A marathon runner is usually skinnier and thus has less surface area than a lineman. The reason the lineman is better at floating is because they displace more water. So when water is displaced, the water pushes against you with equal force what you have displaced and which is why boats float but rocks do not, boats displace more water compared to their surface area. And in this case the boat is the linemen while the rock is the marathon runner who has less surface area per weight ratio