Cold Air Cryotherapy, also known as whole body cryotherapy, is a regimen where individuals are repeatedly exposed to very cold air (-110 °C) for short periods (Westerlund et al, 2009). This study aimed to evaluate the effects of cold air cryotherapy on indices of muscle soreness after an eccentric muscle damaging protocol. Eighteen healthy human volunteers were randomly assigned to either an experimental (n=9) or control group (n=9) (mean±S.D.; height 177.4±7.8 centimetres, body mass 77.0±9.6 kilograms, age 21.2±2.1 years). All volunteers completed a familiarisation session 3 days prior to the commencement of the study. Pre-test measures recorded at the start of the study included Maximal Voluntary Isometric Contraction (MVIC) of the left knee extensors, Peak Power Output (PPO) during a repeated sprint test on a cycle ergometer and muscle soreness measured by questionnaire. Immediately after the pre-tests, the volunteers completed an eccentric exercise bout consisting of 100 maximal eccentric contractions of the left knee extensors, performed on an isokinetic dynamometer at an angular velocity of 1.57rads.s-1. On day 2 the volunteers completed either a control or experimental treatment twice, 2 hours apart. The experimental group stood in a climatic chamber cooled to -110±3°C for 3 minutes. The control group stood in the same chamber for 3 minutes at a temperature of 15±3°C. Tympanic temperature (TTY) was recorded 5 minutes before entry to the chamber and 3, 8, 15 and 22 minutes post treatment. Three post-testing sessions followed, on days 3, 4 and 5, measuring MVIC, PPO and muscle soreness. Data were analysed using a repeated measures ANOVA to compare results of the 2 treatment groups over 4 time points (pre-test, 24, 48 and 72 hours following exposure). MVIC declined to a minimum of 60.6±14.7% immediately after the damaging protocol (p < 0.001) and recovered thereafter to 98.7±12.3% on day 5. Muscle soreness also increased, to a maximum of 279±155.1% on day 3, following exercise (p < 0.001). PPO was not reduced in the days following exercise (p = 0.13). Cold air cryotherapy reduced TTY, to a minimum of 0.3±0.5° three minutes after leaving the chamber, when compared to the control group (p < 0.001). However, the treatment did not effect MVIC (p = 0.49), PPO (p = 0.25) or muscle soreness (p = 0.88). The eccentric contractions protocol used in this study reduced indices of muscle function and soreness, both indicative of muscle damage. Cold air cryotherapy did not alter these indices compared with a control treatment. These data suggest cold air cryotherapy, administered at 24 hours after an eccentric muscle damaging protocol, is ineffective in the treatment of muscle soreness or indices of muscle damage.