How long does it take for muscles to start growing?

When a person starts a resistance training program aimed at increasing muscle mass without any previous training experience, it may take some time before results are visible. Despite the rather large increase in strength during the first few weeks, the muscles do not grow very rapidly. How long does it take for muscles to start growing? And how is it possible that the muscles are getting stronger without growing larger?

This can be explained by the nervous system recruiting more muscle fibers during a specific exercise, which could not be activated before. In addition, autogenic inhibition, or antagonistic muscle activity, is lowered which results in an increase in net produced force, without the muscles having to work harder. Moreover, the antagonistic muscles work even less. In other words, the nervous system optimizes the muscular system and it learns how to use the muscles more effectively without any structural adaptations such as hypertrophy, which cost a lot of energy and protein to realize.

During the first two to three months of resistance exercise, this mechanism plays the largest role in increasing muscle strength. Hypertrophy, while present to a small extent, will become more noticeable when most of the potential of the muscles has been reached and the muscular system receives adequate stimulation to warrant further adaptation. This means that exercise intensity must increase continuously so muscles have a reason to grow, when the nervous system cannot realize any further improvements in muscle coordination. After the period in which the nervous system improves muscular coordination, hypertrophy will become more noticeable.

References:

-Heyward, V.H. Designing Resistance Training Programs. In: Advanced Fitness Assessment and Exercise Prescription. 2009. Human Kinetics, Champaign USA.

-Wilmore, J.H., Costill, D.L., Kenney, W.L. Adaptations to Resistance Training. In: Physiology of Sports and Exercise Fourth Edition. 2009. Human Kinetics Champaign USA.