Why should divers avoid excessive physical exertion at the beginning of a dive?

Divers should avoid excessive physical exertion at the beginning of a dive primarily to prevent increased nitrogen absorption and reduce the risk of decompression sickness (DCS). During the initial stages of a dive, the body is adjusting to the pressure changes and is absorbing nitrogen from the breathing gas proportionately based on partial pressures.

When a diver engages in strenuous activity, the metabolic rate increases, leading to faster absorption of nitrogen into the body's tissues. This concentration of nitrogen increases the risk of forming bubbles when ascending back to the surface, which can lead to DCS.

By maintaining a calm and controlled pace at the start of the dive, divers can manage their nitrogen levels more effectively, allowing their bodies to acclimate to the underwater environment and minimizing the risk of DCS. This principle highlights the importance of diving within one's limits and being mindful of physical exertion during the critical initial phase of a dive.