Trends in cardiorespiratory fitness: The evolution of exercise treadmill testing at a single Academic Medical Center from 1970 to 2012

To identify temporal trends in the use of exercise treadmill testing (ETT) and cardiorespiratory fitness (CRF) estimated by ETT in metabolic equivalents (METs).

We compiled an ETT database of all available treadmill tests-including those with concomitant stress echocardiography and nuclear perfusion imaging studies-performed at Duke University Hospital from January 1, 1970- December 31, 2012. Six different ramp protocols were used in these combined modalities. CRF at maximal exertion was estimated using established metrics. Eligible patients were required to have no missing data on maximal treadmill speed, grade, and protocol.

The most commonly used ETT protocol was the Bruce (n = 28,877), followed by manual test (n = 7390). Since the 1980's, the use of ETT for clinical purposes declined substantially; there was a decreased trend in utilization of 9.4% over the decades 1990-1999 and 2000-2009. When standard protocol (Bruce) was assessed in isolation, trends in CRF decreased progressively from 1970 to 2012 (mean METs (standard deviation): 11.7 (4.3) to 10.5 (3.5)). After adjusting for baseline comorbidities, the trend was reduced to a lesser degree.

The use of ETT at our institution has declined over time, perhaps due to changes in clinical practice. In patients undergoing ETT using the standard Bruce protocol, CRF decreased progressively over the last five decades. Future studies are needed to clarify the etiology of the decrease in use of such a powerful predictor of clinical outcomes in our medical care environment.