A fast lens would be the best thing. I don't think either of the lenses you have will provide sufficient results. Gyms are usually awful for lighting. I shot with an 85 1.8 on my crop body. I would go to either the end and shoot from there or about three feet on the side from the end. You'll probably have to bump your ISO, again this depends on the gym lighting but I typically would have to go as high as 1600 on my XTi.
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Lori Putman flickr
~No one can drive us crazy unless we give them the keys
~~Life isn't about waiting for the storm to pass, it's about learning to dance in the rain!
7D | 300L f/4 IS | 135L | 35L | 100/2.0 | 50/1.4
430 EX, 580 EX II Speedlites
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