Working-Out Highers Your Weight?

Today was the first day to weigh in for the 6 week challenge, well no one told me that I was suppose to weigh in before I worked out until afterwords I went to the trainer and asked her if I can weigh in now. She told me I couldn't because when you work out you weight will be higher. It's amazing how you do learn something new everyday. So Wednesday, I'm going to workout again, but this time, I'll make sure I get measured and weighed before I work out.