It's the recovery from the controlled damage and stress which produces the improvement.
All forms of personal growth require high stress to produce improvement, whether physical, mental, or emotional.
The purpose of intense physical exertion itself is to break you down, to damage muscles, to stress tendons, ligaments, bones, and neuromuscular connections to the point that they are forced to adapt. That is why only very difficult and unpleasant physical demands get results.
Building strength and power is meant to wreck your body and to blow your mind, but in a careful, controlled way.
We have all had the experience of feeling like a deadlift barbell is glued to the floor. Then somebody else, or your own head, says "You can do this, just get it off the floor" and suddenly "giving it your all" shifts and the meaning of "your all" expands into new territory.
With exercise, we should gain muscle weight. Unless we're fat, we should put on solid weight.
After an hour or so of power lifting, we recommend 48 hrs. with just an hour of Active Recovery before another day's power lifting. Passive Recovery is just decent sleep and adequate protein intake (over 80 gms/day). Active Recovery gets the blood moving, includes activities which require minimal recovery time, like calisthenics, cardio intervals, speed walking, etc. - just no heavy weights.
It all works together that way, at least for the middle-aged, in 5 or so hours of structured exercise - which is less time than most people waste watching TV and movies:
Monday: Half of your power lifts and accessory lifts/pushes
Tuesday: 30 minutes cardio intervals + some calis
Weds: 30 mins cardio intervals + some calis
Thurs: The other half of your power lifts and other accessory lifts/pushes
Fri: An hour of high-intensity calis
Sat: 45-60 minutes of Active Recovery mixed, less-intense cardio (meaning you can breathe - not intervals, eg treadmill at 3.5 mph, or rowing, running, swimming, elliptical, boxing exercises, dance class, stair machine, spinning, Aerobic class) is good for maintaining endurance and will not fatigue you for the weekend. These all count as good Active Recovery.)
Sunday is the Lord's day. Take a stroll to the diner after church.
All other weekend things like hiking, outdoor chores, playing sports, sex, etc do not count as exercise. Strength-oriented Yoga is neither fish nor fowl. Good stuff, but I would include it as recreational effort like sports. Anyway, doing those sorts of things happily are the rewards of fitness.
To keep it simple, the cardio intervals stress and strengthen your heart, the lifts strengthen your neuromuscular and bone systems, the calis address your overall athleticism plus cardio, endurance is for endurance, and all of the synergies and overlaps are just good for the brain and for preparedness for life in abundance.
People with little kids and/or demanding 14 hr/day jobs have trouble finding time for fitness. It's reality, but it's a shame because fitness is easier to maintain than to regain. Believe me, as Trump would say. I have been regaining it for 2 years, so I know.
Addendum: If you are fatter than you want to be, none of the above will help very much with that. Fat loss is 90% diet and that is 90% about carbs.
