In other words, myofibrillar hypertrophy leads to a greater density of the contractible myofibrils which increases the ability to exert strength and is best accomplished by training heavy weights with low reps, and sarcoplasmic hypertrophy is an increase in the volume of the non-contractible muscle cell fluid called sarcoplasm (which makes up to 30 % of the muscle's size), doesn't lead to an increase in muscular strength and can be achieved by performing high - rep, low - load training. (fitnessandpower.com)
They occur as a result of the running blood and nutrients into the non-contractile part of the muscle cells also known as sarcoplasm. (fitnessandpower.com)
This is a fast way to increase the size of a muscle, but since sarcoplasm is a fluid and can't contract... it won't make the muscle significantly stronger. (pathtofatloss.com)