what actually happens inside your body when you decided to do physical exercise and strength training

Heart Changes: efficiency, resting heart rate decreases, increase in stroke voulme (ammount of blood pumped in 1 beat)

Lungs: the efficiency of the lungs improve

Muscles: Increase strength, the cross sectional area of the fibres increase , muscular endurnace maybe formed, defnition maybe created etc

Bones Changes: increase in bone density due to oestoblatic formation via the attachments (ligaments and tendons pulling on bones) and any impact related exercise from forces like gravity.