TEST #2: Single Leg Squat Test ( SLST) - The SL Squat (SLST) test assesses the athlete’s ability to perform a partial squatting motion on one leg. Due to the fact that so much athletic activity involves single limb activity, this is a crucial test and will provide you with an idea of the athlete’s ability to stabilize his or her extremities while in motion. This will provide a great deal of insight into potential weaknesses, tightnesses and where the athlete’s limitations are with regard to the lower extremity activities. Performance on this test can be directly linked in particular to power generation in the lower body.
During this test, the subject stands on one leg while the other leg is bent to between 45-90 degrees. The subject is asked to squat down to 45° and repeat the motion 10 times. Once the subject completes 10 repetitions, he/she is then asked to perform the same test on the opposite side for 10 repetitions. During this test, you are assessing the ability to perform the test, whether there is excessive lumbar flexion vs. knee flexion, whether there is a variance between the right and left sides, if there is adduction/internal rotation at the hip or knee and if the subject is able to stay balanced during the course of the examination.
Clinical Implications of the 45° Single Leg Squat Test
There are numerous deviations that show up in athletes performing 45° SL Squat Test. Below is a list of some of the most common deviations associated with the 45° SL Squat Test and the associated clinical implications.
Hip adduction and internal rotation with ascent/descent or trendelenburg – As above, these three movements are combined together due to the fact that they are so often associated with one another. In this test, these deviations can become even more apparent. If weaknesses exist, they often appear when the athlete attempts this test first with a notable drop in the pelvis (trendelenburg), followed by an accompanying adduction at the hip with internal rotation of the femur. In this example, the subject has a slight trendelenburg at the hip along with significant adduction at the hip with slight internal rotation at the femur. The combination of these motions occur secondary to poor core stability, and/or poor gluteus medius strength or endurance.
Suggested Corrective Exercise: These individuals respond well to core strengthening and gluteus medius strengthening (PNF step-up/side-stepping series).
Trendelenburg/Cork screwing – if there is weakness in the hip, this will often become more pronounced in a single leg stance position. Most often, this will present itself as a trendelenburg (as described above). If the weakness in the hip is significant enough, then there may be a loss of control at the hip resulting in a “cork screwing” motion.
In this particular example, the subject starts to “cork screw” at the hip, resulting in significant side bending in the lumbar spine and eventually loss of balance.
Suggested Corrective Exercise: Due to the extent of weakness of the hip and core, these subjects do remarkably well with isolated strengthening and endurance exercise training for the gluteus medius and the core as well as a proprioceptive retraining program.
Asymmetry – as the force demands increase for the entire lower kinetic chain with this test, bilateral asymmetries become more apparent. Using the example from above, we can see when we compare the subject’s left leg to his right, that there are notable asymmetries. If these are left unchecked this leads to increased potential for injury on both legs.
- Variance in ability to perform
- Decreased number of repetitions able to perform on right vs. left
- Variance in concentric strength – variance in difficulty with ascent right vs. left. This is most notable with inability to obtain full knee extension on right vs. left.
- Variance in eccentric strength – variance in difficulty with descent right vs. left. You will most often see the subject compensate with decreasing the range of motion they will descend to on one side vs. the other.
- Variance in hip strength – resulting in a trendelenburg or cork screwing on side vs. other
- Difference in hip or ankle range of motion or range to which the athlete is able to descend or ascend.
Suggested Corrective Exercise: These athletes do well with single leg training protocols (single leg press, single leg squats, and single leg functional activities).
Inability to perform – if an athlete is simply not able to perform the squat or if he/she is not able to perform without losing balance. If they are unable to complete the test as a result of weakness, then a closer assessment of the squat should be performed, looking for lateral shift in particular.
Suggested Corrective Exercise: If there is significant lateral shift, these subjects respond well to the squatting protocol (squat pause protocol, rapid squats, rotational lunges). If the inability to perform this test is a result of loss of balance, then these athletes respond well to the Single Leg with Dynamic Lower Extremity Movement exercise progression.
Dr. Nessler is a practicing physical therapist with over 17 years sports medicine clinical experience and a nationally recognized expert in the area of athletic movement assessment. He is the developer of an athletic biomechanical analysis and author of a college textbook on this subject. He serves as the National Director of Sports Medicine for Physiotherapy Associates, is a Safety Council Member for USA Cheer National Safety Council and associate editor of the International Journal of Athletic Therapy and Training.