Effects of Cryotherapy on Lower Leg Deep Tissue Temperature Changes: As Measured in Healthy Volunteers by Using MRI Technique

Background: Since the 1950s, researchers have studied temperature changes in deep tissues caused by cooling stimuli. However, these changes have not been investigated non-invasively. Moreover, opinions are divided as to whether the temperature in the joints rises or falls. The present study investigated the effects of cooling on various tissues in the body, including muscles. Methods: Seven healthy subjects (four males and three females) were enrolled (age, 21.5 ± 0.8 years; height, 165.2 ± 10.7 cm; weight, 63.1 ± 12.17 kg). The research was conducted at the Department of Radiology, Okubo Hospital (Akashi, Hyogo, Japan) between March 2015 and December 2020. Magnetic resonance imaging (MRI) was performed on both lower legs in a noncooled resting state. The right lower leg was cooled for 15 minutes using an ice bath, then both legs were examined by MRI (Experiment 1). After two weeks, the left lower leg was cooled, and MRI was performed on both legs (Experiment 2). After the subsequent two weeks, MRI was performed on both legs without cooling (Experiment 3). The target areas were subcutaneous and adipose tissues, muscle, bone, and cartilage. T(1) signal intensity changes after cooling were examined for each tissue. Normality was confirmed by the Shapiro-Wilk test in advance, and the effect size (Cohen's d) was calculated as a post-test when a significant difference was found. Results: In Experiments 1 and 2, T(1) signal intensities in subcutaneous tissue, lateral inframalleolar fat pad, the extensor digitorum longus, and abductor hallucis muscles were significantly higher in the cooled than in the noncooled leg (P < 0.05). No significant differences were observed in tissues on the noncooled side. Conclusions: A 15-minute cold stimulation, such as that used for ankle sprains, reduced temperatures in subcutaneous adipose tissue, muscles, and the lateral inframalleolar fat pad. As the lateral inframalleolar fat pad was effectively cooled, the joint capsule and ligaments immediately below may have also been cooled. It is important to consider the tissue intended for cooling when performing cryotherapy. An ice bath below the lower leg is effective for promoting the recovery of damaged tissue.