Difference between the IRV and ERV are given below:
Total lung capacity minus the volume of air in the lung at the end of a normal inspiration. This means that we have a reserve volume that we can tap into as tidal volume increases with exercise or activity.
IRV is about 2500 – 3500 mL in the human lungs.
Difference between the volume of air left in the lung at the conclusion of normal expiration versus at the conclusion of maximal expiration. That means that we have a "reserve" volume which we can tap into when our tidal volume increases with exercise or activity.