Gluteus medius electromyographic activation pattern during weight-bearing functional tasks in females with and without patellofemoral pain

This research is a cross-sectional study comparing the gluteus medius (GM)electromiographic (EMG) activation pattern between females with and without patellofemoral pain. GM EMG activation pattern. Subjects will be reported to the Musculoskeletal Laboratory for a single testing session. Prior to testing, subjects will perfome a 5-minute warm-up walking on a treadmill (Proaction BH Fitness Explorer) at a 1.66 m s -1 speed. Before the electrode placement, the skin will be shaved, abraded and cleaned with isopropyl alcohol. Bipolar silver/silver chloride (Ag/AgCl) surface electrodes (Meditrace TM 100, Mansfield, Canada, CA) will be placed one-half of the distance between the iliac crest and the greater trochanter, and also midway between the anterior and posterior superior iliac spines over the muscle belly of the GM. Surface electrodes, will be placed parallel to the GM muscle fibers. The reference electrode will be positioned on the radial styloid process. EMG signals as well as the footswitch data will be obtained using an eight channel module (EMG System ), consisting of a signal conditioner with a band pass filter with cut-off frequencies at 20-500Hz, an amplifier gain of x1000 and a common mode rejection ratio >120dB. The data will undergo to an analog to digital conversion (12 bits) with a sampling frequency of anti-aliasing> 1000 Hz and an input range of 5mV. The raw EMG data will be stored on a personal computer for analysis with a custom program in Matlab (Mathworks, Natick, Massachusetts, USA). The maximal voluntary isometric contraction (MIVC) for the GM to normalize the raw EMG data will be performed using the isokinetic dynamometer (Biodex Multi-Joint System 2, Biodex Medical Incorporation, New York, NY, USA). GM MIVC will be measured with the subject positioned in the side lying position. The dynamometer’s axis rotation will be aligned with a point on the subject representing the intersection of two straight lines. One line will be directed inferiorly from the posterior superior iliac spine toward the knee, and the other line will be directed from the greater trochanter of the femur toward the midline of the body. The lever arm of the dynamometer will be attached with straps five centimeters above the superior patella border. The hip will be placed in a position that is neutrally aligned in all three planes. The subjects will be instructed to keep their toes pointed forward and not to bend their knees. Subjects will complete two 5-second GM MVIC. Rest intervals of one minute will be given between trials. The EMG signal collected during the second trial will be used to normalize the signal collected during walking, descending stairs and single leg jumping. To determine the foot contact with the floor during the functional activities, a footswitch (EMG System) will placed in each subject’s shoe of the lower extremity being tested. The footswitch will be placed under the rearfoot during the walking testing and under the forefoot during the descending stairs and single leg jumping tests. The familiarization procedures and the evaluations will be conducted in a random order amongst the subjects. The subjects will performe a minimum of 1 minute of walking practice, 3 descending stairs and 3 single leg jumping practice trials before data collection to familiarize themselves with the evaluated activities. After a 3 minutes rest interval, we will collect the GM EMG activity during the testing procedures. To evaluate the GM EMG activity during walking, the subjects will walk during 1 minute on a motor driven treadmill matching a cadence of 117 steps/min monitored with a digital metronome (Quick Time QT-05). The descending stairs activity will be evaluated in a 3 steps custom made stairs with a height of 20 cm and depth of 27,5 cm. Subjects will be told to stop at the top of the stairs and wait for instructions to descend. After the command “ready, set, go”, the subjects will be instructed to step down first with their evaluated limb at a rate of 154 steps/min controlled by a digital metronome. Subjects will performe two trials with a rest interval of 1 minute between them. Only data for the first step down will be analyzed. To evaluate the single leg vertical jump, the subjects will performe 3 single leg jump as high as possible after the verbal command “ready, set, go”. It will be given one minute rest interval between each test. Subjects will be asked to begin the single leg jump with the non evaluated limb and to land with the evaluated limb.