This brings me to a commonly-debated fitness topic: does performing cardio limit strength training's effects on building muscle and strength? Or, phrased in a more common way, does cardio "kill my gains?"
As you would guess after reading the first paragraph, the answer to these questions is...it depends.
Cardio and Strength TrainingGenerally, performing large amounts of cardiovascular exercise (walking, running, cycling, etc.) along with strength training will limit less strength and muscle growth. This was shown in a review of almost 40 studies (1). When compared to people who only strength trained, men and women who performed strength and cardio exercise added strength and muscle...but not as much.
There are many reasons for this:
- Glycogen (1). Glycogen is the stored form of glucose. Glucose is the main fuel source for strength training. When cardio is performed on consecutive days, glycogen is depleted, leaving less energy for strength training. As a result, a person performing a large amount of cardio likely won't be able to lift as much weight or perform as many repetitions in strength workouts.
- Overtraining (1). As mentioned in the previous post, an excess of training can be noticed in a person's strength levels. One study noted people were able to gain strength for the first several weeks when performing both types of exercise. Afterwards, strength levels decreased! Were they exercising too often to fully recover from each workout?
- Muscle fibers and protein synthesis (2). Strength training and cardio training stimulate different responses in cells (larger myofibrillar proteins for hypertrophy vs. more mitochondrial content). Also, to grow muscle, muscle protein development needs to exceed muscle protein breakdown for long periods of time (weeks or months). Performing long endurance workouts interrupts the emphasis on muscle protein development by promoting a focus on protein breakdown.
However, as I mentioned in the introduction, cardio does not always limit muscle and strength development. From what I noticed, there are two conditions when cardio doesn't contradict the benefits of strength training. In fact, in these circumstances, cardio might even enhance muscle and strength!
Frequency of TrainingThe majority of the studies in the review focused on large amounts of training, featuring long workouts which were performed 4-6 days per week for EACH type of exercise...for a total of 8-12 workouts per week (1)!
Two studies showed cardio and strength training together can be just as effective, if not more effective (3,4). A difference with these studies was the frequency. A study from 2002 showed the combination can actually lead to more muscle growth than strength training alone. In this study, cardio and strength training were performed on the same day and for three days per week (3). A second study, published in 2009, showed almost equal gains in strength from strength training alone when compared to strength training and cycling. The participants only worked out two days per week (4).
In both cases, people rested most days of the week and did not exercise on consecutive days.
Type of Cardio Training
When cardio is performed less frequently, the type of cardio matters. Cycling, when combined with strength training, complemented strength training more effectively than walking or running on a treadmill did (4). In one case, combining cycling and strength training together improved hypertrophy, or muscle growth (3). Researchers speculate that cycling is better for strength as it mimics the joint movements of some strength training (4). It's possible that other cardiovascular exercise methods that mimic strength training movements, such as the row ergometer, could also enhance strength training results when performed less frequently.
ConclusionDoes cardio "kill your gains?" It depends, of course. If strength and hypertrophy are your main concerns, research indicates sticking to 2-3 cardio workouts per week to develop the most strength and muscle you can. Also, focus on a cardio method such as cycling or rowing that is similar to strength training movements. If you are an endurance athlete or simply enjoy daily cardio, strength training will still help you gain strength and muscle...you just won't develop to your maximal level.
- Nader, G.A. (2006). Concurrent strength and endurance training: from molecules to man. Medicine, Science, Sports, and Exercise, 38(11), 1965-1970.
- Hawley, J.A. (2009). Molecular responses to strength and endurance training: are they incompatible? Applied Physiology, Nutrition, and Metabolism, 34, 355-361.
- McCarthy, J.P., Pozniak, M.A., & Agre, J.C. (2002). Neuromuscular adaptations to concurrent strength and endurance training. Medicine and Science in Sports and Exercise, 34(3), 511-519.
- Gergley, J.C. (2009). Comparison of two lower-body modes of endurance training on lower-body strength development while concurrently training. Journal of Strength & Conditioning Research, 23(3), 979-987.