What's the point of vigorous exercise?

With all the research showing that short, high intensity intervals are effective in improving fitness, and how 30 minutes of moderate intensity level exercise is effective in improving your health, you may well be asking yourself if there is any point in engaging in high amounts of vigorous exercise activity. Well, if you are asking yourself this question, I've got something for you.

We know that active people have about a 30% reduced risk for developing cardiovascular disease compared with inactive individuals. , but is there any evidence that vigorous activity confers any additional protection? The research that has been done hasn't really controlled for the duration of activity, or total energy expenditure. However, new research out this month looks at this issue. The purpose of the study by Andrea Chomistek at the Harvard School of Public Health and colleagues was to look at the relationship between vigorous intensity physical activity compared with moderate intensity activity and the risk of major chronic disease in men. In addition, they looked to see if there was an incremental relationship between the total amount of vigorous activity and risk of disease. That is, if you increase the amount of physical activity you do, does it increase your protection - or is there another kind of relationship, say it gives you more protection if you do 20 minutes of vigorous activity, but any more than that is a waste of time, because it doesn't give you any further benefit.

This study looked prospectively at these relationships among 44,551 men aged 40-75 years old in 1986. Their leisure time activity once collected every two years between 1986 and 2006 through questions on average total time per week spent on each of ten activities. Walking pace - casual (<2miles/hour), normal (2-2.9miles/hour), brisk (3-3.9 miles/hour), or striding (>=4miles/hour) was also assessed. A MET score was assigned to each activity - which essentially gives you an idea of the activity's energy cost, and there are set methods for assessing this. During these 22 years of follow-up, the researchers document 14,162 cases of major chronic disease, ranging from cardiovascular events, cancers, and deaths from other causes.

The results suggested that once risk factors like weight and smoking were accounted for, vigorous-intensity physical activity was linked to decreased risk of major chronic disease and cardiovascular disease. Moderate-intensity physical activity was also associated with decreased risk, but the association was weaker. When the activities were looked at individually, the results showed that running, tennis and brisk walking were each associated with lowered cardiovascular disease risk. There was no link detected between either vigorous or moderate-intensity physical activity levels and risk of cancer.

This study might underestimate the potential benefit of vigorous levels of activity. For many of the activities measured, there was no way to assess the intensity at which they were performed e.g. cycling and swimming. Some may have performed them at a truly vigorous intensity, whereas others may have been performing the same activity at lower levels of intensity. This probably lowers the ability to differentiate between the effects of vigorous and moderate intensity physical activity. Where they did have the intensity data, the researchers found a strong inverse relationship with cardiovascular risk - the more intense the activity, the lower the risk of cardiovascular disease.

Is too much vigorous-intensity exercise bad for you? What about marathon running? 

A really interesting angle on this study was examining if too much vigorous-intensity activity is harmful. One recent study on marathon runners and coronary artery calcification (CAC) found that a CAC score of >=100 was present in 36% of runners and CAC score amongst marathoners exceeded that in control subjects, matched for age and cardiovascular risk. A CAC score above 100 indicates increased burden on the heart. Furthermore, CAC burden and frequent marathon running were correlated with subclinical myocardial damage - meaning a potentially higher coronary heart disease risk than you would otherwise think. Another study found that 50% of older lifelong endurance athletes showed evidence of myocardial fibrosis - whereas aged matched control and younger athletes had none.

This current study found no evidence of increased cardiovascular risk for high amounts of vigorous-intensity physical activity - even for men in the top 1-2% of vigorous activity. They even found that running for 5 or more hours a week was associated with the lowest cardiovascular risk. 

Although the authors suggest that this should be reassuring for long-distance runners, they cannot exclude the possibility that more extreme levels of activity reported by this population of middle-aged and older men might be harmful to health, and increased risk of chronic disease.