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Biomechanics

Biomechanics - Poster Session A

Poster E3 - Capturing the Neuromuscular effects of fatigue during repetitive box lifting with varying precision

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

Introduction:  The primary aim of this pilot study was to investigate the differences in the muscular activity of the lower back and lower extremities during a repetitive lifting task requiring low-precision and high-precision box placement. This was done to observe the muscular fatigue that occurs during these tasks overtime, which can lead to injuries in the lower back. Muscular fatigue is where the strength of a muscle group diminishes over time after repeated or maximal use [1]. When muscular fatigue starts to set in, the body needs to replenish many metabolites such as oxygen and ATP while lactic acid builds up, which all negatively impact muscular performance. This muscular fatigue is affected cognitively throughout low precision and high-precision lifting tasks that can be present in the workplace, which causes lower back injury. Lower back injury has been the cause for 38.5% of all work-related muscular disorders, including disorders in occupations such as laborers, store workers, and healthcare workers [2]. In these occupations, lifting heavy objects, stoop lifting, and overall lack of good posture and strength are all factors for injury. These tasks all have a common thread with causing muscular fatigue that leads to injury. The United States’ economy losing 87 billion dollars (about $270 per person in the US) because of individuals being unable to work as well as the individual being unable to provide for themselves [3].

Materials and

Methods:  The study with 1 male subject was conducted with the subject having a height, weight, and age of 1.63 meters, 60.6 kg, and 19 years. The experiment consisted of 4 Electromyographic (EMG) Delsys-Trigno Wireless sensors, with two attached to the Erector Spinae in the L4/L5 positions to the left and the right of the spine and the other two being connected to the Biceps Femoris on each leg. A box with a weight of approximately 10% of the subject’s weight was used and placed on a table. Before the task, a maximum voluntary contraction (MVC) was performed on each previously mentioned muscle. A leg curl against tension was used to obtain the MVC for each of the subject’s Biceps Femoris. A lower back extension against tension was performed by the subjects for the MVC of the subject’s Erector Spinae. The task consisted of two-15-minute blocks with a 5-minute block of rest. The first 5 minutes would have the subject perform a non-precision lift then switch to a high-precision lift for 5 minutes, then back to a low-precision task for the last 5 minutes. This process would be repeated after rest, but instead starting with the high precision task. The data obtained from the EMG was passed through a 4th order Butter-Worth Filter low-pass filter with a 45-450 Hz cutoff. Growth-charts were used to analyze the change in activity overtime. Growth-charts are percentile curves that show the 90th , 50th and 10th percentiles of muscle activity.

Results, Conclusions, and Discussions: The growth charts from Figure 1 showed that there is a general increase in electrical activity with all the muscle groups experimented on. The left erector spinae activity doesn’t change throughout the pilot. However, for the right erector spinae, the activity is shown to be higher and to have a higher range of electrical activity, which would’ve been when the subject would be performing a high-precision task. This indicates a muscular imbalance, which could be caused by overuse of the right erector spinae [4]. Muscular imbalance is a disorder that affects the joints and posture on an individual, which can lead to injury as one group of muscles exerts more force than the other. When the stronger of two muscles pulls harder, it displaces the neighboring joints, which pulls the nearby muscles as well. This is an issue for repetitive stoop lifting, because if only one muscle group can load excessive weight, it puts unnecessary strain on the weaker surrounding muscle groups that can lead to tears. The results may show a higher risk of low back injury; however, further analysis is needed with a larger sample group to be sure. For the right biceps femoris, the electrical activity rises near the end of the lifting tasks. This shows that there isn’t much activity change occurring. However, for the left biceps femoris, the electrical activity growth is very consistent and there’s no noticeable change between the different tasks. This could indicate a muscular imbalance with a reliance on the left biceps femoris. Further analysis is needed to make stronger conclusions about the muscular activity in all muscle groups. The overall increase in electrical activity indicates muscle fatigue, but further analysis is required to determine. The limitations mainly lied with the subject performing the incorrect task as a well as the scope of the pilot. The lab aims to mitigate these limitations by making sure the people perform the tasks correctly and to understand if fatigue or cognitive activity affects the task performance. Acquiring kinematic motional data as well as brain activity to determine cognitive effects could both help meet limitations.

Acknowledgements (Optional):  We would like to acknowledge the undergraduate research students at the Center for Advanced Robotics Texas A&M - Jimit Mahadik, Aline Moller and Swarali Akella for their contributions to the data collection for this pilot study.