The popularity of ultramarathon trail running has increased rapidly in recent years, with thousands of events now held annually around the world. Ultramarathons are broadly defined by an event distance that exceeds the traditional marathon (42.195 km) and typically range from ~45 to 170 km. In contrast to the traditional marathon, ultramarathon events are frequently contested in extreme environments, such as deserts or mountain ranges, that expose participants to severe heat, cold or high-altitude conditions.
Racing an ultramarathon in an extreme environment will induce unique physiological demands on the body, and specifically on the heart and lungs. Understanding the physiological impact of an ultramarathon is important for prescribing appropriate training programs to prospective participants and for offering suitable medical monitoring during events. While completing an ultramarathon is known to transiently impair cardiac and lung function, the effects of a mountainous ultramarathon on the pulmonary circulation and transfer of gases between alveoli in the lungs and the pulmonary capillaries (i.e., the heart-lung interface) is not well understood.
Our study published in the September 2024 issue of Medicine & Science in Sports & Exercise®, examined the effects of ultramarathon racing on heart and lung interactions, with a particular focus on alveolar–capillary function and the accumulation of water in the lungs. We partnered with race organizers and the Ultra Sport Science Foundation to set up remote physiology laboratories and study runners competing in the Hong Kong 100 (a 100 km sea-level race with ~5,500 m ascent), Courmayeur–Champex–Chamonix (a 100 km high-altitude race with ~6,000m ascent) and Ultra-Trail du Mont Blanc (a 171 km high-altitude race with ~10,000m ascent). Each participant completed a series of heart and lung assessments before and after crossing the finish line, including ultrasound to assess cardiac function and lung water content. Lung diffusion measurements were conducted at rest and during exercise to quantify gas transfer across the alveolar-pulmonary capillary membrane and pulmonary capillary blood volume (the main components of gas transfer from the lungs to the blood).
Participating in these ultramarathon events caused a mild increase in lung water content and a transient decrease in lung diffusion that was predominantly caused by a reduction in pulmonary capillary blood volume and, to a lesser extent, reductions in alveolar–capillary membrane gas transfer. An interesting finding was that some participants had marked increases in lung water and more profound decreases in lung diffusion. While for most runners the reduction in lung diffusion and alveolar–capillary function is transient and unlikely to pose an acute clinical concern, some individuals may be susceptible to a more severe impairment. Additional studies are required to determine if subsets of participants with a greater magnitude of lung water accumulation and impairments in lung diffusion are at risk of adverse health events (such as developing pulmonary edema) during an ultramarathon, or if the heart-lung interface adapts and remodels in response to long-term ultramarathon training and competition.
The popularity of ultramarathon trail races is growing, particularly for youth, masters, and female athletes, and there are many physical and social health benefits of endurance exercise training and competition. However, ultra endurance events (whether footraces or other modes of exercise) are taking place in increasingly remote and challenging environments. Accordingly, there is a need for more knowledge and studies evaluating the unique physiological and logistical demands of these events. This will help optimize the management of medical monitoring during an event to ensure participant health and safety, and to elucidate the long-term health impacts of running farther, higher and for longer.
Glenn M. Stewart, PhD, is a senior research fellow at the University of Sydney and Royal North Shore Hospital in Australia. From a young age, Glenn was fascinated by the capacity of the human body to endure strenuous exercise, and in 2016 he completed his doctoral studies on the impact of endurance exercise on the heart. Following his Ph.D., Dr. Stewart completed a fellowship in the Department of Cardiovascular Medicine at Mayo Clinic in the United States and now leads an interdisciplinary research program within the Charles Perkins Centre at the University of Sydney. He is a member of the American College of Sports Medicine®, and his research focuses on the impact of chronic cardiopulmonary diseases and environmental conditions on heart and lung function during exercise.
