ABSTRACT
The purpose of this study was to examine whether repetitive muscle tasks in low weight load might influence the fatigue of forearm muscles, and to identify ergonomic risk factors of forearm muscle fatigue in these tasks. Sixteen healthy male volunteers performed eight wrist extensions in different frequency, weight and angle loads while being instructed to keep a dominant upper limb posture as constant as possible. Surface electromyograph (sEMG) was recorded from right extensors digitorium (ED), flexor carpi radialis (FCR), flexor carpi ulnaris (FCU) and extensor carpi ulnaris (ECU) during the task performance. Our results showed that mean power frequency (MPF) and median frequency (MF) values of ED, FCR and FCU were significantly lower (P<0.05) at high frequency load level than at low load level. However, MPF and MF values of ED were significantly lower (P<0.01) in higher load groups of frequency, angle and weight than in lower load groups. These results indicated that the fatigue of muscles varied in the same task, and the number-one risk factor of ECU, ED and FCR was angle load.
Subject(s)
Young Adult , Cumulative Trauma Disorders/complications , Cumulative Trauma Disorders/physiopathology , Electromyography , Forearm/physiology , Muscle Fatigue/physiology , Muscle, Skeletal/physiopathologyABSTRACT
The purpose of this study was to examine whether repetitive muscle tasks in low weight load might influence the fatigue of forearm muscles, and to identify ergonomic risk factors of forearm muscle fatigue in these tasks. Sixteen healthy male volunteers performed eight wrist extensions in different frequency, weight and angle loads while being instructed to keep a dominant upper limb posture as constant as possible. Surface electromyograph (sEMG) was recorded from right extensors digitorium (ED), flexor carpi radialis (FCR), flexor carpi ulnaris (FCU) and extensor carpi ulnaris (ECU) during the task performance. Our results showed that mean power frequency (MPF) and median frequency (MF) values of ED, FCR and FCU were significantly lower (P＜0.05) at high frequency load level than at low load level. However, MPF and MF values of ED were significantly lower (P＜0.01) in higher load groups of frequency, angle and weight than in lower load groups. These results indicated that the fatigue of muscles varied in the same task, and the number-one risk factor of ECU, ED and FCR was angle load.
ABSTRACT
Three bacteria of decomposing lecithin and 4 bacteria of dissolving aptite were incubated for 4 weeks with sand media respectively. Phosphorus in the sand was extracted with distilled water and measured by different methods. It was found that the bacteria have a quite different ability to release P from the materials. Part of the P released became organic phosphorus compounds in microbial tissue. However, a large amount of the P was reserved in microbial cells in a form of phosphates. The direct measurement of P in the extract by molybdenum blue method would underestimate the capacity of the bacteria to release P from the materials. The correct approach was that the sand was fumigated with chloroform and then digested with acid before the measurement by molybdenum blue method.
ABSTRACT
Four bacterial and 8 fungal isolates were incubated in media for 6 days. It was found that organic acid content in the media increased largely, but pH decreased sharply. Phosphorus content in the media enhanced dramatically as well. The fungal isolates showed stronger ability to dissolve phosphate rock than the bacterial ones. These isolates excreted not only quite distinct volume of organic acids but diverse organic acid chemicals. The fungi produced more kinds of organic acids than the bacteria. However, there was no significant relationship between the total quantity of organic acids and P content in the media.
ABSTRACT
Three bacteria of decomposing lecithin and 4 bacteria of dissolving aptite were incubated for 4 weeks with sand media respectively. Phosphorus in the sand was extracted with distilled water and measured by different methods. It was found that the bacteria have a quite different ability to release P from the materials. Part of the P released became organic phosphorus compounds in microbial tissue. However, a large amount of the P was reserved in microbial cells in a form of phosphates. The direct measurement of P in the extract by molybdenum blue method would underestimate the capacity of the bacteria to release P from the materials. The correct approach was that the sand was fumigated with chloroform and then digested with acid before the measurement by molybdenum blue method.