Author(s): NUKADA, H., HOTTA, R.1, KAMIMURA, T.2, GOTO, K.3, Institution: TOHO UNIVERSITY, FACULTY OF MEDICINE, Country: JAPAN, Abstract-ID: 508

INTRODUCTION:
Whole-body cryotherapy (WBC) is widely used in sport medicine as a therapeutic method for acute muscle injury and to promote faster recovery after intense physical activity. WBC has been shown to decrease levels of inflammatory markers, suggesting its potential role in managing systemic inflammation. However, the morphological investigation of the effects of WBC has not been conducted. We assessed the histological effect of WBC on acute muscle injury induced by bupivacaine (BPVC) using rats.
METHODS:
BPVC (0.5% BPVC hydrochloride 0.5ml) (Marcain, Aspen Japan) was injected into the middle portion of the left tibialis anterior muscle in Sprague-Dawley rats (male, 300-350g). One session of WBC involves the following procedure: under anesthesia, the rat is placed in a cryochamber (approximately -100℃) designed by Mayekawa MFG, Co., Ltd. for 60 seconds. This procedure is repeated three times with a 3-minute interval between each session. Rats treated with WBC were divided into two groups: 1) those that received WBC immediately (0), 2 and 4 hours after BPVC injection (BPVC+WBC 0h group), and 2) those that received WBC 24, 26, and 28 hours after BPVC injection (BPVC+WBC 24h group).
The tibialis anterior muscle was then collected 24 hours after the WBC treatment for morphological assessment. The area of intramuscular edema was evaluated using binary image analysis in ImageJ. Edema was identified as expanded interstitial spaces filled with black pixels, in contrast to the white areas representing muscle fibers. Artifact regions were similarly identified and excluded from the analysis. The area of cellular infiltration was also analyzed using binary imaging. The control groups included rats with BPVC injection only (BPVC group), saline injection and sham surgery.
RESULTS:
Muscle edema and cellular infiltration were significantly less in the BPVC+WBC 0h group compared to the BPVC group. The severity of cellular infiltration was more pronounced in the BPVC+WBC 24h group than in the BPVC+WBC 0h group. Morphometrically, the area of edema was significantly smaller in the BPVC+WBC 0h group compared to the BPVC group: 0.06±0.02% vs. 0.13±0.02% (as a percentage of the whole muscle area), p=0.02, respectively. The transverse area of the whole muscle was not significantly different between BPVC+WBC and BPVC rats.
CONCLUSION:
When WBC was performed immediately after acute muscle injury, muscle edema and cellular infiltration were significantly inhibited. However, when WBC treatment was delayed after injury, the effect was limited. Since a notable decrease in pro-inflammatory cytokines with WBC has been reported, these results suggest that WBC performed immediately after injury suppresses the release of inflammatory cytokines during the acute phase of injury. In conclusion, WBC suppresses the acute inflammatory response after muscle injury and is more effective when performed immediately after the injury.