Biomechanical analysis of hip and thigh muscle activities during single leg sit to stand in normal, healthy adults.
Ambrose, Thomas SPT; Barone, Emily SPT; Duhammel, Zachary SPT; Ludwig, Caroline SPT; Parish, Jena SPT; Mohamed Kohia, PT, Ph.D., MS
Purpose/Hypothesis: The objective of this study was to find out the electromyography (EMG) activity in targeted muscles of the lower extremity during single leg sit to stand when accounting for leg dominance and the use of armrests. It was hypothesized that greater EMG activity would be seen in the non-dominant leg compared to the dominant leg and without the use of armrests as compared to the use of armrests. It was also hypothesized that some muscles tested would show a greater EMG activity than others. Subjects: A total of 56 subjects between the ages of 18 and 35 years old with no history of knee injuries participated in this study. Six subjects were excluded from the final count due to faulty data collection. Materials/ Methods: Surface bipolar electrodes were attached to the adductor magnus, tensor fasciae latae, sartorius, gluteus medius, gluteus maximus,vastus medialis, vastus lateralis, rectus femoris, biceps femoris, and semimembranosus to record the EMG activity of those muscles during single leg sit to stand. Patients were asked to perform four total trials: dominant leg with armrests, dominant leg without armrests, non-dominant leg with armrests, and non-dominant leg without armrests. Rest periods were allotted between trials. Results: There was a significant difference in muscle activation with the use of an armrests/no armrest (.008) with greater muscle activation without the use of the armrests (355.473 > 316.545). There was a significant difference between the dominant leg/nondominant leg (.024) with greater muscle activation during use of the nondominant leg (370.263 > 301.756). There was also a significant difference between the following 7 muscle pairs (.000): Vastus Lateralis > Adductor Magnus (474.75, 243.68, p.000); Vastus Medialis > Adductor Magnus (441.83, 243.68, p.000); Semimembranosus > Gluteus Medius (406.85, 187.75, p.000), Vastus Lateralis > Gluteus Medius (474.75, 187.75, p.000); Vastus Medialis > Gluteus Medius (441.83, 187.75, p.000); Vastus Lateralis > Rectus Femoris (474.75, 259.48, p.000); and Vastus Medialis > Rectus Femoris (441.83, 259.48, p.001). Conclusions: The results of this study suggest that muscle activity is greater without the use of an armrest and with the use of the non dominant leg during single leg sit-to-stand. The data also highlights the 7 muscle pairings that have a significant difference and are therefore most crucial during sit-to-stand, allowing for physical therapists to better prevent related injuries, enhance stability for functional activities, as well as plan lower extremity strength training rehabilitation programs. Clinical relevance: Based on the results of this study, it is our recommendation to consider the patient’s leg dominance when developing a plan of care, as their is a significant increase in EMG firing of the non-dominant leg during single leg sit-to-stand. Also, the use of the upper extremity decreases the firing rate of lower extremity musculature which can be used to progress a patient into more difficult tasks. Finally, the results show that during a single leg sit-to-stand the vastus lateralis and vastus medialis have high EMG activity in comparison to hip abductors (gluteus medius), adductors (adductor magnus), medial hamstring (semimembranosus) and the rectus femoris. This data encourages the clinician to utilize a single leg sit-to-stand in patients that require more isolated firing of the vastus medialis and vastus lateralis, such as a patient with patellar tendinopathy from weak knee extensors.