Research challenges how we prescribe exercise for cardiac patients
17 January 2017
A new study questions the safety of medical indicators currently used to measure exercise intensity levels for cardiac patients.
Dr Kate Woolf-May, a Reader in Health and Clinical Exercise Sciences at Canterbury Christ Church University, has spent over a decade researching metabolic equivalents (MET) which are used to determine exercise intensity and for the prescription of exercise for cardiac rehabilitation. Results published from her latest studies in the BMJ Open Sports and Exercise Medicine Journal challenges the standard testing procedures for determining exercise intensity in cardiac patients.
Dr Woolf-May explains: “My research shows that METs are not suitable as markers to determine exercise intensity for people recovering from heart attacks. Although the MET is used internationally to determine exercise capacity in cardiac patients, this indicator significantly underestimates the anaerobic demand of exercise upon a cardiac patient. The results show that even for relatively physically active people who have previously had a heart attack, during exercise they work at a higher percentage of their anaerobic threshold, putting a greater strain upon the body. Using a medical marker, such as MET, that does not detect the anaerobic component of exercise should be used with great caution on any cardiac patient.”
MET values are used to determine exercise intensity, as well as for prescribing exercise. As exercise intensity increases the MET value also increases. For example, light intensity exercise, for example walking at 2.5mph is about 3.0 METs; moderate intensity exercise, normally used in public health physical activity recommendations is regarded as being within the range of 3.0 – 6.0 METs and vigorous intensity exercise around 6.0+ METs.
At rest and during exercise energy sources are a mix of aerobic and anaerobic, but mainly aerobic in sustained exercise. As exercise intensity increases the anaerobic component becomes greater. As exercise intensity continues to increases and the balance shifts towards anaerobic metabolism, exercise is termed above the anaerobic threshold (AT). Exercise beyond this point cannot be maintained for very long as fatigue will set in. It is known that those with cardiac disease reach the point of AT sooner than non-cardiac individuals and the more severe the disease the sooner this point is reached.
METs only account for oxygen uptake, and not carbon dioxide production – an indicator of anaerobic metabolism. Therefore, METs are unable to determine the anaerobic component of exercise. Anaerobic metabolism puts a greater strain on the body and for someone with heart disease, if not detected could be highly risky.
Dr Woolf-May concluded: “The findings of the various studies that I and my team have conducted over the years clearly showed that cardiac patients and healthy individuals do not respond similarly to the same amount of physical exercise. Due to these results we would now recommend that a new approach is adopted when prescribing exercise to cardiac patients.”
Read the published report in the BMJ Open Sports and Exercise Medicine.
Notes to editors
Canterbury Christ Church University
Canterbury Christ Church University is a modern university with a particular strength in higher education for the public services.
With 17,000 students across Kent and Medway, its courses span a wide range of academic and professional subject areas.
- 96% of our UK undergraduates were in employment or further studies six months after completing their studies*.
- We are one of the South East’s largest providers of education, training and skills leading to public service careers.
*2014/15 Destinations of Leavers from Higher Education survey