Groin injuries are more common in some sports than others. Due to the anatomical attachments of many hip muscles in the groin, it is thought that there is a relationship between hip adductor strength and groin injuries. This study looked at the muscle activity of the hip adductors in various positions in athletes with and without a history of groin pain. The authors used ultrasound imaging techniques to identify locations for EMG placement for each muscle; however, the authors did admit the possibility for error was definitely present. Next, the participants had hip adduction strength tested isometrically in 6 different positions:
Hips 0: Supine with hips and knees in 0 degrees of extension. The examiner's hand is placed between the femoral condyles so that bilateral contraction of hip adductors would occur.
Hips 45: Supine with hips in 45 degrees of flexion and knees in 90 degrees. The examiner's hand is placed between the femoral condyles so that bilateral contraction of hip adductors would occur.
Hips 90: Supine with hips and knees in 90 degrees of flexion. The examiner's hand is placed between the femoral condyles so that bilateral contraction of hip adductors would occur.
Hips 0 Ankle: Supine with hips and knees in 0 degrees of extension. The examiner's hands/elbows are placed between the ankles so that bilateral hip adduction can be resisted. The toes should be pointing upward during the test.
Hip 70: Supine with one hip flexed to 70 degrees and the knee flexed to 100 degrees. Hip adduction is resisted at the medial femoral condyle while stabilizing the opposite iliac crest.
Sidelying: Sidelying with legs approximately 20-30 degrees apart. The upper leg is held by the examiner, while the lower leg is lifted off the table. The examiner than resists adduction of the lower leg.
Due to electrode placement issues, only 4 muscles were assessed. The gracilis and adductor longus were found to be activated the most in the Hips 45 position. The adductor magnus should be assessed in either the Hips 45 or Hips 0 position, and the pectineus should be assessed in the Hips 90 position. The authors theorize that the pectineus is most active in the Hips 90 position because of its alternate function as a hip flexor. The adductor magnus, on the other hand, is particularly active in the Hips 0 position because of its relationship and similarity to the hamstrings. The research found that adduction strength was greatest at 0 degrees of hip flexion, but this was not the position of greatest muscle activity for all the hip adductors, which lead the authors to hypothesize the adduction function of the hamstrings plays a role in hip adduction strength at 0 degrees. The Hips 45 position was found to generally have the most muscle activity. Given the EMG findings, hip adduction strength can be assessed in both the Hips 0 and Hips 45 positions.
A significant decrease in EMG activity was noted in the Hips 0, Hips 70, and Hips 90 positions for individuals with a history of groin pain. The authors believe that groin pain arises from damage to the rectus abdominus/adductor aponeurotic plate that lies on the pubic symphysis. Due to the primary attachment of the adductor longus here, it is theorized that this muscle should take special consideration in testing for groin injuries. Of note was the fact that EMG activity of the hip adductor muscles (for the history of groin pain group) was significantly lower in the Hips 0 Ankle position. This may influence your treatment and return to play plan.