When Running an Hour or Longer, Are You at Risk For Burning Muscle?

It's not the act of going on long runs, but how your individual body uses fuel as well as your level of fitness that can cause atrophy or muscle wasting, according to exercise physiologist and NASM-certified personal trainer Krissi Williford, MS, from Xcite Fitness.

"Running, depending on your pace and length of the run, will use mostly glycogen from carbohydrates," explained ACE-certified trainer and weight-loss health coach Rachel MacPherson. She went on to say that running for an hour will not burn muscle if you have eaten properly in the hours and days beforehand.

Krissi added that muscle loss when doing longer runs also has to do with how efficient your body is at burning calories. "When you start exercising, you aren't that efficient, especially if you haven't been exercising at all," Krissi said, meaning your body will need more calories for fuel.

Over time, your body adapts as your level of fitness improves. "It's easier for the body to do the work on fewer calories because it is more efficient," Krissi said. So the more your body gets used to these longer runs, the lower the risk of burning muscle, as long as you're eating enough.

Rachel said you can go for long runs frequently if you're properly fueling yourself. "As long as you consume enough carbohydrates and calories, you can do several long runs per week. If you're training for a race, be sure to eat enough to sustain your training," she said.

NASM-certified personal trainer Jared Hamilton suggested spacing out your longer runs to allow enough time for rest and recovery. "So instead of doing three long runs on Monday, Tuesday, and Wednesday, I would do them Monday, Wednesday, and Saturday, for example," he said.

"If you aren't taking in enough calories, your body will get energy from somewhere, and it isn't always from fat," Krissi said. "We are made for survival and this is one of the ways we survive."

Rachel added, "If your exercise session is under two hours, you should focus mainly on hydrating yourself during the workout and stick to eating one to two hours pre- and postexercise." Your preworkout meal should contain carbohydrates and protein — a handful or two of carbohydrate-rich food and 15 to 20 grams of protein should do the trick — and should be eaten one to two hours before training. When exercising for two hours or longer, Rachel said, "You can also consume carbohydrates during your session at a rate of about 30 to 45 grams per hour." She added, "It can also be very beneficial to consume protein during your workout if it is very long, about 15 grams per hour."

"I suggest eating before long cardio sessions so you have the energy to perform, and also allow enough time for [the food] to digest so you don't get sick," Krissi said. If you're running early in the morning right out of bed, she said to nosh on something that digests quickly, such as a banana or half a piece of toast with jam — find what works for you. If eating before running makes you feel sick, then skip it.

Eating after your long cardio session is important for recovery and preventing muscle wasting, Krissi said. "Refuel one to two hours postexercise with around 30 to 40 grams of carbs and 10 to 15 grams of protein," Rachel added.

While fueling yourself properly should be your main focus in preventing muscle loss, NASM- and ACE-certified trainer Holly Roser said another way to preserve muscle is to maintain your current strength training program. "Strength training in combination with running will help prevent muscle loss," she said. Here's a weekly workout plan that combines running with strength training.

NASM-certified trainer Jaimi Jansen added that recovery is important, too. Focus on getting enough sleep, eating enough calories to fuel your training, and resting between runs.

While Jaimi said that long-distance running can definitely build endurance, which can improve your performance when doing high-intensity workouts, if you want to build muscle with running, incorporate shorter runs that include sprints.

If you look at runners' bodies, Krissi said, those who run long distances usually "are thin all over with no muscle shape." She added, "Then you have sprinters who look like a workhorse; sprinters have lots of muscle."

If getting leaner and stronger is your goal, shorter runs that focus on high-intensity intervals are proven to burn fat and build muscle, which saves you time and is more effective. Try this 40-minute HIIT running workout. ACE-certified fitness trainer John Kersbergen told POPSUGAR in a previous interview that HIIT workouts paired with strength training three times per week will yield positive results.