Moderately frequent strenuous activity can reduce cardiovascular risk in patients with stable coronary heart disease (CHD) but daily strenuous activity may increase risk although not as much as no exercise at all, a study in Heart suggests.

The study analysed data from a prospective cohort of 1,038 subjects with stable CHD. The majority of the participants were male, over 60 (median 61 years), overweight, current or former smokers and had a history of myocardial infarction and hypertension.

The frequency of self-reported strenuous physical activity during leisure time was assessed repeatedly over ten years of follow-up.

Around 40% said they were physically active 2-4 times a week, 30% reported higher frequency (around 15% daily and 15% 5-6 times a week) and 20% lower frequency, 1-4 times a month, while 10% were rarely or never strenuously physically active.

Multiple Cox proportional hazards regression models were used to assess the association of physical activity level with major cardiovascular events, cardiovascular mortality and all-cause mortality.

There was a general decline in physical activity in the high frequency exercisers and the never or rarely group over follow-up although the proportion who engaged in physical activity 2-4 times a week remained the same.

For all outcomes, the highest hazards were consistently found in the least active patient group with almost a four-fold increased risk for both cardiovascular and all-cause mortality compared with the reference group of moderately frequent active patients: adjusted HR 3.39 (95% CI:1.62-7.10) and 3.81 (95% CI:2.17-6.70) respectively.

The most frequently active patients also had an increased risk of cardiovascular and all-cause mortality: adjusted HR 2.37 (95% CI:1.05-5.34) and 1.77 (95% CI: 0.90-3.47) respectively for those who exercised daily. However, this increase in risk was still modest compared with the risk in the inactive group.

It is accepted wisdom that exercise is beneficial in patients with established coronary disease and guidelines recommend between 30 and 60 minutes of moderate intensity aerobic activity, such as brisk walking, at least five days per week.

The mechanism for the increase in risk with daily strenuous activity compared with lesser degrees of exercise is unclear. It may be that vigorous exercise increases the risk of ventricular arrhythmias and sudden cardiac death during or after exertion, especially in adults with heart conditions.

However, a major limitation of this particular study is the relatively crude assessment of physical activity based on self-reporting.

Therefore, the message for our patients with stable CHD is that no exercise is bad for you and increases the risk of cardiovascular and all-cause mortality but it is important not to overdo it as daily strenuous physical activity also appears to increase the risk. The best way forward is to be moderately active to obtain the optimal benefit from exercise.

Dr Peter Savill