If cardio is an obligatory part of your workout, you’re not alone. When you look around the gym, you see lots of people hitting the weights and then immediately sauntering over to the treadmill, elliptical or stationary bike.

You might think this is how workouts should be structured. Everyone else is doing it, right?

Well, it may be a common practice, but that doesn’t mean it’s the best way to train, especially if you’re trying to get stronger.

A recent study conducted at Northumbria University in the UK looked at how endurance exercise performed in conjunction with a strength workout affects muscle strength and size.

Twenty-four men with training experience performed a six-week strength program, in three groups:  3:1 strength-to-endurance; 1:1 strength-to-endurance; and strength only, with no endurance component. They then tested max strength, size and endurance to measure the effectiveness of each type of training.

The results: the pure strength training program produced the best strength and size gains of the three test groups. The subjects experienced gains of 30.4 percent (strength) and 4.3 percent (size) compared to 24.6 percent (strength) and 2.8 percent (size) for the 3:1 group, and 7.2 percent (strength) and 1 percent (size) for the 1:1 group.

These results demonstrate an inverse relationship between strength and endurance. The more endurance exercise you do, the less you should expect from your strength workouts, and vice versa.

The reason for this is not completely clear, but the researchers hypothesized that the higher volume of work performed in a concurrent strength and endurance program may put too much stress on the body, reducing potential gains. Also, endurance exercise may cause adaptations within muscles that interfere with strength and size improvements.

So should you never do cardio or endurance exercise if you’re trying to get bigger and stronger? Not necessarily.

If you have a specific goal to improve your endurance while also getting bigger and stronger, then endurance exercise is OK. But if you want to make meaningful strength and size improvements, you need to limit your endurance exercise to about one-third of the time you spend lifting. However, if your primary goal is to get the most from your weight training sessions, then kick endurance exercise to the side and focus on getting bigger and stronger.

Reference

Jones, T.W., et al. “Performance and Neuromuscular Adaptations Following Differing Ratios of Concurrent Strength and Endurance Training.” Journal of Strength and Conditioning Research. Published ahead of print. DOI: 10.1519/JSC.0b013e3182903221