Muscle Activity Magnitude and Patterns During Plyometric Exercise on Land and in Shallow Water: 248 Board #86 May 29 9:30 AM - 11:00 AM

PURPOSE: The aim of this study was to compare muscle magnitude and patterns of key lower extremity muscles while performing plyometrics on land and in shallow water. METHODS: 10 Subjects (7 males; age:28.6±6.3 yrs, height:69.4±2.9 in, mass:82.1±8.4 kg, 3 females; age:45.7±6.8 yrs, ht:69.6±3.2 in, mass:84.2±8.3 kg) performed two plyometric exercises (countermovement jump (CMJ), drop jump (DJ)) while in two different environments (on land, in shallow water). A water proof electromyography (EMG) system (Cometa Miniwave Infinity, 2000 Hz) was used to record the signals of the muscle activity. Each sensor measured EMG as well as accelerations (3 dimensions). Four muscles (rectus femoris (RF), bicep femoris (BF), gastrocnemius (GA) and tibialis anterior (TA)) were used to capture EMG data. DJ trials were initiated from a 30.5 cm platform and order of conditions was always land followed by water. Depth of water was set to go no higher than xyphoid process level and no lower than the navel while standing. DATA ANAYLSIS: Resultant acceleration was calculated for each sensor with a composite score calculated as the sum of the resultant acceleration for all sensors. This signal contained a peak upon initiating movement and a peak upon landing to end the movement. These peaks were identified, and EMG data were extracted 0.25 s before and after these discrete events to represent beginning and ending of analysis. Average (AVG), root mean square (RMS) and movement time were each calculated between the two extraction points. AVG, RMS, and movement time were each analyzed using a 2 (jump type) x 2 (environment) repeated measures ANOVA (α=0.05). RESULTS: EMG (AVG or RMS) was not influenced by the interaction of environment and jump type (p>0.05); nor was there a main effect for jump type or environment for any muscle that was measured (p>0.05). However, BFAVG was different for jumps regardless of environment (p>0.05). CONCLUSION: Muscle activity magnitudes appears to not be influenced between environments for CMJ and DJ for any of the four muscles measured.