Change in Submaximal Cardiorespiratory Fitness and All-Cause Mortality Louise de Lannoy, MSc; Xuemei Sui, MD, PhD; Carl J. Lavie, MD; Steven N. Blair, PED; and Robert Ross, PhD Abstract Objective: To evaluate the relationship between change in submaximal cardiorespiratory fitness (sCRF) and all-cause mortality risk in adult men and women. Patients and Methods: A prospective study with at least 2 clinical visits (mean follow-up time, 4.23.0 years) between April 1974 and January 2002 was conducted to assess the relationship between change in sCRF and mortality risk during follow-up. Participants were 6106 men and women. Submaximal CRF was determined using the heart rate obtained at the 5-minute mark of a graded maximal treadmill test used to determine maximal CRF (mCRF). Change in sCRF from baseline to follow-up was categorized into 3 groups: increased fitness (decreased heart rate, <4.0 beats/min), stable fitness (heart rate, 4.0 to 3.0 beats/min), and decreased fitness (increased heart rate, >3.0 beats/min). Results: The mean change in sCRF at follow-up for all 6106 study participants was 0.510.0 beats/ min, and the mean change in mCRF was 0.31.4 metabolic equivalents. Change in sCRF was related to change in mCRF, though the variance explained was small (R 2 ¼0.21; P<.001). The hazard ratios (95% CIs) for all-cause mortality were 0.60 (0.38-0.96) for stable and 0.59 (0.35-1.00) for increased sCRF compared with decreased sCRF after adjusting for age, change in weight, and other common risk factors for premature mortality. The hazard ratios for changes in sCRF and mCRF were not significant after adjusting for changes in mCRF (P¼.29) and sCRF (P¼.60), respectively. Conclusion: A simple 5-minute submaximal test of CRF identified that adults who maintained or improved sCRF were less likely to die from all causes during follow-up than were adults whose sCRF decreased. ª 2017 Mayo Foundation for Medical Education and Research n Mayo Clin Proc. 2017;nn(n):1-7 O verwhelming evidence has estab- lished that maximal cardiorespira- tory fitness (mCRF) predicts cardiovascular disease (CVD) and all-cause mortality beyond risk factors commonly ob- tained in clinical examinations. 1 Despite this evidence, measurement of mCRF has not been widely adopted in clinical practice with barriers including the need for expensive testing systems, specialized personnel, and time. 2,3 A potential alternative to measures of mCRF include tests of submaximal CRF (sCRF). Relatively short (3-5 minutes) tests of sCRF overcome the barriers associated with the measurement of mCRF and may offer a pragmatic alternative to obtain objective measures of CRF in clinical settings. Although objective assessment of sCRF is straightforward, routine measurement in clinical practice competes for the limited time available in a busy office practice. There- fore, sCRF should be measured only if it can provide additional information that influences patient management. We posited that mea- sures of sCRF, in particular the change in heart rate during submaximal exercise, would uniquely reflect cardiovascular adaptations in response to physical activity and thus predict mortality risk above and beyond traditional risk factors. Furthermore, because changes in sCRF are only modestly related to correspond- ing changes in mCRF, 4 we hypothesized that change in sCRF would predict mortality risk independent of change in mCRF. To test our hypotheses we used data from the Aerobics Center Longitudinal Study, which provides the opportunity for the first time to evaluate the relationship between changes in sCRF and mortality in a cohort of From the School of Kine- siology and Health Studies (L.D.L.) and School of Medicine, Division of Endocrinology and Meta- bolism (L.D.L., R.R.), Queen’s University, King- ston, Ontario, Canada; Department of Exercise Science, Arnold School of Public Health, University of South Carolina, Columbia (X.S., S.N.B.); and Department of Car- diovascular Diseases, John Ochsner Heart and Vascular Institute, Ochsner Clinical School, The Uni- versity of Queensland School of Medicine, New Orleans, Louisiana (C.J.L.). ORIGINAL ARTICLE Mayo Clin Proc. n XXX 2017;nn(n):1-7 n https://doi.org/10.1016/j.mayocp.2017.11.020 www.mayoclinicproceedings.org n ª 2017 Mayo Foundation for Medical Education and Research 1