Investigation of the effects of unexpected force on the hip and knee muscles during lifting various weights

Introduction: Our purpose in this article is to analyze and assess the injuries on the bodies of the service laborers caused by sudden applied forces on the extensor lower limb muscles (In the area among the Hip and Knee Joints) during lifting unexpected loads in the workplace. Methods: This study was performed on the eleven invited workers of two chain stores (with an average age, height, weight and BMI of ۲۷.۷۳ yrs., ۱۸۰.۰۱ cm, ۸۴.۵۱ kg and ۲۵.۹۸ kg/m۲ respectively) in a biomechanics laboratory equipped with ۶ Vicon cameras and two AMTI force plates. Our sections considered in this evaluation were the Quadriceps Femoris muscle and the Hamstring muscle; Our testing method was based on Lifting the loads and Holding them for ۵ seconds which included three weights namely light, medium and heavy (or ۲, ۴ and ۸ kg). During the experiments, Participants' legs were located on two force plates. It should be noted that in order to reduce the possible error, the test of each weight was repeated twice. The obtained information was classified and modeled with OpenSim software and at the end the muscle forces were analyzed based on Hill's muscle model.Results: After analyzing the models, the results of muscle forces for all three weights on the both legs Quadriceps Femoris muscle were as follows: In the Rectus Femoris muscle, the light weight had a significant difference in comparison with the other weights, whereas in the medium and heavy such a thing was not observed. These results similarly happened again for the other three muscles: Vastus Medialis, Vastus Lateralis and Vastus Intermedius (P=۰.۰۱). However, in the analysis of the exerted forces on the Hamstring muscles of both legs, the results were slightly different: no significant difference was observed in the amount of forces exerted by the Semimembranosus muscle in all weights; But this result was similar in the Semitendinosus muscle to the Quadriceps femoris muscle. Although the light weight had a considerable difference in comparison with the other weights, it was not observed between the medium and heavy (P=۰.۰۱). Conclusion: According to the findings of this study, in the lifting action especially while rising, the extensor muscles of the knee joint in different groups had a noticeable discrepancy that could be due to the torque generated during lifting. Also, in the hip Extensor muscles, only when the weight became heavier, the required torque for the Extensor changed, and it showed that up to a certain range of weights, applied torques and forces by muscles did not change remarkably. It is recommended that for further research, other parameters can be examined.