If you can't meet the request, be honest, straightforward, and give the reason why. Learning to be assertive about the use of your time can increase your level of self confidence in other areas of your life. Set priorities for yourself. Define what you would like to accomplish in the next three months, and block out the necessary time for it. Schedule a fun exercise activity into your fall routine, just as if it were a meeting you were required to attend.
Exercise promotes wellness and reduces stress.
Don't discount the benefits of your active life, either. Just running up and down stairs is great for your body. Take the team approach to family living. Rather than doing it all yourself, enlist the help and counsel of family members. Have them come up with healthy snacks to have on hand.