Biomechanical Analysis of the Knee Joint Load During a Unilateral Sit-to-Stand Movement

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Background and Objectives: Sit-to-Stand (STS) movements are fundamental activities of daily living. As STS movements can be physically demanding especially for the elderly, bi- and unilateral STS movements are frequently used in motor tests to measure lower limb strength. In contrast to bilateral STS movements, the knee joint loads occurring during unilateral STS movements as well as the influences of chair height or lower limb dominance are still unknown. Methods: In a randomized study approach knee joint loads during unilateral STS movements from three different chair heights have been analyzed using biomechanical motion analysis in a population of 19 healthy middle-aged adults. Additionally, the influence of lower limb dominance and the level of perceived exertion have been investigated. Results: Lower limb dominance had no effect on knee joint load. In contrast, chair height significantly affected the peak shear forces in anterior (high: 3.94 ± 0.63 N/kg; low: 4.09 ± 0.61 N/kg) and lateral (high: 1.52 ± 0.79 N/kg; low: 1.78 ± 0.88 N/kg) direction as well as the peak knee adduction moment (high: 0.56 ± 0.29 Nm/kg; low: 0.65 ± 0.32 Nm/kg). Additionally, chair height but not limb dominance significantly affected the level of perceived exertion (high: 11.1 ± 2.8; low: 12.5 ± 3.5). Conclusion: The detected knee joint loads occurring during a unilateral STS movements are similar to those of other activities of daily living like e.g. stair ascent and thus, unilateral STS movements are applicable for usage in motor tests for middle-aged subjects. While lower limb dominance has no impact on the knee joint load, lower chair heights increase the load on the knee joint. Therefore, chair height should be considered when using unilateral STS movements in motor tests.