You are asking about the effects of a sedentary lifestyle. This is certainly related to physical fitness, or rather a lack thereof, contrary to what some of my fellow members here feel.
There are a number of physiological adaptations that will result from too much inactivity.
I like to say that our bodies are built to be as lazy as possible. Efficiency is the driving force behind survival-if you're not going to use muscle, why spend energy maintaining it?
The effects of inactivity are wide and very detrimental to health.
Your father is going to experience the following:
- Decreased Muscle Mass
- Decreased Immune System function
- Decreased Bone Density
- Decreased Oxygen Consumption (VO2)
Now keep in mind that all the said functions are intertwined with each other-the effects experienced from inactivity go far deeper than most people realize. There are a myriad number of effects that I'm not listing, both because I don't know them all (no one does), and that the human body's system is so well tied together that it's hard to pinpoint any one thing.
The real killer is that last one. Because your father isn't placing a load on his systems to sustain life, his ability to consume oxygen is going to drop. This is an adaptation to his inactivity. Why would the body want to spend more energy maintaining what isn't used?
When the time comes to move and labor intensely, it's going to be that much harder for his heart and lungs to adapt. This is where the risk lies in contracting any sort of cardiac condition (especially heart attack).
This is also why so many elderly die when shoveling their driveways. By decreasing his muscle mass, he's also decreasing his ability to move, and therefore increasing his risk for breaking bones, because there's not enough muscle to counteract imbalances. This doesn't include decreased sensitivity to insulin (prediabetes or diabetes).
This also is why many people die soon after breaking a hip-they're too inactive, so they have no muscle, and in turn they fall and break a hip. They're now bedridden. Because their VO2 is so low and decreases even further, their heart eventually fails.
Your (and your father's) body was not designed to take it easy all the time. It was designed to work-and work efficiently. Our bodies were designed to strive towards being lazy, but not actually be lazy.
If he wants to live longer, he has to move. That's the bottom line. He's going to die if he doesn't.