Fatigue sensation, electromyographical and hemodynamic changes of low back muscles during repeated static contraction.
The effects of work strategy and a rest condition on the physiological changes of the erector spinae muscle were studied. Eleven volunteers repeated fatiguing static contractions of holding an industrial box in 30° trunk flexion for a repetition of 12 times interrupted by rests for which the duration was equal to the duration of each preceding contraction. Each contraction was stopped at two fatigue sensation levels; moderate or strong, which corresponded to Borg's CR-10 3 and 5, as the work strategy conditions. The repeated contractions were performed for a total of eight conditions combined with the two rest conditions, with and without stretch exercise, and two contraction levels of 10 and 40% maximum pulling force in flexed posture (MVC) on separate days. Near-infrared spectroscopy and surface electromyography (EMG) were recorded. Amplitude and median frequency (MF) of EMG, oxy-hemoglobin, and deoxy-hemoglobin were calculated. MF related to fatigue sensation most closely. Oxy-hemoglobin decreased during each contraction. It, however, increased with repetition especially at 10% MVC and the increase was interpreted as adaptation to the work. The effect of the work strategy and the rest conditions was weak. MF decreased more in a strong work strategy condition than in a moderate one.
Movahed
Mehrnoosh
M
Department of Ergonomics, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Kitakyushu, Japan. Movahed@med.uoeh-u.ac.jp
Ohashi
Jun-ya
JY
Kurustien
Nopporn
N
Izumi
Hiroyuki
H
Kumashiro
Masaharu
M
D000328:Adult; D001415:Back / Q000502:physiology; D004576:Electromyography; D015444:Exercise / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000502:physiology*; D012146:Rest / Q000502:physiology; D012677:Sensation / Q000502:physiology; D014937:Work / Q000502:physiology; D055815:Young Adult