Physical activity is unlike some other hazards. Reducing many hazards in their magnitude is always – as a goal – a good idea. Some hazards are related to risk in such a way that less exposure to the hazard is always preferred. Examples are hazards such as exposure to asbestos, or welding flash. No one needs any level of asbestos or welding flash. If zero can be achieved then that is good. The risk-exposure curve begins at the “zero” origin conceptually something like the first figure below.
However physical activity is necessary in some amount. An overly sedentary lifestyle is viewed as being less than ideal. Hence the risk-exposure curve does not begin at the origin. Zero exposure does not equate to zero risk. The relationship is conceptually a bathtub type curve where risk rises with both too little and too much physical activity. The challenge is to avoid excesses of both kinds. Thus there will be examples of physical work where reducing the demand is not only not necessary but not helpful.
Positively correlated hazard-risk curve (e.g. asbestos, welding flash, falls from height)
“Bathtub” type hazard-risk curve (e.g. physical work)