It says here after 45yo you are too old and risk a heart attack from such exercise.(http://www.autoadmit.com/thread.php?thread_id=5805893&forum_id=2\u0026mark_id=5310864#49481438)
It's the only decent cardio a lot of people get in winter(http://www.autoadmit.com/thread.php?thread_id=5805893&forum_id=2\u0026mark_id=5310864#49481468)