Maintaining core body temperature is generally not a significant concern during most thru-hikes, thanks to the effective heat dissipation in various outdoor environments. However, the challenges shift during extended walks, especially in warmer conditions. A substantial portion of the energy exerted during long-distance hiking transforms into heat waste, contributing to an increase in core body temperature.
The situation becomes intriguing when the core body temperature surpasses 38.5 degrees Celsius (101.3 degrees Fahrenheit), categorized as hyperthermia. Hikers breaching this threshold are likely to experience extreme thirst, fatigue, gastrointestinal distress, and an overall discomfort due to the elevated heat. In a research endeavor during a challenging thru-hike, a group of hikers voluntarily wore telemetric devices, enabling a research team to monitor their core body temperature throughout the journey. Many hikers experienced hyperthermia during the most strenuous sections, with the average core body temperature reaching 38.55 degrees Celsius.
It’s noteworthy that these hikers narrowly entered the realm of hyperthermia, and this is not coincidental. The human body employs various mechanisms to prevent the accumulation of heat to hazardous levels. Sweating is one such mechanism, and I will elaborate on it shortly. However, the most effective approach involves regulating hiking pace based on perceived effort. Research indicates a connection between heat perception and effort perception—hikers tend to pace themselves more conservatively as they feel hotter, preventing excessive heat buildup. Interestingly, while it was previously believed that core body temperature itself triggered this protective mechanism, current understanding suggests that the conscious sensation of heat is the primary factor. Hikers tend to slow down even when their skin is warm but their core temperature remains normal.
It’s essential to recognize that this mechanism is not foolproof. Determined hikers can consciously override it, pushing beyond hyperthermia into heat exhaustion, where the core body temperature reaches a perilous 40 degrees Celsius (104 degrees Fahrenheit). When this occurs, the body’s systems may malfunction, leading to dizziness, disorientation, lack of coordination, and potential collapse. Learning from such experiences is crucial; paying attention to warning signs of overheating is imperative during a thru-hike. Just as Scottish runner Callum Hawkins experienced heat exhaustion less than 2 kilometers from the finish line at the 2018 Commonwealth Games Marathon, thru-hikers must not disregard these warning signs on their challenging journeys.
