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. 2025 Apr 12;12(3):264–280. doi: 10.1080/23328940.2025.2488542

Optimizing whole-body cryostimulation exposure duration: Effects of age, sex, and body mass index in achieving target skin temperature

Hela Jdidi 1,✉, Claire de Bisschop 1,*, Benoit Dugué 1,*, Wafa Douzi 1
PMCID: PMC12416175  PMID: 40926788

ABSTRACT

The optimal Whole-body cryostimulation (WBC) exposure duration to reach the target skin temperature may vary depending on individual factors such as age, sex, and body mass index (BMI). Maintaining skin temperatures below 13.6°C is necessary to trigger significant cold-induced analgesia. The aim of our study is to investigate how these variables influence the duration required to reach the analgesic threshold temperature of 13.6°C during WBC. A randomized cross-over controlled trial was conducted with 90 healthy participants, categorized by age, sex, and BMI. Each participant underwent two sessions: a 4 min WBC exposure at −50°C and a control session. Skin temperature was measured using a thermal imaging camera before, during and after cold exposure. Significant differences in skin temperature were observed between groups. Among young participants, normal-weight men required 4 minutes of exposure to reach the analgesic threshold (p < 0.05), while normal-weight women reached it in 3 minutes (p < 0.01). Overweight young men needed 3 minutes and 30 seconds (p < 0.001), whereas overweight young women reached the threshold earlier, at 2 min and 30 s (p < 0.01). For senior participants, both normal-weight men and women reached the analgesic threshold at 3 minutes of exposure (p < 0.001). In contrast, overweight senior men and women needed only 2 minutes and 30 seconds to reach the target skin temperature (p < 0.01). The optimal WBC exposure duration for achieving analgesic effects varies significantly depending on individual characteristics, suggesting that WBC protocols should be tailored to maximize therapeutic benefits.

KEYWORDS: Age, body mass index, cold exposure, gender, sex, skin temperature, whole body cryostimulation

Introduction

Whole-body cryostimulation (WBC) is a cooling technique, where the entire body is exposed to extremely low temperatures, typically ranging from −50°C to −160°C, for short periods, usually between 2 and 5 minutes [1]. WBC is commonly used to alleviate pain and inflammation associated with various diseases, particularly rheumatic conditions such as arthritis, fibromyalgia, and ankylosing spondylitis [2]. It is also employed to enhance sleep quality and support post-exercise recovery [3,4].

The basic premise of cryotherapy is that variations in ambient temperature are detected at the cutaneous level by activating thermosensitive skin receptors. This activation triggers peripheral vasoconstriction, a key regulatory mechanism that reduces heat loss and helps maintain constant core body temperature [5]. Consequently, changes in skin temperature become the primary metric used to guide the cryostimulation process. In fact, the magnitude of achieved skin temperature directly influences the effectiveness of cold exposure in producing analgesic effect while avoiding adverse effects [6]. On one hand, prolonged exposure to cold temperatures carries inherent unnecessary thermal discomfort or excessive skin cooling. On the other hand, insufficient exposure may fail to elicit the desired physiological responses, rendering the intervention ineffective [6]. Thus, striking the right balance in exposure duration is crucial.

To induce significant cold-induced analgesia, it is essential to maintain skin temperatures below 13.6°C. This analgesic response appears to result from several mechanisms, such as reduced sensitivity of receptors and a decrease in nerve conduction velocity (NCV) [7–9]. Research has shown that a skin temperature of around 13.6°C leads to a 10% reduction in NCV, which is deemed ideal for clinical analgesia [10]. The degree of skin cooling during cryostimulation directly influences its effectiveness in eliciting beneficial cold responses while preventing adverse effects. Thus, determining the optimal duration of WBC exposure is essential. For instance, Fonda et al. [11], contended that sessions longer than 2 minutes and 30 seconds (s) are unnecessary, while Selfe et al. [12], suggested that a minimum exposure of 2 minutes was essential to initiate physiological changes in core and skin temperature. The rationale behind the use of longer or shorter exposure times remains unclear and warrants further investigation.

The evaluations of skin temperature should consider individual characteristics. Factors such as the body mass index (BMI), sex, and age can influence the efficacy of WBC. Research shows that lean and overweight individuals may respond differently to cold stimuli [13–16]. These variations may be attributed to the insulating properties of body fat [17]. In fact, studies have found a positive correlation between body fat percentage and the rate of skin temperature reduction, highlighting the role of body fat percentage in cold-induced skin temperature changes [18,19]. These findings underscore the need to consider both BMI and body fat percentage when assessing the cold-induced responses. Regarding sex-related variations, several studies have identified discrepancies between men and women in response to cold exposure. For instance, Cankar & Finderle [20], revealed that women exhibited a more pronounced cutaneous vascular response to local cooling compared to men. Furthermore, women generally have a higher body fat percentage, which, as previously mentioned, may influence how skin temperature changes in response to cold exposure. Additionally, sex-related differences in the body surface area-to-mass ratio contribute to faster heat dissipation in women, potentially resulting in a more rapid decrease in skin temperature [21]. Therefore, considering sex-specific differences can help ensure a more effective WBC exposure. Age is another critical factor influencing thermoregulatory responses to cold. As individuals age, their ability to thermoregulate during cold exposure diminishes [22]. Older adults experience less effective vasoconstriction and shivering, resulting in an increased heat loss and reduced metabolic heat production. This makes age an important consideration when tailoring cold exposure protocols to individual needs.

Despite the widespread use of WBC, there is still debate regarding the optimal duration of exposure. The main objective of this study is to determine the optimal exposure time required to reach the analgesic threshold of 13.6°C considering body composition, age, and sex. Based on established physiological differences, we hypothesize that women, overweight individuals, and older participants may reach the target temperature in a shorter WBC exposure durations. Therefore, our study aims to offer valuable insights into optimizing WBC protocols to enhance effectiveness for diverse populations based on their characteristics. In addition to identifying the optimal WBC exposure duration to reach the analgesic threshold, we investigated post-WBC rewarming responses as a secondary outcome, exploring potential differences based on sex, age, and body composition.

Methods

Participants

Ninety healthy men and women were assigned to 8 groups based on sex, age, and BMI (Figure 1). Participants were divided into two age categories: young adults (18–30 years old) and senior adults (55 to 65 years old). Participants were further classified according to the World Health Organization (WHO) BMI categories: individuals with a BMI of 18.5–24.9 kg.m−2 were categorized as normal weight, while those with a BMI of 25 to 29.9 kg.m−2 were classified as overweight (see Table 1 for participants’ characteristics).

Figure 1.

Figure 1.

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Participant group classification based on sex, age, and BMI.

NYM.G: Normal weight young men group; OYM.G: Overweight young men group; NSM.G: Normal weight seniors men group; OSM.G: Overweight seniors men group; NYW.G: Normal weight young women group; OYW.G: Overweight young women group; NSW.G: Normal weight seniors women group; OSW.G: Overweight seniors women group.

Table 1.

Participant characteristics. Data are presented as mean ± SD.

n Men
 Women
BMI Normal weight Overweight Normal weight Overweight
Age Young Senior Young Senior Young Senior Young Senior
Abbreviation NYM.G OYM.G NSM.G OSM.G NYW.G OYW.G NSW.G OSW.G
N 15 10 15 10 10 10 10 10
Age (years) 21.1 ± 2.1 58.4 ± 3.4 22.2 ± 3.9 57.6 ± 2.8 22.9 ± 2.7 58.9 ± 3.1 22.4 ± 3.1 60.1 ± 4.3
Height (m) 1.8 ± 0.1 1.8 ± 0.03 1.8 ± 0.1 1.8 ± 0.1 1.6 ± 0.1 1.7 ± 0.1 1.7 ± 0.1 1.6 ± 0.1
Weight (kg) 69.0 ± 9.2 70.1 ± 4.7 87.9 ± 5.3 86.2 ± 9.0 56.8 ± 5.5 63.5 ± 8.7 75.6 ± 6.2 71.0 ± 6.3
BMI (kg.m−2) 21.5 ± 1.6 23.0 ± 1.1 27.4 ± 1.2 27.7 ± 1.5 22.1 ± 1.7 23.0 ± 1.2 27.6 ± 1.8 27.8 ± 1.7
Fat mass (%) 14.6 ± 1.8 18.3 ± 4.01 20.8 ± 2.4 25.5 ± 3.9 23.0 ± 5.1 27.5 ± 2.9 35.9 ± 4.3 37.2 ± 3.8
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NYM.G: Normal weight young men group; OYM.G: Overweight young men group; NSM.G: Normal weight seniors men group; OSM.G: Overweight seniors men group; NYW.G: Normal weight young women group; OYW.G: Overweight young women group; NSW.G: Normal weight seniors women group; OSW.G: Overweight seniors women group.

Participants were screened for contraindications to cold exposure, including cold hypersensitivity (Raynaud’s syndrome), cold allergy, history of heart disease, or circulatory pathologies. None of them were on medication. They were instructed to refrain from consuming alcohol, coffee, and performing strenuous physical exercise two hours before and 30 minutes after the intervention. Additionally, for young adult female participants, the inclusion criteria required being non-pregnant and using monophasic oral contraception to maintain stable sex hormone levels throughout all data collection sessions. For senior women, the requirements included being postmenopausal for at least 4 years and with no vasomotor symptoms, such as hot flashes and night sweats.

In accordance with the Declaration of Helsinki, participants received oral and written explanation of the study protocol, including the potential risks and benefits of the experimental procedures. After receiving this information, all participants signed a written informed consent form. The study was approved by the National Ethics Committee (South-East I Committee for the Protection of Persons; number: 2022-A00525-38).

Experimental design

Participants completed two different sessions: an experimental session involving 4 min of WBC exposure and a control session with no cold exposure. The order of the sessions was randomized, with both conducted at the same time of day and separated by a 7-day interval. The cryostimulation protocol took place in a specially designed dual-compartment WBC chamber. Participants first spent 30 seconds acclimatizing in an adaptation zone at −25°C before moving to the primary section, where they were exposed to −50°C with an average wind speed of 2.3 m/s (WBC chamber, Aurore concept, Noisiel, France) [23]. During WBC exposure, participants rotated every 30 s, alternating between facing the fan and turning their back to it. This routine was maintained throughout the session to ensure equal cooling distribution on both the anterior and posterior sides. During exposure to cold, participants wore minimal clothing: bathing suit, socks, protective footwear, gloves, headwear, and surgical mask.

Skin temperature was recorded before WBC exposure, immediately after, and at 5 min intervals for 30 minutes post-intervention. Throughout the exposure period, skin temperature was recorded every 30 seconds. Identical measurements were conducted during the control sessions, which were held at ambient temperature. In both the control and WBC sessions, participants wore the same clothing for consistency. After each session, participants were seated in a room at ambient temperature (21.1 ± 1.4°C), dressed only in shorts. The study was carried out over a three-month period, from December to February, aligning with the winter season in the region.

Measurements

Anthropometric measures: Bodyweight and composition were assessed using a validated 8-point bio-impedance device (Tanita BC418-MA, Tanita Corp., Tokyo, Japan).

Skin temperature: Skin temperature was assessed with a thermal imaging camera (Optrix GmbH, Holzkirchen, Germany) positioned 1.5 meters from the participant. The camera’s emissivity was set to 0.98, and an 80 mm focal length lens was used. Data were collected through Optrix PI Connect software. Additionally, skin temperature inside the cryotherapy chamber was continuously monitored with an integrated thermal camera of the same technology. Skin temperatures of four distinct body segments (trunk, arm, thigh, and leg) were recorded on both the front and back surfaces. The mean skin temperature (MsT°) was then calculated using the Ramanathan formula (1964) [24] as follow: MsT° = 0.3 T° trunk + 0.3 T° arm + 0.2 T° thigh + 0.2 T° leg.

Core body temperature: Two hours prior to each session, participants swallowed a telemetric Tc pill (e-Celsius, BodyCap, Caen, France) that provided continuous measurement of gastrointestinal temperature. Core body temperature (CBT°) was recorded at 1 min intervals during both the WBC exposure and control session. Due to the high cost of the device, core body temperature measurement was limited to evaluating potential gender-related differences, with only groups of young, normal-weight men and women included in this assessment.

Statistical analysis

The results are presented as mean values ± standard deviation. The Shapiro – Wilk test was used to assess the Gaussian distribution. A multifactorial repeated measures analysis of variance (ANOVA) was performed to examine changes in MsT° during (time of measurement × sex × age × BMI) and following (time of measurement × sex × age × BMI × condition (WBC session vs Control session) WBC exposure, as well as Segmental MsT° analysis (body area × sex × age × BMI). Effect sizes for ANOVA results were reported using partial eta squared (ηp2), which indicates the proportion of variance explained by a given factor. Values of 0.01, 0.06, and 0.14 were interpreted as small, medium, and large effects, respectively [25]. When significant interactions between factors was found, post-hoc analyses were conducted using the Bonferroni test. The significance level for all tests was set at p < 0.05. Spearman test was used for correlation analysis between variables. STATISTICA 10.0 software (StatSoft, Inc. Tulsa, OK, USA) was used for the analysis.

A priori power analysis was performed using G*Power (version 3.1.9.7) to determine the appropriate sample size. Based on a previous study reporting an effect size of 0.5 [11], a repeated-measures ANOVA was simulated with an alpha level of 0.05, and a statistical power of 95%. The analysis indicated that a total sample size of 64 participants was required. To account for an anticipated 20% dropout rate, the final sample size was adjusted to a minimum of 80 participants (10 per group).

Study cohort and data compilation

In this study, we aimed to investigate the influence of body composition, sex, and age on the optimal duration of whole-body cryostimulation needed to reach a target skin temperature of 13.6°C. Our participant group included a diverse range of individuals, with young and seniors, both men and women, and representing normal weight and overweight categories. It is important to note that data for young men with normal weight and those with overweight status were previously collected and analyzed in a previous study. The primary focus of that initial study was to examine the effect of BMI on cold-induced thermal responses, revealing significant differences in how individuals with different BMIs responded to cryostimulation. However, the objective of the present study builds upon these findings by incorporating additional variables: sex and age to provide a more comprehensive understanding of how these factors the cooling process during WBC.

Results mean skin temperature changes during WBC exposure

The analysis revealed significant differences in MsT° variation based on sex (F = 18.90; p < 0.001; ηp2 = 0.19), age (F = 7.04; p < 0.01; ηp2 = 0.08), and BMI (F = 32.09; p < 0.001; ηp2 = 0.28), as presented in Figure 2. Additionally, a significant interaction was observed between age × sex × BMI × time of measurement (F = 3.94; p < 0.0 1; ηp2 = 0.05). A significant difference in MsT° values between men and women was observed starting from 2 min of exposure and persisting until the end of the 4 min exposure period (p < 0.01). Women consistently showed lower MsT° values compared to men throughout the exposure period. In the age-based analysis, younger participants showed significantly higher MsT° values compared to seniors starting at 2 minutes 30 seconds, continuing through the full exposure (p < 0.01). Additionally, BMI-based differences appeared as early as 1 min into the exposure and remained significant through to the 4 min period (p < 0.001), with overweight individuals having lower MsT° values than those with normal weight. Spearman correlation analysis revealed a significant negative relationship (R = −0.71; t = −9.34; p < 0.001) between MsT° after 4 min of WBC exposure and body fat percentage (%) (Figure 3).

Figure 2.

Figure 2.

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Effect of sex, age and BMI on mean skin temperature magnitude during WBC exposure.

†: Significant difference between groups (p < 0.05). Data are presented as mean ± SD

Figure 3.

Figure 3.

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Correlation between body fat percentage and mean skin temperature immediately after WBC exposure.

Post-hoc analysis revealed a significant decrease in MsT° compared to pre-exposure values, starting from 30 seconds (p < 0.001) and continuing until 4 minutes of exposure (p < 0.001) for all groups (Figure 4). Among young participants, normal-weight men reached the analgesic threshold at 4 minutes of exposure (p < 0.05), while normal-weight women reached it at 3 minutes (p < 0.01). Overweight young men reached the threshold at 3 minutes 30 seconds (p < 0.001), while overweight young women reached it earlier, at 2 min 30 s (p < 0.01). For senior participants, normal-weight men and women both reached the analgesic threshold at 3 minutes of exposure (p < 0.001), while overweight senior men and women reached it at 2 min 30 s (p < 0.01). Furthermore, measurements of core body temperature showed no significant change during WBC exposure for both normal-weight young men and women (p > 0.05) (Appendix).

Figure 4.

Figure 4.

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Mean skin temperature magnitude during WBC exposure.

NYM.G: Normal weight young men group; OYM.G: Overweight young men group; NSM.G: Normal weight seniors men group; OSM.G: Overweight seniors men group; NYW.G: Normal weight young women group; OYW.G: Overweight young women group; NSW.G: Normal weight seniors women group; OSW.G: Overweight seniors women group. *: Significant difference compared to baseline at all measurement times, for both groups (p < 0.01). Data are presented as mean ± SD

Segmental analysis

The segmentary analysis, as presented in Figure 5, shows MsT° measurements in selected body areas immediately after WBC exposure. Significant differences were observed across all groups, with temperatures in the trunk and upper limbs being notably higher than those in the lower limbs (p < 0.001). Between-group comparisons revealed significant differences between men and women, with a more substantial reduction in MsT° in women (p < 0.001). Furthermore, results showed that overweight and senior individuals experienced a greater decrease in MsT° in the trunk and upper limbs (p < 0.001), compared to their normal-weight and younger groups, respectively.

Figure 5.

Figure 5.

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Mean skin temperature in selected body areas after WBC exposure.

†: Significant difference Between groups group (p < 0.001); η: Significant difference between upper and lower body segments (p < 0.001); Data are presented as mean ± SD

Mean skin temperature changes following exposure

Following WBC exposure, our results showed significant effects of sex (F = 32.3; p < 0.001; ηp2 = 0.16), age (F = 17.9; p < 0.001; ηp2 = 0.10), and BMI (F = 74.6; p < 0.001; ηp2 = 0.31) on MsT° magnitude (Figure 6). Post hoc analysis indicated that overweight participants consistently had lower temperatures than normal-weight participants throughout the recovery period, from 30 seconds to 30 minutes post-exposure (p < 0.01) (Figure 7). Additionally, women exhibited lower temperatures than men from 30 seconds until 15 minutes post-exposure (p < 0.001). Regarding age, significant difference in temperature between seniors and younger participants, were observed only at 30 seconds post-exposure (p < 0.001).

Figure 6.

Figure 6.

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Effect of age, sex, and BMI on mean skin temperature magnitude following WBC exposure.

†: Significant difference between groups (p < 0.01). Data are presented as mean ± SD

Figure 7.

Figure 7.

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Mean skin temperature magnitude following WBC exposure.

NYM.G: Normal weight young men group; OYM.G: Overweight young men group; NSM.G: Normal weight seniors men group; OSM.G: Overweight seniors men group; NYW.G: Normal weight young women group; OYW.G: Overweight young women group; NSW.G: Normal weight seniors women group; OSW.G: Overweight seniors women group. *: Significant difference compared to pre-exposure value, at all measurement times, for both groups (p < 0.001); ‡: Significant difference compared to the preceding measurement, for both groups (p < 0.001); #: significant difference compared to WBC exposure, at all measurement times, for both groups (p < 0.001); Data are presented as mean ± SD

Across all groups, MsT° values were significantly lower following WBC exposure compared to both control sessions and baseline values at all measurement times (p < 0.001). Immediately after exposure and up to 5 minutes post-exposure, there was a rapid rewarming with an increase in MsT° of approximately + 12.8°C. Between 5 and 15 min post-exposure, the MsT° increment was more moderate, around + 3.5°C. Beyond 15 minutes to 30 minutes post-exposure, no further significant increase in MsT° was noted (+1.5°C). However, the measured temperatures remained considerably lower than pre-exposure values.

Discussion

Based on previous research, our study extends the investigation into the optimal duration of WBC exposure, addressing gaps in earlier studies that focused solely on BMI. By incorporating additional variables such as sex and age, we provide a more comprehensive analysis of how individual characteristics influence thermal responses to WBC. This continuity allows to refine the application of cryostimulation by offering practical guidance for healthcare professionals, trainers, and athletes.

The current study investigated how age, sex, and BMI influence the optimal duration of WBC needed to achieve a target skin temperature of 13.6°C. The analgesic effect appears to be mediated by neurophysiological mechanisms, including a reduction in receptor sensitivity and a decrease in nerve conduction velocity (NCV) [7]. According to previous studies, a skin temperature of approximately 13.6°C is necessary to achieve a 10% reduction in NCV, which is considered optimal for clinical analgesia [10]. The results of the present study demonstrated significant variations in MsT° during WBC exposure based on these individual factors, supporting our hypothesis that sex, age, and BMI influence the cooling thermal responses. In summary, our study demonstrated that the optimal WBC exposure duration to reach the analgesic skin temperature of 13.6°C varies significantly depending on sex, age, and BMI. The longest exposure duration to reach the analgesic threshold of 13.6°C was observed in normal-weight young men (4 minutes). This exposure time was reduced by 30 seconds to 1 minute 30 seconds depending on sex, weight status, and age (3 minutes 30 seconds for overweight young men, 3 minutes for normal-weight senior men and normal-weight young and senior women, and 2 minutes 30 seconds for overweight senior men and overweight young and senior women). Overall, women, seniors, and overweight participants required shorter exposure durations compared to men, younger individuals, and those with normal weight. These findings emphasize the need for personalized WBC protocols based on individual characteristics such as sex, age, and BMI. Tailoring exposure durations accordingly can optimize cryotherapy benefits while avoiding unnecessary thermal discomfort or excessive skin cooling. However, internal temperature measurements showed no significant change in CBT during WBC exposure for either men and women, indicating that a 4-minute exposure does not induce hypothermia despite significant reductions in MsT° [18].

Given that the skin is the first organ affected by cold exposure, skin temperature serves as a direct physiological marker of cryostimulation efficiency and analgesic response. In this context, Boselli et al. [26] demonstrated that analgesia is associated with increased parasympathetic dominance, as reflected by higher Analgesia Nociception Index (ANI) values. Given that WBC is often used to modulate autonomic function, achieving the target skin temperature may serve as a standardized and physiologically relevant endpoint for these clinical effects. Finding the appropriate dosage of cold exposure is necessary to avoid very unpleasant and thermal discomfort feelings which could negatively interfere in the physiological responses. However, while our findings revealed statistically significant differences in the exposure duration required to reach the analgesic threshold across groups, the clinical relevance of these small variations remains uncertain. Future studies should explore whether these individualized exposure durations result in distinct physiological responses.

Effects of BMI on skin temperature magnitude during WBC exposure

In a previous study, we explored the impact of BMI on cold-induced responses during WBC, revealing significant differences between normal-weight and overweight young men. In fact, a previous study found that overweight participants experienced faster reduction in skin temperature due to the insulating properties of body fat [27]. This observation aligns with research by Claessens-van Ooijen et al. [14], which reported that individuals with higher body fat percentages experience more substantial decreases in skin temperature due to the insulating properties of adipose tissue. Fat tissues reduces thermal conductivity, which acts as an insulating barrier against heat loss [28,29]. While overweight individuals experience a faster drop in skin temperature, this rapid cooling reduces the thermal gradient between the body surface and the ambient environment, thereby limiting further heat dissipation [30]. This mechanism may help to retain body heat and maintain core temperature. Moreover, in overweight individuals, this more rapid skin cooling may lead to earlier activation of cold-sensitive receptors such as TRPM8 and TRPA1, potentially enhancing afferent signaling to thermoregulatory centers. While this mechanism is physiologically plausible, further research is needed to confirm the specific influence of body composition on cold receptor activation.

The current study builds on these BMI-related findings by incorporating additional variables: sex and age, providing a more nuanced understanding of how these factors interact with BMI to influence thermal responses. Our results demonstrate that the effect of BMI on WBC outcomes is consistent across age and sex groups, with overweight participants consistently reaching the target skin temperature faster than their normal-weight counterparts. However, when considering sex and age, we observed new insights: women, who generally have a higher body fat percentage than men, reached the target temperature more quickly, even within the same BMI category. Similarly, older participants, particularly those with higher body fat, also demonstrated faster cooling, potentially due to age-related decline in thermoregulatory function. Overall, while BMI remains a crucial factor in determining optimal WBC exposure duration, its interaction with sex and age provides a more nuanced understanding of cooling dynamics. These findings suggest that WBC protocols should account for sex-specific and age-related differences in addition to BMI in order to optimize cryostimulation effectiveness.

Effects of sex on skin temperature magnitude during WBC exposure

Sex-related differences in thermoregulatory responses to cold exposure can be attributed to anthropometric and thermoregulatory differences [31]. Generally, women have about 20% less body mass, 14% more body fat, and 33% less lean body mass compared to men, unless they are highly trained athletes, which was not the case in our study [32]. Consequently, achieving the same skin temperature level may require shorter WBC exposure for women. Our results are consistent with those of Polidori et al. (2018a) [33], who observed that women have an average skin temperature 2.6°C colder than men immediately following cryotherapy. This suggests that women are reacting differently when exposed to extreme cold environments. A potential explanation for the faster skin cooling observed in women during WBC exposure lies in the body surface area-to-mass ratio. Women typically exhibit a higher surface area-to-mass ratio compared to men, leading to greater enhance radiative and convective heat loss during cold exposure [21]. This larger relative surface area allows for more efficient heat dissipation through the skin per unit of body mass, potentially leading to the faster reductions in skin temperature observed in our study.

Further evidence supports the hypothesis of sex differences in vascular reactivity to cold exposure. Studies using laser-Doppler flux (LDF) measurements have shown that women exhibit a greater vascular response to local cooling compared to men, indicating a more pronounced cold-induced reaction [20,34]. The cutaneous vascular response to cold is primarily mediated by increased sympathetic output, which enhances α-adrenoceptor activity through the neurotransmitter noradrenaline [35]. Additionally, sex hormones may also influence cold responses. For instance, progesterone has been shown to have an endothelium-dependent vasoconstrictor property [36,37], while estrogens may increase sensitivity to vasoconstrictor adrenoreceptors, leading to a heightened cold response in women [20,38].

Effects of age on skin temperature magnitude during WBC exposure

Our results showed a significant effect of age on MsT° during WBC exposure. As shown in Figure 2, younger participants maintained higher MsT° than seniors, with significant differences appearing from 2 minutes 30 seconds within the exposure and persisting until the end of the session. This suggests that older individuals experience a more pronounced decline in skin temperature. Indeed, the immediate and consistent physiological response to cold exposure includes peripheral vasoconstriction to reduce heat loss and shivering to boost metabolic heat production [39]. However, these protective mechanisms, essential for maintaining body temperature during cold exposure, may diminish with age. Older adults often exhibit reduced cold tolerance compared to their younger counterparts. In this context, Smolander expressed that thermoregulatory capacity decreases with aging [22]. When exposed to severe cold air, older adults struggle to maintain their core body temperature [40]. It has been well documented that the aging process is associated with a reduced vasoconstrictor response to cold [41–43], partly due to diminished released levels of noradrenaline with aging, the key neurotransmitter responsible for vasoconstriction [44]. Additionally, age-related changes such as a decreased metabolic rate and loss of muscle mass [39], further impair heat production, leading to greater declines in MsT° following WBC exposure. Aging is frequently characterized by a loss of muscle mass [45], which is essential for generating heat through shivering, leading thereby to a decline in heat production ability [40]. Our finding support previous research showing that aging is linked to reduced cold tolerance [46,47].

Skin temperature magnitude across body areas

Body segments analysis revealed that the lower limbs experienced a greater reductions in MsT° compared to the trunk and upper limbs, across all groups. This trend was observed regardless of sex, age, or BMI categories. The greater cooling in the lower limbs is likely due to the higher density of cold air in the lower part of the cryostimulation chamber, creating a vertical temperature gradient [48]. Physiological factors may also contribute to this pattern. Lower limbs exhibit a stronger vasoconstriction response to cold, reducing blood flow to the skin and causing a more pronounced drop in skin temperature compared to the upper body. Our findings align with previous studies that reported significant cooling in the lower extremities during cryostimulation [32,48–50]. Furthermore, a significant difference was observed across all body areas between male and female participants with a more substantial reduction in MsT° in women. This observation may be explained by a sex-related fat distribution, generally conceptualized as android (arms, trunk) for men versus gynoid (hip and thigh) for women [51]. Specially, women have 25% more fat on the legs than men, while men have 15% more fat on the chest [52]. Additionally, overweight and senior individuals experienced a more pronounced decrease in MsT° in the trunk and upper limb, compared to normal-weight and younger participants, respectively. This is likely due to the insulating effect of higher fat content in these areas. Similarly, aging is associated with an increased fat mas and a progressive muscle mass loss [53], justifying the observed variations in MsT° across all body areas when comparing seniors to younger individuals. A cross-sectional study showed body fat percentage in men aged 18 to 85 years old, increased from 18% to 36% [54], illustrating how muscle loss and fat gain can alter heat production and transfer, leading to greater decrease in MsT°.

Mean skin temperature magnitude following WBC exposure

Although post-WBC rewarming was not a primary study objective, analyzing this response provides additional insights into how individuals recover from cold exposure and whether factors such as sex, age, and body composition influence this process. Understanding the rewarming phase is also relevant, as it reflects thermoregulatory efficiency and may impact the overall effectiveness of WBC interventions.

Following WBC exposure, a rapid rewarming phase was observed within the first 5 minutes across all groups, regardless of sex, age, or BMI. This rapid rise in skin temperature is primarily driven by reactive hyperemia, a physiological response in which blood flow increases to the skin following cold-induced vasoconstriction [49,55]. The body compensates by dilating blood vessels to restore blood circulation. Between 5- and 15-minutes post-exposure, as skin temperature increases, the thermal gradient between the skin and the environment progressively decreases until the skin temperature exceeds that of the environment. Beyond 15 minutes post-exposure, a plateau is reached, indicating a thermal balance between heat production and heat loss [56,57]. However, skin temperatures remained below pre-exposure levels even at 30 minutes, suggesting that recovery continues beyond this point and indicating the prolonged cooling effects of WBC. These findings are consistent with those reported by Westerlund et al. [5], who reported similar prolonged reductions in skin temperature following WBC. Additionally, Klimek et al. [58] found that thigh surface temperatures did not return to baseline levels until 90 minutes post-exposure.

In terms of individual characteristics, our findings revealed significant effects of sex and BMI on the magnitude of MsT° during post-exposure period. Overweight participants consistently showed lower temperatures compared to normal-weight individuals throughout the recovery period, from 30 seconds to 30 minutes post-exposure. Similarly, women exhibited lower temperatures than men from 30 seconds to 15 minutes post-exposure. This slower recovery in women and overweight participants may be linked to the fat’s lower thermal conductivity [28,29], which hampers the body’s ability to restore skin temperature rapidly. Additionally, women tend to have stronger vasoconstriction responses [35], which may prolong recovery by reducing blood flow to the skin, further delaying the rewarming process. Although aging is generally associated with decreased thermoregulatory capacity – such as reduced vasoconstriction and heat production [39,44], our results showed limited differences between seniors and younger participants during recovery. This suggests that age has a greater impact on the initial cold-induced thermal response rather than during the recovery process. Other factors, such as BMI and sex, seem to play more dominant roles in determining the rewarming process.

Strengths, limitations, and perspectives

While this study provides valuable insights, there are certain limitations. The results are specific to the cryo-chamber used (−50°C and 2.3 m/s wind speed), which may affect their generalizability to other settings. Although the time required to reach the target temperature may vary across different cryo-chambers, the influence of age, sex, and BMI remains a crucial consideration. Another limitation is that the study did not include a wider range of BMI categories, such as obese or underweight individuals, and a broader age range. Future research should include these groups to further explore the effects of cryostimulation on different body compositions and age groups, leading to more individualized and accurate WBC protocols. Lastly, variations in how skin temperature is calculated across studies may pose challenges for direct comparison. In our study, we employed a specific MsT° formula focusing on regions directly exposed to cryostimulation, which may limit comparability with studies using different body regions or formulas.

Conclusion

In conclusion, this study demonstrates that the optimal duration for WBC exposure to reach the analgesic target skin temperature of 13.6°C is significantly influenced by individual factors such as sex, age, and BMI. Our findings reveal that women, seniors, and overweight individuals generally require shorter exposure times compared to men, younger participants, and those with normal weight. Specifically, normal-weight young men required 4 minutes, while normal-weight young women reached it after 3 minutes. Overweight young men needed 3 minutes 30 seconds, whereas overweight young women achieved it in 2 minutes 30 seconds. Among seniors, both normal-weight and overweight men and women, required 3 minutes and 2 minutes 30 seconds, respectively. These findings emphasize the importance of personalizing WBC protocols to maximize therapeutic benefits. By tailoring exposure durations according to these factors, clinicians, trainers, and practitioners can optimize the effectiveness of WBC across diverse populations.

Acknowledgments

The authors would like to thank the participants who volunteered to take part in this study.

Appendix.

Table A1.

Core body temperature.

  Before WBC/Control During WBC/Control
1 min 2 min 3 min 4 min
WBC NYM.G 37.0 ± 0.3 37.1 ± 0.2 37.0 ± 0.2 37.0 ± 0.3 37.0 ± 0.3
NYW.G 37.3 ± 0.4 37.3 ± 0.4 37.3 ± 0.4 37.3 ± 0.4 37.3 ± 0.4
Control NYM.G 37.1 ± 0.2 37.1 ± 0.2 37.1 ± 0.2 37.2 ± 0.2 37.1 ± 0.2
NYW.G 37.3 ± 0.4 37.3 ± 0.3 37.4 ± 0.2 37.3 ± 0.2 37.3 ± 0.2
Open in a new tab

WBC: Whole body cryostimulation; NYM.G: Normal weight young men group NYW.G: Normal weight young women group; Data are represented as mean ± SD.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data supporting the conclusions of this article can be accessed by contacting the corresponding author.

Ethics approval statement

The study was approved by the National Ethics Committee (South-East I Committee for the Protection of Persons; number: 2022-A00525-38)

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Data Availability Statement

Data supporting the conclusions of this article can be accessed by contacting the corresponding author.

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