How do I prevent bruises on my troweling hand (archaeology)?

I've been working an archaeological dig that has a high clay content, thus the difficulty in troweling. How can I prevent my hand from becoming sore and bruised? I've tried switching hands, using my other hand for stabilization, etc. The bruises and joint pain are extreme. Any thoughts? I've switched to screening for artifacts, but the buckets are a tad heavy for me. I guess my main question is how long it takes to get used to this sort of activity.