In her article, Dr. Gulick stated that the Clam-Shell exercises can “reduce knee valgus, improve patellar tracking, and decrease the risk of knee injury in patients with patello-femoral pain syndrome.” Her 4 variations of the Clam-Shell are performed in supine, sidelying, bridge, and side-plank using either Yellow Thera-Band resistance bands or Band Loops.
EMG research presented at the TRAC 2011 meeting by Dr. Bart Bishop showed that the Thera-Band-resisted sidelying Clam-Shell exercise moderately activated the gluteus medius (36% MVIC) and maximus (39% MVIC).
Referencing 2 studies on hip exercise (Ekstrom et al. 2007, Delp et al. 1999), Dr. Gulick suggested performing the Clam-Shell exercise in hip extension to maximize muscle recruitment. In addition, focusing on the eccentric component of the exercise is thought to be important for patients with patello-femoral pain syndrome (Baldon et al. 2009).
It’s important to note that this paper was only a clinical application and not a scientific study. Dr. Gulick presented some evidence to support the Clam-Shell progression, but more research is needed to validate the clinical progression with EMG analysis. Nonetheless, clinicians should feel comfortable prescribing the Clam-Shell exercise based on the best available evidence.
[REFERENCE: Gulick DT. Clam shells: A unique progression for hip external rotation muscle strengthening. Orthopedic Practice. 2012. 24(1):28-29.]