If you do a hard boot-camp class on Monday night and then wake up early to take a tough spin class on Tuesday morning, your body is probably still tired from the previous night’s workout. RELATED: This Is the Best Workout for You, According to Your Personality And remember: The rest is equally as important as the interval-promise. This is so your body can recover enough to repeat the intensity of the work interval.” According to the American Council on Exercise, you should aim for about 30 seconds of rest between intervals if you're seeking to build endurance. “After a hard push, either take a short static rest or active rest, like a light jog or walk. “Not getting enough rest between intervals can be a huge detriment to your workouts,” says Baugh. (Score quickie workouts that will challenge your entire body with Women's Health's 20-Minute Workouts DVD!) Each workout should vary in intensity and duration in order to achieve the maximum benefits. “It’s important to balance the hard efforts with workouts that are easier in order to build endurance and strength.” Instead of hitting up all your favorite classes every week, plan your weekly workouts in advance so you can ensure there’s a purpose for each sweat session. “Going hard all the time, in every workout, can prevent you from seeing the fitness gains you’re working toward because you don’t have enough variety in your workouts,” says Caroline Varriale, physical therapist at Finish Line Physical Therapy in New York City. “Join a local running group where the workouts will be structured and you’ll be surrounded by friends-or strangers!-who can help you push yourself the bit harder that will make a difference.” RELATED: 7 Reasons Your Thighs Aren't Changing No Matter How Much You Work Out Having a hard time making it happen on your own? “Consider getting uncomfortable in a group setting,” says Baugh. “If you’re not pushing yourself past your comfort zone, you’re unlikely to see many changes,” says Baugh. “But you need to make sure you’re doing them with the right amount of intensity.” In other words, it should hurt a little or leave you gasping for air-and that’s a good thing! Without adequate intensity, the body doesn’t experience enough stress to illicit a physiological change. “Most people run intervals to mix up their routine, which is great,” says Baugh. “And it nearly always comes back to workout intensity and rest.” Here are seven reasons you may not be seeing endurance gains-even if you’re working out ‘round the clock. “This is a common theme with athletes of all ages and abilities,” says Anthony Baugh, a NASM-certified personal train at Independent Training Spot in NYC. So why is it that when you hit the road for your regular five-mile loop around the neighborhood, it still feels hard AF every single time?

Your Instagram feed is a steady stream of #fitspiration, and your abs are the envy of your squad. Between the sunrise runs, lunchtime spin classes, and evening yoga practice, the only thing more packed than your fitness routine is your laundry basket.

Does rest time between sets matter