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Abstract-Trunk muscles are designed to fulfill their role of continuous activity throughout the day, but pain and inactivity alter muscles so that they fatigue in normal situations. Lack of endurance of the trunk muscles is an important factor in low back pain (LBP). This paper examines some methods to objectively test endurance of trunk flexor and extensor muscles in static and dynamic situations, and presents results of endurance testing in persons with chronic LBP compared to nonimpaired cohorts. Self perception of fitness affects some test results. Methods for increasing endurance are discussed along with benefits observed from training programs.
Key words: fatigue, low back pain, muscle performance, physical exercise.
INTRODUCTION
The muscles of the trunk are active whether one is sitting, standing, lifting, or rolling over in bed. Adequate endurance of trunk muscles is necessary to good health, and is something taken for granted until the first episode of low back pain (LBP) occurs, an episode said to happen to 80% of the U.S. population at some time in their lives. About half of those individuals will have reoccurrences within the first year of the first episode, leading to a possible history of chronic low back pain (CLBP). This paper examines some methods for testing trunk muscle endurance, some reported values of performance, and the effects of training to increase endurance.
Back fatigue and aching muscles of the back are complaints of people with LBP. Furthermore, lack of endurance of trunk muscles has been identified as a predictor of first-time occurrence of low back trouble in men (1), and as a discriminating factor between those who have had a history of LBP and those who have not (2,3). Endurance is mechanically defined as either the point of isometric fatigue, where the contraction can no longer be maintained at a certain level or as the point of dynamic fatigue, when repetitive work can no longer be sustained at a certain force level (4). Fatigue during a day of repetitive work is expressed by many, but it is difficult to quantify objectively. Although sound individuals can lift up to 85 percent of their maximally predicted loads over 4 hours with little evidence of fatigue (5), they may still describe fatigue, despite the lack of demonstrated physiological...