Intermediate 7 minutes
Fitness and diving: what being in shape actually does for you
Diving looks like a low-effort activity until it isn't
Recreational diving, done well, is a low-effort activity: you move slowly, breathe calmly, and let the water do the work. The problem is that the exceptions (an unexpected current, a swim back to the boat, helping a buddy) don't give warning.
In this article you'll see what the real physical demand of diving is, what being in shape actually contributes, how exercise relates to decompression, and what medical fitness to dive means.
Fitness in diving isn't for swimming faster: it's for having margin. And margin is exactly what separates an unexpected event from an incident.
Diving's real demand
The dive itself is usually the gentlest part of the day. The demanding moments are around it: carrying and hauling gear, entering and exiting the water (especially from shore or up a ladder in swell) swimming on the surface fully geared up, and the unexpected.
Those unexpected events are the part that matters. A swim against current to reach the boat, assisting a buddy, an exit at a different point than planned: these are situations that show up without warning and demand a much higher level of effort than the dive itself.
The body responds to exertion by increasing heart rate, breathing rate, and the amount of blood the heart pumps per minute. With training, that machinery becomes more efficient: the same effort costs relatively less and recovery is faster.
Fitness, then, doesn't speed up your normal dive. What it does is widen the gap between what the situation demands and what you're capable of giving. That's functional reserve, and it's the real reason it matters.
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