Something anyone who trains for the first time or after a long time observes is the Delayed Onset Muscle Soreness (DOMS). Basically, it’s that pain or stiffness you feel in your muscles the day(s) after training, which can last for an entire day or more. 

During physical exercises, our muscles contract and relax. These processes lead to minor damage (microtrauma) to our muscle fibres. During rest, after exercises, our body repairs these micro-tears. The resultant muscles (the muscles that we see after this reparation) becomes stronger and larger than they were prior to the training. So does their adaptability improve as well.

With successive exercises, the repeated-bout effect (the adaptation whereby a single bout of eccentric exercise protects against muscle damage from subsequent eccentric bouts) sets in. So, the soreness improves with successive exercises, and you’re able to even do more than you did the first times. This is why it’s always advised to space out training periods, with one or two days gap or train different muscles in a sort of rotation; this gives time for the torn muscles to repair.

From the above illustration, it’s evident that there cannot be any growth without a tear occurring in your muscles; it is the tear and the consequent repair that results in the building of your muscles.

In life, just as in muscle exercises, you must be willing to go through pains, stiffness, strenuous and unaccustomed exercises to reach the peak. If you’re not willing to cry and go through tears, you may as well relax and watch your TV. 

But if you want to grow, you must be willing to become uncomfortable, for there is no growth in your comfort zone. Your muscles can only hypertrophy under pain, stress and repair.