Design This prospective randomised controlled trial will recruit healthy adult volunteers from a university population to participate. 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 every condition to eliminate the risk of demographic factors confounding the results. Each of the 5 devices being investigated will comprise each of the test conditions. The order in which participants complete the 5 test conditions will be randomised in advance using a computer random number generator. Testing will involve each device being applied and used according to the manufacturers' recommendations. Each testing session will take around 60 minutes to complete, depending on the treatment application guidelines of each device, with at least 24 hours between tests involving the same participant. In total, participants will be giving around 5 hours of time across 5 days to complete their participation.
Protocol 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 5 individual testing sessions, each lasting no longer than 60 minutes. The height and mass of the participants will be measured during the first testing session in order to calculate BMI, and participants' age and sex will be recorded and included in the later data analysis.
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. 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. One of the cryocompression devices (Physiolab S1; Physiolab ice pack; GameReady; Cryo/Cuff; or VPulse) 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 randomly assigned for a given test, a different device will be used. The temperature and pressure settings for each test will be set according to the maximum capability of each device, which varies between devices. The lowest temperature setting that will be used throughout the study will be 1℃ (GameReady device) and the highest pressure setting that will be used is 50 mmHg (GameReady and Physiolab S1 devices). None of the temperature or pressure settings used are deemed to be unsafe or have a high risk of adverse reactions, as long as participants are not contraindicated according to the exclusion criteria for this study.
The temperature of the skin will be measured using a k-type thermocouple attached to an infrared thermometer immediately prior to the application of a device, and then every 5 minutes for the duration of the test. The length of a test will be 30 minutes, in accordance with the manufacturers' instructions/recommendations for each device.
Upon completion of a test, 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 remains 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 initially removed. 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 following measures will be recorded: skin temperature at each time point, minimum skin temperature achieved, time to achieve minimum skin temperature, length of time with skin temperature within therapeutic range of 10-15℃. After each test, participants will also be asked to respond to the following question using a 5-point Likert scale: "How comfortable did you find the treatment you just experienced?" The possible answers to this question will be: "Very comfortable, Comfortable, Neutral, Uncomfortable, Very uncomfortable". This will provide insight into differences in perception of the treatment, which could be relevant for the likelihood of protocol adherence by patients in clinical settings.
Analysis 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.
Ethical issues There is a low risk of cold injury to participants if their skin temperature is reduced to \<10℃ for any prolonged period of time (\>60 mins). The coldest temperature setting for this study is 1℃ (GameReady), which will be applied for 30 mins. However, device temperature settings do not equal the actual skin temperatures achieved, and it is not expected that skin temperatures will be reduced to lower than 5℃ for more than 15 minutes during any test. Therefore, the risk of harm to the participant is deemed to be minimal for this study.
Participants have the right to withdraw themselves and any collected data from the study at any time during, and for the first 7 days 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 Numerical Pain Rating 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 collect-ed data) will be thanked for their time and withdrawn from the study.
