What is meant by muscle mass?
This is the increase in the volume (hypertrophy) or number (hyperplasia) of the cells that make up the muscle and results in an increase in the cross section of the muscle itself.
How do you increase muscle mass?
Increasing the load on the bone levers. Having said this which could be peaceful for everyone, we should understand how to create the load necessary for the increase in muscle mass technically called hypertrophy.
In the world of bodybuilding when we talk about load, we commonly associate the amount of weight that we can lift for a certain number of repetitions. It has been shown that different loads and repetitions produce equally different results in terms of hypertrophy, strength and endurance.
The optimal load to create hypertrophy seems to be around 70/85% of the maximum load for a number of repetitions ranging from 6 to 12.
When working with weights or counterweight machines we almost always perform open kinetic chain exercises. Except for a few cases such as the squat which, in my opinion, could be defined as a functional exercise in cat. cin. closed with overload, the other exercises use a counterweight on the distal end which obviously, as an open system, will be mobile.
Differently in functional work exercises are used almost exclusively (I say almost because the concept of "functional") should be defined in which the distal end, i.e. the furthest from the center of the body, is fixed (wall, floor, bar, rings, trx , etc...), therefore with a closed kinetic chain.
Going back to hypertrophy, one can easily understand that in functional work the repetitions can be the same as those done with weights but the load becomes difficult to reproduce as there will always be a limit of one's own body weight and, when becomes strong enough to exceed the maximum reps for hypertrophy, it's game over.
In reality, things are not quite like that!
The fateful load is given neither by the counterweight nor by the body weight, but rather by the stress to which bothone and the other subject the muscle itself, , in this case to the elastic component and the sarcomere..
This stress can vary based on many factors such as the length of the levers, the distance between the insertions, the number of fibers that are activated by the motor neurons and the speed of execution of the movement..
For this reason, the limit of body weight in functional work will be exceeded by creating more unfavorable levers and/or slowing down the speed of execution perhaps until the movement is blocked (isometry)
It goes without saying that a barbell curl done by two morphologically different subjects will give equally different results; same thing goes for a traction on the bar.
All the variables that I have listed above play a fundamental role in triggering those mechanisms that will increase the production of hormones and the consequent increase in muscle mass and they are all variables that can be modified both with weight training and with functional work. but there are substantial differences especially in the activation of the fibers.
AUTHOR
Tony Lo Grasso
released on April 19, 2015
English 
Italian