Participating in an event like the Sydney Marathon needs to be approached sensibly, experts say. (Dean Lewins/AAP PHOTOS)Participating in an event like the Sydney Marathon needs to be approached sensibly, experts say. As thousands prepare for this month's Sydney Marathon, heart specialists say runners who have prepared ahead of time are unlikely to have trouble. "The risks of physical inactivity are far more than the potential risks associated with marathon running." Physical activity, when done safely, can improve heart function and reduce long-term cardiovascular risk, says Victor Chang Institute Heart, Exercise and Research Trials head Andre La Gerche.