You may have heard conflicting reports of whether or not runners burn muscle and lose mass when running. In fact, you may have even wondered about it when looking at the all-muscle-and-bone elite runners. Or even when noticing the size difference between football running backs and linebackers. Is burning muscle a myth or do you need to be worried about finding ways to build muscle mass though cross-training?
The claim you burn muscle when running isn’t a myth — but it is also a bit complicated. There are other factors at play, most important how much fuel your body has to pull from other sources first.
“Muscle protein provides a small part of the energy for any exercise — including running — so you do indeed use a bit of muscle as fuel for running,” confirms Scott Saifer, MS, head coach at Wenzel Coaching, who has a master’s in exercise physiology and has been coaching athletes and cyclists from the beginner to the professional level for more than 25 years. “The number typically given is that 10% of the energy for endurance sports comes from protein, but the truth is much more complicated. The fraction of energy coming from protein depends on the availability of other sources of energy such as muscle glycogen, blood sugar and fat.”
As Saifer explains, if you have low energy stores in other places, you’ll use more muscle protein (and vice versa). This isn’t unique to running, he explains, sharing that it is similar to strength training. As you workout, some damage is inflicted on your muscles. However, if you have adequate levels of protein, your muscles will grow larger and stronger. So if you’re worried about whether or not running leads to muscle loss in your legs, Saifer says it could go both ways, but you do have some control over the outcome.
You will never completely stop the loss of muscle protein when running; however, you can find a balance between muscle loss and growth. If you make sure your body has enough fuel in other areas to pull from, you can reduce what is pulled from muscle protein. Saifer explains that one way to do this is by getting a quick dose of carbohydrates after you exercise to restore muscle glycogen and preserve mass.
“Muscle continues to break down after exercise,” Saifer continues. “That effect can be reduced by consuming foods that increase insulin, which means moderate- and high-glycemic. On runs longer than 45 minutes, consume some easily-absorbed carbohydrate (such as an athletic energy drink during exercise) and, if you tolerate it, have breakfast before a morning run.”
You may think cross-training would play a large role in building muscle, but in this case, Saifer says it can vary dramatically from runner to runner. One study, published in Exercise and Sport Sciences Reviews in 2014, determined aerobic exercise is enough to produce skeletal muscle growth. “Collectively, these data warrant that aerobic exercise training should be acknowledged to increase skeletal muscle mass and be considered an effective countermeasure for muscle loss with advancing age,” researchers concluded.
Don’t let the idea of burning muscle keep you from running — or send you to the gym to try to overcompensate with some strength training. Saifer reiterates that as long as you balance muscle protein breakdown (or muscle burning) and protein synthesis (muscle building), you shouldn’t notice much change.
“Don’t be afraid of mild muscle damage or using a bit of muscle protein as exercise fuel,” Saifer concludes. “World champion runners experience these things and there’s no way to get stronger or become a champion without them.”