I am 6 months now, but the first trimester I was just so tired I could barley get on with the day. Well now I am back, I can not run like I used to but I do do hard walks, or climbs as I call it 3 times a week. Then the other days I do normal 40 to 60 mins walks at lunch. I found that if I over do it I get pains, but my sister was a working out machine while pregnant she would come from the gym completley sweaty. You should check with your doctor but as long as you are not too tired or dehydrated you should be able to do what you did before...