It is a well known fact in sports science that steady state cardio training inhibits muscle hypertrophy. When endurance athletes lift weights, they get stronger and increase the size of their type 2 muscle fibers (fast twitch fibers). Yet they rarely gain muscle mass. For endurance athletes, this is great news. They get stronger while improving their oxygen efficiency. For people trying to gain muscle mass, I suggest you pay attention to the science.
Endurance vs. Strength Training and Muscle Mass
In this study, well trained cyclists with no strength training experience performed a 12 week strength training program. A group of non-cyclists, with no endurance training performed the same program. During the study, the cyclists continued with their normal endurance training in addition to the strength training program. The non-cyclists only performed the strength training program. At the end of the study, non-cyclists had gained about 2 pounds of muscle. The cyclists had gained zero.
Researchers believe that high volume training from doing BOTH resistance training AND steady state cardio endurance training leads to hormonal changes that impair muscle growth. (See Study) The bottom line: If you are trying to gain muscle, lay off the endurance training. (For information about the best supplement for building muscle, read this.)
But what if I want to lose fat?
The superior method of losing fat is through resistance training. Let’s compare 45 minutes of steady state cardio training with 45 minutes of strength training. 135 pound person running 6 mph, for 45 minutes will burn approximately 430 calories. When the person stops running, the caloric effects of the training session are over. A 135 pound person lifting weights for 45 minutes will burn approximately 290 calories. However, pay heed to the after burn effects of strength training, which is where weightlifting really pays off. Strength training creates micro-trauma to the muscle fibers, which creates a cascade of hormonal and metabolic changes in the body. This trauma releases waste products that must be expelled from the tissue, which requires a lot of cellular energy (more burned calories for up to 6 hours after the workout). Next, the body goes to work rebuilding the damaged muscle tissue, which requires still more calories for up to 24 hours after the training session.
Since workout intensity varies greatly, it is difficult to calculate with any accuracy the number of calories burned in recovery. However, we can safely assume that if the workout is intense enough to create muscular trauma, then the body will burn more than 140 additional calories. This simple fact makes strength training superior to endurance training from a purely caloric perspective. (For more tips on losing bodyfat, read this.)
Hormones are Your Friends
An additional benefit of strength training is that damaged muscle tissue rings an alarm in the endocrine system, telling the body that new muscle is required (See Study). This triggers glands to release a cascade of hormones, including testosterone, growth hormone, thyroxine, and epinephrine that assist in building more muscle tissue and further facilitating future positive changes in body composition (reducing fat and increasing muscle mass). (See Study) (Note: Females only have about 10% of the testosterone as males, but even at this level, powerful metabolic changes occur.) Endurance training has the opposite effect, often increasing serum cortisol levels. (See Study)
Losing fat and gaining muscle is often more challenging than improving endurance. If your goal is to improve your endurance, compete in a triathlon, or become a better cyclist, then prolonged cardio training is essential to your training regimen. Keep it up! If a marathon is not in your future and you want to change your physique, then you are better off hitting the weights and hanging up your running shoes for a while. The cardio training is doing little to reduce your belly fat. Lifting heavy things is way more effective, and it has a nice side effect of bigger biceps.