The relationship between cardio and muscle growth is much more complex than people make it out to be. Aerobic exercise provides many beneficial effects on the cardiovascular system that cannot be achieved through resistance exercise; however, there are appropriate times to perform cardio that will not interfere with muscle gains.
DOES CARDIO MAKE YOU LOSE MUSCLE? WHAT DOES THE SCIENCE SAY IS THE OPTIMAL AMOUNT?
DOES CARDIO BURN MUSCLE KEY POINTS
- Recent research lays doubt that cardio burns muscle as commonly suggested.
- Training with cardio and resistance exercise in excess can cause blunted muscle growth.
- The greater the frequency, intensity, and duration of cardio, the greater its impact on reducing muscle growth.
- The interference effect seems more prominent with running, whereas cycling has less impact.
- The benefits of adding cardio to resistance exercise are improving cardiovascular function and muscle blood flow.
- Cardio can enhance recovery by increasing blood flow to muscles and improving cardiovascular health.
6/3: RESEARCH UPDATE: DOES CARDIO BURN MUSCLE? A STUDY FINDS CONCURRENT TRAINING MAY CAUSE A SMALL DECREASE IN TYPE I FIBERS
Training with aerobic and resistance exercises has sometimes been shown to produce less than favorable increases in muscle growth. This blunted effect on muscle growth is known as the interference effect.
There have been conflicting studies on the interference effect. Some studies show a blunted effect on muscle growth, whereas others have found no effect of combined cardio and resistance exercise.
DOES CARDIO BURN MUSCLE: NOT ACCORDING TO NEW STUDIES
A recent meta-analysis examined 15 studies with more than 300 subjects, the duration and type of cardio, and the outcomes on muscle growth of type I and II fibers.
After the researchers performed the analysis, they found a small reduction in muscle hypertrophy when aerobic exercise was combined with resistance exercise. The reductions in muscle size were found in type I fibers, which were affected the most.
The researchers suspected that since aerobic exercise mainly affects type I fibers, the combined effect of cardio and resistance exercise can cause negative adaptations in these muscle fibers.
Interestingly, they only found reductions in muscle size when running was combined with resistance exercise, whereas no effect was found with cycling. Running is associated with repetitive eccentric loading and stretch-shortening activities, whereas cycling provokes a higher emphasis on concentric work and a longer time under tension.
This may, in turn, be associated with greater inflammatory stress induced by running than cycling, possibly increasing redox and metabolic stress that may blunt the responsiveness to strength exercise.
None of the other subgroup analyses (i.e., based on concurrent training frequency, training status, training modality, and training order of same-session training) revealed a statistically significant interference effect for fiber hypertrophy.(12) To minimize the effect of the interference effect, here are some suggestions:
· Perform cardio and resistance exercises spaced at least 6 hours apart. Preferably cardio in the morning and resistance exercise in the afternoon.
· If you have to perform both, perform resistance exercise first, followed by cardio.
4/25: NEW META-ANALYSIS ON THE BEST CARDIO FOR MUSCLE GAIN
- The data indicate that strength training before aerobic exercise, but not aerobic exercise before strength training, is more effective for improving muscle strength.
- Aerobic exercise resulted in acute moderate declines in measures of muscle strength but not power in trained male individuals.
- There was a negative influence of prior moderate-to-high intensity and longer aerobic exercise durations (i.e., > 30 min) on muscle strength in trained male individuals. Low-intensity and short-duration (i.e., ≤ 30 min) aerobic exercise appear not to compromise strength performance.
- Compared with running exercise, cycling causes larger decrements in lower limb muscle strength. (11)
RESEARCH UPDATE: SHOULD YOU DO CARDIO WHEN TRYING TO GAIN MUSCLE?
When the first publication on concurrent training was released, people went crazy and perceived that aerobic exercise blunted muscle growth. First, the studies regarding concurrent training should be placed in context.
The studies that showed a blunted effect on muscle growth did excessive aerobic exercise (i.e., 40 minutes of aerobic exercise six days a week) combined with a 40-minute weight training program. (13)
Previous research suggests that the interference effect depends on several factors, such as training frequency, duration, and exercise intensity. (14) A 2021 meta-analysis compared the interference effect, which comprised over 43 studies with over 1,090 participants. The meta-analysis examined explosive strength, maximal strength, and muscle growth.
The study results concluded that concurrent training did not interfere with muscle growth or strength gains compared to strength training alone. However, they found that explosive strength was reduced with concurrent training, likely because of excessive fatigue.
The researchers found that separating resistance from aerobic exercise by 3 hours resulted in no reductions in explosive strength.(15) Don’t perform explosive exercise immediately after resistance and aerobic exercise. It is best to wait greater than 3 hours to perform an explosive exercise.
IS YOUR CARDIO KILLING YOUR GAINS….PROBABLY NOT
Lifters frequently use cardio to promote fat loss and build lean muscle. Recent studies indicate that when lifters do cardio right after resistance exercise, it might reduce the muscle growth effect. This observation has led many lifters to consider avoiding cardio when their goal is muscle building. However, the link between cardio and muscle growth is more nuanced than many assume. While aerobic workouts benefit the cardiovascular system in ways resistance exercises can’t, there are ideal times to incorporate cardio that won’t compromise muscle development.
There has been a ton of research on the interference effect. Research has shown that performing excessive cardio and weight training together can impair muscle growth. Cardio won’t completely stop muscle growth gains, but it can slow down the process.
Most research has been done on the leg muscles showing lower muscle growth when cardio and resistance exercise are combined. Some have speculated that it disrupts anabolic signaling pathways, glycogen depletion, excessive fatigue, etc.[1] Training with excessive aerobic exercise and resistance exercise stimulates fewer anabolic signaling pathways.
DOES CARDIO BURN MUSCLE?
Cardio can take valuable resources (i.e., calories) away from muscle growth. The factors that determine whether combing cardio and resistance exercise together blunt muscle growth is the type of cardio you do, the volume and intensity of the cardio performed, and whether you do cardio in a close period with weight training.
High-intensity cardio after resistance exercise was found to result in less muscle growth (1.8%), whereas moderate-intensity exercise had a lesser effect (3.6%) compared to resistance exercise performed alone (4.1%).[2] One meta-analysis found that the greater the frequency and duration of cardio, the greater its impact on reducing muscle growth.[3]
Studies on Does Cardio Burn Muscle
A 2021 meta-analysis found that concurrent training is more adverse for trained individuals than untrained ones, but spacing your cardio apart from resistance exercise by three hours seemed to block the interference effect from reducing strength gains in trained athletes.[4]
Most studies looking at the interference effect have used running and weightlifting; however, a recent meta-analysis found no impact of cycling and weightlifting on muscle growth.[5] Researchers suspect that since running involves high eccentric contractions, like excessive eccentric training, this can cause excess muscle damage.
Cycling does not have high eccentric contractions, hence less muscle damage. However, a recent study found that high-intensity cycling directly after resistance exercise can cause an interference effect for strength gains but not muscle hypertrophy. Researchers divided women into two groups. One group performed only resistance exercise for six weeks. The other group completed the resistance exercise and did high-intensity interval cycling 10 minutes after each lifting session. The cycling protocol consisted of 10 × 1-minute intervals at maximum aerobic power, with the workload being increased by 5% each week.
There was 1-minute of passive rest between each interval. If you can imagine doing 10 one-minute maximal sprint sessions after a workout, you know how this study ended. The resistance-only training session increased power tests such as the countermovement jump, but the combined high intensity and cycling group did not. However, despite the differences in power production between the two groups, there was no difference in muscle size or strength between the two groups.[6]
Studies on Does Cardio Burn Muscle
If you must do cardio, make sure it is after resistance exercise. Researchers found that 1-RM was significantly less when resistance exercise was done before cardio in a meta-analysis.[7] If you perform cardio first, you can deplete valuable glycogen, which will lead to reduced subsequent resistance exercise performance and volume. Reduced glycogen stores have been found to negatively affect anabolic signaling pathways.[8]
Combining both activities in a single session leads to greater glycogen depletion, increased sympathetic nervous activity, and increased stress hormones, impairing the recovery process.
Keep in mind that excessive cardio will result in a greater caloric deficit, and as you know, it’s tough to gain muscle when you are in a caloric deficit. A recent meta-analysis found that an energy deficit impairs building muscle mass.
They also found that an energy deficit of 500 calories per day prevented building lean mass in response to resistance training in a state of normal energy balance.[9] Most experts believe a caloric surplus of 300-500 calories per day can enhance lean muscle mass while minimizing unnecessary gains in fat. It is much easier to gain muscle if you eat a caloric surplus.
DOES CARDIO BURN MUSCLE KEY KEY POINTS
- Recent research suggests that cardio does not burn muscle when adequate calories are consumed.
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