Background The Genghis Khan Ice Marathon took place in January 2016 in the mountains of the Terelj National Park, Mongolia in a temperature of minus 35 ⁰C.

Objective To assess the experience, preparation, race strategy and effect of exercise in a group of ultrarunners undertaking a marathon in extreme cold.

Design Prospective observational study.

Setting Extreme environment.

Participants Multinational group of experienced ultrarunners (n=9, male 5, female 4, age range 25–53 years).

Interventions Pre and post race questionnaires. Post-race email surveillance.

Main Outcome Measurements Experience, preparation, clothing, equipment, nutritional strategies for race. Adverse effects encountered when competing in the marathon. Perceived effort of race on the Borg Scale. Two weeks post race illness or injury surveillance.

Results All nine ultrarunners completed the questionnaires and follow up. Concerns about safety in a remote environment were universal. Consensus was present regarding clothing, equipment, hydration and nutrition. The race was completed in 3:05–5:50. No significant difficulties were encountered. The cold air caused freezing around the nostrils and irritated the airways. No-one experienced cold induced bronchospasm. Clothing froze due to sweat and expired air. There were no cases of hypothermia. There were two cases of frostbite; earlobe (moderate) and nose (mild). Borg scale of perceived exertion values ranged from 13–17 (mean 15). Two week follow up; two cases of viral URTI's reported. No athlete reported DOMS in the post race period.

Conclusions All athletes were experienced in ultrarunning. They shared concerns regarding competing in a remote, extreme cold environment. All were adequately prepared pre race in terms of clothing, equipment and race nutrition strategy. This level of experience contributed to the lack of complications during the race and in the post race period. No athletes experienced DOMS presumably related to lack of peripheral muscular perfusion during exercise in extreme cold.