Re:BMI is not accurate (Score 1)

It is a common technique to manage your buoyancy with the amount of air in your lungs for snorkeling and SCUBA diving. Most everyone will sink without air in their lungs and float with thier lungs full. If you have a considerable amount of muscle and a small lung capacity, you could sink on a full breath of air. This is very unlikely to happen though since training will often increase your lung capacity.