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Shooting bodybuilders on stage, the art and technique of contest photos has changed dramatically since we know have very evolved systems of digital photography. Until this happened we had to shoot stage photos on film. A much more difficult enterprise. Since there are still people who choose to do photography using film, I'll describe how this had done before contrasting the techniques involved with what is necessary to do competition photos using digital photography.
The first consideration is what kind of light is being used. Light has color temperature so outdoor light at midday is fairly blue while the light you get at sunset is much warmer, with more reds. Different kinds of artificial light can differ a great deal of color variation as well. Spot lights are bluish. Tungsten stage lights are more red. If you are shooting color negative film this is not a problem. Color adjustments are made when the negative is printed so one kind of negative film can work for most circumstances. But in my pro career the magazines I worked for wanted us to use transparency film - color slides. Unlike negative film, color slides come in different color temperatures: primarily daylight and tungsten. If you chose an inappropriate kind of film you get results that are way too blue or much too red, depending.
The problem using tungsten transparency film for shooting bodybuilding contests - or any other subject taking place on a theater stage - is that there is often not enough light and the film itself has relatively little sensitivity. Tungsten film is only 160 ASA (one way of measuring film speed) which is not very fast. You can "push" it - that is double the development time to achieve 320 ASA - but in many cases the stage lights are dim enough to make this a problem. One solution in situations like this is using very fast lenses - that is, lenses that open up to a very wide aperture to let in a lot of light. However, to get both close ups as well as wide-angle shots your have to have access to long (telephoto) lenses. Telephoto lenses tend to be more expensive. And when you add the requirement they also be very fast you are talking about a considerable investment in equipment.
There was also the necessity of using slow shutter speeds - again to try and achieve the required level of exposure. Big lenses and slow shutter speeds call for using a tripod. Shooting a bodybuilding competition therefore turned into a physical effort where the photographer usually worked with at least two cameras, needed to change lenses and wrestled around with a tripod and camera bag in crowded proximity to bunch of other photographers in the press pit.
Comes digital photography and all of this changed. Shooting RAW, no need to worry about color temperature. That's something you set later on in Photoshop or Lightroom. Photographers are no longer limited to low ASA sensitivities. My Canon 5D Mark III produces perfectly acceptable images at a setting of 2000 ISO (another scale of measuring sensitivity) and even higher settings also produce totally useable images. This means you can shoot in very low light with slower lenses and faster shutter speeds. This is a real revolution. In fact, after shooting film for so many years I was very slow to start using higher ISO settings. I would shoot at ISO 1200 and get too many blurry images from slower shutter speeds when I should have been using (and would now when required) ISO settings of 2000, 2400 or whatever is needed.
The above is a description of the technical aspects of shooting bodybuilding contests. But there is an artistic side to this as well. Bodybuilders hitting poses on stage flex and hold, then relax. If they are doing an individual posing routine, they hit poses and do various (some more than others) transition moves as well. If there is a line up of bodybuilders hitting poses they won't necessarily all be totally flexed at the same time. The job of the photographer is to time the shots to capture the poses at exactly the right time. This isn't something that can be taught. It takes experience and trial and error. And as what happens doing photos of any live event, you are going to have a lot of images that have to be edited out.
By the way, one major aspect of shooting contests that has changed radially is the cost. When I was shooting for magazines they picked up the expenses. But I remember going to a photo store and buying as much as $1000 worth of film for a weekend job. And then that film had to be processed. Anyone shooting freelance would go broke having to come up with that much money. But with digital the cost of shooting is zero and the cost of processing is the same.
So photographers nowadays can afford to shoot bodybuilding contests freelance, on spec or simply for themselves.