Icing horses’ legs after work is often used to cool the soft tissues, kickstart recovery and slow the inflammatory response. At Cryochaps, we recommend applying our ice boots for 10-15 minutes after exercise. However, some of our customers tell us that they ice their horses’ legs for longer. For example, some riders will leave their horses’ ice boots on in the lorry for the journey home.
This blog article delves into the science behind why we recommend icing horses’ legs for just 10-15 minutes after work.
Icing Horses’ Legs After Work: Why 10-15 Minutes?
Human research indicates that icing after exercise (not injury) for between 10-15 minutes with a temperature under 15°C is recommended. However, for horses’ legs it’s common to see 30 minutes recommended.
Where has this come from? Most likely a recommendation from the old days when there was little guidance in the standard textbooks on ice application, and the advice varied greatly.
Studies in humans started to see changes in 2001. A systematic review identified the original literature on cryotherapy in acute soft tissue injury and produce evidence based guidance on treatment. A systematic literature search was performed using Medline, Embase, SportDiscus and the database of the National Sports Medicine Institute (UK) using the key words ice, injury, sport, exercise. Temperature change within the muscle depends on the method of application, duration of application, initial temperature, and depth of subcutaneous fat. The evidence from this systematic review suggested that melting iced water applied through a wet towel for repeated periods of 10 minutes is most effective. The target temperature is reduction of 10-15 degrees C. Using repeated, rather than continuous, ice applications helps sustain reduced muscle temperature without compromising the skin and allows the superficial skin temperature to return to normal while deeper muscle temperature remains low. It is concluded that ice is effective, but should be applied in repeated application of 10 minutes to be most effective, avoid side effects, and prevent possible further injury.
The horses’ lower legs have no subcutaneous fat, no muscle and the tendons themselves have a poor blood supply. Therefore, the impact of ice and compression should – in theory – be more pronounced.
Whilst we should not rely solely on research into human medicine (horses and humans are, after all, different species), we can draw some comparisons.
A possible comparison between horses and people, where there are studies to show the effects of icing, is the achilles tendon. The human achilles tendon is similar in structure to the horses’ flexor tendons and also has little subcutaneous fat, is near the surface and also has a poor blood supply.
Studies with Cryocuff, an ice and compression wrap, on the human achilles tendon have shown that repeated periods of 10 minutes of ice and compression application are most effective. This is suggested to be because the most marked effects on the microcirculation (i.e. the circulation of blood in the smallest blood vessels and capillaries) are evident within the first 10 minutes after application.
There is also evidence from in vitro studies, which demonstrate no damage to the tendon cells when they are maintained at 10°C for 1 hour.
So why not ice for longer than 10-15 minutes? Surely it won’t do any harm?
Why We Don’t Recommend Prolonged Icing
The Risk of Tissue Damage with Prolonged Icing
Keeping tissues too cold for too long has the potential to cause superficial tissue damage and nerve palsy (impairment of the nerve cells’ ability to transmit signals) after only 20 minutes. Internal temperatures of under 15°C can cause inflammation and oedema (fluid build-up) and increase lymphatic permeability (i.e. absorption of fluids). This reverses the initial beneficial effects of icing, which causes vasoconstriction (limiting bleeding into uninjured tissue) and anti-inflammatory effects.
The Increased Effectiveness of Ice Combined with Compression
Cryochaps are one of the few equine ice boots that provide both ice and compression. Ice and compression reduces blood flow more than just ice alone. By reducing blood flow, the inflow of heat from the rest of the body is reduced. Ice and compression does produce significantly colder internal tissue temperatures than ice alone. Colder temperatures decrease tissue metabolism, which in turn slows the inflammatory response. A 10°C drop in temperature produces a 50% decrease in metabolic rate. So, with ice and compression you appear to be getting an extra ‘hit’ of cold.
Reducing blood flow also reduces tissue oxygenation. This has been proved in studies with the Aircast Cryo/Cuff, which uses both ice and compression. However, oxygen is a double-edged sword as oxygen leads to free radicals, which play an important role in inflammation and the inflammation itself is better to be reduced rather than prevented. At the same time, it is also central to the healing process.
The Importance of Removing Ice and Compression
Studies with the Cryo/Cuff in the achilles tendon injury demonstrated better tissue oxygenation after removal with an application time of 10 minutes compared with baseline, suggesting an increase in blood flow after removal of ice and compression.
Removal – as we have always said at Cryochaps – is one of the most important parts of icing, precisely because it causes a sudden rush of oxygen to the area. It is also beneficial to let the horse walk round after removing Cryochaps to invigorate the blood flow to the legs. You can find out more about the importance of removing ice and compression here.
Evidence From Equine Research Studies
Two studies in live horses (Kaneps and Petrov) investigated the temperatures of the skin and the SDFT after 30 and 60 minutes of ice water immersion. This is not to say we should be icing that long, but the interesting fact was the SDFT temperatures dropped very quickly to between 10 and 15 °C within the first 10 minutes and then started to plateau. The leg did not get colder after the first 10 minutes.
The implication is that the body starts trying to prevent the leg getting too cold and increases blood flow to the limb after 10 minutes to prevent a further decrease in SDFT temperature below ~10-15°C which of course could be damaging for long periods of time and the body is desperately trying to prevent this.
Effectively, the evidence suggests that the horse’s body may be adapted to prevent exposure of the soft tissues in the lower legs to low temperatures for prolonged periods. This implies that prolonged icing could be problematic.
The Cryotherapy Debate Continues
Of course, more research is always needed and we can only act based on what science currently exists. However, the evidence we do have points towards icing for prolonged periods (more than 10-15 minutes) being either:
- of negligible effect
- reducing the positive effects of removing the ice and compression
- possibly being harmful
To summarise, the debate over cryotherapy is likely to continue and there are still gaps in our knowledge. Some of the human research is not directly comparable to horses. For example, we know that horses can greatly reduce blood flow to the extremities without tissue damage as would occur in people (e.g. frostbite). We also have to recognise that equine tendons reach high temperatures as a result of exercise and that we know this is damaging.
Back to the Start: Why Ice For Just 10-15 Minutes?
When icing your horse’s legs after exercise, you are trying to limit inflammation, decrease pain and take the heat out of the tendons as quickly as possible. Furthermore, you want to get that oxygen rush after removal. You can find out more about what we are trying to achieve when cooling our horses’ legs here.
If the horse’s leg does not get any colder after 10 minutes, you achieve the anti-inflammatory effects of lowering leg temps in a short hit of cold, and allow the natural warming of the leg, which takes a while after ice removal. Alternatively, if you leave the ice boots on for a longer period, the horse’s body starts fighting the effects of ice and compression after 10 minutes, reversing vasoconstriction. Furthermore, the horse may become agitated as lengthy cold application can be painful in itself.
Therefore, we ask what are the benefits of using ice boots for longer than the recommended 10-15 minutes?