From my experience, this is true. When I worked out with a trainer, the first time was at the peak of the cycling season. We did absolutely no lower body work, except low weight leg presses, and focused on upper body and core. The second time I worked with him, was December-March. We did do lower body stuff, but it still had to be tempered by how much x country skiing I was doing; I am very sensitive to over training and I need a lot of muscle recovery time.