Progressively overloading the body with weights will cause change. The number of repetitions per set, the number of sets, the tempo, the rest between sets, and the weight used are all factors in this.. By combining these in certain ways different effects can be caused. In this article we consider the number of reps. The effects are:-
- Neurological (The connection between mind and muscle via the nerves improves)
- Myofibrillar (The number/size of muscles fibres grow)
- Sarcoplasmic (The muscles capacity to store fuel grows)
- Capillaric (The number of blood vessels supplyi the muscle increase)
None of these effects can be isolated. But they are on a continuum and certain rep ranges favour one effect more. The list above is from low to high reps. At low reps the body is trying to get the as much of the muscle to work at once. Just move that damned weight, now! If it can't be done quickly then the body needs more muscle so that it can sustain the lift. This is because the body can't contract 100% of the muscle fibres at once, so as they fatigue the unused ones take over to complete the lift. This is all done using energy stored within the muscle. To sustain a number of repetitions the body uses up the fuel stored within the muscles, the body responds by increasing the muscles ability to store fuel. Once the muscle runs out of fuel then it must be supplied by the bloodstream, this results in new capillaries being grown to feed fuel and oxygen and remove the burnt fuel. So these result in four effects:-
- You become more powerful (mass/time) : 1-3 reps
- You become stronger : 3 - 6 reps
- You develop anaerobic endurance : 6 - 12 reps
- You develop aerobic endurance : 18 reps + (yes there is a gap; 12 - 18 reps is generally considered inefficient for most bodyparts)
Use the rep ranges above as guides; everyone is different. Use a notebook to create a history of training that you can use to work out what's best for you.
At the upper end you will gain little size. At the lower you will gain some, but much slower then being in the middle. This observable in athletes, Olympic Lifters tend not to be as big as Powerlifters who tend not to be as big as bodybuilders, and all three are bigger than marathon runners. There are individual exceptions to this, i.e. some Olympic Lifters do high reps for some exercises which cause them to grow. Genetics, and drugs, may also shift the optimal rep ranges too. A muscle gets bigger so it can exert more force, or so it can store more fuel. Hypertrophy happens when you increase in strength or anaerobic endurance.
An athlete should spend most of their time in the rep ranges suited to their sport. Some time should be spent in others, i.e. greater capillary development will help a body to get food to the muscle to rebuild it after weightlifting and cause the muscle to grow quicker. More muscle fibres will benefit the Olympic LIfter because they will have more strength to convert into power through neurological adaptation.
You may come across people describing the muscle built at lower rep ranges as looking denser than that at higher reps. This refers more to the fact that the strength per kilo is higher in someone that trains for strength. The look of a muscle is affected far more by your level of body fat.