“Dynamic Trendelenburg”: Single-Leg-Squat Test for Gluteus Medius Strength

Abstract

UNCTIONAL TESTING is often used to assess components of multilevel tasks. Although functional tests are used regularly, the reliability and validity of the tests are often not thoroughly investigated. The single-leg squat is one such test that is used by clinicians and has been suggested to assess general leg strength and muscle endurance.1 The single-leg squat is described with various techniques including a single-leg squat with hand support, squatting with an external load, and a lunge activity.2 No standardized method is used, and no relationship has been documented to determine what the single-leg-squat test is actually assessing. It has been suggested that the single-legsquat test can be used to assess various dysfunctions affecting the kinetic chain.3 Zeller et al. used a three-dimensional camera system to report kinematic differences between men and women performing a single-leg squat.2 They reported that women had approximately 4° more hip adduction than men did when performing the singleleg squat.2 Zeller et al. suggest that the increased hip adduction might be caused by difficulty in controlling the hip musculature resulting from a weak gluteus medius muscle.2 No information presently exists on the relationship between hip-adduction angles and gluteus medius strength. The Trendelenburg sign is a very simple test that indicates gluteus medius weakness4 and can be used to identify injuries that result from an unlevel pelvis. The injuries and disorders that can be caused by a weak gluteus medius are numerous and include torn anterior cruciate ligaments, eversion ankle sprains, shin splints, scoliosis, and other malalignment injuries up and down the kinetic chain.4,5 Novice clinicians might find it hard to iden tify a weak gluteus medius because the underlying cause of these disorders might be caused by the hip but manifest elsewhere along the kinetic chain. Maintenance of a single-leg stance is necessary during running, cutting, and decelerating activities.2 If a weak gluteus medius is present during these dynamic activities, it might be difficult to observe the pelvic drop as a clinician would during Trendelenburg’s test. A single-leg-squat test includes the static Trendelenburg position but incorporates movement into the test to make it more dynamic. It is hoped that the “dynamic Trendelenburg” can be used to identify gluteus medius weakness during more dynamic tasks than in the original Trendelenburg test. As an athlete performs a single-leg-squat test, the clinician must visually observe the task and base decisions regarding the athlete’s strength on these subjective observations. These observational practices are commonly used but are rarely put under the scrutiny of scientific examination. Previous research of a clinician’s ability to identify deviations from a normal movement pattern has yielded only low to moderate reliability.6 Thus these tests should be used with caution by clinicians when making decisions regarding athlete care. Several functional tests are available for clinicians to evaluate their athletes. In order to make sound clini