Brady Whetten and Dr. Ken Knight, Department of Exercise Science

Cryokinetics is a popular tool for rehabilitating acute joint sprains. It involves numbing the limb with ice water immersion, followed by active exercise, repeated for a total of five bouts (8). The major limitation of this therapy is that the cold immersion necessary to induce numbness is quite painful during the initial immersion. Clinical experience shows that the sensation of pain decreases after repeated bouts. Research to confirm this observation, however, has shown either no habituation (6) or a slower rate of habituation (7) than indicated by clinical observation.

The Visual Analog Scale is often used to determine changes in pain during therapeutic modality research (1,2). Generally the Visual Analog Scale is administered to subjects without their knowledge of previous scores. Could this be a source of difference between clinical experience and research data? This issue has been studied but only during clinical sessions dealing with patients (1,2,3,4,5). There have been no studies on normal subjects or with cold-water immersion to analyze the effect of being able to see previous Visual Analog Scale ratings in a research setting.

The two conflicting studies of habituation to cold differed in socialization. The one that concluded that habituation did not occur restricted socialization (6), whereas the one that confirmed habituation encouraged subjects to socialize (7). The standard setting for a clinical cryokinetic treatment session is a social atmosphere with patients interacting with therapists and other patients (8). Does this influence the habituation to cold-induced pain?

The questions that this research project asks are: 1) Does knowledge of pain ratings during previous ice water immersions affect the rating of pain during the present ice water immersion? 2) Does socialization influence habituation to cold? This will give greater insight into the process of habituation to cold-induced pain. A greater understanding of this process will lead to a more effective administration of cryokinetics. We also plan to give a greater understanding of the measurement of pain, which will give health-care professionals that treat pain a greater understanding of what they are dealing with which will ultimately lead to better treatment.

In this study, 20 subjects reported to the laboratory on two occasions, one week apart. During both sessions, they underwent a simulated cryokinetics treatment by immersing their ankles (up to 0.5 cm above the malleolus) in 1° C ice water 5 times with 3 minutes of exercise between immersion bouts. The first immersion was for 21 minutes followed by four bouts of 5 minutes each. During each session subjects filled out the Visual Analog Scale at the beginning and end (within 5 seconds) of each immersion bout and each exercise period. In addition, pain was monitored every 3 minutes during the initial immersion bout and every 2:30 of the 5-minute immersion bouts. During one of the two sessions, subjects had access to their previous VAS scores. During the other session they were blinded to their previous scores. The subjects were also divided into an isolation group and a social group. The 10 subjects in the isolation group performed the immersion bouts alone, whereas the social groups performed their immersion bouts in groups of five, where they were encouraged to socialize.

There was no significant difference in habituation to cold-induced pain between the socialization and isolation groups. Our power was quite low, so this may be due to an insufficient number of subjects

The accuracy of the Visual Analog Scale markings was greatly decreased when subjects were blinded to their previous markings. Overall, 42% of subjects’ pain scores were inconsistent with whether they felt their pain was more, less, or the same than the previous marking. Subjects were incorrect 90% of the time that they reported the same amount of pain, 20% of the time they reported less pain, and 10% of the times they reported more pain. Also, 8 subjects on 11 different occasions indicated that they were either experiencing more or less pain but marked the same amount of pain on the scale. The accuracy of perceived pain as reported on the Visual Analog Scale is compromised when access to previous pain ratings is not allowed.

In conclusion, there is an increase in accuracy when the Visual Analog Scale is admitted with access to previous pain ratings. There is no significant difference in habituation to cold-induced pain between socialization and isolation groups. We plan to continue the study with additional subjects to further analyze these questions.