Muscles are an important part of your body, and as a strength training athlete or bodybuilder you should understand how muscles work.
There are three very different types of muscle, skeletal muscle, cardiac muscle and smooth muscle. Skeletal muscle are directly attached to the bones via tendons, these are the visible muscles that you train in the gym. Most skeletal muscles (like your biceps) are attached to a movable part, while the other end is attached to a fixed part. Skeletal muscles also have opposing muscles, one contracts (biceps) while the opposite muscle extends (triceps).
Smooth muscles are also known as involuntary muscles, and can be found within walls of organs like your stomach and intestines or the muscles that allow you to move your eyes or continue to breathe. Involuntary muscles work without conscious thought. Cardiac muscle is found only in the heart.
There are 640 muscles in your body, and as most muscles come in pairs, there are around 320 pairs. Muscle tissue is made of muscle cells which contain thousands of myofibrils or strands. These muscles are covered by layers of connective tissue known as facia.
Muscle Fiber Types
Skeletal muscle fibers have metabolic and mechanical differences that allow them to be classified into different types. Each muscle in your body is made up of a bundle of small fibers and each bundle contains three types of fibers: slow twitch, fast twitch and intermediate. The percentage of each fiber type varies greatly by individual. Knowing YOUR mix of fiber types can help you plan exactly how you should train each particular muscle group in your body.
Slow twitch fibers are responsible for long-duration, low intensity activity such as walking or any other aerobic activity.
Fast twitch fibers are generally white muscle fibers and are responsible for short-duration, high intensity activity, explosive, very short-duration activity such as Olympic lifts as well as short-to-moderate duration, moderate-to-high intensity work seen in most weight training.
Intermediate fibers (fast oxidative-glycolytic fibers) are fast twitch muscle fibers which have been converted via endurance training. These fibers are slightly larger in diameter, have more mitochondria as well as a greater blood supply and more endurance than typical fast twitch fibers.
How Do Rep Ranges And Muscle Fibers Affect Training?
Until fairly recently, there were only two types of training in the gym – powerlifting or bodybuilding.
Powerlifters are only interested in increases in strength and perform very low reps at very high weights with the goal of constantly increasing their one rep maximum. Bodybuilders are interested only in increasing muscle size (and shape).
The school of thought has always been heavy loads (1-5 RM) promote strength gains, moderate loads (6-12 RM) produce max increases in muscle mass, and light loads (15+ RM) produce the greatest improvements in muscular endurance. However, if your goal is size (hypertrophy) adding moderate weights at higher rep ranges to promote endurance may convert fast twitch fibers to intermediate fibers which are larger in diameter.
A study published in the Journal Of Sports Science And Medicine compared the muscular adaptations in a “bodybuilding-type” routine versus a “powerlifting-type” routine in resistance-trained men. The study confirmed the “strength-endurance continuum” concept, and found that the powerlifting-type routine (1-5 RM) produced the greatest strength increases. Contrary to prevailing thought, both routines produced similar increases in hypertrophy of the biceps brachii.
Training with heavy weights maximizes muscle strength and training with moderate to heavy loads promotes greater increases in muscle mass as detailed in the chart below: