But to what degree? I'm relatively healthy but I'm not about to run a marathon. I am really just looking for standard if there is any.
Muscle is important, but depending on what you believe to be the most likely of scenarios for you to face, I would refrain from over emphasizing on muscle mass. Focus on endurance is extremely important.
I've watched entry level grunts who were previous body builders fall out of conditioning hikes with their packs on their backs nearly every time. Well, they may not "fall out" in each case, but they certainly struggle to keep up because their focus was on muscle and not stamina/endurance. Or watch the same guys struggle to keep going once they step into the ring because of their size compared to a leaner, more stamina driven guy. In a SHTF situation, it's more likely to be needed to hike/run a distance than to be able to bare handed pick up an engine block (for example) IMO.
Fitness is sort of relative, because people often associate large muscles with being fit and indeed everyone has a different build. There are larger framed guys and smaller framed guys. That doesn't mean they should focus on muscle strength/size to a point where it won't serve a purpose outside of a gym or otherwise limit their capabilities elsewhere (flexibility, stamina, etc.)
On top of that, maintaining that size/strength requires a level of food intake/nutrition that you're not likely to achieve in a disaster situation.
Strength is certainly important, but reaching a level which is likely not necessary outside of a gym for any given task isn't going to be too prudent for a survival situation. Focus on stamina, endurance, and LEAN muscle growth.
Sounds to me like Mrs Kidd has been paying a little too much attention to the muscular guys at the gym and *someone* doesn't like it...
I think physical fitness is VERY important for survival or fighting, or for life in general.
There needs to be a proper balance of strength, power, speed, endurance and flexability, along with general health and remaining injury and disease free as much as possible. For most of us, life happens and that balance changes. Seeking to rebalance is the key, always. So, you get out of the Army and gain 50 pounds, new job, 3 kids, married/divorced etc. Or you suffer an injury, could be a car accident, a fall, or an overuse/chronic injury and that sets you back. Or you get sick, and that lays you low, maybe even changes your life forever. Dunno. But the key is to fight your way back. To be as fit as you can be, at your stage in life, at your age and to work around any limitations as best you can.
I know 28 year old dough balls who can't hump a ruck more than 100 yards or do a push up, let alone drag a 185 pound man from a burning car and return fire. I know 63 year old men who can run 26 miles, do 500 push ups and, slide into cover to run a belt fed and make it all look easy. (but they take ibuprofen).
I guess your level of physical fitness should be task oriented. What will you have to do? Be realistic. Then start there.
Many good things have been said, so I really don't have a whole lot to add. However, I have gained some valuable insight in my time studying martial arts and one of the most profound reasons for physical fitness came from the Chinese. Strength and flexibility will allow you to inflict more damage than you take. Your risk of accidental injury is going to be far less than it would be if you sit around and do nothing. I never really realized what all of that meant until one reckless winter where I took two bad falls and luckily ended up with bruises instead of broken bones. I later had a DEXA Scan and at 32 years-old had the bone mineral density (BMD) of a professional football player, so there's really no luck involved. So, the physical prep left me no convincing at all, as physical health is something I don't want to wish I had if SHTF.
I know 63 year old men who can run 26 miles, do 500 push ups and, slide into cover to run a belt fed and make it all look easy. (but they take ibuprofen).
I'm working toward getting ready for the Warrior Dash later in the year. It is a 2 1/2k race with obstacles involved. I figure that if I can complete that then I should at least be in good enough shape for a period of survival in a crisis situation. I know I can do a lot of things because I have done them just to test myself but I have never been a runner so I figured why not sink or swim now rather then later when my life could depend on it. That being said I believe physical fitness will be a huge factor in a SHTF event and even more then that just being in good health rather then "fit."