Many of the 70-year olds who were supposed to train the least, ended up training even more than the group assigned a moderate exercise regime. This made it difficult for the researchers to interpret the results.

Overly enthusiastic 70-year olds messed up study on physical activity

The researchers wanted to find out if exercise prolongs life and protects against disease. But a disobedient control group gave them trouble. They exercised more than they were supposed to.

A study at the Norwegian University of Science and Technology, NTNU, which was supposed to examine the effect of physical exercise among the elderly, didn’t quite go as planned.

Some of the 70-year olds hijacked the study. They were supposed to train the least, but they ended up training lots.

This gave the NTNU-researchers trouble when interpreting results, according to the daily medical newspaper Dagens Medisin.

Important message to health personnel

The unexpected effect is still very interesting, according to researcher Dorthe Stensvold. She is one of the researchers behind the study, which was recently published in the BMJ.

The participants in the study may have been motivated by knowing that their fitness levels and health would be regularly monitored throughout the study, she believes. And this in turn is an important message to health personnel.

“Asking older adults about their exercise habits can be enough to make them start exercising”, she says to the newspaper.

“It’s never too late for older adults to start exercising”, she and co-authors write in a comment published on BMJ Opinion.

The Hawthorne-effect

In the world of science and research, this effect is far from unknown. It even has a name, the Hawthorne-effect – which describes what may happen when participants involved in a study alter their behavior because they are part of the study.

This same Hawthorne-effect has however also been criticized by many. Researchers at the Inland Norway University of Applied Sciences are among the critics of the original Hawthorne-studies that gave the name to the supposed effect.

In an article written by the Inland University and published on last year, they write that some critics believe “that the Hawthorne effect does not point to any clear mechanism. Instead, it is used as a general and far-fetched vague explanation of why the observations were unexpected.”

Another reason for why the control group ended up doing a lot of exercise may be that they were motivated before they even joined the study.

“Our study revealed a serious challenge in finding a suitable control group in life-style interventions”, the researchers write in BMJ Opinion. “People signing up for studies looking at the effect of life-style changes, are in general healthy and/or very motivated to change lifestyle.”

Divided into three groups, two received organized training

The goal of the NTNU-study was to see if physical exercise could extend the lifespan of older adults. The researchers also wanted to find out if there was a difference in doing high intensity training versus more moderate exercise.

A total of 1567 Norwegians of both sexes participated in what was called the Generation 100-study. They were 72 years old when the study started.

The researchers divided the participants randomly into three groups. The control group was the largest.

One group was to do high intensity interval training twice a week, the other group was assigned steady and moderate intensity training for 50 minutes two days a week. These two groups were offered organized training.

The third group, the control group, was merely told to follow the official recommendations from Norwegian health authorities. They were not offered organized training.

Ideally, the researchers should have had a control group that did not do any exercise. But it would have been unethical to ask somebody to not be physically active for five years. The Norwegian health authority recommends moderate exercise for half an hour a day, five days a week.

The researchers monitored and followed up on the three groups for five years.

It turned out the control group exercised more intensely than those who were assigned the moderate training scheme.

All groups lived longer than the average

There was higher survival among those who participated in the study, compared to this same age group, 70-77 years, on average in Norway.

On average, 90 per cent of older adults in this age group in Norway will survive the next five years. In the study, 95,4 per cent of older adults in this age group survived.

The researchers conclude that all groups of participants experienced health benefits by exercising. Any differences between the groups were not significant.

In the interval training group however, 3 per cent of the participants had died after five years. The percentage was 6 per cent in the moderate group, according to an article written by NTNU and published on

“The difference is not statistically significant, but the trend is so clear that we believe the results give good reason to recommend high-intensity training for the elderly,” Stensvold says in the article.

She hopes national recommendations will be updated “to encourage older people even more strongly to do high intensity training – either as their only form of exercise or to supplement more moderate training.”

According to the researchers, theirs is the “longest and largest randomized controlled exercise trial evaluating the effect of supervised exercise training versus physical activity recommendations on mortality in older adults.”


D. Stensvold mf: Effect of exercise training for five years on all cause mortality in older adults—the Generation 100 study: randomised controlled trial. Summary. BMJ, 7.October, 2020.


Read the Norwegian version of this article on


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