You probably knew somebody who passed away from coronary heart disease or stroke. Such cardiovascular diseases account for 31% of deaths worldwide – more than anything else – and the frustrating thing is that most of these deaths are preventable by sticking to the fundamental tenets of a healthy lifestyle.
To prevent cardiovascular diseases, it’s useful to have tests that identify people who are at high risk of them. And while assessments of health are becoming ever more sophisticated, we simply don’t know much about how to interpret and act on the outputs of many of the novel tests that have emerged recently, as I wrote about briefly in this blog. The truth is that some very crude ways of assessing health (such as self-reported health) are probably actually much (much!) stronger predictors of future health outcomes than are far more costly avant-garde tests.
As I’m often on the lookout for new ways of assessing health, I’m always pleased when people identify effective, simple, and affordable health tests. So, I was pleased when Tommy Wood recently shared with me this new research by Professor Stefanos Kales’ team from the Department of Environmental Health at the Harvard School of Public Health. Soon after, Dan suggested I share some thoughts on it, so here goes!
To begin, what did Kales and his colleagues do?
Does push-up performance predict risk of cardiovascular diseases?
The researchers looked at the results of push-up tests completed by male firefighters* from Indiana fire departments between 2000 and 2007. The push-up test was a part of regular physical examinations, which included other fitness assessments, lifestyle questionnaires, and physiological tests.
In the push-up test, the firefighters had to do as many repetitions as possible, in time with a metronome set to 80 BPM. The test ended if they reached 80, missed three or more metronome beats, or stopped for other reasons, such as fatigue.
The scientists then split the firefighters into five categories** according to their push-up scores. To assess whether push-up scores predicted risk of dying from cardiovascular disease in the following 10 years, the researchers referred to a registry of firefighter deaths.
The results?
Men who can do the fewest push-ups have the greatest risk of cardiovascular disease
Compared with those who could do 10 push-ups or fewer at baseline, the incidence of cardiovascular disease was substantially lower in men who could do more push-ups***. In fact, cardiovascular disease incidence was 96% lower in men who could do more than 40 push-ups. Men who had the poorest push-up performance were also markedly more likely to die from cardiovascular events.
Compared with men who could do 10 push-ups or fewer, the incidence of cardiovascular disease was 96% lower in men who could do more than 40 push-ups
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The scientists also explored the results of tests of cardiorespiratory fitness completed by the firefighters****. Interestingly, push-up test results were more strongly predictive of future cardiovascular disease than cardiorespiratory fitness test performances were.
Perfect push-ups?
So, performance in a free test that can be completed almost anywhere predicts risk of future cardiovascular disease in young and middle-aged men.
Cool!
There are, however, some details that I’d like to place under the microscope.
First, this study doesn’t actually show that push-up performance is an independent predictor of cardiovascular events. At baseline, people who could do more push-ups had more healthy levels of established risk factors for cardiovascular disease – variables such as blood pressure and blood concentrations of lipids and sugar. To make this even more explicit, the people who were worse at push-ups at baseline already had worse cardiovascular health.
Likewise, people have come up with algorithms that use multiple cardiovascular disease risk factors to calculate a risk score***** that better predicts a person’s disease risk than is possible using a single risk factor (such as blood pressure), and we don’t know if adding push-ups to the algorithms would enhance the predictive accuracy of these scores.
Related to all of this, please don’t interpret the results as suggesting that getting better at push-ups will reduce your risk of disease! While it does seem to be the case that people who climb out of the pit of low cardiorespiratory fitness reduce their risk of death due to cardiovascular disease and other causes, Kales’ team’s study doesn’t show this.
Interestingly, the results show that push-up scores were more strongly related to future cardiovascular events than were cardiorespiratory fitness scores. However, the test of cardiorespiratory fitness wasn’t maximal. Instead, it estimated maximal cardiorespiratory fitness based on the men’s heart rate responses to a submaximal treadmill test, reducing the accuracy of the cardiorespiratory fitness scores. Honestly, it would surprise me (a lot) if we eventually find out that push-ups truly are more predictive of cardiovascular disease risk than cardiorespiratory fitness is.
The study also had quite a small sample size for one of this nature – in total, there were just 37 cardiovascular events among people who had push-up data. This probably explains a few of the slightly wonky results (don’t worry about specifics), and had there been more people then I’m certain that clearer differences would have emerged between several of the push-up groups.
This research adds to a strong body of evidence showing that higher strength fitness associates with lower risk of various diseases and therefore lower risk of dying from any cause. In general, scientists have previously focused on maximal grip strength or maximal knee extensor (quadriceps) strength. This latest study is a little different though, because push-ups are really a measure of strength-endurance, not maximal strength. And because of the determinants of performance in strength-endurance activities, I expect this capacity to more strongly associate with risk of cardiovascular disease than maximal strength******. And I anticipate that lower-body strength-endurance better predicts risk than upper-body strength endurance, particularly since 1) it’s so important to independence in old age (think about how you get up from a chair), and 2) lower-body strength seems to decline faster with age than upper-body strength does.
Finally, remember that this study was of young and middle-aged men only, so we shouldn’t automatically infer that similar results would have been found in women or elderly men, for example. This said, I see no reason why these findings wouldn’t hold for other populations, although the push-up might need to be modified for some people (very elderly people might be too weak to do a single push-up, for instance, and certain orthopedic issues will rule it out too).
Pushing on
To summarize, it seems that performance in the humble push-up might be a useful way to identify men who are at high risk for developing cardiovascular disease. So, if you’re a young or middle-aged man, why not give the test a go? You could then retest every six months or so and see whether your scores are going in the right direction. For those of you who want to try the test, here is what a good push-up looks like. Aim to standardize the days on which you do the test – do the push-ups when fresh, at the same time of day, and after consuming a similar diet each time.
Looking ahead, we’ll begin rolling out our humanOS physical activity program this year, and in our first course we dive into the many reasons that getting fitter is one of the best things most people can do for their health… watch this space!
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*Age 21 to 66 years at baseline (mean, 39.6 years). Mean body mass index (a measure of weight relative to height) at baseline, 28.7 kg/m2. The researchers included 1,104 firefighters in their analysis.
*The groups were 0 to 10, 11 to 20, 21 to 30, 31 to 40, and over 40 push-ups, respectively.
***This accounts for differences in the numbers of people in the different categories. Also, since age and body mass index affect both push-up scores and cardiovascular disease risk, the scientists adjusted for these variables in their analysis, implying that men who could do more push-ups didn’t have lower risk of cardiovascular disease simply because they were younger and leaner.
****A modified Bruce Protocol. In this test, maximal oxygen uptake (a measure of cardiorespiratory fitness) is estimated by heart rate responses to a submaximal incremental treadmill test. The scientists again divided the firefighters into five groups, this time according to estimated maximal oxygen uptake.
*****Such as the Framingham Risk Score.
******I recognize, of course, that strength-endurance is in part dependent on maximal strength: If you can squat 300 lbs once, you’ll be able to do more repetitions with 200 lbs than if you could only squat 220 lbs once.
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