If you’re routinely leaving puddles of sweat on the gym floor, then you have every right to expect performance gains. You should feel yourself growing stronger, see fat become muscle. If that’s not happening, then something you’re doing (or not doing) is holding you back. But don’t give up. Instead, take a minute to diagnose the problem. The best place to start: Right here, with the four biggest workout mistakes that screw up the most workouts.

Biggest Workout Mistakes that Mess Up Most Athletes

MISTAKE #1: You’re not resting between sets

“Most people do not understand the importance of rest periods,” says Gavin McHale, a Winnipeg-based kinesiologist and certified exercise physiologist. “They have been called ‘the middle child of strength training’ as no one seems to respect or understand them as they should.”

Here’s what McHale wants you to know: Taking breaks between sets is what recharges your neuromuscular system and gives you the power to push past your barriers. Breaks also regulate your body’s hormonal response, a key process underlying muscle growth. So if you’re doing back-to-back sets without resting, you’ll never hit your full potential.

Related: Is Working Out Before Bed a Bad Idea?

So how long should you rest? Well, that depends: The more weight you’re lifting, the longer you need to recover. Here’s a general plan to follow:

• For low-weight, high-rep (more than 12) sets, rest for 30 seconds.
• For moderate-weight, medium-rep (eight to 12) sets, rest for 45 to 90 seconds.
• For high-weight, low-rep (six or less) sets, rest for two minutes.

If you find it difficult to wait around while your muscles recover, try killing time by performing some gentle mobility work between sets, McHale says. Foam rolling will do the trick.

MISTAKE #2: You keep checking your phone

While cutting rest too short is a problem, so is resting too long. You want to keep your intensity up, and a study from Kent State University found that your heart rate and exercise satisfaction dip as soon as you start texting.

Worse still is the phone’s effect during cardio, when looking down can wreck your form. “When we look at our phones during aerobic exercises like running, we decrease our workout intensity and postural stability, the latter which could increase the risk of injury,” explains Michael Rebold, Ph.D., C.S.C.S., director of Integrative Exercise Science department at Hiram College.

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If you feel the urge to use your phone for anything more than music (which can improve workout performance) and a timer (great for keeping your rest periods in the target zone), switch it to airplane mode before you leave the locker room.

MISTAKE #3: You’re using calories as your benchmark

Bad news, calorie counters: The gadgets you rely on are failing you. Cardio machines use simple estimates to determine your energy expenditure, and not surprisingly, most of them are wildly inaccurate.

A study from the University of California at San Francisco’s Human Performance Center found that treadmills overestimate calorie burn by an average of 13 percent. The elliptical is even worse, putting out numbers that were 42 percent too high. So your 400-calorie workout? That might have only been 230 calories. A JAMA Internal Medicine study of 12 different types of wearable fitness trackers found that while they’re better than the cardio machines, they still have problems; they either significantly over- or underestimate calorie expenditure.

Ditch the calorie counting and focus on your heart rate to gauge your cardio intensity, recommends Paul Landi, a certified exercise physiologist and fitness director at Professional Physical Therapy in Connecticut. You can do this with a basic heart-rate monitor that wraps around your chest.

Here's how to use it: To determine your max heart rate, subtract your age from 220. (So if you’re 30, your max heart-rate is 190.) Then, during high-intensity intervals, you should work hard enough to keep your heart rate between 75 and 90 percent of your max. (For the 30-year-old, that’s roughly 143 to 171.) Between intervals, or during steady-state cardio, keep working, but let your heart drop into a tough-recovery zone at 65 to 75 percent of your max.

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There are many ways construct workouts around this data, but here’s a simple 26-minute interval plan that’s guaranteed to strengthen your arteries while helping you familiarize yourself with heart-rate data:

• Run for 5 minutes at 60 to 75 percent of your max heart rate.
• Sprint for 2 minutes as close to 90 percent as you can handle.
• Repeat that series (5 minutes running, 2 sprinting) three times, and then finish with a final 5-minute run (at 60 to 75 percent of your max).

MISTAKE #4: You’re Running on Crappy Fuel

You know your diet is important, and you probably also know that it’s a hell of a lot easier to snarf down 1,000 calories than it is to work it off. But more than that, if you’re eating junk food, your body will fail you in two significant ways: It won’t provide the steam you need for intense workouts, and it won’t have the building blocks your muscles require for growth.

“Food is fuel, and you are a sports car,” Landi says. “Put the best gas you can in the tank.” One review published in Nutrition Journal notes that your diet’s nutritional profile significantly influences your body’s ability to recover after exercise and keep it out of a catabolic (read: muscle-wasting, fat-storing) state.

To build more muscle and burn more fat, focus on replacing processed foods with more vegetables and lean protein sources such as chicken, eggs, dairy, and legumes, says Landi. And the more you can time your meals around big workouts, the more you’ll notice your body transforming.

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