Effect of cold exposure on fuel utilization in humans: plasma glucose, muscle glycogen, and lipids

Haman, F., Péronnet, F., Kenny, G. P., Massicotte, D., Lavoie, C., Scott, C., & Weber, J. M. (2002). Effect of cold exposure on fuel utilization in humans: plasma glucose, muscle glycogen, and lipids. Journal of Applied Physiology, 93(1), 77-84.

Given the recent weather and elite finishing times of the 2018 Boston Marathon; runners question how the conditions on race day affected their performance. Let’s recap the conditions and stats of Marathon Monday. 2018 faced grueling conditions on Monday as heavy rain poured and wind gusts hit twenty-to-30-mile-an-hour headwinds with a wind-chill in the 20s. Being reported as the coldest Boston Marathon temperatures in three decades. Experts anticipated the harsh Boston Marathon conditions would result in slower finish times for both elites and amateurs. There were 2,220 did not finish (DNF), the dropout rate this year was 50.0% higher (4.5% v 3.0%) than in 2017, a higher percentage of men dropped out this year than women (5.0% of men dropped out this year vs 3.8% of women), and a higher percentage of men didn’t start the race who entered (14.7% for men, 13.3% for women).

Shivering thermogenesis in cool environmental conditions prevent an increase in heat production and decrease in core temperatures. Carbohydrates (CHO) and lipids fuel involuntary muscle contractions induced by shivering. Previous research proves that both plasma and muscle glucose play a significant role in heat production during cold exposure. The current study revealed that that fuel only plays a minor role in total heat production, and that low-intensity shivering plasma glucose oxidation is highly stimulated. Mild cold exposure showed that muscle glycogen oxidation doubled, providing ~75% total CHO oxidized. The finding that lipid oxidation increased fourfold as the preferred fuel utilization, which accounts for as much of the heat production then all other metabolic substances helps explains why many elite runners experienced hypothermia and/or DNF.

“Muscle glycogen stores have a predominant role, providing three times more glucose units for oxidation than the circulation. Past studies reveal that human glycogen availability modified through diet and exercise while shivering, affects fuel selection and perhaps the bodies cooling rate.

Exercise studies determined that lipid oxidation predominates for prolonged work at all intensities, including a marathon (26.2 miles). To sum it up, lipids (50%), muscle glycogen (30%), circulatory glucose (10%), and protein (10%) are unequally shard during low-intensity shivering. Could the low body fat of elite distance runners have affected their ability to perform while shivering? Possibly, as a non-elite female came in second, and only minutes behind Olympian and elite Des Linden. Future studies may unfold due to the historical events on Marathon Monday.

MA