A beginner is of course someone that is still getting used to training, learns which exercises target which muscles, gets acquainted with the training equipment, weights, bars, machines…, learns how to perform exercises with proper form, how to breathe while exercising; but there is another criterion that makes them a beginner.
The firstest adaptations that take place with someone just starting weight training are in the neuromuscular system. Thus, a beginner is someone who is still getting his neuromuscular system used to exercise. These neuromuscular adaptations if they exercise regularly, occur during the first several months.
What kind of adaptations are we talking about? Your orders to move muscles, are gotten through to the brain as signals, and the brain executes them through the nerves which carry these signals through to the muscles. If the brain can’t effectively relay signals to a muscle, the muscle wouldn’t work. When you start with a training program, that connection between the brain and the muscles is not yet properly set up regarding the lifting of weights. Trembling of the muscle while weightlifting, when they shake under the effort of lifting the weights, shows that the brain tries to give an order to the muscles to do something of which they are not used to. They get confused. Workout after workout, the brain is more able to activate more motor units (nerves and muscle fibers).This results in greater strength because there is now an improved coordination.
Most of the strength gains in the beginner’s phase of weight lifting, result from this improved relationship between you, the brain and the muscles, not only from increased muscle mass. Even someone can lift weights too low to cause a good muscle growth, but still will cause neuromuscular adaptation, without having muscular growth.
After this a person would have experienced progress and an increase of strength. He should know how to do the exercises properly. But mostly, after the beginning period it’s someone who’s body has already adapted to the physical stress imposed from exercise. Muscles are no longer confused, the body isn’t uncoordinated, it knows what’s happening to it.
After this adaptive period for the nervous system, the increase of strength occurs mostly because of the increase of muscle mass. Then you enter into a phase of weight lifting wherein it is extremely important what training program you use: which exercises you do, what intensity, how many repetitions, etc.