Gastrointestinal temperature of elite and recreational adult runners during a 100‐mile ultramarathon under heat exposure
Abstract
This study examined gastrointestinal temperature (T GI ) during and body mass (BM) changes pre/post the Western States Endurance Run 100 (WSER), a 100‐mile ultramarathon in hot conditions. Thirty‐nine participants ingested a telemetric pill 30–90 min before the WSER start, and BM was measured pre‐ and post‐race. Environmental conditions were recorded every 30 min at 15 locations along the course. In‐race T GI data were obtained from 23 finishers (54%; 7 females; 42 ± 11 years), including 2 podium finishers and an additional top‐10 finisher. Participants finished in 14–18 h ( n = 4), 19–25 h ( n = 6), and 26–30 h ( n = 13). Peak T GI averaged 38.90°C ± 0.55°C (range 37.76°C–40.09°C) with 9 runners exceeding 39°C and 2 exceeding 40°C. Faster finish times were associated with higher peak T GI ( r = −0.57, p = 0.004). Seven runners (30%) reached peak T GI in the final 2% of the race. Mean BM change was −1.8% ± 3.1% (range −7.4% to +6.4%), with no associations observed between BM change and peak T GI or finish time. Ambient temperature ranged 5°C–39.6°C and was associated with higher T GI ( r = 0.80, p = 0.008). Despite ambient temperatures approaching 40°C, T GI >40°C were rare and transient. Faster runners experienced greater thermal strain, likely reflecting higher metabolic heat production and exposure to the hottest course segments. Hyperthermia risk may be highest near the race finish and during the most demanding segments.
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BibTeX
@article{mougin2026gastrointestinal,
title = {{Gastrointestinal temperature of elite and recreational adult runners during a 100‐mile ultramarathon under heat exposure}},
author = {Loïs Mougin and Richard Stennett and Brett Ely and Baptiste Morel and Larry O'Neill and Chris Esh and William Adams and Daniel Longman and Richard Blagrove and Lee Taylor and Stephen Mears},
journal = {Physiological Reports},
year = {2026},
month = sep,
doi = {10.14814/phy2.71089},
url = {https://hal.science/hal-05747001v1},
note = {CC BY},
}
RIS
TY - JOUR
TI - Gastrointestinal temperature of elite and recreational adult runners during a 100‐mile ultramarathon under heat exposure
AU - Loïs Mougin
AU - Richard Stennett
AU - Brett Ely
AU - Baptiste Morel
AU - Larry O'Neill
AU - Chris Esh
AU - William Adams
AU - Daniel Longman
AU - Richard Blagrove
AU - Lee Taylor
AU - Stephen Mears
PY - 2026
DA - 2026/09/07
JO - Physiological Reports
DO - 10.14814/phy2.71089
UR - https://hal.science/hal-05747001v1
AB - This study examined gastrointestinal temperature (T GI ) during and body mass (BM) changes pre/post the Western States Endurance Run 100 (WSER), a 100‐mile ultramarathon in hot conditions. Thirty‐nine participants ingested a telemetric pill 30–90 min before the WSER start, and BM was measured pre‐ and post‐race. Environmental conditions were recorded every 30 min at 15 locations along the course. In‐race T GI data were obtained from 23 finishers (54%; 7 females; 42 ± 11 years), including 2 podium finishers and an additional top‐10 finisher. Participants finished in 14–18 h ( n = 4), 19–25 h ( n = 6), and 26–30 h ( n = 13). Peak T GI averaged 38.90°C ± 0.55°C (range 37.76°C–40.09°C) with 9 runners exceeding 39°C and 2 exceeding 40°C. Faster finish times were associated with higher peak T GI ( r = −0.57, p = 0.004). Seven runners (30%) reached peak T GI in the final 2% of the race. Mean BM change was −1.8% ± 3.1% (range −7.4% to +6.4%), with no associations observed between BM change and peak T GI or finish time. Ambient temperature ranged 5°C–39.6°C and was associated with higher T GI ( r = 0.80, p = 0.008). Despite ambient temperatures approaching 40°C, T GI >40°C were rare and transient. Faster runners experienced greater thermal strain, likely reflecting higher metabolic heat production and exposure to the hottest course segments. Hyperthermia risk may be highest near the race finish and during the most demanding segments.
SN - 2051-817X
ER -