Soreness after a weight training session or any other conditioning activity is common after you have taken an extended layoff. Usually greater than two weeks with no exercise to help maintain your fitness. That is why we talk about "active rest" performing recreational activities
(e.g., swimming, walking, a mild sport) so that your muscles are not maximally stressed-but they are doing something-so the detraining effect is not as dramatic when you return to the gym.
Otherwise it is like you are starting all over We know this from bed rest studies. If a person has not been physically active for a period of time or the activity is new to them, soreness will result after a training session. That is why proper progression is so important in a program. The soreness after a training session usually appears 24 to 48 hours later. Therefore, it is called delayed onset muscular soreness or DOMS. If it appears immediately then you have really produced some major tissue damage in the workout and have done too much and have potentially injured yourself.
While the severity of DOMS can range from minor to major injury, smart training programs use progression so that it does not become severe. The exact cause of DOMS is unclear but one popular theory is that the physical activity results in small to large amounts of damage to the muscle tissue. If the damage is severe enough, swelling can occur in the muscle. Sensations of pain are always present.
In our laboratory we have found that compression garments worn in recovery can reduce the swelling but the sensations of pain require an over-the-counter analgesic or ice treatments. Improper progression appears to be the major contributing problem. Lifting too much weight or too many sets in an exercise when you are not ready for the stress starts the whole sequence of events. Thus, DOMS is preventable. Even experienced lifters who perform a new or novel exercise in their training routine with too much weight can see similar problems occur. One way to help avoid excessive soreness is to allow time to become accustomed to the training stimulus. Use proper progression back to your training level. Do not start where you left off.
Build back up over a period of 6 to S training sessions or more depending on the amount of time you were unable to train. Best of luck and remember to be safe and smart with anything in life.