1. Appropriateness of the metabolic equivalent (MET) as an estimate of
School of Sport and Exercise Sciences, University of Kent, The Medway Building, Chatham Maritime, Kent. ME4 4AG
Appropriateness of the metabolic equivalent (MET) as an estimate of
exercise intensity for post-myocardial infarction patients
K.Woolf-May & S.N. Meadows
Introduction
Exercise is an important intervention used in cardiac rehabilitation to improve patient health outcomes and for secondary prevention of cardiac and other co-morbidities. In recent times there has been some debate amongst researchers and practitioners over the use of equations and indices, which are mainly based on healthy individuals, to estimate exercise intensity. Often these are used to provide assistance with exercise prescription and/or to establish exercise capacity for risk stratification purposes, in settings like cardiac rehabilitation. The metabolic equivalent (MET) is one such metric.
1 MET ~ VO2 of 3.5 ml.kg.min
Results
Significantly lower HR values in post-MI participants that were related to β-blocker medication (F (2,5)=18.47, p<0.01), with significantly higher VCO2/VO2 (F (2,5)=11.25, p<0.001) and gross kcals/LO2/min (F (2,5)=11.25, p<0.001). Analysis comparing lines of regression showed, during the CET: post-MI participants worked at higher percentage of their anaerobic threshold (%AT)/MET (F (2,90)=18.98, p<0.001), as well as during active recovery (100–50 W) (F (2,56)=20.81, p<0.001); during seated recovery: GLM analysis showed significantly higher values of VCO2/VO2 for post-MI participants compared with non-cardiacs (F (2,3)=21.48, p=0.001) as well as gross kcals/LO2/min (F (2,3)=21.48, p=0.001).
Study Aims
Whether during exercise metabolic equivalents (METs) appropriately indicate the intensity and/or metabolic cost for post-myocardial infarction (MI) males.
Whether post-exercise VO2 parameters provide insight into the intensity and/or metabolic cost of the prior exercise.
Methods
15 male phase-IV post-MIs (64.4±6.5 years) and 16 apparently healthy males (63.0±6.4 years) were recruited. Participants performed a graded cycle ergometer test (CET) of 50, 75 and 100 W, followed by 10 min active recovery (at 50 W) and 22 min seated recovery. Heart rate (bpm), expired air parameters (VO2, VCO2) and Borg (6 – 20) ratings of perceived exertion (RPE), the latter for exercise only, were measured.
Figure 1. Percentage of anaerobic threshold-metabolic equivalent (MET) relationship during cycle ergometry, active and seated recovery for post-MI vs non-cardiacs
Conclusion
METs take no consideration of any anaerobic component, therefore failing to reflect the significantly greater anaerobic contribution during exercise per MET for phase-IV post-MI patients. Given the anaerobic component will likely be greater for those with more severe forms of cardiac disease, current METs should be used with caution when determining exercise intensity in cardiac patients.
Limitations
MET investigation studies need to be extended to other cardiac populations beyond male post-MIs. Females and older cardiac groups need to be investigated and informed. This study utilised cycling, which is not the norm exercise mode used in Phase III and IV cardiac rehabilitation classes. Lactate measurement should be incorporated to better quantify anaerobic component.
Further Research Recommendations
Similar investigations need to be conducted using popular Phase III and IV exercise modes, e.g. circuit training, gym-based training, walking, and across a greater range of cardiac patients.
Table 1. Participant resting characteristics
Post-MIs (n=15)
Mean±SD (range)
Non-cardiacs (n=16) mean±SD (range)
Age (years)
64.4±6.5 (53-73)
63.0±6.4 (51-73)
Body mass (kg)
88.4±13.5 ( )
83.1±10.5 ( )
BMI (kg.m2)
27.7±3.7 ( )
26.6±3.2 ( )
HR (bpm)
58.7±7.4 (48-73)
70.3±(55-89)
VO2 (ml.kg.min)
3.47±0.57 ( )
3.61± ( )
VCO2 / VO2 (L/min)
1.02±0.18 ( )
0.96±0.24 ( )
kcal.LO2.min
5.25±0.13 ( )
5.25±0.08 ( )
References
Meadows, S., Woolf-May, K., Kearney, E. (2013) Metabolic equivalents for post-myocardial infarction patients during a graded treadmill walking test. JEPOnline, 16(2):
Woolf-May, K. & Meadows, S. (2016) Appropriateness of the metabolic equivalent (MET) as an estimate of exercise intensity for post-myocardial infarction patients. BMJOpen Sport Exerc Med 2016; 1:e doi: /bmjsem
Woolf-May, K., Meadows, S., Ferrett, D. & Kearney, E. (2017) Metabolic equivalents (METs) fail to indicate metabolic load in post-myocardial infarction patients during the modified Bruce treadmill walking test. BMJOpen Sport Exerc Med 2017; 2:e ; doi: /bmjsem