The 2nd option is correct.
When the muscles no longer have the energy needed to produce a contraction it's called as 'muscle fatigue'.
=》The accumulation or stack up of lactic acid in the muscle due to anaerobic respiration is one of the main causes of muscle fatigue.
=》This fatigue reduces the muscle's efficiency to work & contract & makes the person weaker.
_____
RainbowSalt2222 ☔
