Experimental Study On The Lifting Techniques And Fatigue Recovery

Part 1 An experimental study on the manual lifting techniquesObjective In the experimental condition of controlling some lifting factors (weight,horizontal distance, vertical height, frequency and duration time), using surfaceelectromyography, electrocardiology and Borg scale to investigate the effects ofphysiological indexes of different manual lifting techniques, thereby, objectively evaluatedthe suitability of these lifting techniques, and provided some supports for formulatingreasonable lifting technique.Methods 30 college volunteers, 15 male and 15 female, randomly selected squat, stoopand semi-squat lifting techniques to lift the object which was placed on the ground. Theobject was 36cm×26cm×28cm wooden case, the weight was the 25% of the averagemaximum muscle force (11kg for male and 6kg for female), the horizontal distance was40cm, the vertical height was the distance between the floor and the subjects'metacarpophalangeal joints level of straightened standing, the frequency was 12 times/min,the duration time was 4.5 min. Before the lifting task, all subjects rested 20 min in sitting,among the lifting tasks, rested 15 min in sitting, after the lifting task, all subjects rested 20min in sitting.Results In three lifting techniques, all the heart rates of male and female were higher thanthose at rest (P＜0.05). Among three lifting techniques, the heart rates of male and femalewere the lowest in stoop and the highest in squat (P＜0.05). Although the values of Borgscale of three lifting techniques were no statistical difference, however, the values of squatwere high, the values of Stoop and semi-squat were low.In three lifting techniques, male and female percentage of the maximum voluntary electricalactivation (MVE%) of root mean square values (RMS) of surface myoelectric amplitude ofRT10, LT10, RL3 and LL3 were higher than those at rest (P＜0.05). Male median frequency (MF) of surface electromyography of RT10, RL3 and LL3 were lower than those at rest(P＜0.05), however, male MF of LT10 were higher than those at rest (P＜0.05). Female MFof LT10 and LL3 were higher than those at rest (P＜0.05), however, female MF of RL3 werelower than those at rest (P＜0.05). Male mean power frequency (MPF) of electromyographyof LT10 were higher than those at rest (P＜0.05), however, male MPF of RL3 and LL3 werelower than those at rest (P＜0.05). Female MPF of LT10 were higher than those at rest(P＜0.05).Among three lifting techniques, male MVE% of RT10 was the highest in squat (P＜0.05),male MVE% of LT10 was the highest in semi-squat (P＜0.05), male MVE% of RL3 was thelowest in squat (P＜0.05), male MVE% of LL3 was the lowest in semi-squat (P＜0.05).Female MVE% of RT10, RL3 and LL3 were the highest in stoop (P＜0.05), however,female MVE% of LT10 was the lowest in stoop (P＜0.05). Male MF of LT10 was the lowestin stoop (P＜0.05), male MF of RL3 was the lowest in semi-squat (P＜0.05), male MF ofLL3 was the lowest in squat (P＜0.05). Female MF of RL3 was the lowest in stoop (P＜0.05).Male MPF of LT10 was the highest in squat (P＜0.05), male MPF of LL3 was the lowest insquat (P＜0.05).The analytical results of Jointed EMG Amplitude and Spectrum Analysis (JASA) showedthat the 4 positions of erector spine muscles of male subjects emerged 9 times fatigue of insquat, 8 times fatigue in semi-squat and 10 times fatigue in stoop. However, the 4 positionof erector spine muscles of female emerged 10 times fatigue in squat, 7 times fatigue insemi-squat and 8 times fatigue in stoop.Conclusions In three lifting techniques, the heart rates and MVE% of erector spinemuscles in male and female subjects were both higher than those at rest. Among threelifting techniques, the heart rates of male and female subjects were highest in squat and thelowest in stoop. All of waist and back erector spine muscles were tired in three liftingtechniques, but the times of fatigue were the least in semi-squat, in terms of decreasingfatigue of local muscles, we can conclude that semi-squat was an optimal lifting technique. Part 2 An experimental study on fatigue recovery of the manuallifting techniquesObjective Accumulation fatigue of erector spine muscles in waist and back was one ofimportant risk factors for low back pain. In order to decrease the risk of low back pain ofoccupational employer because of accumulation fatigue, we studed the change of the heartrates and surface electromyography activity and frequency of erector spine muscles in resttime among three lifting techniques and recovery time after three lifting techniques of 30volunteers, so that provided some suitable experimental data for recovery time.Methods 30 college volunteers, 15 male and 15 female randomly selected squat, stoopand semi-squat lifting techniques to lift the object which was placed on the ground, theobject was 36cm×26cm×28cm wooden case, the weight was the 25% of the averagemaximum muscle force(11kg for male and 6kg for female), the horizontal distance was40cm, the vertical height was the distance between the floor and the subjects'metacarpophalangeal joints level of straightened standing, the frequency was 12 times/min,the duration time was 4.5 min. Before the lifting task, all subjects rested 20 min in sitting,among the lifting tasks, rested 15min in sitting, after the lifting tasks, all subjects rested 20min in sitting.Results After 15 min rest, among three lifting techniques, all male MVE% of RT10 andLT10 after stoop and MVE% of LT10 after squat were not complete recovery, the otherswere complete recovery. All female MVE% of LT10 after three lifting techniques werecomplete recovery, the others were not complete recovery. All male MF of LT10 after squatand MF of LL3 after semi-squat were not complete recovery, the others were completerecovery. All female MF of RT10, LT10, RL3 and LL3 after stoop, female MF of LT10 andLL3 after squat and female MF of LL3 after semi-squat were not complete recovery, theothers of female MF were complete recovery. Male MPF of RT10 and LT10 after squat andmale MPF of LL3 after semi-squat was not complete recovery, the others were completerecovery. Female MPF of LT10 after squat and stoop and female MPF of LL3 after threelifting techniques were not complete recovery, the others were complete recovery.In the last 20 min recovery, the male and female MVE% of RT10 were recovered to the resting level in 2 min and 6 min, respectively. The MVE% of LT10 of male and femalewere recovered to the resting level in 5 min and 2 min, respectively. The male MVE% ofRL3 and LL3 were both recovered to the resting level in 1 min. The female MVE% of RL3and LL3 were not completely recovered to the resting level in 20 min. All the male andfemale MF and MPF of RT10 and LL3 were recovered to the resting level in 1 min. All themale and female MF and MPF of LT10 were recovered to the resting level in 2 min. Themale MF of RL3 was recovered to the resting level in 16 min. All the male MPF of RL3were recovery to the resting level in 2 min. All the female MF and MPF of RL3 wererecovered in 1 min.In the last 20 min recovery time, with the time increasing, the heart rates of male andfemale were decreasing. The heart rates of male and female were recovered to the restinglevel in 14 min and 5 min, respectively.Conclusions 15 min rest were sufficient for most erector spine muscles of male and werenot sufficient for most erector muscles of female. In the last 20 min rest, except RL3 andLL3 were not complete recovery, the other MVE%, MF and MPF of erector spine muscleswere complete recovery. However, all the heart rates were complete recovery in 20 minrest.