My experience with exercise is that, in the beginning, it was pretty easy for me to walk a mile very quickly. One year post diagnosis, I turned my ankle carrying four bags of groceries not noticing the curb and I was hopping or in a wheelchair for about 5 months. It warmed up and I started working in the pool. I did lots of "peddling" sitting on a noodle and I was finally able to start walking again. Now, a year later, I can still walk for 1/2 mile on the treadmill and walk around the stores for 30 minutes or so.
I have lots of pain, mainly in my joints and back. I feel better when I'm moving around but, when I overdo it, I feel like I've run a marathon. When I walk, my legs feel like I'm walking in knee deep water. It takes more effort to move but I still walk fast and don't use a walker or cane. When I walk slow, my balance is bad.
After that fall, I've been very careful.
I was a very heavy exerciser prior to ALS. I ran, biked, hiked, surfed, played golf and softball and worked out at the gym 2-3 times a week. Exercise was my drug of choice.
Even now I feel so much better psychologically when I get up out of the chair often; walk down to get the mail, or grocery shop.
Just be very careful not to fall. It took 6 months of fun off my life and made my back pain much worse.