To put some light onto the subject i copied extract from Joe Defrancos Article " Why all Muscle was not created equal "
Sarcoplasmic hypertrophy is an increase in the volume of the non-contractile muscle cell fluid, sarcoplasm. This fluid accounts for 25-30% of the muscle’s size. Although the cross sectional area of the muscle increases, the density of muscle fibers per unit area decreases, and there is no increase in muscular strength (2). This type of hypertrophy is mainly a result of high rep, “bodybuilder-type” training (3).
One of the biggest problems I see with the training of power athletes (football players, baseball players, basketball players, wrestlers and even powerlifters) is too much emphasis on training in the 10 – 15 rep range. This type of training has its place, yet should not be the focal point for these athletes. For example, most football lineman benefit from added bulk to prevent from getting pushed around on the field. “Bodybuilding” methods, using these rep ranges, can be beneficial if incorporated during the season to prevent muscle mass loss, as well as after the season to add bulk, which may have been lost during the season. Also, there is some scientific evidence that states a bigger muscle may have a better chance of becoming a stronger muscle once maximal strength training methods are employed. The key to remember is that this type of hypertrophy has little to do with such explosive movements as hitting, running, throwing, jumping or performing a one-rep max. This is why professional bodybuilders, whose training mainly hypertrophies the Type IIA fibers and causes an increase in the non-contractile components of the muscle (sarcoplasmic volume, capillary density, and mitochondria proliferation) are not the fastest or even the strongest of all athletes. This is despite the fact that they generally have more muscle than any other class of athlete! I consider this type of hypertrophy to be form over function.
Myofibrillar hypertrophy, on the other hand, is an enlargement of the muscle fiber as it gains more myofibrils, which contract and generate tension in the muscle. With this type of hypertrophy, the area density of myofibrils increases and there is a significantly greater ability to exert muscular strength (2). This type of hypertrophy is best accomplished by training with heavy weights for low reps (3).
One must remember that the average football play lasts 4.5 seconds, it takes about 3 seconds to complete a 1 RM, it takes less than a second to swing a bat, less than a second to throw a punch and less than a second to jump for a rebound. As you can see, most athletic activities are explosive in nature. This is why it is imperative for athletes to incorporate maximal strength training methods (1-5 reps), which train the part of the muscle responsible for these explosive contractions, into their routines. Repetitions in the 1-5 rep range, using 85 – 100% of a 1RM, also have the added benefit of training the nervous system – which I feel is the most overlooked component of training the athlete. Some of the many benefits of training the nervous system are: increased neural drive to the muscle, increased synchronization of motor units, increased activation of the contractile apparatus, and decreased inhibition by the protective mechanisms of the muscle (golgi tendon organ) (1). These training methods also hypertrophy the pure fast twitch fibers – the high-threshold, Type IIB fibers. Incorporating these training methods into your routine at the right time will undoubtedly improve your muscles ability to generate more force and contract maximally during any sporting activity. In essence, myofibrillar hypertrophy is what I would term functional hypertrophy.
Although the human eye cannot tell these two types of hypertrophy apart, the difference will always become quite apparent as soon as it’s time for an athlete to put his/her muscle to use. As athletes and strength professionals, I feel we all have a responsibility to prevent ourselves from getting into the “3 sets of 10” rut. It is our job to educate ourselves, be creative, and put together the most result-producing programs available for our athletes or ourselves. This may mean incorporating both types of hypertrophy training into your routine, depending on your goal and training phase. But remember that no matter how bad those high-rep sets of leg extensions burn, they will never build the strength, power, and functional hypertrophy of a heavy set of squats or deads!