This article is discussing the interesting correlation between having more money and being more mobile in the golden years.
The research, published in the current New England Journal of Medicine, found that Americans ages 55 to 84 who are wealthier have an easier time walking, carrying, reaching, lifting objects and climbing stairs than those with less money.
The focus seems to be on how money can lead to good health, which is ultimately backwards. The real answer is that the people in question are intelligent about how they approach life in general, and that fact is what leads to both money and good health.
The question is simply one of making good choices in life vs. making bad ones. If you’re likely to eat garbage, not get any exercise, remain sedentary for your entire life, etc. then you also probably lack the behaviors that make people rich. It’s the single cause (living smart) that leads to both outcomes, not one outcome leading to the other.
On to the next mystery…