Search

Study Design: A repetitive lifting test in the sagittal plane was performed with a submaximal load at a maximal lifting rate to understand the effects of fatigue on kinematic and kinetic measures of performance., Objectives: To quantify the effect of fatigue during a highly repetitive lifting task, in terms of lifting force transmitted to the load, joint motion patterns, and internal joint load sharing., Summary of Background Data: Industrial surveillance and epidemiologic data suggest that repetitive lifting is a risk factor for low back pain. Previous studies examining the effect of fatigue have either been constrained to isolated trunk movement, or have not explored the internal load distribution and potential alteration in the loading patterns., Methods: Sixteen healthy male subjects performed repetitive lifting in the sagittal plane with a load equal to 25% of their maximal lifting capacity, at a maximal lifting rate. Changes in lifting performance were determined from the power transferred to the box, joint kinematics, and joint kinetics. Data from three cycles at the start and end of the exercise were tested for the effect of fatigue using repeated-measures analysis of variance., Results: Fatigue was documented by a reduction in average lifting force and hip and spine torque generation, whereas internal joint load sharing was relatively unchanged. The fatigue was associated with decreased knee and hip motion, and increased lumbar flexion. Decreased postural stability also was evident., Conclusions: The significant decrease in postural stability and force generation capability because of the repetitive lifting task indicated a higher risk of injury in the presence of unexpected perturbation. Multijoint coordinated lifting tasks provide a more realistic protocol to study neuromuscular fatigue.

A novel testing protocol was used to investigate changes in neuromuscular performance, muscle recruitment, and spinal loading as subjects became fatigued while performing an isometric endurance test of varying torque requirements. There was decreased accuracy in maintenance of a reference torque but no change in response time as subjects became fatigued. The study of trunk-muscle recruitment indicated significant increases in internal oblique and latissimus dorsi muscle activity. This change in recruitment led to changes in spinal loading despite a relatively constant torque output. The use of an electromyogram (EMG)-assisted model demonstrated that when subjects are expected to become fatigued during test performance, the assumption of a constant maximal stress capacity of the muscle may not be robust.

Because of the inability of strength tests to accurately discriminate between low back pain patients and healthy subjects, a multifactorial evaluation of low back pain patients is warranted. It is postulated that measurements of endurance, kinematics, postural stability, and coordination, in addition to strength, are necessary to fully document the patients' functional capabilities. This research study was conducted in order to understand the effects of fatigue on the above factors. Twelve healthy male subjects performed a repetitive lifting test in which a submaximal load was lifted at a maximal rate. Knee, hip, and trunk motion was measured using videography and electrogoniometry, postural stability was measured using a forceplate, and coordination parameters were determined using phase-plane analysis. Fatigue was documented by a 31% reduction in lifting power. At the end of the endurance test, there was less knee and hip range of motion and greater spine peak flexion, while the coordination measures demonstrated that there was greater hip and lumbar spine extension earlier in the lifting phase. The postural stability declined as the test endured. Utilization of these measures may guide physical therapists in their rehabilitation of low back pain patients.