The super-easy way to add more weight to your next leg day

You might not be pushing yourself at the gym as hard as you think: People tend to choose weights that are way less heavy than they can actually handle, a new study in the

In the study, researchers recruited eight experienced lifters who worked out with a personal trainer and 13 who lifted on their own. They had each lifter self-select the load they would use to complete 10 reps on four exercises: bench press, leg press, leg extension, and bicep curl.

Then, 48 hours later, they returned to the gym to have experts test their 1-rep max. They came back another 48 hours after that for the pros to test their 10-rep max.

Overall, the people used to working out with a personal trainer tended to self-select significantly more weight for their lifts, ranging from 12 percent more on the leg extension to 27 percent more on the bench press—even though the trainer wasn’t there with them for the study.

But both groups tended to select weights that were significantly lower than what their tested 1-rep max and 10-rep max proved they could handle, with the greatest difference noted in lower-body exercises. That’s a problem, since it’s likely they weren’t challenging themselves enough to see results in strength and muscle growth they’re looking for.

Still, the lifters who worked with a personal trainer selected higher loads in relation to their maxes than the lone lifters did. In fact, the average self-selected load for all exercises in people who lifted with a trainer was 54 percent of their 1-rep max, compared to 50 percent of their 1-rep max in those who lifted without a trainer.

Many people tend to underestimate how much they can actually lift, the researchers write. In fact, many of their participants expressed astonishment when they found out what their 1-rep maxes and 10-rep maxes really were.

The group with personal trainers tended to rate their exertion levels during their lifts in the study as higher, too—an average of 7 percent greater on their lifts. This shows that people who work out with trainers are accustomed to higher levels of exertion in their workout, a benefit that carries over even to when the trainer isn’t physically there with them, the researchers write.

So if you want to add weight to your lifts, it might be worth it to invest in a personal trainer to help you figure out what you can safely lift while still challenging yourself.

Good news is, you may not have to cough up as much cash as you think. In the study, the benefits persisted even when the trainer wasn’t physically there with them—so you don’t have to keep the pro on indefinitely.