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Modulation of cold-induced shivering activity by intermittent and continuous voluntary suppression.

INTRODUCTION
This investigation assessed the physiological effects of voluntary suppression of shivering thermogenesis in response to whole-body cooling.


METHOD
Eleven healthy volunteers underwent passive air cooling (10°C), across three visits: NO_SUP, where participants allowed their body to freely regulate against the cold; FULL_SUP, where participants constantly suppressed shivering; INT_SUP, where participants intermittently suppressed shivering (5 min phases), interspersed with 5 min free regulation. Shivering was assessed via electromyography (EMG), mechanomyography (MMG) and whole-body oxygen uptake (V̇O2), while body temperature and heat exchange were assessed via skin temperature, rectal temperature, and heat flux sensors.


RESULTS
A 29 % increase was observed in shivering onset time in the FULL_SUP trial compared to NO_SUP (p = 0.032). Assessing shivering intensity, EMG activity decreased by 29 % (p = 0.034), MMG activity decreased by 35 % (p = 0.031), while no difference was observed in V̇O2 (p = 0.091) in the FULL_SUP trial compared to NO_SUP. Partitioning the no-suppression and suppression phases of the INT_SUP trial, acute voluntary suppression significantly decreased V̇O2 (p = 0.001), EMG (p < 0.001) and MMG (p = 0.012) activity, compared to the no suppression phases. Shivering activity was restored in the no-suppression phases, equivalent to that in the NO_SUP trial (p > 0.3). No difference was observed in thermal metrics between conditions up to 60 min (p > 0.4).


CONCLUSIONS
Humans can both constantly and periodically suppress shivering activity, leading to a delay in shivering onset and a reduction in shivering intensity. Following suppression, regular shivering is resumed.