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Cold Acclimation in Humans: Effects of Changes in Brown Fat on the Recruitment and Shivering Pattern of Superficial Muscles

During cold exposure, humans rely primarily on shivering thermogenesis (ST) and to a lesser extent on nonshivering thermogenic (NST) processes in an attempt to counteract increases in heat loss. Recently, cold acclimation has been shown to increase the volume and activity of brown adipose tissue (BAT). The purpose of this study was to quantify changes in ST intensity, muscle recruitment and shivering pattern (i.e. continuous vs burst shivering) following 4 weeks of cold acclimation in young men. Nine participants were exposed to a cold condition for 180 min using a liquid‐conditioned suit (LCS) perfused with 4°C water before and after cold acclimation (2hr/day at 10°C using an LCS, 5 days/week, for 4 weeks). Changes in ST were monitored by surface electromyography (sEMG) in 12 superficial muscles of torso, arms and legs. For all these muscles, results showed that ST intensity, their relative contribution to total ST and shivering pattern (total number of bursts, burst rate and burst intensity) remained unchanged following this level of cold acclimation. In previously published work, we showed that these same subjects increased BAT volume by ~45% and metabolic activity increased ~120% following cold acclimation (Blondin et al., JCEM 2014). While this suggested an increase role of NST following acclimation, the present study shows that this increase in BAT activity does not alter shivering intensity and/or recruitment pattern of muscles specifically measured in this study. Additional work will be needed to determine whether the activity of deeper muscles is affected by changes in cold acclimation.