Does running build leg muscle?

If you’re looking for a stronger or more muscular lower body, you might be wondering; does running build leg muscle? Whether you’re thinking of pounding the streets or investing in the best treadmill, it’s well worth knowing how this form of exercise affects your body.  

According to the Sports and Fitness Industry Association, over 50 million Americans run and jog regularly. Common health benefits of running, highlighted by the NHS, include improving your fitness, maintaining a healthy weight, boosting your mood, and reducing your risk of long-term illnesses, such as heart disease, type 2 diabetes, and stroke. 

And, while weightlifting and resistance training is heavily associated with muscle gain, there is increasing evidence to suggest running could help with this too. It may just involve mixing up your running styles, increasing intensity, and/or incorporating strength training.

Does running build leg muscle? What you need to know

Before we look into whether running builds leg muscle, it’s important to understand how muscle building occurs. According to Healthline, muscle building, or muscle hypertrophy, happens when exercise causes micro-tears within and damage to the muscle fibers; this triggers a repair response in the body which fuses the fibers together and, consequently, increases the mass and size of the muscle. The major muscles that running works are your hip flexors, quadriceps, glutes, hamstrings, and calves.

In a 2017 study published by the International Journal of Exercise Science, university students and five older subjects took part in a 10-week high-intensity interval training program and it was identified that: “aerobic exercise is an effective mode of activity for the promotion of cardiorespiratory fitness and increase in the whole muscle size of the quadriceps."

Manhattan-based RRCA certified run coach and physical therapist Dr. Victoria Sekely told Fit&Well that muscle building is limited if solely focused on running.

When asked: “Does running build leg muscle?”, she said: “Yes and no. Someone completely new to running who hasn’t done any strength training before, initially, will notice an increase in muscle strength. However, if a runner focuses specifically on endurance, they wouldn’t necessarily see any muscular strength gain from running.

“Our [leg] muscles are impacted by running but only to a certain point,” Sekely continues. For recreational runners who aren’t necessarily beginners, she would recommend a more deliberate strength training routine in addition to running.

The aforementioned study also reaffirms that running alone isn’t sufficient to build leg muscle and incorporating sprint and muscle training, like HIIT, can help you gain muscle strength. Nutrition and a healthy balanced diet are also critical to muscle gain, according to Mayo Clinic.

How far do you have to run to build leg muscle?

We’ve established that endurance running does build leg muscle but only to a certain extent, so is there a specific amount of running you should be doing to achieve this?

It is different for everyone in terms of their anatomy, Sekely told Fit&Well. But even when running for a specific distance, she claims building leg muscle is limited.

“In terms of endurance running, once a certain mileage is hit, the increase in mileage counteracts the muscle-building strength,” she explains.

In fact, long-distance running could cause muscle damage and, therefore, hinder muscle growth. A study, published by the Journal of Physical Therapy Science, of 30 male amateur runners split into three groups that ran 6.2, 13, or 26.1 miles (10, 21, or 42 km) concluded that all groups experienced marked increases in measures of muscle damage. Plus, the levels of these measures rose as the running distance increased and remained high even on the third day of recovery.

Further, much of the current research in this area points towards increasing intensity as opposed to distance as key to building leg muscle through running. Sekely recommends performing hill sprints as the best way to do this. 

“This is because you’re adding elevation and power from sprinting,” she explains.

As for how much intense running we should be doing, a study, published in Exercise and Sport Sciences Reviews, found that the most effective way to encourage muscle growth in the lower body with cardio is to exercise for 30-40 minutes four to five days a week with an intensity of 70-80% heart rate reserve (the difference between your maximum and resting heart rates).

Is it ok to run with sore legs?

It’s useful to be able to distinguish between muscle soreness and injury caused by exercise. According to the NHS, sore muscles after physical activity, known as delayed onset muscle soreness (DOMS), can occur when you begin a new exercise program, alter your exercise routine, or increase the duration or intensity of your workout. Whereas “an injury is actual damage to the muscle or fascia,” explains Sekely.

“An injury will prevent you from doing the activity because of pain or an increase in pressure whereas [muscle] soreness is something that is likely after exercise and shouldn’t prevent you from living your life,” she adds. 

Victoria believes that it is okay to run with sore legs bearing in mind the effort is kept gentle.

“[To optimize] performance and injury reduction, you should limit the amount of hard effort back-to-back. For instance, if you’ve done an interval run or a hard strength workout, I would not recommend doing a hard run with sore legs. It increases your risk of injury and poor form. That said, an easy, slow recovery run to flush the legs out, [is great].”

If you are planning to run with sore legs, a warm-up could help. Victoria emphasizes the importance of always doing a warm-up before a run, whether you’re sore or not.

“You don’t want to shock your muscular system; running is not necessarily easy and you shouldn’t hop up from an eight-hour day sitting at your desk to go for a two-hour run. It can be as simple as doing a couple of squats and heel raises then a fast walk before starting your run. [Your warm-up] doesn’t have to be complicated, but it does have to happen.”

The NHS recommends using ice packs, painkillers, or having a massage to treat DOMS.