Clamshells are one of the most prescribed exercises for individuals with knee pain. This exercise is intended to target the hip abductors, specifically the gluteus medius muscle. EMG studies have found good activation of both the gluteus medius and gluteus maximus muscles during the clamshell. Additionally, the clamshell has been shown to preferentially activate the gluteus medius while minimizing activity in the tensor fascia latae (TFL).
While the clamshell is intended to have good activation of the gluteal muscles, the exercise will only be as effective as the person instructing the movement. In regards to movement patterns, the body always takes the path of least resistance (i.e. the repetitive, facilitated movement pattern). Individuals who will benefit from performing the clamshell exercise likely have difficulty engaging the gluteus medius. Proper cueing is necessary to avoid compensatory motions.
How to Prescribe
The video below contains a 3-part progression for performing the clamshell exercise. When the client can perform 20-30 repetitions without compensation, I progress to the next level of the exercise.
Author: Jim Heafner PT, DPT, OCS
Sahrmann, S. (2002). Diagnosis and treatment of movement impairment syndromes. St. Louis: Mosby.