I started boxing classes about 2 months ago, and have found it to be excellent cross-training for cycling. The class I go to spends a lot of time on core work and leg strength (who knew - there are at least 20 different versions of squats!) in addition to cardio with the punching bags. It has really helped me up my game - so much so that yesterday I went cycling after two weeks out of the saddle and was faster than my last ride! What a fun surprise.