A new system at the Aquatic and Fitness Center in Bala Cynwyd, Pennsylvania, is helping fix that problem.
It's starts with a heart rate monitor, but it has a lot of other features as well.
I strapped the MyZone device around my chest, and met up with trainer Derrick Howie.
"I am going to adjust the speed as we go up," he says.
As he takes me through a workout, I can monitor my effort on screens around the gyms.
As my heart rate goes up into the yellow zone.
I know I'm getting the most out of my workout.
"You can actually assure that you will be burning more fat and more calories," says fitness director Matt Schoell.
Schoell says the My Zone is tailored for each individual so results are precise.
And as you see your effort in real time.
It will also be uploaded to your personal profile online so you can track all your workouts, both inside and outside the gym.
I wore mine to "Joltin Jabs" where many Action Newsers take a boxing fitness class.
"I just click on the day."
Then I checked out my results- heart rate, effort and calories burned.
"Good job," says Howie.
Trainers can also use it to plan workouts for you, to help you reach your goals.
You can also challenge others to compete.
"Those challenges can be set up as weight loss goals, calorie burning goals or what's called time in zones,"
Schoell says MyZone is for anyone looking to get in better shape or lose weight.
Anthony Fuscaldo says it helped him drop ten pounds.
"I thought I was working out hard before, turns out I could have done more," he notes.
He says as soon as he started pushing himself to get in the yellow and red zones, he started seeing results.
Right now the MyZone system is only at the Aquatic and Fitness Center in Bala Cynwyd. It costs $73 dollars for members.
But there are other similar systems out there.
And experts say this is the wave of the future when it comes to working out.
Aquatic and Fitness Center. Trainer Derrick Howie