For six weeks, one should not exert after the mesh repair. The pain is one of the reason, but the tissue healing too is affected, if one over exerts. Any surgery entails cutting of the various layers of the tissues, thus weakening of those tissue. All of them need adequate time to heal and gather strength, before over exertion is allowed. So growing of the tissue into the mesh interstices will be affected and delayed if one over exerts in the initial period. The other reason of avoiding over exertion is chance of leakage of fluid or blood in the tissues due to exertion, which too can hamper the healing.
Please feel free for your follow up questions.