A CK-MB test may be used as a follow-up test to an elevated CK in order to determine whether the increase is due to heart damage or skeletal muscle damage.
Scuba organizations say recreational divers shouldn't go below about 130 feet, but one Egyptian diver recently ventured a bit deeper -- going more than 1,000 feet below the ocean surface and setting a world record in the process.
I never dive I used to do it in sea waves and even there once I bumped my head at the bottom a few times. For a shallow racing-type dive, a zero-freeboard pool should be at least 4 ft deep (and 6 ft would be better). So if you want to be able to dive in from any point along any edge of the pool, it would need to be 4-6 ft deep over its entire 'footprint'. For a vertical entry, significantly more depth is needed to reduce the risk of serious head/neck injury.