Hi Kaboom,
If recent weather is anything to go by you'll probably be stuck with grey, overcast skies at best, so you may need to use some fill flash to help the shutter speed, to avoid unwanted motion blur. At the weigh-in, this shouldn't be a problem but I'd probably avoid using the flash when the guys are lifting those weights, as it may be off putting to them. Talk with the organiser and the strongmen on the day to find out if its okay to use the flashgun. You always have the option of boosting the ISO too, so take test shots to see how they turn out.
A fast lens will certainly be a bonus. A 50mm f/1.8 would be great for portraits at the weigh-in, whereas something like a 28-80mm f/2.8 would be more suitable for the actual events. This would allow you a decent amount of zoom to frame the shots, in case space is too limited for shooting with a fixed focal length lens (especially if there is movement along a course, etc.).
As well as the posed ones, I'd aim to take some candid shots prior to the weigh-in, of the guys preparing themselves both physically and mentally. Shots of the equipment would be good too. If it were me, I'd be looking in particular to capture the excruciating expressions on their faces and the essence of the power the human body can produce.
Switching your camera metering mode to centre weighted should ensure a good exposure of the athletes. If its
only lifting weights and not events like flipping tractor tyres down a track, it might also be worth prepositioning yourself with a tripod to further eliminate motion blur/camera shake, if the outdoor light isn't great.
Although the strongmen will start off in a fixed position for any "clean & jerk" lifts, they can tend to stagger a bit under the strain. It might be worth setting the AF mode to continuous servo so that focus is maintained. I'd also go for spot focussing as opposed to any 3D / multipoint tracking modes.
It might also be an idea to list your camera and available lenses here, so that people can offer advice for the project.
Hope that helps