Lifting weights causes the small muscle fibers involved to break down during each workout. The muscle tissue breaks down more or less depending upon your workout intensity and duration. The process of muscles breaking down occurs very early on in your workout as your muscle tissue becomes depleted of its main energy source, glycogen. The breaking down of muscle tissue is a necessary process for building muscle size and endurance, but too much of it can be counterproductive.
The general recommendation for resistance training, according to Certified Strength and Conditioning Specialist (CSCS) Phil Davies, is to exercise for 45 to 60 minutes per session. The intensity and amount of weight you’re lifting also plays a role in your performance in the weight room. The goal is to break down muscle but not to the extent in which it starts to produce signs of overtraining, such as poor exercise performance and excessive muscle soreness. Your muscle tissue will break down with each set you perform, but keeping each workout under 60 minutes can increase the odds of staying within the optimal range for muscle gain rather than muscle atrophy, or loss of muscle.
Cortisol is a hormone released by the adrenal glands and plays a major role in how your muscles break down. Your muscle tissue stores the body’s preferred source of energy in the form of glycogen, which comes from carbohydrates. Glycogen stores are used up very quickly as you lift weights, especially during intense exercise with heavy weights. In an effort to “find” energy from other sources, your body releases cortisol. Cortisol causes your muscle tissue to break down and uses the resulting amino acids for energy. Help control the release of cortisol by making sure you eat plenty of carbohydrates, such as vegetables and whole grains, with each meal.
By the end of each workout, your muscle tissue has incurred significant trauma. The recovery period following your weight training session is when your muscle repairs itself and grows in size. Len Kravitz, Ph.D. of the University of New Mexico suggests that 24 to 48 hours is an adequate recovery period between working the same muscle groups. However, untrained individuals may require up to a full week of rest before the symptoms of muscle breakdown subside. These symptoms include immediate muscle soreness, delayed onset muscle soreness (DOMS), poor exercise performance and lack of sleep.
The body can continue to break down muscle tissue post-workout to make up for the lack of glycogen. According to the National Strength and Conditioning Association (NSCA), this process is known as muscle catabolism, and it can lead to muscle atrophy. Consuming a carbohydrate snack after your workout will slow down the catabolism process by returning your glycogen stores back to normal. The NSCA suggests consuming 1 g of carbohydrates per kilogram of body weight after each workout. It also states that 15 g of protein after each workout helps promote muscle synthesis, which is the process of repairing and growing muscle tissue.
- Sports Fitness Advisor; The FITT Principle of Training; Phil Davies
- University of New Mexico: How Do Muscles Grow?; Young sub Kwon, M.S. and Len Kravitz, Ph.D.
- University of New Mexico; Recovery in Training: The Essential Ingredient; Jonathan N. Mike, M.S., Len Kravitz, Ph.D.
- National Strength and Conditioning Association; Post-Exercise Nutrition: Recommendations for Resistance and Endurance Training; Debra Wein, MS, RD, LDN, CSSD, NSCA-CPT, Georgiana Mitrus, MS