Today’s guest post comes from Tavis Bruce. A while back, I asked Tavis to pull together an article examining the literature on cryotherapy with athletes, and as you’ll see below, he really overdelivered. Enjoy! -EC

Sports and ice go together like peanut butter and jelly (or steak and eggs, if you’re into Paleo). From ice packs to ice baths, various forms of “cryotherapy” have long held a sacred place in sports medicine to treat acute injuries and facilitate recovery from training or competition. But despite its popularity and widespread use, the evidence in support of cryotherapy remains equivocal.

More recently, cryotherapy—particularly the use of ice baths, or cold water immersion—has come under increasing scrutiny from both the scientific community and the strength and conditioning industry at large…and rightfully so! However, in the process, we may be swinging the pendulum too far in the other direction, indicated by those who have come to the conclusion that “ice baths are a complete waste of time for every athlete in every sport in every possible situation.” Now, others may disagree with me on this one; but, the evidence (or lack thereof) for cryotherapy appears to be a little more nuanced than that.

I guess what I’m trying to say is: I’m not so sure I’m ready to throw the ice out with the bathwater just yet. Perhaps, instead of pondering black-and-white questions like, “to ice or not to ice?” we should be asking:

“When is ice appropriate?”

I’d like to examine why.

A quick note before we get started: this article will not discuss the use of cryotherapy for the management and/or rehabilitation of acute soft tissue injuries. I am NOT a medical professional; I just play one on Facebook.

As such, this article will only cover the efficacy of cryotherapy as a post-exercise recovery strategy.

Is there a Physiological Rationale for Cryotherapy?

Note: I’m not going to spend much time discussing the physiological rational (the “why”) behind cryotherapy for two reasons. First, the mechanisms are still quite hypothetical. Second, and more importantly, it’s a bit outside the scope of this article to convey practically relevant and actionable information for my fellow coaches and athletes. We can debate the mechanistic stuff until the cows come home, but in my humble opinion, the gold standard measurement for post-exercise recovery is the measurement of performance variables. And, I like to think that most athletes, coaches, and sports scientists would agree with me. That being said, I do think it’s always a good idea to establish if there is at least a physiological rationale for any method we may use with ourselves and/or our athletes. With that said…

Cryotherapy results in various physiological changes (most of which are temperature-dependent) that have long been proposed to exert a therapeutic effect post-exercise. Although the most cited physiological change is a blunted inflammatory response, there exists a range of other effects through which cooling the body after exercise may accelerate the recovery process. Of note, cryotherapy may:

• Improve tissue oxygenation1 and removal of metabolic waste (2) by reversing exercise-induced muscle edema (3,4).
• Reduce reactive oxygen species (ROS)-mediated muscle damage (5) by reducing local metabolism (1).
• Induce analgesia by decreasing nerve conduction velocity (6) in addition to directly activating sensory afferents (7).
• Restore parasympathetic tone by increasing vagal tone (8,9).

In addition, cold water immersion (or “ice baths”), a popular form of cryotherapy, may have additional benefits resulting from the compressive forces experienced during water immersion, but I won’t be covering them in this article (see Wilcock et al. [10] for a good review). For more information on the physiological effects of cold water immersion and other forms of cryotherapy, I encourage you to check out this (open access!) review by White and Wells.

The Effects of Cryotherapy on Recovery from Sport or Exercise

Perceptual Measures of Recovery

Cold water immersion reduces perceptions of fatigue (11-16) and increases perceptions of recovery (17,18) and physical readiness (19) between training sessions; however, it doesn’t seem to have much of an effect on ratings of perceived exertion (RPE) during subsequent training bouts (20-23).*

*Except for when CWI is used as a precooling strategy before exercise. (More on precooling later.)

Delayed-Onset Muscle Soreness

Though it’s pretty well accepted that cooling injured tissue can temporarily reduce or relieve pain (24), it’s not really clear if post-exercise cooling has any effect on delayed-onset muscle soreness (DOMS): the type of soreness you feel in the days following a bout of intense or novel exercise.

There is some evidence that cold water immersion (CWI) alleviates DOMS better than passive recovery (25), particularly when CWI is used following exercise that involves a large degree of metabolic stress (26) (e.g., running, cycling, or team sports). However, this effect is less clear when CWI is compared to warm (27), thermoneutral1 (4,28), or contrast (27,29,30) immersion, and recent evidence suggests that CWI may be no more effective than a placebo (19) for relieving DOMS. Collectively, these findings highlight the perceptual nature of muscle soreness and the importance of athletes’ perceptions of cryotherapy (or any recovery method, for that matter).

Icing and cold water immersion may help reduce delayed-onset muscle soreness after running or team sports, but the effect likely depends on the athlete’s belief in cryotherapy as a method of recovery.

Range of Motion

There is conflicting data on the effect of cooling on range of motion (ROM). Cooling alone does not appear to improve ROM (28,31-38), but it may enhance the effects of stretching (39-43) by increasing stretch tolerance (44). On the one hand, this increased tolerance to stretch does not appear to translate into long-term improvements in ROM (45-47). On the other hand, heat combined with stretching may have more lasting effects than stretching alone (44).

If your goal is to restore lost ROM following exercise, combine heat (not cold!) with stretching.

Strength

The short-term effects of post-exercise cooling on recovery of strength characteristics are mixed and seem to depend on the type of exercise stress from which you’re trying to recover before you hit the weights.

There is some evidence that CWI may reduce or recover losses in maximal voluntary contraction (MVC) following simulated team sports (48-50) or intermittent sprint exercise (51-53), but not after downhill running (54) or cycling (55,56). And, in the only study of its kind, Broatch et al. found that CWI following high-intensity sprint intervals recovered MVC no better than a thermoneutral placebo (19).

Roberts et al. demonstrated that CWI was effective for restoring submaximal (but not maximal) strength between two lower body training sessions within the same day (57). Vaile et al. found both cold and contrast water immersion were effective at restoring strength up to three days after heavy eccentric strength training (27)*, but most studies show no or non-significant improvements over this time period (28,58-62). However, it’s important to note that all of these studies used (potentially) “less effective” cooling methods (such as when only the exercised muscle is cooled) compared to more therapeutic methods such as whole-body CWI.

*I highlight the study by Vaile et al. because it is the only study that compared multiple hydrotherapy modalities in trained males, and in a cross-over design with a “washout” period between treatments of sufficient duration to eliminate any residual effects of the repeated bout effect. Thumbs up for study quality!

Cold water immersion may help recover muscle contractile properties following running or team sports. Benefits following resistance training are less clear and may require the use of cold water immersion over local cooling of exercised tissue.

Jump Performance

Most studies show significant recovery of jump performance within 24-48 hours post-exercise with no clear additional benefits to CWI (18,49,53,63,64). Furthermore, CWI may impair jump performance within the first two hours (57) possibly due to the acute effects of cold exposure on force production (65).

Here’s the deal: jump performance seems to recover just fine on its own. However, there is some evidence that CWI may maintain jump performance in scenarios of accumulated fatigue, such as during tournament play in team sports. One study of basketball players found that the CWI maintained jump performance better in players who saw more playing time throughout a 3-day tournament (66).

Sprint Performance

Like jump performance, many studies report that sprint performance returns to baseline within 24 hours after exercise, regardless of treatment intervention (18,49, 61). Accordingly, most studies do not find a benefit in favor of CWI compared to other recovery interventions because the initial exercise bout was not sufficiently intense to elicit a significant 24-hour performance decrement.

However, when exercise was sufficiently intense to affect 24-48 hour sprint performance, CWI maintained repeat-sprint performance (a measure of speed-endurance) better than thermoneutral immersion (67), contrast water therapy (12,13,48), and passive recovery (12,13,48,67).

The effect of CWI on absolute speed is less clear. Of the two studies I found, one found no benefit to CWI over passive recovery on immediate and 24-hour recovery of 50-m dash time (68), while the other showed that CWI maintained 20-m speed better than compression or stretching over a 3-day simulated basketball tournament (66).

There’s not a lot of data on the effects of CWI on same-day recovery of sprint performance, but one study showed no significant differences in repeat-sprint performance between CWI and passive recovery immediately and up to two hours after intermittent sprint exercise in the heat (61). This ties in well with the research in sprint cycling that shows neutral—or even detrimental—effects on 30-second Wingate performance following CWI when sufficient re-warming does not occur (69,70). This makes sense: reduced muscle temperature will negatively affect muscle contractile properties (71), impair energy metabolism (72), and slow nerve conduction velocity (6,73), which collectively will negatively affect the force- and power-generating capabilities of muscle. Thus, caution should be taken when using CWI between or prior to exercise that requires a high-degree of muscular force (sprinting, jumping, etc.). Athletes should allow sufficient time to rewarm following CWI and make sure to include a dynamic warm-up before their next event, which has been shown to offset the negative effects of cold exposure on power production in the vertical jump (65).

When exercise is sufficiently intense, CWI may help restore short-term (<48 hour) sprint and jump performance. However, reduced muscular temperatures negatively affect the force-generation capacities of muscle. Thus, when using ice baths between two training sessions or events within the same day, it is important to allow the body sufficient time to re-warm and/or to include an extensive dynamic warm-up.

Endurance Performance

Given the number of endurance athletes that use ice baths to recover between workouts or events, it was somewhat surprising that very few studies looked at endurance performance following recovery periods of 24 hours or longer. Two of those studies showed that CWI improves endurance performance following a 24-hour recovery period (17,74), and two other studies demonstrated similar recovery benefits across 3-day (75) and 5-day (23) training blocks.

Most studies that looked at the effects of CWI on recovery from endurance exercise utilized recovery periods of <60 minutes between exercise bouts. But here’s the thing: When an athlete takes an ice bath between two bouts of exercise with a short (<1 hour) duration between bouts that ice bath creates a “precooling” effect for the second bout. Precooling is proposed to increase performance (particularly in hot conditions) by increasing heat storage capacity, reducing thermal strain, and decreasing perceived exertion by reducing core body temperature prior to exercise (76).* And, based on the abundance of data showing a benefit to precooling on endurance performance** (particularly in hot conditions), this is probably why we see such an immediate recovery of endurance performance following CWI (56,77-81). This effect diminishes with longer recovery periods (82), presumably as core body temperature returns to baseline.

*If you’re interested in learning more about precooling check out this (open-access!) systematic review as well as the results of two recent meta-analyses here and here.

**Just to reiterate: the beneficial effect of precooling likely does not hold true for short-duration, maximal efforts (see above).

Ice baths may be useful for recovering endurance performance, particularly when an athlete has to compete in multiple games or events in one day.

The Effect of Regular Cold Water Immersion on Long-Term Training Adaptations

Very few studies have looked at the effects of ice baths on long-term training adaptations. But, the evidence-to-date paints a pretty clear picture:

Strength Training

The evidence is pretty clear on this one: regular use of CWI impairs long-term gains in muscle mass and strength (83-86) at least in part by blunting the molecular response to resistance exercise (84). This seems to apply to both trained (84) and untrained (85,86) individuals.

Ice baths blunt the acute molecular response to resistance training and impair long-term gains in muscle mass and strength. Athletes should reconsider using ice baths after strength training, particularly in the off-season or preparatory period when the focus is on adaptation rather than performance.

Endurance Training

The evidence for the effects of CWI on adaptations to endurance training is not so clear. One study in competitive cyclists found that regular CWI neither enhanced nor interfered with cycling performance over a three-week training block (87). Furthermore, recent evidence suggests that regular CWI may actually enhance molecular adaptations to endurance training (88). However, it’s important to interpret these results with caution, as molecular adaptations do not always reflect functional outcomes and the study did not measure changes in performance. Of note, there is some evidence that regular CWI at very cold temperatures (5ᵒC) for very long durations (>30 minutes) may disrupt local vascular adaptations and attenuate improvements in VO2max to endurance training in untrained subjects (85).

There is no direct evidence to suggest that ice baths enhance nor interfere with endurance training adaptations. In trained athletes, ice baths can be used sparingly after endurance training, but regular use is not recommended, particularly during the preparatory period when the focus of training is on adaptation. Finally, ice baths of excessive duration or at extremely cold temperatures should be avoided.

Major Take-Aways

The evidence for cryotherapy is pretty mixed, but there are some patterns that seem to emerge from the literature:

• Cold water immersion and other forms of cryotherapy reduce exercise-induced inflammation.
• This reduction in inflammation may lead to reduced perceptions of fatigue and muscle soreness and increased perceptions of recovery which may benefit performance in the short-term.
• Importantly, the short-term recovery benefits of cryotherapy may depend considerably on the mode exercise (i.e. the type of stress), the physiological and perceptual qualities one is trying to restore, and (as I will discuss further in Part 2) the athlete’s belief in cryotherapy as a recovery modality.
• Meanwhile, a growing body of evidence indicates that inflammation is a necessary process for tissue regeneration and, as such, regular use of cold water immersion may impair long-term muscular and vascular adaptations to exercise.
• As such, cryotherapy should be used sparingly, particularly in the off-season when the goal is to maximize training adaptations.

In Part 2, I will address:

• whether baseball pitchers should ice their arms
• whether there an optimal cooling method, temperature, or duration
• whether cryotherapy is just one big fat placebo
• practical recommendations for athletes and coaches

Stay tuned for Part 2!

Note: the references for this entire article (including the upcoming part 2) will be posted as the first comment below.

About the Author

A native of the Great White North, Tavis Bruce (@TavisBruce) is no stranger to the effects of cold on athletic performance. He holds a Bachelor of Kinesiology and Health Science from the University of British Columbia, where he pitched for the Thunderbirds baseball team for three seasons. Tavis is currently the Director of Education for the Baseball Performance Group, where he integrates his passion for sports science with his love of baseball. He can be contacted at tavis.bru@gmail.com.