text{glucose} \rightarrow \text{lactic acid + energy in the form of ATP}\) Glucose close glucoseA simple sugar used by cells for respiration. is not completely broken down, so less energy is ...

So you been sprinting, Lily? Just a bit of cramp? So that's the lactic acid building up. When an athlete does too much or runs too vigorously, not enough oxygen can be delivered to the muscles.