During the swimming portion of a triathlon, athletes can use a wetsuit if water temperature is below a threshold value. There are two general categories of wetsuits: Full sleeve (FSW) and sleeveless (SLW). It is not known if the type of wetsuit worn influences muscle activity patterns. PURPOSE: Compare shoulder muscle activity patterns while wearing different wetsuit designs. METHODS: Subjects (n=7; 45.7±8.0 yrs, 174.8±10.5 cm, 70.1±9.4 kg) completed three swim conditions on the same day: no wetsuit (NWS), FSW, or SLW. Rest was provided between conditions as needed. Muscle activity (posterior deltoid (PD), anterior deltoid (AD)) was measured (2000 Hz) using a water proofed electromyography (EMG) system (Cometa). After a self-directed warm-up, subjects swam a length of the pool at a ‘somewhat hard’ pace (25 m or 50 m depending on pool set up). EMG data were processed by removing any zero offset, calculating the absolute value, and smoothing (low-pass, cutoff frequency = 4 Hz). PD smoothed data were used to identify the beginning and ending points of five consecutive stroke cycles with extracted data time normalized. Pearson correlation coefficients (r) were calculated between NWS-FSW, NWS-SLW, and FSW-SLW for each extracted pattern data set per muscle with each r transformed to a Z-score. Z-scores and r were each compared between conditions using a 1 x 3 (wetsuit condition) repeated measures ANOVA (α=0.05). RESULTS: Neither r nor Z-score for either muscle was influenced by wetsuit condition (p>0.05). PD EMG patterns were moderately correlated between conditions (NWS-FSW NWS-SLW FSW-SLW: r=0.66±0.16, 0.65±0.16, 0.62±0.20) whereas strength of AD correlations were weak (r=0.37±0.33, 0.42±0.19, 0.39±0.21). CONCLUSION: Muscle activity patterns of PD were more strongly similar than AD between swimming without a wetsuit then with a wetsuit as well as between wetsuit conditions. The weaker AD correlations between conditions may be influenced by horizontal position due to buoyancy force and/or possible resistance to shoulder movements of the wetsuit.