Cryotherapy after surgery is widely utilised and has numerous practical applications for post-operative rehabili-tation. Previous research has suggested that during cold therapy, the skin temperature of the knee should be reduced to 10-15°C to maximise the therapeutic benefits of cooling while avoiding the risk of cold injuries such as nerve damage and frostbite (Wilke and Weiner, 2003; Bleakley, McDonough and MacAuley, 2004). The degree to which the pressure applied by a cuff to the knee has an effect on the achieved skin temperature of the treatment area is unknown.

The aim of this study is to determine the effect that different pressure settings have on skin temperature around the knee during a 30-minute cryocompression treatment.

This prospective randomised crossover trial will recruit healthy adult volunteers from a university population to participate. To avoid the involvement of individuals with unequal relationships, participants will be recruited through the form of advertisements on staff and student noticeboards, and through an email invitation sent to students within the faculty that the study will take place. A power analysis demonstrated that a total of 30 participants would be required to achieve a power of 0.8 and alpha error probability of 0.05 for a small-medium effect size of f=0.2. Each participant will take part in each condition within the study in order to eliminate the risk of demographic factors confounding the results: Conditions will be conducted in a random order and will be named: A, B, and C. These conditions will involve the device being worn while ice-water is circulated through the knee sleeve at a maintained temperature of 8°C with a pressure of either 25 mmHg, 25-50mmHg, or 25-75 mmHg, respectively. Randomisation will be performed using a computer random number generator. Each testing session will take 45-60 minutes to complete, with at least 24 hours between tests with the same participant. In total, participants will be giving around 3 hours across 3 days to complete their participation.. Participants will not be compensated for taking part in the study, nor will they be charged.

All eligible participants will first be required to provide informed consent prior to their participation in the study. Once this has been obtained, participants will each attend a single testing session that should last no longer than 60 minutes. The height and mass of the participants will first be measured in order to calculate BMI, and participants' age and sex will be recorded to allow for later analysis to determine any confounding influence of these factors on the results.

Participants will be required to remain in a seated position with their leg in full extension and elevated, parallel to the floor, for the duration of each test session. The leg that will be used for the study will be randomly selected for each participant, and will remain the same for each condition. Skin temperature will be measured using a thermocouple, which will be attached with tape 20 mm distal to the patella. The Physiolab S1 cryocompression device will then be attached to the leg of the participant and the test will begin. Depending on the condition to which a participant has been assigned for a given test, the S1 will maintain the temperature of the water flowing through the device while applying one of three different pressures.

The temperature of the skin will be measured using a k-type thermocouple attached to an infrared thermometer immediately prior to the application of the S1 device, and then every 5 minutes for the duration of the test. The cuff will be worn for 30 minutes as per the manufacturer guidelines for cold therapy treatments. After 30 minutes, the cuff will be removed. If the temperature of the skin has been reduced to within 10-15℃, skin temperature will continue to be monitored every 5 minutes after the cuff has been removed until it rises above 15℃, at which point the test will end. This will allow for the total time to be measured that skin temperature re-mains within the target therapeutic range as a result of a single application of the cryocompression device. If the skin temperature is not reduced to within 10-15℃ while the cuff is worn, then the test will end after the cuff is removed at 30 minutes. Upon completion of the test, the temperature sensor will be removed from the leg of the participant; thus completing their participation in the test. Once each participant has taken part in all conditions, they will have completed their participation in the study.

The data will be analysed to detect any differences during testing compared to baseline measures, and between groups. All data will be first subjected to a Kolmogorov-Smirnov test to assess whether they are normally distributed. A repeated measures analysis of variance will be performed on all normally distributed data. A Friedman test will be performed on any data that are not normally distributed.

There is a low risk of cold injury to participants if their skin temperature reduces to <10℃. Skin temperature will be monitored every 5 minutes throughout the study and testing will be terminated if a participant's skin temperature dips below this threshold. Therefore, the risk to participants in this study is minimal.

Participants have the right to withdraw themselves and any collected data from the study at any time during and after their participation, without having to give a reason. They also have the right to terminate a test session at any time. Testing shall also be terminated as a result of any adverse reactions that emerge. Adverse reactions (e.g. pain) to the testing protocol are not expected due to the low-risk nature of the study, however any that occur shall be recorded and monitored until things return to baseline/normal. In order to monitor any pain/discomfort that might occur, a Visual Analogue Scale (0-10 scale) will be within sight of the participant at all times during testing: a test will be terminated if reported pain/discomfort exceeds 5/10, though none is expected. Any reported pain (or other adverse reactions) shall be stored along with the data collected for that participant. If a test is terminated for a reason that could be mitigated in future, participants will be offered the opportunity to repeat the test another day, should they wish to continue taking part in the study. If a test is terminated due to an adverse reaction that can not be mitigated in future, the participant (and any collected data) will be thanked for their time and withdrawn from the study.

Inclusion Criteria:

• >18 years of age.

Exclusion Criteria:

• BMI >40 kg/m2
• History of nerve damage or sensory deficit in the lower limbs (including frostbite)
• Hypersensitivity to cold, including hives
• Active inflammation or pain of the knee
• History of thrombosis, embolism, or other conditions related to impaired peripheral circulation
• Suffering from diagnosed diabetes, multiple sclerosis, rheumatoid arthritis, spinal cord injury, cardio-vascular disease, hypertension, Raynaud disease, cryoglobulinemia, or haemoglobinuria
• Confirmed or suspected tissue infection, an unstable fracture, a skin condition, or a tumour in the treatment area
• Cognitive impairment or communication barriers

No individual data will be shared outside of the researchers directly involved in the data collection itself.