlate with increased disability in the elderly, greater risk for hospitalization, cognitive decline and nutritional status. We used grip strength to estimate MF and felt that this measurement would contribute to increased physical activity and resistance training. We did observe an increase in resistance training but not total exercise time. The increase in resistance exercise was largely driven by those individuals with grip strength below norm. Given the overall high level of baseline physical activity and lower level of resistance training at baseline it appears that having a below norm grip strength shifted physical activity to resistance training from other activities.
The strengths of this study are its size and diversity. The study participants exhibited a wide range of age (18–92 mean 46) and BMI (16–61, mean 25) but were predominately white (92.3%).
The study limitations were the self-selected population that was already very active as exhibited by the high baseline EVS. In this active group the EVS may have been less accurate in measuring their physical activity. This active group may have been more receptive to feedback on their CRF and MF accounting for the short term significant increases in the lifestyle and resistance physical activity but with less potential to observe an increase in EVS over time. The results are also limited by follow up data being provided from only 62.5% of the study population. We also did not perform follow up CRF or MF measurements.
In summary we did not find that our measurements of CRF and MF using a step test and grip strength increased overall exercise or physical activity as measured by the EVS during the ensuing year. The utility of our intervention was likely limited by a self-selected very active population. Less active individuals in both the control and intervention groups (those not meeting current exercise guidelines) did significantly increase their reported exercise activity at 6 months. We found that the fitness measurements appeared to stimulate an increase in lifestyle and resistance training exercise at short term follow up and that the increase in resistance training was largely driven by those having a below norm grip strength. This indicates a potential benefit of recording the EVS and providing current exercise recommendations to less active individuals. Even very active individuals may benefit from measuring grip strength and providing norms to stimulate greater participation in resistance training activities. Given these encouraging improvements in exercise activity it may be useful to more widely record EVS and perform CRF and MF estimates.