How'd they break? Did the nose end come off, the body dissemble from the axle, the retainer mech crap out? Have they suffered in the past, by grounding out in turns, hitting curbs, potholes, etc?
Your weight or their capacity to handle it don't seem the most likely cause to me. You're not all that big, and Look typically makes pretty good stuff. Maybe you got a bad set, maybe they were dinged, maybe....?
A forum community dedicated to Road Bike owners and enthusiasts. Come join the discussion about bike parts, components, deals, performance, modifications, classifieds, troubleshooting, maintenance, and more!