The Variability of Neuromuscular Control During Knee Extension Performance
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Movement variability that occurs while performing repetitions of any particular motion can be due to errors in one’s ability to select the required parameters for executing the movement. However, it has been suggested that an optimal amount of variability exists in a healthy system providing adaptability to varying situations while producing negligible errors. Investigation of the consistency of movement variability in a system may provide information regarding joint control and integrity since the functionality of a system can be disrupted by injury. Rupture of the anterior cruciate ligament is associated with deficits in knee joint stability and mobility, as well as altered movement patterns. There is value in developing a simple clinical test that can measure knee joint stability and evaluate the degree of knee damage and rate of progress during rehabilitation. The main objectives were to investigate the normal range of variability during repeated knee extensions in healthy subjects and subjects with a reconstructed anterior cruciate ligament, and to evaluate the reliability of the method. There were 30 participants in the control group and 8 in the subject group. All were physically active a minimum of 2-3 times per week for a total of 2-3 hours. Mean variance and mean correlation were used to evaluate variability in this study. Change in mean variance and mean correlation, standard error of measurement and intra-class correlation coefficient were used to evaluate reliability. The results showed the range of values for movement variability in control and subject groups. Standard error of measurement indicated mean correlation (1.31% to 2.38%) was more reliable than mean variance (21.80% to 54.87%). Mean variance and mean correlation significantly increased with speed, and mean correlation was significantly higher for dominant legs during trials at 70 beats per minute.