Struggling to do push-ups? You may be at risk of hea...

"How many push-ups you can do could predict your risk of heart disease," the Metro reports.

The headline is prompted by a new study involving around 1,000 male firefighters (average age 40) from Indiana in the US, who attended regular physical and medical assessments during a 10-year period.

Perhaps unsurprisingly, the more risk factors for heart disease or stroke a person had, such as smoking, being overweight, or having high blood pressure or cholesterol, the lower their exercise capacity.

About 3% of men developed heart disease during follow-up. The researchers calculated that the more push-ups a person did, the lower their risk of heart disease.

Forty push-ups was the magic number reported in the media, but in fact being able to do any number over 10 press-ups (the comparison group) had a lower risk.

There are many limitations to this research, including the specific sample of US firefighters and the low rate of heart disease.

Risk assessments based on small numbers are more likely to give chance findings.

Push-up capacity may be a marker for physical fitness and health, and we know exercise is good for the heart.

But doing 40 push-ups a day will not do you much good if you're neglecting your health in other ways, such as smoking, eating a poor diet and drinking too much alcohol.

Where did the story come from?

This study was conducted by researchers from the Chan School of Public Health and Harvard Medical School in the US, and other institutions in the US and Europe.

Funding was provided by the National Institute for Occupational Safety and Health, the Harvard Education and Research Center for Occupational Safety and Health, and grants from the FEMA Assistance to Firefighters and the Department of Homeland Security.

The article was published in the peer-reviewed journal JAMA Network Open, and is freely available to access online.

The UK media has rather overexaggerated these findings by applying them to all men in general, whereas the study only involved a small sample of US firefighters.

Both the Metro and the Daily Mirror highlighted the result of 40 push-ups being "the magic number" for preventing heart disease, but in fact being able to do 10 or more push-ups was also associated with lower heart disease risk.

What kind of research was this?

This was a cohort study of male firefighters from Indiana in the US who attended clinical examinations that included assessments of their exercise capacity.

They then analysed whether how many push-ups they could do was associated with subsequent cardiovascular disease (such as heart disease or stroke).

With such a study design it's hard to attribute push-up capacity directly to heart disease risk, as many other related health and lifestyle factors (confounders) could be having an influence.

What did the research involve?

The study involved 1,104 male firefighters (average age 39.6) from 10 fire departments in Indiana who underwent regular medical checks between 2000 and 2010.

Assessments included height, weight, blood pressure and heart rate, blood tests, treadmill and push-up tolerance.

They also completed health and lifestyle questionnaires, including questions on smoking, alcohol and family history of heart disease.

The main outcomes assessed were new diagnoses of heart disease from enrolment up to 2010.

Cardiovascular events were verified by periodic examinations at the same clinic or by clinically verified return-to-work forms.

What were the basic results?

Push-up capacity was found to be inversely associated with baseline risk factors for heart disease, such as body mass index (BMI), blood pressure, cholesterol, smoking status and peak oxygen consumption during exercise.

In other words, as these risk factors increased, push-ups decreased.

There were 37 cardiovascular disease events among the 1,104 men, so affecting around 3%.

Those with higher push-up capacity had a lower risk of heart disease.

The researchers divided the men into 5 categories, with the lowest being able to do 0 to 10 push-ups and the highest over 40.

Compared with the reference group of 0 to 10, all categories above this had a lower rate of heart disease.

The smallest risk figure was for over 40 push-ups (incidence rate ratio 0.04, 95% confidence interval [CI] 0.01 to 0.36).

How did the researchers interpret the results?

The researchers concluded: "Higher baseline push-up capacity is associated with a lower incidence of cardiovascular disease events.

"Although larger studies in more diverse cohorts [groups of people] are needed, push-up capacity may be a simple, no-cost measure to estimate functional status."

Conclusion

It would seem obvious that push-up capacity may indeed serve as a marker of physical fitness.

This may also then be associated with other cardiovascular risk factors, such as BMI, blood pressure, heart rate, cholesterol and whether or not the person smokes.

So in that sense it's highly plausible push-ups could be one very loose marker for potential heart disease risk.

But as a one-off factor in itself, it's hard to see how the number of push-ups you can do would influence your risk of heart disease.

If you have trained yourself to do a lot of push-ups but are still following unhealthy lifestyle habits, it's probably not going to protect you a great deal.

Aside from the confounding influence of other health and lifestyle factors, the study had other limitations.

The sample of male firefighters from 1 region in the US is not representative of everyone.

There were also only 37 incidents of heart disease. Further subdividing these men into 5 groups by how many push-ups they did gave small numbers, which makes the risk analyses less reliable.

It's difficult to be sure of the direction of events in this 10-year assessment period and whether physical assessments were definitely done before anyone developed heart disease.

And there's a chance that assessing heart disease through return-to-work forms or the firefighter's clinic assessment could miss or wrongly classify some cases.

Nevertheless, the findings support general health advice to take regular exercise in line with government recommendations, eat a balanced diet, limit how much alcohol you drink and not smoke to protect the health of your heart.