Most of us recognize the importance of athletes and body builders gaining muscle mass; however, increasing muscle mass is just as important for fitness enthusiasts looking to improve body composition or aging individuals looking to sustain function and independence into their 60’s and beyond. The technical term for muscle growth is “fiber hypertrophy,” with fiber referring to the muscle cell itself and hypertrophy simply meaning “enlargement of.” The scientific community generally accepts that the only way to increase muscle size is through hypertrophy (increasing the size of existing fibers), as opposed to hyperplasia (the creation of new muscle fibers). And, while some exciting new research suggests that hyperplasia may, in fact, occur under certain circumstances, most of the existing research addresses the best methods for achieving hypertrophy.
When muscle fibers increase in size they simply store more protein internally (a process called accretion). The amount and rate at which protein is stored are primarily controlled by special hormones that circulate around the bloodstream and communicate with muscle fibers, telling them how much protein to store. These hormones are considered anabolic hormones because they are involved in tissue building. The three hormones critical to the process of muscle growth are testosterone, insulin, and growth hormone, and enhancing their release with the right type and amount of training can maximize muscle growth.
Unfortunately, very few good systematic reviews of the optimal training parameters (sets, reps, intensity, rest interval, frequency, etc.) for muscle hypertrophy have been published. However, in 2007, an extensive literature review was published on training for muscle hypertrophy, which concluded the following: (1) the ideal training frequency for muscle growth is 2-3 days per week, per muscle; (2) the ideal training volume (reps per session) is between 40-80 per muscle group; and (3) the ideal training intensity is around 70-80% of one-rep max, which corresponds to about 8-12 repetitions per set (Wernborn et al, 2007).
This literature review, as well as research from other leading experts in the field (Kraemer & Fleck, 2004. Willardson, 2006. Frye, 2004.), suggests that the ideal training program for muscle growth is one that trains each major muscle group 2-3 times per week (preferably separated by 48-72 hours), performing between 8-12 reps per set and 4-8 sets per muscle group. Exciting research on the relationship between rest interval length and muscle growth suggests that the optimal rest interval between sets be approximately one minute (Willardson, 2007). A protocol such as this maximizes anabolic hormone release and enhances protein storage in the muscle, thereby leading to optimal muscle growth when compared to other (heavy/fewer rep or lighter/more rep) training protocols.