This normally depends on how fit you were before giving birth and whether or not you had a normal delivery or a caesarean section. After a normal birth and a caesarean section its worth waiting until you have your six week check at the doctors before starting strenuous activity such as jogging aerobics or an exercise class.
However if you had a normal birth then regardless of fitness pelvic floor exercises can be started as soon as a new mum feels ready. However do not do full sit ups until your pelvic floor has recovered fully.
If you exercised right until the end of your pregnancy then light exercises can be started almost straight away. I swam until the day before my first daughter was born and with a fairly easy delivery I started light exercise almost straight away. I was taking my baby for a walk within a week of the birth. However after the birth of my third baby I had a much more difficult birth and I did not start any exercise apart from pelvic floor exercises until after my six week check at my doctors. I think with so many of these things only you know how you are feeling!
So if you are feeling really well just start off gradually with light stretching and taking your baby out in the buggy. Listen to your body if you are over doing it then you will know. If you are feeling physically tired try and rest more. If you are over doing it, instead of your bleeding (lochia) reducing after birth it could start getting heavier again. If this happens its worth consulting your doctor.
If as so many new Mums find you wet yourself just a little at times when you laugh or sneeze then exercising hard will aggravate this. Its worth looking at increasing your pelvic floor exercises again. These can be done stood doing the washing up or stood in the bus queue and nobody need know just by clenching the muscles of your pelvic floor!!!
After having my third baby my stomach just was not going back in the way that it had with my other babies. I had something called diastasis rectus abdominus which basically meant my stomach muscles had stretched too much during pregnancy. My mid wife diagnosed me with this and with lots of lower tummy exercises and pelvic floor exercises I was able to rectify it myself but it is important not to do full sit ups until it has healed.
Lastly if you had back pain or pelvic pain during pregnancy consult your GP or a physiotherapist before exercising.
After your six weeks check and everything has returned to normal more strenuous exercise is an option but start gradually! things to consider:
There is some research to suggest that after strenuous exercise that your milk will have higher levels of lactic acid and that this could change the taste of your milk for your baby. I never noticed any difference with my babies but that was my personal experience other mothers may notice other effects! If you have experienced differently we would love to hear through your comments below.