How Accurately are Maximal Metabolic Equivalents Estimated Based on the Treadmill Workload in Healthy People and Asymptomatic Subjects with Cardiovascular Risk Factors?

Abstract

Maximal exercise capacity expressed as metabolic equivalents (METs) is rarely directly measured (measured METs; mMETs) but estimated from maximal workload (estimated METs; eMETs). We assessed the accuracy of predicting mMETs by eMETs in asymptomatic subjects. Thirty-four healthy volunteers without cardiovascular risk factors (controls) and 90 patients with at least one risk factor underwent cardiopulmonary exercise testing using individualized treadmill ramp protocols. The equation of the American College of Sports Medicine (ACSM) was employed to calculate eMETs. Despite a close correlation between eMETs and mMETs (patients: r = 0.82, controls: r = 0.88; p < 0.001 for both), eMETs were higher than mMETs in both patients [11.7 (8.9 – 13.4) vs. 8.2 (7.0 – 10.6) METs; p < 0.001] and controls [17.0 (16.2 – 18.2) vs. 15.6 (14.2 – 17.0) METs; p < 0.001]. The absolute [2.5 (1.6 – 3.7) vs. 1.3 (0.9 – 2.1) METs; p < 0.001] and the relative [28 (19 – 47) vs. 9 (6 – 14) %; p < 0.001] difference between eMETs and mMETs was higher in patients. In patients, ratio limits of agreement of 1.33 (*/÷ 1.40) between eMETs and mMETs were obtained, whereas the ratio limits of agreement were 1.09 (*/÷ 1.13) in controls. The ACSM equation is associated with a significant overestimation of mMETs in young and fit subjects, which is markedly more pronounced in older and less fit subjects with cardiovascular risk factors.

Key words

exercise capacity - peak oxygen consumption - metabolic equivalents - treadmill

References

• 1 Agostoni P, Bianchi M, Moraschi A, Palermo P, Cattadori G, La Gioia R, Bussotti M, Wasserman K. Work rate affects cardiopulmonary exercise test results in heart failure.  Eur J Heart Fail. 2005;  7 498-504
• 2 American College of Sports Medicine .Guidelines for Exercise Testing and Prescription. 6th edn. Baltimore; Lippincott-Williams & Wilkins 2000
• 3 Bland J M, Altman D G. Statistical methods for assessing agreement between two methods of clinical measurement.  Lancet. 1986;  1 307-310
• 4 Fletcher G F, Balady G J, Amsterdam E A, Chaitman B, Eckel R, Fleg J, Froelicher V F, Leon A S, Pina I L, Rodney R, Simons-Morton D G, Williams M A, Bazzare T. Exercise standards for testing and training: a statement for healthcare professionals from the American Heart Association.  Circulation. 2001;  104 1694-1740
• 5 Gulati M, Pandey D K, Arnsdorf M F, Lauderdale D S, Thisted R A, Wicklund R H, Al-Hani A J, Black H R. Exercise capacity and the risk of death in women.  Circulation. 2003;  108 1554-1559
• 6 Maeder M, Wolber T, Atefy R, Gadza M, Ammann P, Myers J, Rickli H. A nomogram to select the optimal treadmill ramp protocol in subjects with high exercise capacity: validation and comparison with the Bruce protocol.  J Cardiopulm Rehabil. 2006;  26 16-23
• 7 Mancini D M, Eisen H, Kussmaul W, Mull R, Edmunds Jr L H, Wilson J R. Value of peak exercise oxygen consumption for optimal timing of cardiac transplantation in ambulatory patients with heart failure.  Circulation. 1991;  83 778-786
• 8 McConnell T R. Oxygen uptake. When to measure and when to estimate.  J Cardiopulm Rehabil. 2003;  23 190-192
• 9 Myers J. Applications of cardiopulmonary exercise testing in the management of cardiovascular and pulmonary disease.  Int J Sports Med. 2005;  26 (Suppl 1) S49-S55
• 10 Myers J. Optimizing the clinical exercise test: a commentary on the exercise protocol.  Heart Fail Monit. 2004;  4 82-89
• 11 Myers J, Bader D, Madhavan R, Froelicher V. Validation of a specific activity questionnaire to estimate exercise tolerance in patients referred for exercise testing.  Am Heart J. 2001;  142 1041-1046
• 12 Myers J, Buchanan N, Walsh D, Kraemer M, McAuley P, Hamilton-Wechsler M, Froelicher V. Comparison of the ramp versus standard exercise protocols.  J Am Coll Cardiol. 1991;  17 1334-1342
• 13 Myers J, Gullestad L, Vagelos R, Do D, Bellin D, Ross H, Fowler M B. Clinical, hemodynamic and cardiopulmonary exercise test determinants of survival in patients referred for evaluation of heart failure.  Ann Intern Med. 1998;  129 286-293
• 14 Myers J, Prakash M, Froelicher V, Do D, Partington S, Atwood J E. Exercise capacity and mortality among men referred for exercise testing.  N Engl J Med. 2002;  346 793-801
• 15 Nevill A M, Atkinson G. Assessing agreement between measurements recorded on a ratio scale in sports medicine and sports science.  Br J Sports Med. 1997;  31 314-318
• 16 Pollock M L, Bohannon R L, Cooper K H, Ayres J J, Ward A, White S R, Linnerud A C. A comparative analysis of four protocols for maximal treadmill stress testing.  Am Heart J. 1976;  92 39-46
• 17 Roberts J M, Sullivan M, Froelicher V F, Genter F, Myers J. Predicting oxygen uptake from treadmill testing in normal subjects and coronary artery disease patients.  Am Heart J. 1984;  108 1454-1460
• 18 Sullivan M, McKirnan M D. Errors in predicting functional capacity for postmyocardial infarction patients using a modified Bruce protocol.  Am Heart J. 1984;  107 486-491