Intrasession and Intersession Reliability of Quadriceps' and Hamstrings' Electromyography During a Standardized...

The objective of this study was to develop a standardized test to determine quadriceps and hamstrings muscle activation in a position emulating a noncontact anterior cruciate ligament injury. We assessed the intrasession and intersession reliability of surface electromyography (EMG) of the dominant leg after single-leg landing from a standardized hurdle jump. Eighteen subjects (10 males, 8 females) participated in 4 repeated sessions. During each session, individuals performed 3 successful jumps over a hurdle set to 75% of their maximal countermovement jump height and landed on their dominant leg. A jump was only considered successful if the individual could maintain the landing position for longer than 2 seconds after initial ground contact. In one of the 4 sessions, subjects were tested again after a 4-minute rest. The activation of the vastus lateralis (VL), vastus medialis (VM), and biceps femoris (BF), were examined by quantifying the root mean squared (RMS) EMG for 2 seconds immediately after the initial contact. Data from all 3 successful jumps were used to generate intraclass correlation coefficients (ICC), which were then used to determine intrasession and intersession reliability of surface EMG for each muscle. Intrasession reliability was excellent with ICC values of 0.96, 0.94, and 0.93 for the VL, VM, and BF, respectively. Additionally, intersession ICCs were 0.92 (VL), 0.95 (VM), and 0.94 (BF). The standardized hurdle jump with single-leg landing seemed to be a reliable technique for measuring muscle activation for 3 muscles that contribute to knee stabilization.