I won’t kid you, in general trade work is not as easy on the body as working behind a desk. If you cherish life as a coach potato, then the trades are not for you.
Some jobs are more demanding than others. Construction jobs typically require more physical exertion than service and maintenance work. Construction inevitably involves some amount of heavy lifting. Service work less so, although you still have to be in decent shape to handle situations where certain jobs may require some elbow grease and your work space may be constricted. As a service technician, you’ll often find yourself having to work with tools in crawl spaces or atop ladders working with upraised arms. These are not tasks for physical weaklings.
Yet, trade work isn’t as physically demanding as it used to be. Much of the (literally) back-breaking work has been eliminated by modern material handling equipment. Also, compared to the days of old, modern tools and equipment are often designed to minimize long-term debilitation from ergonomic injuries caused by repeated low-level stress on hands and arms. Ergonomics is a word nobody even heard of a few decades ago.
Some longtime trade workers may still develop back, shoulder or other physical ailments over time. These can be minimized by staying in good physical condition and learning proper techniques of lifting and moving heavy objects.
Also keep in mind that no profession is totally without risk. People in sedentary desk jobs have to guard against obesity and heart problems stemming from lack of exercise.
Most skilled trade workers take pride in their physical conditioning and would get bored sitting behind a desk all day. Many work out at a gym or health club in addition to tackling the physical chores of their daily job. Staying in shape has many health benefits that more than compensate for any sore muscles trade workers may experience on any given day.