Personal comfort systems (PCS) that warm or cool local body parts promise individual thermal comfort, energy saving and (metabolic) health in non-neutral thermal environments. However, research on work performance while using a PCS is scarce. We previously tested a PCS that warms the extremities and cools the head and reported that the PCS improved thermal comfort during a ramp of 17-23C but did not at a stable temperature of 25C. In the current study, its effects on cognitive performance, subjective measures and task-induced heart rate measures are investigated. Eighteen participants completed two randomized, eight-hour-long dynamic office scenarios: one is PCS scenario and another one is without PCS scenario. The results show warming the extremities slightly slowed reaction time for a simple task at 19C (p < 0.05) whereas it exerted no effect on complex task performance in 17-21t. At 25C however, cooling the head improved complex task performance (p = 0.053), which derived from participants' effort increase, whereas it did not affect simple task performance. These findings suggest that the PCS' effects on cogni-tive performance depended on the task type. Cooling the head, independent from its influence on thermal comfort, plays a significant role in complex cognitive performance in slightly warm conditions.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Personal comfort systems (PCS) that warm or cool local body parts promise individual thermal comfort, energy saving and (metabolic) health in non-neutral thermal environments. However, research on work performance while using a PCS is scarce. We previously tested a PCS that warms the extremities and cools the head and reported that the PCS improved thermal comfort during a ramp of 17-23 (cid:1) C but did not at a stable temperature of 25 (cid:1) C. In the current study, its effects on cognitive performance, subjective measures and task-induced heart rate measures are investigated. Eighteen participants completed two randomized, eight-hour-long dynamic office scenarios: one is PCS scenario and another one is without PCS scenario . The results show warming the extremities slightly slowed reaction time for a simple task at 19 (cid:1) C (p < 0.05) whereas it exerted no effect on complex task performance in 17-21 (cid:1) C. At 25 (cid:1) C however, cooling the head improved complex task performance (p = 0.053), which derived from participants’ effort increase, whereas it did not affect simple task performance. These findings suggest that the PCS’ effects on cogni- tive performance depended on the task type. Cooling the head, independent from its influence on thermal comfort, plays a significant role in complex cognitive performance in slightly warm conditions. (cid:1) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Abstract The classical textbook interpretation of thermal comfort is that it occurs when the thermoregulatory effort is minimized. However, stimulating human thermoregulatory systems may benefit health and increase body thermal resilience. To address this gap, we tested a novel personal comfort system (PCS) that targets only the extremities and the head, leaving the rest of the body exposed to a moderately drifting temperature (17–25°C). A randomized, cross‐over study was conducted under controlled laboratory conditions, mimicking an office setting. Eighteen participants completed two scenarios, one with a PCS and another one without a PCS in 17–25°C ambient conditions. The results indicate that the PCS improved thermal comfort in 17–23°C and retained active thermoregulatory control. The torso skin temperature, underarm‐finger temperature gradients, energy expenditure, substrate oxidations and physical activity were not affected by the PCS in most cases. Only slight changes in cardiovascular responses were observed between the two scenarios. Moreover, the PCS boosted pleasure and arousal. At 25°C, the PCS did not improve thermal comfort, but significantly improved air quality perceptions and mitigated eye strain. These findings suggest that human physiological thermoregulation can be stimulated without compromising thermal comfort by using a PCS that only targets the extremities in cold conditions.

In our modern society, artificial light is available around the clock and most people expose themselves to electrical light and light-emissive screens during the dark period of the natural light/dark cycle. Such suboptimal lighting conditions have been associated with adverse metabolic effects, and redesigning indoor lighting conditions to mimic the natural light/dark cycle more closely holds promise to improve metabolic health. Our objective was to compare metabolic responses to lighting conditions that resemble the natural light/dark cycle in contrast to suboptimal lighting in individuals at risk of developing metabolic diseases. Therefore, we here performed a non-blinded, randomised, controlled, crossover trial in which overweight insulin-resistant volunteers (n = 14) were exposed to two 40 h laboratory sessions with different 24 h lighting protocols while staying in a metabolic chamber under real-life conditions. In the Bright day–Dim evening condition, volunteers were exposed to electric bright light (~1250 lx) during the daytime (08:00–18:00 h) and to dim light (~5 lx) during the evening (18:00–23:00 h). Vice versa, in the Dim day–Bright evening condition, volunteers were exposed to dim light during the daytime and bright light during the evening. Randomisation and allocation to light conditions were carried out by sequential numbering. During both lighting protocols, we performed 24 h indirect calorimetry, and continuous core body and skin temperature measurements, and took frequent blood samples. The primary outcome was plasma glucose focusing on the pre- and postprandial periods of the intervention. Spending the day in bright light resulted in a greater increase in postprandial triacylglycerol levels following breakfast, but lower glucose levels preceding the dinner meal at 18:00 h, compared with dim light (5.0 ± 0.2 vs 5.2 ± 0.2 mmol/l, n = 13, p=0.02). Dim day–Bright evening reduced the increase in postprandial glucose after dinner compared with Bright day–Dim evening (incremental AUC: 307 ± 55 vs 394 ± 66 mmol/l × min, n = 13, p=0.009). After the Bright day–Dim evening condition the sleeping metabolic rate was identical compared with the baseline night, whereas it dropped after Dim day–Bright evening. Melatonin secretion in the evening was strongly suppressed for Dim day–Bright evening but not for Bright day–Dim evening. Distal skin temperature for Bright day–Dim evening was lower at 18:00 h (28.8 ± 0.3°C vs 29.9 ± 0.4°C, n = 13, p=0.039) and higher at 23:00 h compared with Dim day–Bright evening (30.1 ± 0.3°C vs 28.8 ± 0.3°C, n = 13, p=0.006). Fasting and postprandial plasma insulin levels and the respiratory exchange ratio were not different between the two lighting protocols at any time. Together, these findings suggest that the indoor light environment modulates postprandial substrate handling, energy expenditure and thermoregulation of insulin-resistant volunteers in a time-of-day-dependent manner. ClinicalTrials.gov NCT03829982. We acknowledge the financial support from the Netherlands Cardiovascular Research Initiative: an initiative with support from the Dutch Heart Foundation (CVON2014–02 ENERGISE).

This is the first study to examine the effect of cold-induced shivering on subsequent glucose tolerance determined under thermoneutral conditions. Plasma glucose and insulin concentrations increased during the oral glucose tolerance test post shivering. Additionally, insulin sensitivity indices suggest insulin resistance following cold exposure. These results provide evidence for an acute post-shivering response, whereby glucose metabolism has deteriorated, contrary to the results from earlier studies on cold acclimation.