Question

Why do we get body pains after doing vigorous exercise?

Answer 1

Because of deposition of lactic acid in our muscles.

Explanation:

When we do some strenuous physical activity, oxygen can't be supplied to muscles as quick as it is needed which creates an oxygen debt in muscle tissues. So, the muscle cells begin to carry out anaerobic respiration along with the aerobic one to meet `"ATP"` requirement. Thus breakdown of glucose in the absence of oxygen starts. The two pyruvates formed as a result of glycolyis are converted into two lactic acids`(C_3H_6O_3)` are produced. This lactic acid is being deposited in our muscles tissues.

Equation for anaerobic respiration in muscles:

`2(C_3H_4O_3) to 2(C_3H_6O_3)`

The deposition of lactic acid in muscles causes soreness of muscles and muscle fatigue. Muscle fatigue causes a feeling of tiredness and exhaustion after workout.
At rest, `"1/5"` of lactic acid is broken aerobically. The energy of which is used to change remaining `"4/5"` lactic acid into glucose in liver cells. Thus oxygen dept is repaid. So, the pain doesn't last for long time. And it's also not that bad because it renders our muscles with greater efficiency.

`Note:`
If pain can be felt even after two days of intense muscular activity then the condition is termed as Delayed Onset Muscle Soreness abbreviated as `"DOMs"`. It causes edema, inflammation, microscopic injuries to the myofibrils and greater degree of muscle soreness as compared to normal one.

Hope it helps...