Metabolic equivalents fail to indicate metabolic load in post-myocardial infarction patients during the modified Bruce treadmill walking test

Abstract

Aim To investigate the suitability of metabolic equivalents (METs) for determining exercise intensity in phase-IV post-myocardial infarction (MI) men during the modified Bruce treadmill walking test (MBWT). Methods Twenty phase-IV post-MI men (mean±SD, aged 64.4±5.8 years) and 20 healthy non-cardiac male controls (59.8±7.6 years) participated. Participants performed a MBWT. Throughout the participants' heart rate (HR), heart rhythm, expired air parameters and ratings of perceived exertion (RPEs) were measured. MET values were compared between groups and those currently ascribed to each stage of the MBWT. Results General linear model analysis found no significant differences between groups during the MBWT for VO 2, VCO 2, HR, METs or RPEs (Borg 6-20 scale). Ascribed METs did not differ from mean METs of post-MIs or controls other than at stage 5 where post-MI METs were significantly lower. Irrespective, the post-MI group worked at a higher percentage of their anaerobic threshold (AT) (respiratory exchange ratio, RER=1.0) (F (2,5) =7.22, p<0.008), higher RER (F (2,5) =11.25, p<0.001) with increased breathing frequency (F (2,5) =7.22, p<0.001). Regression analysis revealed AT to be VO 2 25.6 (mL/kg/min) for post-MI versus VO 2 31.1 (mL/kg/min) for controls. Gross energy expenditure (kcal/min) was greater for the post-MI group compared with controls (F (2,5) =11.22, p<0.001). Throughout the MBWT, post-MI group worked at a higher %AT/MET than controls (F (2,196) =211.76, p<0.01). Body composition did not strongly influence %AT/MET, parameters of VO 2, METs or RPE. Conclusion During the MBWT, post-MI men worked more anaerobically per MET (%AT/MET) than controls. Therefore, current METs based on non-cardiac individuals appear unsuitable in determining the full metabolic load of the exercise intensity for cardiac patients during the MBWT.