Stagework says:

Traditionally, ex-sailors were hired as flymen since they were physically fit and used to heaving ropes to raise sails. A flyman’s job used to be very physically taxing, but now, in many theatres, the job of flying scenery is mechanised and only requires a person to control a computer. Flying scenery is often not a job on its own, but can be a part of the role of stagehand or theatre mechanist.

Some of the duties of a flyman are loading and unloading scenery, maintaining and repairing the flying equipment and scenery, building and setting up stage scenery and suspended scenery, raising and lowering suspended scenery during a performance, operating the mechanical components of the stage, and storing and setting up scenery. As you can see, a flyman’s job involves a lot of the technical work behind the scenes, and in smaller theatres where the flying systems are not mechanized, there is still a lot of physical labour involved.

The Crescent Theatre says:

Many set pieces, cloth backgrounds, gauzes etc are suspended over the stage and “flown” in when they are needed. The Crescent stage has approximately 30 flying bars, all hand operated. Flyers move the bars up and down by pulling on ropes, accessible from the fly gallery, approximately 25 feet above the stage level. All the bars are counterbalanced so that, even if a heavy piece of scenery is suspended from the bar, it does not require super-human strength to move it. A head for heights helps!