Pacing for the Out-of-Shape
If you are out of shape and trying to lose weight and build strength, start with small increments that you are able to handle, such as doing only ten sit-ups, push-ups, squats, and jumping jacks. Then rest until the burning sensation subsides but no more than a minute. Then do another round until you have completed your workout time. Dedicating 15-30 minutes is a good amount of time for a balanced workout. If you have a pull-up bar (make sure you have one at your SHTF retreat; good plans for building one exist online), do as many pull-ups as you can manage, then immediately switch to chin-ups, and do the same. Also, pump out a few dead lifts. Try to complete at least two of these sessions per day. One long one (20-30 minutes) with a short one (10-20 minutes) is a good plan. Three work out session (one long and two short) is excellent.
For running, going two or three times a week is good. Run incrementally, meaning run until you can’t and then walk until you’re breathing well. (Don’t continue running if you’re forced to start gasping for air with your mouth open. Slow down until you’ve recovered and your heart rate is slower; then resume running.) As for speed, don’t sprint at top speed. Start out at a jog, and increase your speed as you become more fit. At first, it may seem you aren’t moving much faster then walking, but don’t rush. You’ll get speed (and endurance) with patience. As for distance, start with half a mile and see what you can handle. Ideally for practical maintenance fitness, your distance should be what you can complete in about an hour or so. You don’t want to spend the whole day running.
Continual/Maintenance Fitness Training
You must practice “continual fitness training”. What I mean by this is, instead of taking the elevator, use the stairs. Walk those couple of blocks instead of taking a taxi. Instead of ordering in that pizza from a few blocks away, walk to pick it up. Don’t sit at your desk on break; go down to distribution, and see if you can help lift boxes. If you’re out in the country (sweet!), carry those couple of five-gallon buckets  of water instead of pulling out the ATV. Walk over to get that shovel . It’s really not that far. Here, those who live in the country have a distinct advantage, as their daily occupations usually require a lot more physical activity. Consequently, they don’t have to do as much dedicated exercise. The country rocks!
Persevere, continually increasing the amount and intensity of your workouts, until you have reached your maintenance point!
Rough Idea of Your Maintenance Point
The maintenance point is the point where you are merely exercising to maintain your current fitness, not trying to increase, varies widely by person. There is no reason, unless you are a professional athlete, to say, “I should spend more time working out, just because I can.” Remember, the point of practical fitness, which I would venture is the best form of exercise, is to enable you to live a productive, healthy life aside from your dedicated exercise; it’s not that you live to workout. Some factors that determine your personal maintenance point will be age, activity level, gender, build, and metabolism. Needless to say, if you don’t do much physical activity in your daily occupation, you’ll need to devote more time and effort to working out. (I don’t think that office jobs are the healthiest. We are designed for physical activity. But, do your best!) Also, you will slow down with age, but let your body dictate that rate, not you. By maintaining a high level of activity, you will live longer and age more gracefully. There is no reason why older men cannot be strong and fast too.
Determining Your Maintenance Point
Here I will throw out standards of fitness excellence and you can determine your maintenance point with them in consideration.
To complete 50-75 sit-ups, 30-65 push-ups, 30-50 non-weighted squats (if you add a barbell  and extra weight, the number of reps reasonably decreases), and 10-15 pull-ups and chin-ups each in a continuous set is superb. If you can accomplish these figures in continuous sets of their respective exercises, you are in excellent shape, for an average six foot 180-210 pound male. The standards for females will be proportionally less. Go for two sets of these proportions a day, so you complete 100 push-ups a day and 200 sit-ups. These are military standards of excellence, which is all you would need for practical fitness. If you are in this good shape, spend the rest of your time elsewhere. There is no need for spending more time working out, without leaving the realm of practical fitness.
For running, to pass the Basic Training fitness exam, you must complete two miles in 16 minutes (for the 17-25 age group). If you can run two consecutive miles in roughly 20 minutes and five or six miles in an hour, you are in excellent running shape. Of course, your times may decrease proportionally with age, but with constant effort and work you should still be in fighting shape into your 50s. Once you can complete these run times, try to be able to do so carrying a pack with at least 25 pounds in it, or if you’re really brave do it in full kit. If you can run good time still, you are ready for TEOTWAWKI . Running in local 5k races also gives you good practice of running under pressure. Your performance will be markedly different when the pressure is on, as opposed to the daily jog.
It was a long one, but you’ve finished this article, and the S hasn’t HTF yet. That wasn’t the point. We don’t want to wait for that. The information I have tried to provide you here is for you to get in shape now so you’ll be ready for the moment of truth. That way you won’t be one of the people in a daze, saying, “How could this happen!?! What will I do?” It most certainly can happen. We live on the edge of a knife. When things go over the edge, you will be physically able to take charge and chart a course for victory through the chaos. Who will people be more willing to follow, to work with, to band with: someone who swaggers about bellowing, or someone who can take the end of the rope and pull the hardest? With strength, courage, honesty, charity, and nerves of steel, we will leave Captain Sofa and his beer bellied looters in the dust and be on our way to rebuild civilization. I hope I’ve been able to help, by this humble contribution.