6. Watching TV or Reading.
"People tend to get on cardio equipment and think they're paying the piper, but they're so into their book they're wasting precious caloric time," says Pillarella.
The bottom line is that when you're focused on other things, your workout suffers, she says.
You can walk at a 4 mph pace for 45 minutes and burn 300 to 400 calories, says Pillarella. But you could get the same calorie burn in 20 to 25 minutes doing intervals (running or walking as fast as you can for a minute or two) every 90 seconds.
"It's the total number of calories burned that counts," she says.
If you need a diversion to make it through your session on the elliptical machine, try music, suggests Comana. Invigorate your workout with a fresh mix on your iPod instead of spending your time staring at the crawl on Fox News.
"Music can inspire you to pick up the tempo," Comana says.
7. Resting Too Long. The machine you want to use is occupied, so you grab a towel, get a drink of water, run to the bathroom -- and the next thing you know, 10 minutes have passed.
To avoid such time-wasting, rest only 30 to 90 seconds between strength exercises, says Comana.
To maximize time, alternate a set of exercises for your biceps with a set for triceps, he says. That allows you to shorten the rest interval in between -- while one muscle group is working, the opposing group is getting active recovery.
You can also save time during your warm-up by mimicking exercises you'll be doing in the workout. For example, Comana says, if you plan to work your legs by doing lunges and squats with weights, warm up with high knee steps, butt kicks, lunges with a twist, and sumo squats.
"Perform movements that are the same as you'll do in the exercise so that you can better prepare the body for the exercise," advises Comana. "You're warming up the joints while tying into the neuromuscular system to create movement preparation."