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Muscular load characterization during isometric shoulder abductions with varying force.

Authors
Iridiastadi-H; Nussbaum-MA; van DieŽn-JH
Source
J Electromyogr Kinesiol 2008 Aug; 18(4):695-703
NIOSHTIC No.
20043294
Abstract
This study sought to characterize muscle loading and fatigue during static shoulder abductions with varying force. In a supine posture, participants maintained fixed shoulder abductions against a time-varying external resistance, generated by a dynamometer-spring mechanism. Patterns (cumulative distribution) of the external resistance were varied by selecting different 10th and 90th percentiles of the distribution. Dynamometer angular velocities were also varied, to reflect different rates of cyclic muscle contraction. The degree of local fatigue development was assessed by common measures, including endurance time, strength reduction, and perceived discomfort. Myoelectric (EMG) signals were continuously obtained from the middle deltoid muscle throughout experimental exercise (60min max). Changes in EMG root-mean-square (RMS) and spectral measures (derived from 1-s windows at peaks in the cyclic contractions) were used as manifestations of muscle fatigue. For each minute, the RMS signal was further reduced using two methods, the cumulative probability distribution of EMG (CPDE) and exposure variation analysis (EVA). The former resulted in three percentile values (10th, 50th, and 90th), whereas the latter method resulted in 10 different measures (grouped by EMG activity level and duration). A main finding of the study was the applicability of several common fatigue indicators for these cyclic, repetitive exertions. Overall, the use of CPDE and EVA to characterize task differences and predict muscle fatigue was found to have limited value.
Keywords
Humans; Men; Women; Muscle-function; Muscles; Musculoskeletal-system; Musculoskeletal-system-disorders; Fatigue; Force; Posture; Physical-fitness; Physical-reactions; Physiology; Physiological-function; Physiological-effects; Contraction-joints; Author Keywords: Localized muscle fatigue; Electromyography; CPDE; EVA; Exposure assessment
CODEN
JEKIE3
Publication Date
20080801
Document Type
Journal Article
Email Address
nussbaum@vt.edu
Funding Type
Cooperative Agreement
Fiscal Year
2008
NTIS Accession No.
NTIS Price
Identifying No.
Cooperative-Agreement-Number-U19-OH-008308
Issue of Publication
4
ISSN
1050-6411
Source Name
Journal of Electromyography and Kinesiology
State
VA
Performing Organization
Virginia Polytechnic Institute and State University
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