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Biomechanics

Biomechanics - Poster Session A

Poster E2 - Asymmetry of Lower Limb Muscle Fatigue and Knee Wobble During a Wall Sit

Thursday, October 24, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Assessment of lower limb muscle function is an important clinical approach to understanding patient injuries and post-intervention progress. The current methods for quantitative analysis of lower extremity muscle strength, fatigability, and function require a trained professional and are time consuming. Surface electromyography (sEMG) is a noninvasive tool for measuring muscle activity, and can be used to track muscle fatigue, while inertial measurement units (IMUs) are low-cost, simple devices that can be used to measure human motion. Previously, we have shown that muscle fatigue assessed by sEMG is correlated to knee wobble assessed by IMU during a wall sit activity on a single limb. Therefore, the goal of this study was to determine if muscle fatigue and knee wobble are similar between limbs during a wall sit activity. This finding will help determine whether future knee wobble measurement devices would need to be worn on both limbs or on a single limb for clinical measurement of lower extremity muscle fatigue. We hypothesized that there would be no difference in results between legs in both sEMG and IMU data.

Materials and

Methods:  Nineteen participants (9F, 10M) volunteered for this study, which was approved by the Bucknell University IRB (2324-114). Subjects gave informed consent before data collection began, and participant heights and weights were recorded. Participants were identified as not having any musculoskeletal/neuromuscular diseases or injuries that would prevent them from performing a wall sit. Eight sEMG sensors (Delsys Trigno Avanti Sensor, in sEMG mode) with 2148 Hz sampling frequencies were placed bilaterally on the gluteus maximus, semimembranosus, vastus medialis, and medial gastrocnemius head. An IMU (Delsys Trigno Avanti Sensor, in IMU mode) with a 370 Hz sampling frequency was placed on the lateral aspect of each knee. IMUs measured translational and angular acceleration in three directions (X along the femur, Y along the tibia, Z perpendicular to X and Y). Participants sat on a stool against a wall with a 90 degree knee angle. The wall had grip tape and a yoga mat was secured to the floor to prevent slippage during data collection. Following removal of the stool each participant was instructed to hold the wall sit position until self-selected failure. In Matlab extracted signals were filtered using a fourth order bandpass butterworth filter. Each set of data was split into ten intervals and the mean frequencies (MNF) of each interval were extracted using a fast fourier transform and the area under the resultant acceleration curve (AUC) was calculated. To determine whether there was a significant difference between legs of each subject, paired t-tests were performed for MNF and AUC.

Results, Conclusions, and Discussions: Visually, the muscles with the largest overall decrease in MNF appear to be the gluteus maximus and the semimembranosus (~10 Hz, Fig. 1), which agrees with our prior work showing greater gluteal fatigue during a wall sit. For the IMU data, the area under the curve (AUC) clearly increased throughout the activity (Fig. 1). Of the 100 paired t-tests that were performed for all 19 subjects and for all subjects combined, 62 were found to be statistically significant (p < 0.05) when comparing between limbs.

Our results suggest that the muscles in the left and right legs do not fatigue evenly during a wall sit activity. However, further analysis is needed to determine how fatigue asymmetry is related to knee wobble, and how lower limb injuries affect fatigue asymmetry during a wall sit. OurMNF results show that both the gluteus maximus and semimembranosus might be better muscle groups to target in fatigue assessment during a wall sit, although this requires further detailed statistical analysis. It should also be noted that some of the participants in this study did not exhibit the expected decreases in MNF over the course of the wall sit, which we have classified as non-responders in our prior study. These non-responders may be due to differences in what a person believes their ‘failure’ is, leg preference (which could affect how the right and left leg fatigue for each subject), and sEMG sensor placement and adhesion. In summary, we collected and analyzed data from trials of a wall sit that measured muscle fatigue from the gluteus maximus, semimembranosus, vastus medialis, and the medial head of the gastrocnemius and acceleration data of knee wobble. Combined MNF data shows that while both the left and right frequencies do decrease, they do not decrease evenly, and knee wobble shows a clear increase during the activity (Fig. 1). Future work is needed to develop robust models to explore correlations between muscle fatigue and knee wobble so that simple, low-cost IMUs could be used in a clinical setting to estimate lower limb muscle fatigue.

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