I've been doing low carb (more atkins than SB) for about 6 months. But, the past 2 months I have been very lax and I am working on getting back to strict.
Anyhow, from my experience the first 2-3 weeks of low carb are the hardest. If you are doing fine, and feeling good, you will probably not notice any difference when you exercise, especially if you are starting a new exercise plan. I do bootcamp classes 4-5 times a week and have not seen a big noticeable difference related to my carb intake.
If you were a big runner beforehand and just made a drastic dietary change, then you might see some difference. But in your situation I think you will be fine.
lowcarbfriends.com has a great forum if you want to check it out!
M, mommy to A 2005, E 2007, and L 2010