Everyone responds to exercise differently - if you take 10 people and put them on the same workout routine for three weeks, some will improve dramatically, but others may not appear to have changed physiologically at all. In some cases, a few people may even appear less fit.
Previously, this led researchers to think that some people are 'non-responders', meaning exercise just doesn't work for them. But more and more research is starting to indicate that the whole 'non-responders' idea is just a myth.
One recent study found that people who don't become stronger or more fit from one type of training did respond to other types of workouts - some people respond better to long endurance workouts, others to sprints - but importantly, everyone responded to something.
Now a new study adds even more to the picture, though this one comes with some tough advice.
Some people just need to work out more to see results.
This particular study took 78 healthy adults and divided them into five groups, with each going through one, two, three, four, or five 60-minute workouts every week for six weeks.
Most people who did only one workout each week didn't become more fit because of the training, but there were also seeming 'non-responders' in the groups that worked out two and three times per week.
The researchers took all those 'non-responders' and put them in another six-week program which involved doing two additional workouts each week.
So people who had initially been doing one 60-minute workout each week transitioned to three 60-minute workouts (or 3 hours of exercise total) each week, and people who'd been doing 3 hours of exercise each week were bumped up to doing five.
Everyone's maximum power and cardiovascular fitness improved.
This indicated, the researchers wrote, that exercise is "dose-dependent", meaning that if your body isn't responding to training, you probably just need to do more (obviously, not to the point of injury).
As tough as that may sound, these are encouraging findings, according to Michael Joyner, a physician and Mayo Clinic researcher, who is one of the world's top experts on fitness and human performance. He wrote a commentary to go along with the study in the Journal of Physiology.
That's because even modest levels of fitness provide "impressive protection" for health and mortality, Joyner tells Business Insider via email.
Still, in his commentary Joyner points out that many people already have a hard time hitting the recommended amount of exercise, which is at least 150 minutes of moderate activity per week.
Even if people know that some more time working out may make a huge difference, that may not be enough to encourage them to do it.
But the fact that we're learning more about this is useful. In some cases, it may encourage people to build more activity into their commutes (like biking or walking to work instead of driving).
"I think we need to build as much physical activity into life as possible," Joyner says.
He says this sort of active transportation has "incredibly powerful effects on obesity".
In other cases, people might just want to put in the extra time at the gym. And of course, as other research has shown, the best fitness hack to get past non-response may be finding a different workout that does work.
That's one of the reasons most trainers say there's no one workout routine for everyone - instead, find something that works for you and that you like enough to keep doing.
When you look at the many benefits of exercise, from improved cardiovascular health to stress reduction and mood-boosting effects, it's worth it.
"I think most people need to do a mixed collection of various activities with some high intensity exercise if possible, but the key to remember is to simply do something almost every day," says Joyner.
This article was originally published by Business Insider.
More from Business Insider: