One of the most researched subjects since the inception of exercise science, is which rep ranges promote optimal muscle growth. Now depending on the rep range that you choose, or rather, become fatigued/fail in, will in turn elicit a corresponding muscular adaptation. Traditionally, lower reps and higher weight, produce more Power and Strength. Higher reps and lower weight, produce more hypertrophy (size) and muscular endurance.
To take it one step further, much of the research points to Total Volume (reps X sets) or Tonnage (reps X sets X weight) in being a key factor in muscle growth. Beginners, however, due to the lack of neural development, need slightly more repetition (practice) to become proficient before these principles become “the rule.” An illustration of the optimal training rep ranges for a particular adaptation is here:
As whole body movements/exercises are concerned, mainly in the realm of athletic performance, this formula still holds very true…. but of course, sometimes you must reach outside the box to see what’s out there…
As a whole body, average people are made up of about 50% Fast Twitch and 50% Slow Twitch muscle fibers (a small percentage are interchangable with training, but is negligible in this discussion). Fast Twitch muscle fibers are big, strong, and fast (duh) – and likewise, respond best to exercises that are heavy and/or fast. Slow Twitch fibers are smaller, weaker, and are much more fatigue-resistant – and likewise, respond best to exercises that are lighter and longer in duration. All muscles contain both, however some muscle groups are built for speed and power, and others for posture, support, and stabilization over long periods.
Recent research, however, has began to examine the fiber type distribution of individual muscle groups, in effort to give better insight as to how to train individual muscle groups for maximal engagement as it pertains to bodybuilding. The theory is that certain muscle groups that are “more fast twitch” should be trained heavy and/or fast, and muscle groups that are “more slow twitch” should be trained with higher reps. Essentially, you’re training a muscle group according to it’s fiber type predominance, or simply, what it’s best at.
A Review article published by Strength and Conditioning Research, aimed to categorize particular muscle groups and identify the predominant fibers in such muscles. A summary of their findings is illustrated below, and highlight the rep ranges which may serve an individual muscle best:
As hypertrophy of any muscle isn’t significant until > 5 reps, anything lower is omitted from this table. What you may notice is that a few, large muscle groups, tend to be very versatile and can grow and build strength from a wide variety of rep ranges (quads, glutes, chest, back). Smaller muscle groups, however, tend to serve a much more specific purpose, be it strength, or endurance. It does not mean that you never venture out of these rep ranges for a particular muscle group, however this is where you should tend to spend the most time during training. Likewise, many core exercises (squats, bench press, etc.) utilize multiple muscle groups, which makes the application of this information less valid, and the first table should always be referenced first. However for accessory work, it may be worth stepping into these rep ranges on a more consistent basis for optimal performance,