The rest that wears you out: Why a day at the beach can be exhausting

Every day, a community garden and a seaside promenade separate Carmen Gutiérrez from Sardinero Beach in Santander, Spain. Despite the proximity, she avoids venturing onto the sand when she has work ahead of her. "The beach is tiring," she confesses. Returning home after hours by the sea, she feels no inclination to unpack her belongings; instead, she yearns to rest on the sofa.

This sensation is familiar to many holidaymakers. While lying on a towel under the sun appears relaxing, returning from a day at the beach often leaves people feeling fatigued and low on energy. Javier Ceballos, a sports medicine specialist, explains that the reason lies in three physiological mechanisms. The first is thermoregulation, as the body prioritizes maintaining a stable temperature of around 37ºC (98.6ºF) when the ambient temperature rises.

To achieve this, the body activates a complex system that consumes energy even when motionless. The hypothalamus, the brain's thermostat, instructs blood vessels to dilate and initiates sweating to cool the body. However, these processes come with a cost, as the heart works harder and fluid loss contributes to fatigue. Additionally, fluid loss occurs even when still, leading to dehydration which further strains the heart.

The second mechanism involves the body's defense against solar radiation. Ultraviolet rays can generate oxidative stress and damage skin cells, triggering an inflammatory response and releasing immune-signaling molecules that make the body feel tired. Finally, walking on sand is more strenuous than walking on firm ground, requiring nearly twice as much energy due to the sinking sensation and increased muscle effort.

To minimize beach fatigue, Ceballos recommends staying hydrated, avoiding peak sun hours, using adequate sun protection, and taking regular breaks in the shade.