One of the most common question asked by patients when dealing with new (acute) or long-standing (chronic) injuries is, “should I Use Ice”? The majority of healthcare providers advise icing for new injuries (onset to 72 hrs), and then heat for injuries of a longer duration. The purpose of this post is to examine the efficacy of therapeutic icing.
Pathophysiology of Icing
The prevailing theory of icing is that it causes blood vessels to narrow (vasoconstriction). Vasoconstriction is thought to reduce the ability of inflammatory agents from exiting the blood vessels and entering the surrounding tissues (decreases permeability). If permeability decreases, then swelling of the surrounding tissues is thought to decrease as well. The goal of decreased swelling after an injury with ice is to limit secondary muscle damage from low-oxygen and decreased cellular metabolism. This theory makes sense from a scientific perspective; however, empirical evidence to support this claim is mixed. Conflicting studies have shown both increases and decreases of swelling in extremities with the use of ice after an injury.
It should be noted that increased swelling following icing is thought to be a result of damage to superficial lymphatic vessels and not caused by reflexive vasodilatation – Hunting Reaction (explained in a later paragraph).
There are also conflicting theories that using ice immediately after an injury may delay and impede the repair process. Finally, there is limited evidence to suggest that ice improves recovery time after an injury. In summation, more high quality and large-scale studies are needed to determine the effect of icing on inflammation and recovery time.
Icing and Nerve Function
As mentioned, research is inconclusive on the effectiveness of icing on swelling and inflammation. Nevertheless, therapeutic icing is used to treat injuries in practically every sport, so one would assume that there must be some benefit to icing after an injury. So what does the evidence say?
Research has shown that ice decreases the speed of a nerve (conduction speed). It also increases the time it takes for a nerve to fire a second time after the initial conduction (latency of a nerve). To help illustrate this fundamental principle think of a nerve as a light switch. Normally, a light turns on immediately when you flip the light switch. A light should also be able to turn on and off as fast you are able to flip a light switch. Now think of ice as a fluorescent light. When you turn on a fluorescent light there is a delay in the time it takes for the light to turn on (conduction speed). There is also delay if you turn the light on and off again (latency).
Icing and Pain
Decreased conduction speed and increased latency of a nerve has been shown to reduce pain and decrease strength. Studies have shown that icing increases the amount of pressure that an athlete with a leg injury can stand compared to a placebo group. This wording is a little confusing but essentially means that icing decreased the athlete’s pain compared to no treatment. Nevertheless, icing has been shown to be comparable to TENS (Dr.Ho) for reducing low back pain. There are also conflicting studies that show icing and heat to have comparable effects on pain reduction.
Icing and Strength
As mentioned previously icing alters nerve function decreasing strength. Research has shown that icing an osteoarthritic knee for 20 continuous minutes, 5 days a week for 3 weeks significantly decreased quadriceps strength compared to no treatment. The decrease in strength following icing explains why ice is effective for decreasing muscle spasms and tightness (hypertonicity).
An interesting caveat is that research has shown a correlation between skin temperature and nerve conduction speed. As skin temperature decreases so does nerve conduction speed. For this reason athletes should avoid icing before an athletic competition.
Icing Methods: Skin/Muscle Temperature
A decrease in skin temperature correlates with reduced nerve conduction speed. However, do different application methods effect skin and deep muscle temperature the most?
A research study compared different application methods of ice and their effect on skin and deep muscle temperature. The study compared cubed, crushed and wetted ice (6 parts cubed ice to 1 part water). The researchers found that wetted ice decreased skin (17.0C) and deep muscle temperature (6.0C) more than cubed and crushed ice. The greatest decrease of skin and muscle temperature occurred at 18 minutes of continuous icing. The greatest change of deep muscle temperature occurred 2 minutes after icing stopped and these alterations remained significant for up to 75 minutes. Deep muscle temperature persisted for up to 72 hours with wetted ice.
Icing Methods: Nerve Function
Decrease skin temperature corresponds with a slower nerve conduction speed. It can be assumed then that the icing method that decreases skin temperature the most would also have the greatest effect on nerve conduction speed.
One study investigated nerve conduction speed reduction with therapeutic icing applied by an ice pack, ice massage and ice bath. The authors found that an ice bath had the greatest decrease in nerve conduction speed. The interesting caveat in this study was that skin temperature decreased the least for subjects in the ice bath treatment group compared to those subjects who used an ice pack or ice massage. The authors attributed this discrepancy to reflexive blood vessel dilation – hunting reaction.
Hunting reaction is when the blood vessels reflexively enlarge after being exposed to a cold stimulus for a prolonged period of time. Interestingly, the reason the blood vessels enlarge is because the speed of the nerves controlling the muscles of the vessels slow with prolonged cold exposure. Decreased nerve conduction causes the smooth muscles of the blood vessels to relax, causing vasodilatation. Hunting reaction explains why skin and deep muscle temperature peaked at 18 minutes with wetted ice. It also explains the discrepancy in skin temperature and nerve conduction speed in the ice bath study. Having explained hunting reaction, is there an icing protocol that would avoid reflexive vasodilatation?
A study compared 20 minutes of continuous icing with 10 minutes of icing, 10 minutes of rest and 10 minutes of icing again (intermittent protocol). Each protocol was carried out every two hours for 72 hours. Researchers found that the intermittent protocol significantly decreased pain compared to 20 minutes of continuous icing. Although this study did not compare temperature changes between the two protocols, it is possible that the greater pain reduction in the intermittent protocol could be attributed to hunting reaction.
Research is inconclusive for decreased swelling, improved recovery time and impaired/delayed muscle recovery with icing. Icing has been shown to decrease nerve conduction speed and latency. This explains the pain reduction and decreased muscle strength with icing. However, there does not appear to be a difference between ice and TENS (Dr.Ho) for pain reduction. Furthermore, results are mixed for pain reduction with heat compared to icing. The 10/10/10 protocol (intermittent) decreases pain the most. Wetted ice for 18 continuous minutes decreases skin and deep muscle temperature the most; whereas, ice bath had the greater decrease in nerve function.
To surmise, there is no consistent evidence to support using ice for decreasing swelling and inflammation. In fact, icing might impede with tissue repair. Icing does decrease pain but the benefits are similar to TENS and heat. Nevertheless, if you want to ice following an athletic competition I recommend wetted ice using the 10/10/10 protocol. I would also avoid an ice bath before an athletic competition.