What are the health benefits of cold exposure?

Cryotherapy generally refers to the exposure of the entire or part of the body to very cold air or nitrogen gas. Whole body cryotherapy protocols call for 2-3 minutes of exposure to air at -100°C, while partial body cryo suggests 20–30 s exposure in temperatures of −10°C to −60°C, then 2 to 3 min in at −110°C to −150°C [4]. Cryotherapy has been shown to reduce muscle soreness, decrease inflammation, and provide pain relief [5]. Due to the significantly low temperature, cases of cryotherapy misuse have resulted in severe burns and death [1].

Cryotherapy must use such a low temperature because air has a low heat transfer coefficient, meaning that little heat flows through it. Ice actually has the greatest thermal conductivity coefficient at 2.18k, while water is 0.58k and air is 0.024k, meaning that ice is most effective at removing heat from the body [6]. 

Since it’s logistically difficult to dig yourself into a bucket of only ice, cold water immersion (CWI), also known as winter swimming, ice bathing, or cold plunging, is the best modality for inducing the therapeutic effects of cold [7]. Water has 40x higher thermal conductivity than air, so more heat gets transferred out of your body to cold water compared to cryotherapy [8]. Recent meta-analyses suggest a variety of current CWI protocols, but long term benefits have been found from as little as 11 minutes total per week in a study of winter swimmers at a range of temperatures [9]. Most studies set water temperatures at least below 15°C (59°F) [10, 11].

Cryotherapy vs Cold Water Immersion

Today, cold therapy has many forms, including whole or partial body cryotherapy, ice massage, ice packs, and cold water immersion (CWI). All forms have been found to have various degrees of pain relief benefits by reducing nerve conduction velocity in sensory nerves and thereby decreasing the perception of pain [3]. The difference between each form and its benefits lie in the degree of body exposure to cold and the thermal conductivity of the method.

Cold Therapy Today

Humans have used cold water for health benefits as far back as 3500 BC. The Ancient Greeks used cold water for therapies, relaxation, and socialization [1]. In the 4th century BC, Hippocrates documented the medicinal and analgesic benefits of cold, going even so far to say, “The water can cure everything” [2]. 

In the 1970’s, Japanese Dr. Toshima Yamaguci popularized whole body cryotherapy, a technique that uses cold air to remove heat from the body tissue. He advocated its use as a treatment for rheumatoid arthritis and general pain management when he found it cured 80% of his patients [1]. Since then, cryotherapy has become widespread for its effects on metabolism, athletic recovery, pain management, mental health, neurodegenerative protection, and immune function.




The observed differences between male and female BAT suggest the influence of sex hormones [73]. Estrogens likely boost BAT activity and growth [74] by both directly acting on brown adipocyte nuclear receptors [75] and indirectly influencing the sympathetic nervous system [76]. Conversely, androgens appear to inhibit BAT growth and UCP1 expression [77, 78]. This is evident in mice studies where reducing androgen levels through testis removal increased UCP1 expression in both BAT and WAT [79, 80]. Moreover, the influence of hormones on BAT seems to have important human implications; for instance, women with PCOS, marked by elevated testosterone levels, have decreased BAT activity and are more prone to obesity [81, 82].

Why This Matters

There is some evidence that men and women have different BAT amounts and activity. In female mice, there are clear distinctions in their brown adipose tissue characteristics compared to their male counterparts. These differences include a higher density of mitochondria and increased height of cristae, which are internal structures of the mitochondria [56]. Additionally, they have elevated levels of UCP1, a protein essential for heat generation in BAT [56]. Female mice also exhibit a greater sensitivity to substances that stimulate BAT (adrenergic stimulation) [56]. In female mice, WAT shows a higher propensity for browning [57]. This browning potential is further underscored by elevated UCP1 expression in their WAT [58].

Among humans, distinct sex differences in BAT characteristics and response to cold have been observed. Studies have reported higher BAT activity and mass in prepubertal girls compared to boys [59]. Though BAT prevalence tends to decrease as individuals age, this sex difference remains significant, with females consistently displaying greater BAT prevalence than males across various studies [60-65]. The potential for WAT to undergo browning and elevated UCP1 expression is also more pronounced in women [66, 67]. Furthermore, females have been found to exhibit increased cold-induced thermogenesis [68].

However, it's worth noting that these differences in BAT between the sexes might not necessarily be solely anatomical. They could also be attributed to varying sensitivities to cold between men and women. Many experiments conducted to study BAT were done at room temperatures, which do not maximize BAT activity like cold exposure would [69]. Indeed, research indicates that there are sex differences in the body's thermal, metabolic, and cardiovascular responses to cold exposure and even in the perception of cold [70].

Two significant studies highlight this nuanced understanding. The first study reported no significant difference between young men and women in the relative amount, distribution, and glucose uptake of BAT when measured after cold exposure using the gold standard 18F-FDG PET/CT [71]. However, this study noted a limitation: they based their measurements on glucose uptake, which might not fully capture BAT's activity, especially considering BAT's high utilization of fatty acids [28, 72].The second study showed that BAT was slightly, though not significantly, higher in pre-menopausal women than in men [68].

Sex Differences 

Cold exposure increases brown fat activity to maintain our core body temperature by generating more heat. This is vital to the continuation of bodily processes that keep us alive [42]. BAT activity increases by shifting energy producing processes from creating chemical energy to creating more heat. The brain releases norepinephrine, which tells white fat to break down and release energy as fatty acids. These fatty acids then activate a process in brown fat [43].

As adults, we joke that although our K-12 education did not teach us how to do our taxes, it hammered into us that the mitochondria is the powerhouse of the cell, a normally useless fact outside of science labs. However, it’s important here. Biology classes usually teach how cells synthesize ATP, our body’s form of energy, through cellular respiration: glycolysis in the cytoplasm, the Krebs or citric acid cycle, and oxidative phosphorylation along the electron transport chain and ATP synthase. This last step makes the most ATP, or chemical energy. Brown fat uses mitochondrial uncoupling, which basically shifts part of this energy making process to producing heat instead of ATP [44, 45].

The fatty acids released from white adipose tissue travel to the inner mitochondrial membrane of brown adipocytes and bind to a protein channel for protons called uncoupling protein 1 (Ucp1) [46]. As Ucp1 is upregulated, which means that more of these proteins are sent to the inner mitochondrial membrane, more protons go through this protein channel instead of ATP synthase, which would have made ATP [46]. The protons can go through Ucp1 instead to make more heat [42]. Cold exposure has been found to stimulate the expression of Ucp1 more in women than in men [40]. 

How Brown Adipose Tissue (BAT) Produces Heat When Exposed To Cold

Brown fat (BAT) burns energy as heat and is mostly found around the spine, above the collarbone, near the kidneys, and in the neck area [29-31]. Body imaging studies show a strong positive relationship between BAT activity and metabolic rate. They’ve also found that the less active BAT is, the higher BMI and body fat adults have [40,41], and the less protected individuals are from obesity and other metabolic diseases [22, 37]. BAT activity affects the entire body; it produces 101 adipokines, or hormones produced by fat tissue, that target many organs, both near and far from it. Some of these adipokines have hormonal functions that increase BAT activity, improve glucose and lipid regulation, or signal the nervous system, blood vessels, and immune cells [16]. 

How Browning Happens

When we enter cold water, both our skin temperature and inner core body temperature drop. To prevent a harmful decrease in body temperature, our bodies both reduce heat loss through blood vessel vasoconstriction and generate more heat (thermogenesis) through two main mechanisms: shivering, when our teeth chatter and hairs stand on end, and non-shivering thermogenesis [38]. Studies have found that when the body gets cold, it first uses non-shivering thermogenesis, as regular cold exposure can actually delay the onset of shivering [22]. Non-shivering thermogenesis increases metabolism by activating brown fat. When maximally stimulated, brown fat can produce up to 300x more heat per unit mass than any other organ in the body, making up about 10% of total daily heat production [39]. 

Body fat can store and burn energy- but it depends on the type. The body has three types of fat: white, brown, and beige. White fat, or white adipose tissue, stores energy as triglycerides and breaks these down to release energy as free fatty acids and glycerol [24]. Too much white fat can cause obesity and several types of metabolic diseases [25]. Brown fat, or brown adipose tissue (BAT), burns energy as heat and affects body temperature, how much energy your body burns each day (energy expenditure), and body fat accumulation [26,27]. Due to its numerous impacts, BAT is related to metabolic disorders such as insulin resistance, diabetes, dyslipidemia, fatty liver, cardiovascular disease, hypertension, and atherosclerosis [28]. BAT is mostly found around the spine, above the collarbone, near the kidneys, and in the neck area [29-31]. Beige adipose tissue is white adipose tissue that has been modified into brown adipose tissue by exercise, cold exposure, diet, or specific drugs [32, 33]. Brown and beige fat cells (adipocytes) are metabolically identical [34]. 

The amount of brown adipose tissue humans have decreases with age and its degree of activity depends on how often it is induced. It is well confirmed that individuals with less BAT have a higher BMI [28].Fascinatingly, the total body fat in people with no BAT activity increased with age, but it did not in people with detectable BAT activity from their 20s to 40s. This suggests that the decline in BAT activity due to age speeds up the accumulation of body fat [37]. 


Brown Fat & Obesity

Since non-shivering thermogenesis takes place in BAT mitochondria, it makes sense that brown adipocytes have more mitochondria than white adipocytes [44]. White adipose tissue (WAT) is not thermogenically active, as it does not express the Upc1 protein [47]. However, stressors such as exercise and cold exposure can trigger “browning” to produce beige adipose tissue, which is when white adipose cells are induced by exercise, cold, diet, or medicines to express the beneficial thermogenic characteristics of brown fat [48]. There is evidence that the norepinephrine secreted via the sympathetic nervous system and T3 and T4 from the thyroid are involved in cold induced browning [49]. One study suggests that this change occurs when cold exposure triggers the expression of thermogenic proteins like Upc1 in subcutaneous white fat that were previously dormant [50]. What’s interesting is that once these beige adipocytes have been reprogrammed, they quickly remember their new heat generation potential when re-exposed to cold, which as white adipocytes could not do before [51]. 

Factors like exercise, temperature shock, and diet change the mitochondria in brown and beige adipocytes [48]. Mitochondria are essential to non-shivering thermogenesis, and brown and beige adipocytes that have greater BAT activity from cold exposure have not only more, but also have larger mitochondria compared to WAT cells [52]. Regular cold exposure only enhances this characteristic, as cold exposure causes mitochondrial fission, where one mitochondria splits into two [53]. These mitochondria have a more packed linear cristae, which allows UCP1 to access more free fatty acids and increase heat production [52]. While evidence demonstrates that there’s no functional difference between brown and beige adipose tissue [34], others have shown that cold exposure must be continued regularly to maintain these changes in fat cells [54]. 

Cold exposure can be a novel treatment for metabolic disorders by increasing energy expenditure through increased BAT volume via browning [14] or maximizing BAT activity [16]. By increasing energy demand when activated and thereby pulling glucose and triglycerides from the blood, it has powerful anti-glycaemic, antilipidemic, and anti-obesity effects [29, 55]. 

How Ice Baths Increase Metabolism: The Mechanism

Cold water immersion has been shown to increase metabolic rate by as much as 350% by prompting the body to use more energy to maintain the core body temperature [12]. A recent study found that regular ice bathing increases resting energy expenditure by up to 500-1000 calories per day [9]. Regular CWI induces adaptations in the body’s brown adipose tissue (brown fat, or BAT), which causes these metabolic changes. Cold exposure can both increase the amount of BAT or increase its activity [13]. Therefore, cold plunging is a very promising treatment for the root cause of metabolic disorders such as obesity, diabetes, atherosclerosis, and metabolic syndrome [9, 14-16]. 

A 2020 study demonstrated that visceral obesity decreased after 20 whole body cryotherapy sessions in both healthy postmenopausal women and those with metabolic syndrome [17]. Another study found that regular winter swimming decreased body fat in men by elevating plasma adiponectin levels [15]. A 2023 study of soldiers found that regular cold exposure reduced waist circumference and abdominal fat in men [18]. When combined with exercise, cold exposure was found to increase fat loss and lean muscle in males [19]. These results have been attributed to increases in brown fat volume and activity. Interestingly, it’s been found that this metabolic response may be more pronounced in men, while women have shown a greater insulative response [20]. Studies show that cold exposure increases BAT volume by as much as 45% and can double the total BAT energy burning activity [21, 22]. This increase in metabolic rate can raise the body’s demand for energy [23], so individuals who may use cold water immersion as a weight loss treatment should prepare and strategize for this effect.


The mood benefits of cold exposure are intrinsically tied to its influence on neurotransmitters. In the peripheral nervous system (PNS), beta-endorphins produce pain relief by binding to opioid receptors, particularly the mu subtype. When beta-endorphins bind to these receptors, they inhibit the release of tachykinins, specifically substance P, which is essential for transmitting pain signals, thereby reducing the signal of pain from being perceived by the brain [86]. In the central nervous system (CNS), beta-endorphins also bind to mu-opioid receptors that are concentrated in multiple regions involved in pain control. Instead of inhibiting substance P, in the CNS, they work by inhibiting the release of GABA, an inhibitory neurotransmitter. This inhibition leads to an excess production of dopamine, a neurotransmitter associated with pleasure, resulting in a feeling of pleasure [86].

Cold exposure is known to significantly elevate levels of norepinephrine, a neurotransmitter that regulates the body's "fight or flight" stress response [93]. Additionally, cold showers have been linked to a suppression in psychosis-related neurotransmission within the mesolimbic system [83]. This system is crucial in our emotions and feelings of reward, and its altered activity could have profound effects on our mental well-being. Moreover, dopamine, a neurotransmitter often referred to as the "reward chemical", plays a central role in the motivation, anticipation, and learning centers of the brain [94]. A surge in dopamine levels, as induced by cold exposure, often leads to feelings of euphoria and pleasure . The cold-induced synaptic release of norepinephrine in the brain, coupled with a rise in plasma beta-endorphin, potentially fosters mental health and stimulates brain development. The hypothesis from a study by Shevchuk postulates that the robust sensory signals received by the brain from the cold receptors in the skin during immersion could be the primary reason behind the observed antidepressive effect [83]. In essence, the intense signals from the skin's cold receptors may initiate a series of neurochemical reactions in the brain, enhancing mood and mitigating depressive symptoms without leading to dependency or significant side effects [83]. In conclusion, the intricate interplay between cold exposure and neurotransmitter activity offers promising avenues for natural mood enhancement, potentially revolutionizing our understanding of holistic well-being interventions.

How Ice Baths IMPROVE MOOD: The Mechanism

Cold exposure has been shown to have antidepressant properties [83]. In a world where depression is predicted to be the third largest burden of global disease by 2030, improving mental health is an immediate priority [84]. Cold exposure improves mood by activating the sympathetic nervous system and triggering an increase in β-endorphins and norepinephrine [85]. Beta-endorphins are a type of natural endorphins molecules that produce a sense of pain relief and enhanced mood; they have a stronger effect than morphine on the body [86].

Just a single instance of cold water immersion was shown to skyrocket dopamine levels by 250% and norepinephrine by 530% [12]. Such surges can potentially lead to feelings of euphoria, alertness, and a general sense of well-being, as these neurotransmitters are crucial for mood, attention, and our body's response to stress. The amplification of norepinephrine could treat chronic fatigue syndrome or at least increase function in the associated brain areas [87]. Norepinephrine seems crucial for a positive mood, as research has demonstrated that the depletion of norepinephrine can lead to depression [88]. Reports have demonstrated that cold exposure can improve depressive symptoms; ten cryotherapy sessions in adults reduced depression and improved quality of life and mood [89]. A case study showed that cold water swimming immediately improved depressive symptoms after each swim and gradually reduced overall symptoms in a woman over a 1 year follow up period [90]. Even daily 2-3 minute cold showers over several weeks to a month can significantly relieve depressive symptoms [83]. 

Chronic cold exposure has been shown to have further mental health benefits; long term cold exposure demonstrated a significant reduction in perceived anxiety across all participants, male and female [18]. A combination of intentional breathing and cold exposure showed a reduction in perceived stress compared to controls [91]. Research suggests that cold showers can reduce brain activity linked to psychosis within the mesolimbic system, which plays a significant role in our emotions and feelings of reward. So, altering this brain system’s activity could have profound effects on our mental well-being [92].

Enhances mood

The consistent surge in norepinephrine during cold exposure is a key player in the enhanced cognitive outcomes. Norepinephrine is a neurotransmitter that is intricately tied to our attention, memory learning, and alertness [104]. When levels of this neurotransmitter are boosted, as with cold exposure, cognition and mood improve [105, 106]. On the contrary, when norepinephrine activity is low, cognitive functions tend to lag [96, 97]. This neurotransmitter also plays a pivotal role in the body's "fight or flight" stress response, preparing the individual to respond to environmental demands quickly [93]. Additionally, the sensory overload from the skin's cold receptors during immersion sends a cascade of signals to the brain. This heightened sensory input stimulates numerous brain areas, further driving the antidepressive and mood-enhancing effects of cold exposure [83]. The resulting cognitive benefits, such as improved memory and attention under stress, might be a result of the combined effects of these neurochemical and sensory pathways, making cold exposure a promising natural and side-effect free intervention for cognitive enhancement [54].

How Ice Baths IMPROVE Attention & Focus: The Mechanism

Cold exposure, particularly through immersion in cold water, has been demonstrated to have substantial effects on cognitive functions. As previously mentioned, a remarkable surge in norepinephrine, sometimes as much as 530%, is observed after just a single instance of cold water immersion [12]. Norepinephrine plays a pivotal role in vigilance, attention, focus, and mood regulation [95]. When norepinephrine activity is low, symptoms such as inattention, decreased cognitive ability, diminished focus, lethargy, and depression are often manifested [96, 97]. Even brief exposures, such as 20 seconds in cold water at 40°F (4.4°C), have been shown to immediately increase norepinephrine levels by 200-300% per session throughout an entire 12-week experiment [98]. The same cognitive boost was found in another group in the same experiment that was exposed to whole-body cryotherapy for two minutes at a freezing -166°F (-110°C), although the effect typically diminished within an hour post-treatment for both groups [98]. Encouragingly, this increase in norepinephrine doesn't seem to diminish with habituation, meaning repeated cold exposures consistently trigger its release [21, 98].

Additionally, as individuals engage in regular winter swimming over the course of weeks and months, it tends to gradually alleviate feelings of tension, fatigue, and negative mood [99]. By the fourth month, swimmers felt more vigor and were increasingly energetic, active, and brisk compared to the control group. Working memory, a critical component of cognition, was also found to improve with repeated cold water immersion [100]. Attention deficit hyperactivity disorder (ADHD) is characterized by poor attention, working memory, and hyperactivity or impulsivity [101]. It’s been proposed that the mechanism for ADHD involves impairments in the brain’s norepinephrine and dopamine pathways, as drugs targeting the former have proven to be effective [102]. Interestingly, repeated cold exposure may also maintain cognitive performance under stress. Elite skiers exposed to regular cold water immersion maintained attention on cognitive tasks under cold stress far better than subjects who weren't adapted to the cold [103].


According to Choo and colleagues (2022), cold water immersion doesn't diminish maximal strength [111]. The rationale behind this might be that CWI, particularly within parameters of 8–15°C (46- 59°F) and 3–20 min, doesn't considerably lower muscle temperatures beyond resting levels. Therefore, the total strength our muscles can produce isn't significantly changed or weakened [120-124]. However, a contrasting perspective from Leeder et al. (2012) suggests that CWI might not effectively promote muscle strength recovery post-exercise, possibly due to the intricate damage mechanisms at the cellular level post eccentric exercise [113].

Resistance Training Mechanisms

After intense workouts, the body experiences oxidative stress, leading to inflammation and muscle fatigue. Cold exposure has been shown to counteract these effects. Research indicates that cryotherapy can elevate testosterone and catecholamines levels, essential components in the body's stress and activity response [127]. Furthermore, it reduces markers of oxidative stress and the inflammatory response linked to secondary muscle damage, such as creatine kinase (CK), lipid peroxidation, IL-1β, and IL-6 [8, 111]. 

Jump Mechanisms

Studies have recorded notable increases of up to 3 cm in sit-and-reach performance in both male and female participants with cold exposure prior to exercise [118, 119]. Such flexibility improvements could, theoretically, translate to gains in other physical performances metrics, but they warrant caution. The enhanced flexibility might be rooted in a pain-reducing, analgesic effect induced by the cooling. While this might sound advantageous, athletes might not perceive when they're pushing their bodies beyond safe limits, potentially leading to injuries [8].

The primary reason for pre-exercise exposure to cold is the significant impact it has on the sympathetic nervous system, leading to a substantial release of norepinephrine, also known as noradrenaline [83]. Research has demonstrated that this release can be substantial, with potential increases of up to 530% [12]. This neurotransmitter plays pivotal roles in vigilance, focus, and mood [95], and can counteract symptoms like inattention, diminished cognitive abilities, low energy, and depression, which are typically associated with reduced levels [96]. Therefore, cold exposure immediately prior to exercise may give individuals a “hyped up” feeling from the rush of noradrenaline as they begin exercising. 

Pre-Cooling Pain Tolerance

Post-Exercise Cooling Mechanisms: Oxidative Stress

As for jumping, research shows that while immediate performance after CWI might suffer due to reduced tissue temperatures and reduced rate of force development, there's an upswing in performance after 24-96 hours, likely due to the decreased inflammatory response and associated muscle damage, indicated by reduced CK levels [111].

How Ice Baths Improve exercise performance: The Mechanism

Cold water immersion has emerged as the most efficient method for body cooling, showcasing cooling rates between 0.15°C to 0.35°C/min, resulting in average performance enhancements of 2% to 3% [107]. This range of improvement is particularly noteworthy when you consider that even a 0.5% to 1% enhancement can drastically increase the likelihood of an athlete's victory, depending on the event's duration [108, 109]. However, current research indicates that the advantages of cold exposure for athletic performance are closely linked to the type of exercise, as the timing of exposure and the areas of the body subjected to cooling can yield varying effects on different forms of physical activity.


Ice Bathing and Resistance Training

In resistance training, pre-exercise cooling can enhance strength performance for both men and women [110]. An increasing number of experiments on post-exercise cooling has started to tease out previously mixed findings [113]. A 2013 meta-review found that post-exercise cold exposure did significantly improve maximal strength and a recent 2023 meta-review detailed that this benefit more specifically occurs 24-48 hours after exposure [107, 111]. Cold exposure during rest periods between sets also demonstrated benefits. Grahn et al. found that palm cooling between sets increased work volume in bench press exercises by 40% in a three-week period, pull-ups by 144% in six weeks, and 1 rep max bench press strength by 22% over a ten-week period [112].

Does Ice Bathing Blunt Muscle Growth?

Recently, several studies warn that cold water immersion after resistance training sessions might impede muscle hypertrophy and strength gains, suggesting that CWI could blunt the signaling pathways and inflammation necessary for muscle growth and adaptation [114, 115]. However, an evolving perspective argues that the recovery benefits of CWI, especially during intense training phases, might outweigh its potential to mute muscle development [116]. A strategic approach proposed by some researchers is to use CWI around more technical or aerobic sessions and steer clear of it immediately after strength or hypertrophy-focused sessions [111]. For those who wish to optimize both recovery and muscle growth, a consideration could be to either utilize CWI right before strength sessions, wait at least 4 hours post-strength session, or reserve CWI for days for aerobic or non-hypertrophic workouts.

Ice Bathing and Power: Jumping

Choo et al.’s (2022) meta-review found an interesting trend with jump performance and CWI [111]. In the short term, especially within the first 6 hours post-CWI, there's a noticeable decline in jump performance. However, this decline reverses with time, with improvements becoming evident 24 and even more pronounced 96 hours later. Leeder (2012) and Poppendieck et al. (2013) concur on this trend, noting CWI's efficacy in enhancing recovery rates for muscle power post-exercise [107, 113].

Ice Bathing and Power: Sprinting

Sprint performance post-CWI reveals intriguing dynamics. An exciting study recently highlighted that cooling just the feet between rowing sprints could heighten arousal levels and enhance repeated power performance in active young men [117]. However, cold water immersion seems to dent sprint performance 1-6 hours after, although the amount of the body submerged in water in those studies is not clear [111]. This contrasts with earlier findings of improvements in sprint performances post-CWI, but this study did not discern the length of time the results were found after cold exposure [107]. The divergences in these outcomes highlight the complex interplay of factors like the body depth and duration of CWI, individual physiological responses, and the specific conditions under which sprints are performed.

Ice Bathing and Endurance Training

Cold exposure has significant effects before and after endurance training on hotter days. Cold exposure methods before exercise, ranging from drinking cold fluids to using ice vests, packs, or cold-water immersion (CWI), can elevate endurance exercise performance in hotter conditions [8]. Another meta-review exhibited how CWI within an hour after exercise in warm temperatures (26°C to 40°C or 79°F to 104°F) significantly aids acute recovery [111].

Oxidative stress, a significant contributor to muscle fatigue and recovery duration, is curtailed by cold exposure. Pre-cooling methods, whether whole body or partial, have demonstrated a reduction in oxidative stress markers, which correlate with decreased injury and illness rates, allowing athletes to participate more in the competitive season [8]. Moreover, the pre-cooling method suggests that it could stabilize lysosomal membranes, minimizing micro-injuries caused by intensive exercise [8].

Pre-Cooling Oxidative Stress

However, pre-cooling can be detrimental to certain types of exercise, especially those that involve power and explosive movements. Since cold exposure can lower tissue temperatures and therefore reduce the rate of force development, athletes need to ensure they are completely warmed up if CWI is used between back to back performances [111]. This means athletes may want to refrain from whole body exposure to cold or avoid cooling the specific muscles used in exercise just before an event. However, it's possible to adjust the protocols to cool a different part of the body, causing a drop in core temperature without directly impacting the muscle groups crucial for exercise.

Selective Use of Pre-Cooling

Additionally, the hydrostatic pressure exerted by the water during cold water immersion can independently facilitate post-exercise recovery. This pressure makes fluids move from the spaces between cells into the blood vessels, which might help reduce swelling and damage to the tissues. The increase in central blood volume and cardiac output helps get rid of waste faster, which might help muscles work better [107].

Hydrostatic Pressure

In the sprinting domain, the conflicting findings in meta reviews over the past 10 years suggest a nuanced relationship between cold exposure and sprinting [107, 111]. Some of these differences could be a result of the different cooling methods used in the studies or the varying decreased tissue temperatures, which could affect the rate of force development. A possible explanation for CWI induced sprinting benefits could be tied to improved neuromuscular coordination [107]. Wu and colleagues’ study on foot cooling allows for another possibility, that cooling only part of the body might fend off fatigue by heightening excitatory drive and tapping into additional motor units without decreasing the temperature of muscles that are involved in force development [117]. Choo’s findings reminds power athletes to ensure they are completely warmed up if CWI is used between back to back performances, refrain from using whole-body or target-tissue cold exposure immediately before events, or modify protocols to use a different body part so the core temperature drops without directly affecting the target tissue of exercise [111].

Sprint Mechanisms

Endurance Mechanisms

Endurance benefits of cold water immersion in hot weather could primarily stem from the lowered body temperatures and heart rate, improving the body's performance capacity. By reducing the thermal and cardiovascular strain that was induced by the prior endurance activity, CWI aids in rapid recovery [125]. Additionally, while CWI can amplify endurance signaling pathways and boost the expression of proteins necessary for mitochondrial growth after a single endurance session, cold exposure’s impact on mitochondrial biogenesis seems limited over long-term endurance training [115].

Potential Reasons for Contrasting Findings

Divergent results across studies could be attributed to a few factors. First, the chosen cooling temperatures in experiments might play a significant role. A second factor is the timing of cold exposure relative to exercise. One study found that short intervals (less than an hour) between exercise and CWI might lean more towards the benefits of pre-cooling rather than post-exercise recovery [126], but another suggests that CWI after resistance training sessions can hinder muscle hypertrophy and strength gains [115]. Therefore, until research demonstrates more conclusive evidence for pre-, intra-, and post- cooling protocols, athletes and coaches should use individual discretion to maximize performance and recovery based on individual experimentation and preference. 

While the evidence for cold exposure's benefits is robust, the exact mechanisms behind its efficacy are not entirely clear. It’s possible that cold exposure boosts the opioid system and metabolic rate, which could reduce muscle pain and hasten the recovery of tired muscles [127]. One traditional theory for CWI's pain-reducing effect is that it curtails inflammation triggered by strenuous workouts and increases the parasympathetic, or rest and digest, response [1]. Cooling can decrease muscle blood flow and tissue temperature, potentially lessening inflammation [130]. This could be achieved by water immersion’s ability to reduce the pressure on pain-signaling nerves [113]. Cold-induced narrowing of blood vessels might also play a role, lessening fluid movement into spaces between cells, further reducing inflammation [113]. Another interesting finding is that CWI may be more effective post high-intensity exercises than after eccentric ones, but the exact reasons for this remain speculative [113]. The placebo effect might also have a role. One study argued that the benefits of CWI could stem from athletes' strong belief in its effectiveness [129]. Finally, while pre-cooling techniques have shown potential in pain reduction, there's a caveat. Diminishing pain sensations could inadvertently raise injury risks if athletes don't sense when they're pushing their bodies too hard [8].

How Ice Baths Reduces Muscle Soreness: The Mechanism

Whole body cryotherapy can reduce muscle soreness [1]. Recent research demonstrates that cold water immersion improved the perception of soreness, recovery, and fatigue [111], especially when performed at temperatures under 15°C [128], echoing earlier findings [113, 127]. Interestingly, CWI seems more effective for pain relief after high-intensity workouts than after eccentric exercises [113]. Pre-cooling techniques, too, have been spotlighted for their capacity to diminish perceived pain. For instance, partial body cryotherapy (PBC) enhanced flexibility in both men and women, which could potentially be attributed to a pain-reducing effect [8]. However, it's worth noting a recent study suggested that the pain-relief from CWI might, in part, be a placebo effect [129].


One primary mechanism behind cold exposure’s ability to relieve pain posits that cooling a body part reduces its nerve conduction velocity, making pain receptors less sensitive [3, 134]. This concept of slowed sensory nerve conduction is also backed by studies that found cryotherapy to have a hypoalgesic effect, with CWI being particularly effective in this regard [7, 134, 135]. 

Moreover, cold exposure has been shown to release of β-endorphin from the brain by activating the sympathetic nervous system [85]. β-endorphins are discharged into the bloodstream in response to factors like pain stimuli, stress, cold, and inflammation. This neurotransmitter has a significant role in inhibiting the perception of pain at various levels of the nervous system, including the spinal cord, brain stem, and subcortical centers [85]. Additionally, the significant surge in norepinephrine levels following CWI sessions, even with regular exposure over months, might play a crucial role in pain reduction [98, 136]. 

Another proposed mechanism revolves around the reduction of inflammation through cold exposure. By decreasing muscle blood flow and tissue temperature, inflammation resulting from strenuous activities can be curbed. This was evident in a study by Gregson et al., which found notable reductions in both femoral artery blood flow and muscle temperature post cold immersion [113]. A potentially connected theory suggests that the reduced inflammation lessens pain sensations by decreasing the pressure on pain-signaling nerves. Given the multitude of mechanisms and their interplay, it's clear that cold exposure therapies offer a multi-faceted approach to pain management.

How Ice Baths DECREASE CHRONIC PAIN: The Mechanism

Dr. Toshima Yamaguchi popularized cryotherapy in 1978 in Japan as an effective treatment for rheumatoid arthritis that cured 80% of his patients [1]. The first forms of cryotherapy were developed primarily to alleviate pain and address this condition along with neurodegenerative disorders and other inflammatory conditions [8]. Studies have found that regular winter swimming provided relief to individuals suffering from conditions like rheumatism, fibromyalgia, and asthma, and generally elevated the swimmers' well-being [99]. Furthermore, a research study conducted in Indonesia highlighted that cold-water immersion significantly improved joint mobility, physical activity, and overall quality of life while reducing stress, anxiety, depression, and pain in adults suffering from gout arthritis [131]. Even the simple act of taking cold showers has been shown to have pain relief effects, potentially owing to a boost in the production of the analgesic opioid peptide, beta-endorphin [92, 132, 133]. Notably, cryotherapy has also shown efficacy in mitigating pain in women with primary dysmenorrhea, which is discussed in depth in a later section [5]. Since cold exposure can reduce pain while still enabling movement or exercise, it is beneficial for healthy individuals and for those rehabilitating from a specific ailment [3].


Cold exposure likely decreases inflammation through multiple pathways, as there are numerous connections to oxidative stress balance, neurotransmitter release, and brown adipose tissue metabolism. A key determinant of inflammation is the balance between oxidative stress and the body's defenses. Oxidative stress arises due to a disproportion [142] between reactive oxygen species (ROS) production and antioxidants, which can neutralize ROS and prevent cellular damage [143]. While ROS are produced during normal cellular processes, excessive ROS are linked to a plethora of inflammatory diseases [144]. Cold exposure has an interesting effect on the ROS/antioxidant balance: it seems to increases ROS production, which is necessary for thermogenesis [145], but also bolsters the body's antioxidant defenses, though these effects can vary based on specific conditions of the cold exposure [146].

Inflammation could also be reduced by cold exposure’s release of β-endorphins from sympathetic nervous system activation [85]. These endorphins not only play a part in pain modulation but also in dampening immune responses [147]. Some disorders characterized by inflammation, like rheumatic diseases, have shown diminished levels of β-endorphins. This lack might exacerbate such disorders, suggesting the potential therapeutic role of β-endorphins in inflammation control [148]. Beta endorphins also reduce the stress response of inflammatory cytokines and increase the levels of anti-inflammatory cytokines, which have been found to play a part in many psychological and physiological disorders [147]. 

Furthermore, brown adipose tissue metabolism seems to play a part, especially concerning liver inflammation. Cold exposure has been shown to elevate BAT metabolism of succinate, which can affect liver immune cell infiltration and overall inflammation [28]. It's worth noting that patients with polycystic ovary syndrome, a condition marked by inflammation, have less active BAT, suggesting a connection between BAT activity and inflammation [82, 149].

How Ice Baths Reduce Inflammation: The Mechanism

Chronic inflammation is increasingly recognized as a major factor underlying many diseases including obesity, diabetes, arthritis, cancer, cardiovascular disease, and various autoimmune diseases [137]. Recent studies have discovered that chronic inflammation is a significant determinant of successful longevity and overall health [138], making it crucial to curtail. Interestingly, studies have observed that centenarians tend to have lower levels of inflammation [138]. 

Cold exposure through regular winter swimming and cryotherapy has shown beneficial changes in markers linked to inflammation and oxidative stress [85, 139]. Moreover, whole body cryotherapy (WBC) has been utilized to alleviate oxidative stress and anti-inflammatory biomarkers post-exercise [8] as well as decrease pain and inflammatory symptoms in disorders like rheumatoid arthritis and fibromyalgia by reducing inflammatory cytokines [4]. WBC can also decrease lower back pain and inflammation with exercise [85] and lower markers of oxidative stress and endothelial inflammation before exercise [140, 141]. These human studies expand upon animal studies, in which cold exposure has been found to reverse the expression of inflammation factors [13].


Cold exposure causes the nervous system to trigger changes in brown and white adipose tissue. The brain sends norepinephrine to break down white adipose tissue, which releases fatty acids that are taken up by BAT [28]. This provokes greater BAT activity by intensifying its heat generation (thermogenesis) capabilities, which increases the body’s energy expenditure [42]. This means that the body is burning more energy. Research has established that cold exposure is the best stimulator of BAT [28]. This is important because studies show that higher BAT activity in humans is directly related to lower blood glucose levels [156]. Chondronikola and colleagues (2014) demonstrated that BAT has a significant effect on how the entire body uses glucose, suggesting that BAT plays a key role in glucose balance and insulin sensitivity in humans [157]. 

Furthermore, Bartlet et al (2017) reported that high metabolic activity in BAT can play a role in removing harmful cholesterol from the body [155], while Cairó demonstrated that BAT activation decreases hyperglycaemia and hyperlipidaemia [158]. Research is starting to highlight that the amount of active BAT a person has correlates directly with disease. 

Becher and colleagues studied 53,475 patients with and without BAT and found that individuals with BAT had better blood glucose, triglycerides, and HDL, as well as lower rates of Type 2 diabetes, dyslipidemia, hypertension, coronary artery disease, and congestive heart failure [159]. These findings align with past studies that linked active brown fat to a lower risk of diabetes [62] and healthier arteries over a 5-year period [160]. There's also evidence suggesting greater BAT activity might be connected to reduced liver fat in humans [161-163].

However, we don’t know exactly how this works yet. There are a few different ways cold exposure changes how and where the body burns energy, which would affect insulin, glucose, and lipid levels. 

How Ice Baths Improve Glucose, Insulin, & Lipid Markers: The Mechanism

Cold exposure has been shown to improve insulin sensitivity, glycemia, and lipid profiles, which could improve metabolic disorders such as insulin resistance, diabetes, dyslipidemia, fatty liver, obesity, cardiovascular disease, hypertension, and atherosclerosis . Several studies demonstrated that cold water swimming significantly increased insulin sensitivity and decreased insulin concentrations in both experienced and inexperienced swimmers [150-152]. Regular whole body cryotherapy also decreased insulin resistance and improved glycemia in postmenopausal women with type 2 diabetes meticulitis. In the same study, 10 whole body cryotherapy sessions decreased fasting blood glucose in premenopausal healthy women, postmenopausal healthy women, and postmenopausal women with metabolic syndrome, and this decrease intensified in the latter group [153]. Søberg et al. (2021) also demonstrated that winter swimmers had lower blood glucose levels than controls, suggesting improved glucose clearance [9]. In a 2020 study, total cholesterol, triglycerides, and low-density lipoprotein decreased after regular whole body cryotherapy in adult males [154]. When used before an hour of exercise, whole body cryotherapy decreased total cholesterol, low density lipoprotein, and triglyceride levels after just 10 treatments [140]. Furthermore, exposure to cold may help fight off atherosclerosis by boosting the body's "good" HDL cholesterol and improving how it processes cholesterol [155].


BAT Uses Mostly Fat to Generate Heat 

Some researchers claim that BAT is a powerful sink to drain and directly use both glucose and triglycerides from the blood [16]. It’s well established that cold-triggered BAT in humans primarily uses fatty acids as fuel to generate heat [9, 28, 72, 164-173]. These fatty acids come from the cold-induced noradrenaline release from the brain, which prompts the breakdown of white fat into triglycerides for the body, especially BAT, to use [28, 54, 158]. 

Does BAT Use Glucose to Generate Heat?

Although scientists agree about how BAT uses fatty acids, the mechanism behind BAT’s impact on glucose use and insulin sensitivity is inconclusive. The glucose has to go somewhere, the question is just where. 

Mice studies show that chronic cold exposure increases glucose uptake directly to brown adipose tissue, which would immediately explain the improvements in glucose levels and insulin sensitivity [44, 165, 174]. In humans, Blondin and colleagues (2014) similarly demonstrated a significantly increased glucose uptake in BAT after cold acclimation [21]. While Van der Lans et al. (2013) did not see an increase in the rate of BAT glucose uptake, they did find an increase in the overall amount of BAT glucose uptake [175]. 

However, more recently, Søberg et al. (2021) did not find a difference in BAT glucose uptake between winter swimmers and controls [9]. Since cold-activated BAT primarily uses fatty acids for fuel, some suggest that measuring BAT glucose metabolism cannot accurately reflect how active this tissue really is [9, 164, 176]. Therefore, it’s possible that cold exposure causes BAT activation that triggers increased glucose uptake in other parts of the body, such as skeletal muscle [173, 177] or white adipose tissue [178]. 

Indirect Mechanisms

Another possible explanation for the cold-activated, BAT-mediated improvements in glucose, insulin, and lipid profiles are the hormones that BAT secretes. BAT produces 101 adipokines, or hormones produced by fat tissue, that target many organs, both near and far from it. Some of these adipokines have hormonal functions that increase BAT activity, improve glucose and lipid regulation, or signal the nervous system, blood vessels, and immune cells [16]. Two adipokines of particular interest to researchers are adiponectin and fibroblast growth factor 21 (FGF21). 


Adiponectin is a hormone secreted by both white and brown adipose tissue, but can also be produced in muscle and in the brain [179]. It has been found to increase energy use, fat breakdown, glucose use, maintain insulin sensitivity, and act as an anti-inflammatory [180]. These functions suggest adiponectin plays a key role in preventing insulin resistance, type 2 diabetes, atherosclerosis and other age related diseases [181]. Fascinatingly, research shows that adiponectin may promote increased longevity, as elevated levels have been found in centenarians [15]. Adiponectin levels decrease in individuals with obesity [181], as well as in those with metabolic syndrome, which indicates endocrine dysfunction and insulin insensitivity [182]. 

Does Cold Exposure Affect Adiponectin?

Cold exposure in both air and water has been found to increase adiponectin levels through non-shivering thermogenesis, which is mediated by BAT [54]. Adiponectin has also been associated with white adipose tissue browning due to cold [183]. Experiments show that a single cold exposure event increased adiponectin levels in men by 20% and two cold exposures increased levels by 70% [179]. Regular winter swimming has been reported to impact fat loss, and evidence suggests that the secretion of adiponectin from cold-induced non-shivering thermogenesis may contribute to it [15]. Evidence suggests that since regular cold exposure can increase adiponectin levels, it would have a positive impact on insulin resistance, diabetes, atherosclerosis, and age related diseases, leading to overall positive health effects [54]. 


Fibroblast growth factor 21 (FGF21) is mostly released from the liver, but increased levels have been found in BAT that has been activated by cold exposure [184]. FGF21 plays a major role in metabolism. It stimulates BAT heat production to increase energy expenditure, enhances insulin sensitivity, protects liver cells from fat stress, and acts on the brain to suppress sugar intake [185]. It also prompts increased WAT glucose utilization and browning [186]. FGF21’s widespread, multifaceted impact on metabolism indicates that it could be part of the mechanism behind cold exposure’s ability to improve glucose, insulin, and lipid markers. 

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