When someone plays a video game, entire time the nervous system overworks: Eyes send information to brain, in turn brain decides next move, it asks fingers to execute the action, eyes observe whether desired result has been achieved or not, and again brain gets signals, brain decides and this cycle continues for hours. In the process, neurotransmitters at the end of axons get exhausted by sending impulses across synapses.
To concentrate on screen, ciliary muscles of eye must contract to adapt the lens for short range focus. Thus eye muscles become fatigued. Generally the thumb, used for holding pen/pencil becomes numb after a long session of video gaming.
Generally people think they are refreshed after gaming, but they are not. They have stopped a part of brain to stress another part. And eyes are really tired, visual signal transmission will not be as good imediately afterwards.
So, I refrain myself from commenting upon time you spend in playing a game, rather I must remind you that after a session of 15 minutes gaming you win and you rejoice but gratifications are not so frequent when you try to study and learn things. Children may then complain that 'studying is boring', but actually their expectations have become unreal.
When there is physical activity, our heart rate and breathing rate significantly increase. This helps in supplying more blood and more oxygen to brain tissues. Draining of wastes is also fascilitated. These benefits could not be drawn by playing video games, and obviously your muscles do not spend any energy.
I forgot to mention sprained neck and cervical pain.
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