Excellent book. IMO it should be considered required reading for all on this site.

15-20 years back my typical run was 4.5 miles in ~34 minutes. These days when I run it's with a dog on a leash and the risk of injury is much higher. Walking is a much better survival mode.

Being physically fit is always good going into a survival situation if for no other reason than the mental stress. That said, survival is rarely a race. If you're alive at the end with all your fingers and toes, you did good. If you're alive but missing a few parts, you need to reassess your limitations. Personal opinion.