Study On The Workload During Static Hand-arm Posture Holding And Jumping Training With Electromyography

Musculoskeletal disorders(MSDs) are a kind of work-related diseases, all parts belonging to musculoskeletal system are involved. Low-back pain and cervicobrachial disorders are the common musculoskeletal disorders. Musculoskeletal disorders are focused more and more with the development of the industry. It was reported that the annual costs of MSDs varied between 0.5-2% of the GDP in the member countries of the European Union. In addition, MSDs can not be cured effectively sometimes. so evaluation and assessment and control and mechanism about MSDs are worth studied today. Force and maintain posture and repeatedly movements and vibration are relation to MSDs. Surface electromyography(sEMG) is a valid and non-invasive method for assessment of muscle action. So we hope to further study the loads on the muscles with sEMG and investigate the moderate working posture by these studies. Two experiments were designed according to the daily work activities, one for muscle activity under static posture and the other for jumping loads on the muscles.PartⅠStudy on the workload during static hand-arm posture holding with electromyographyObjectivesThe purpose of this study was evaluating workload of static hand-arm posture by Electromyography and finding the suitable posture of static hand-arm work which can provide scientific advices for ergonomics design.MethodsThe surface electromyography (sEMG ) and rating of perceived exertion(RPE) were recorded from 14 subjects in ten arm positions (0oelevation and 0oabduction and 0cm extension, 45oand 90oand 135oand 180o elevation , 45oand 90oand 135oabduction, 20and40and60 cm extension) during 90s with no load on hands. 210s were given for rest after each position was finished. During the work, the sEMG was detected from brachioradialis, bieceps brachii,deltoid, trapezius all the time. Before the work, the maximum voluntary contraction (MVC) are evaluated for all muscles, at the same time, sEMG were recorded for percentage of maximal voluntary electrical activation(MVE%). RPE were recorded at each position. The position (0oelevation and 0oabduction and 0cm extension) were the control position. The subjects have no musculoskeletal disorders in 24 hours before the experiment. Weight and height et al of the subjects were recorded.The sampling frequency of sEMG was 1024Hz, frequency filtering was 20-500Hz, FFT switching frequency was 1HZ. MVE% ,time domain index,and MF and MPF,frequency domain index ,were analyzed.ResultsIn time domain, MVE% increased with the increasing of elevating angles, abducting angles, extending distances separately in all muscles. It indicated significant dose response relation. The difference between 45oelevation and the control was no statistical significance (p>0.05) in every muscle, but the differences were significance (p<0.05) contrast with the control at 90oand 135oand 180o elevation. At 45oabduction, contrast with the control ,neither bieceps brachii nor trapezius, the difference was statistical significant (p>0.05),but deltoid had great changes(p<0.05) among four angles during abduction. At 20cm extension, contrast with the control, significant difference only occurs at brachioradialis(p<0.05). At the same time, RPE increased with the increasing of elevating angles, abducting angles, extending distances also.Frequency domain analysis showing, MPF obviously decreases (p<0.05) with the increasing of elevating angles, abducting angles, extending distances of the hand-arm,which indicated muscles were fatigue. While with elevating and abducting to the extremum(180o elevation 135oabduction), MPF increased again. In the extending posture, each muscle's MPF gradually decreases with the distance increasing. the changes of MF were similar to MPF.ConclusionsThe results declared, workload of static hand-arm posture gradually increased with the increasing of elevating angle, abducting angle, extending distance of the hand-arm. At the places which deviated neutral posture nearly, such as 45o elevation, 45o abduction and 20 cm extension, the muscle stress is lower(some MVE% have not obvious difference with that of neutral posture) . It shows, in work, the arm should be near to the body to operate. If the neutral posture is difficult to carry out, the other easeful choice is elevating<45o, abducting<45oand extending <20 cm. MPF and MF indicated that if the time exceed 90s during every position, the involved muscles will fatigue and need a rest. In a all, these results provide a scientific evidence for ergonomics design on labor postures.MVE% and MPF are the valid indexes for reflecting static posture loads and Muscles fatigue by stress. And RPE can also be a valid index for static posture loads. at the same time , some differences between physiology assessments and psychology assessments.PartⅡStudy on the Workload during Jumping Training with ElectromyographyObjectivesThe purpose of this study was evaluating loads of muscles involved during Jumping Training by surface electromyography, investigating factors affecting on musculoskeletal disorders and supplying guides about training.Methods38 volunteers of paratroopers participated in this study. The subjects have no musculoskeletal disorders in 24 hours before the experiment. They performed jumping from three kinds of height platform(1m,1.5m,2m), sEMG was recorded from 8 kinds of muscles(tibialis anterior,gastrocnemius,semitemdinosus ,bieps femoris ,rectur femoris, rectur abdominis, erector spinae L3 ,trapezius) under three conditions. Before the test, MVE% was measured from every muscles for normalize the RMS. Netral posture was recorded firstly for reference. Analysing sEMG in time and frequency domain to compare changes of different muscles under diferent conditions. In addition, linear correlation was performed to analyse the relationship between weight and MVE%(2m)。ResultsIn time domain, MVE% of every muscle was greater than the neutral posture (p<0.05).and MVE% of every muscle increasing with the increasing of the plat high. MVE% of gastrocnemius, bieps femoris, rectur femoris exceed 100%. MVE% of tibialis anterior ,gastrocnemius, bieps femoris, rectur femoris,trapezius were more than 70%. During allconditions, semitemdinosus was more sensitive than others because the difference among the netrl,1.0m,1.5m,2m was significant(p<0.05).In the frequency, MPF of all muscles were increasing with the increasing of height . MPF of tibialis anterior,gastrocnemius, rectur abdomini were higher than neutral posture(p<0.05) ,MPF of erector spinae L3 was lower than neutral (p<0.05).Changes of MF were similar to MPF.And no relation between weight and MVE%(2m)in all muscles。ConclusionsThe loads of muscles during the jump training were very large. Loads of the leg exceeded the limit. The height of plots is the risk factor to musculoskeletal disorders. Lower plats (1m) were recommended for the training. Or, some exercises were taken on to protect ankle and leg and waist.