Skip to main content
  • Meeting abstract
  • Open access
  • Published:

Mild cooling of the feet does not aid night-time vigilance


Vigilance is related to core temperature (TC) and skin temperature (Tsk). Biological day reflects a high TC, alertness and modest Tsk; night reflects vice versa [1, 2]. At rest, TC is regulated largely via controlling blood flow in extremities (and thus Tsk); vasodilation strongly predicts reduced vigilance [3] and faster sleep onset[4]. In narcolepsy, high daytime extremity temperatures and a smaller distal-to-proximal gradient (DPG) indicates higher sleep propensity [5]. Cool extremities have been linked observationally to delayed sleep onset in the elderly, and experimentally shown to reduce sleep propensity in narcolepsy [6]. Therefore, the aim of this study was to test the hypothesis that cooling the feet would maintain vigilance during extended wakefulness in healthy adults.


A randomised cross-over experiment was completed using nine healthy young adult participants with normal sleep patterns. After providing informed consent, and a daytime familiarisation, they undertook three 3-h laboratory sessions in which water-perfused booties were used to provide Mild cooling, Moderate cooling or no cooling (Control). Sessions were in a dimly-lit room, beginning at 2230. Each 30 min consisted of quiet rest interspersed with a 10-min psychomotor vigilance task (PVT), 7-min Karolinska Drowsiness Test (KDT), and ratings of sleepiness, perceived body temperature and thermal discomfort. EEG spectral powers (theta, alpha and beta) were determined within the PVT and KDT. Analyses were by repeated measures ANOVA (α = 0.05) with post-hoc contrasts with Bonferroni correction.


Foot temperatures in Control and Mild and Moderate cooling averaged 34.5 (0.5), 30.8 (0.2) and 26.4 (0.1) °C (all P<0.01). Yet, the upper-limb DPG remained stable (at ~0.3 °C) regardless of condition (P = 0.57). The decline in TC (~0.35 °C) was also unaffected by condition (P = 0.84), as was vigilance (interaction for response speed: P = 0.45). A small and transient reduction in sleepiness was evident with cooling (P = 0.046); otherwise sleepiness and vigilance deteriorated in conjunction with the fall in TC in each condition (r > 0.80). Participants felt cooler throughout both cooling trials, but thermal comfort was unaffected (P = 0.43), as were almost all EEG parameters during the KDT. All dependent measures were affected by time.


Several lines of evidence implicate a role for distal temperature in declining vigilance in the evening [36]. The extent of foot cooling used in the current study was not sufficient to alter natural homeostatic thermal- and sleep-progressions, except for a transient and minor rise in wakefulness. More substantive cooling of the extremities might be required to impact vigilance; by affecting the regulated night-time reduction in TC or causing a distracting affect from Tsk itself (which would aid wakefulness but may impair cognition).


In healthy, young adults, TC and vigilance decline regardless of mild or moderate cooling of the feet, and any effect on sleepiness is small and transient.


  1. Karasek M, Winczyk K: Melatonin in humans. J Physiol Pharmacol. 2006, 57: 19-39.

    PubMed  Google Scholar 

  2. Lack L, et al: The relationship between insomnia and body temperatures. Sleep Med Rev. 2008, 12: 307-17. 10.1016/j.smrv.2008.02.003.

    Article  PubMed  Google Scholar 

  3. Raymann R, Van Someren E: Time on task impairment of psychomotor vigilance is affected by mild skin warming and changes with aging and insomnia. Sleep. 2007, 30: 96-103.

    PubMed  Google Scholar 

  4. Krauchi K, et al: Warm feet promote the rapid onset of sleep. Nature. 1999, 401 (6748): 36-37. 10.1038/43366.

    Article  CAS  PubMed  Google Scholar 

  5. Fronczek R, et al: Altered skin temperature regulation in narcolepsy related to sleep propensity. Sleep. 2006, 29: 1444-1449.

    PubMed  Google Scholar 

  6. Fronczek R, et al: Manipulation of core body and skin temperature improves vigilance and maintenance of wakefulness in narcolepsy. Sleep. 2008, 31: 233-240.

    PubMed Central  PubMed  Google Scholar 

Download references

Author information

Authors and Affiliations


Corresponding author

Correspondence to James D Cotter.

Rights and permissions

Open Access  This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.

The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

To view a copy of this licence, visit

The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Sixtus, R., Galland, B.C. & Cotter, J.D. Mild cooling of the feet does not aid night-time vigilance. Extrem Physiol Med 4 (Suppl 1), A114 (2015).

Download citation

  • Published:

  • DOI: