When I use to race back in the mid 70's to mid 80's I use to warm up. Science wasn't as exact back then as it is today, but I would run first for about 5 minutes then get on the bike and ride for about 5 to 10 minutes depending on how far the race was. On a century race I never warmed up since everyone was going slow anyways in the beginning I just use that time to warm up.