Because if you want to make good body then you must be take rest after your exercise session in order to give your wear and tear sufficient time to fix.
Common joints:
*neck(minor).
*shoulder(chances increases if your shoulder's shape is like popped out)
Elbow(it's common pain if you work hard
For your triceps especially skull crushers and dumbbell extension)
*wrist(most of the boys oftenly complaining about wrist pain while barbell curl etc. It can be minimize by wrist support)
Knee(this the common pain if you are leg workout lover , you can minimize it by doing leg exercise with right technique and by don't giving pressure on your knees while lifting weights).
NOTE:
1.EAT
2.TRAIN YOURSELF HARDER
3.SLEEP WELL.
REPEAT
REPEAT
REPEAT
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