Which of the following is NOT a physical factor affecting diving capabilities?

High swimming skill is not a physical factor that directly affects diving capabilities. Instead, it reflects a diver's comfort and proficiency in the water, which are valuable traits for safe and effective diving but do not inherently impact the physiological aspects involved in diving.

In contrast, the other factors listed—recent head injury, inadequate rest, and recent ingestion of alcohol—are physical conditions that can influence a diver's health and safety during a dive. A head injury can affect cognitive and physical functions; inadequate rest can lead to fatigue, impairing attention and decision-making; and alcohol consumption can impair judgment and increase the risk of accidents underwater. These factors are crucial to consider for ensuring a diver’s well-being and capability when engaging in scuba diving activities.