I have a few friends who are trying to get a lean body after they saw my fitness progress. Most of them are very surprised to know that I have a kid. Some of them asked me what types of workout that suit them especially when trying to get their pre-natal weight. I must say that different people have their own different 'style' and 'preference' to do workout. Some of us would go for Zumba, or Insanity workout. But as for me, I'd stick to something that's more on building muscles, and burning some fats (i.e. HIIT, TaeBo, etc).
