The XXVI th Annual Occupational Ergonomics and Safety Conference El Paso, TX, USA June 5-6, 2014 ISBN: 1 Knee Strength and Muscle Oxygenation Changes due to Prolonged Kneeling Alexa Hernandez Principe 1 , Blake Johnson 1 and Dr. Naira Campbell-Kyureghyan 1 1 University of Wisconsin-Milwaukee, Milwaukee, WI Corresponding author's Email: campbeln@uwm.edu Author’s note: The authors would like to thank Madiha Ahmed, Daniel Lomo-Tettey, and Patrick Dix, for their help in the data collection process. We are also very grateful to all the subjects for volunteering in the study. Abstract: There are many occupational tasks that require the worker to kneel for a prolonged period of time, such as utilities, mining, construction, etc. Even though kneeling is generally perceived as a static task, it induces muscle fatigue in the knee flexors and extensors. Fatigue analysis has been done primarily through electromyography. Knee strength is important for stability; functional stability of the knee is dependent on the timely and efficient contraction of the supporting musculature. The aim of this study was to measure and quantify the changes associated with a prolonged kneeling task. In particular the knee strength and muscle oxygenation in the upper leg muscles during prolonged kneeling were investigated. Eight subjects (7 male and 1 female) were recruited to participate in this study. Subjects were asked to kneel on a kneeling mat for up to 30 minutes while maintaining a 90 knee flexion posture. Before and after the kneeling trial, isometric knee flexion and extension strength was recorded. Throughout kneeling the muscle oxygenation of the upper leg muscles - Rectus Femoris and Bicep Femoris - was recorded. After completion of the kneeling trial, a reduction in muscle oxygenation levels of 10% and 14% was observed in the Rectus Femoris and Bicep Femoris muscles respectively. The loss of muscle oxygenation is indicative of an increased susceptibility to fatigue. No significant change was observed in knee flexion or extension strength, but large variations in strength change were observed between subjects. The results of this pilot study indicate that there is a need for more in depth research with respect to the effect of a prolonged kneeling task on biomarkers that could potentially lead to the increased risk for injury. Keywords: Safety, Ergonomics 1. Introduction There are many occupational tasks that require the worker to kneel for a prolonged period of time. Very often these tasks are performed in a restricted or confined space that forces workers to remain in the same posture while kneeling. In some sectors of industry, such as utilities, mining, construction, etc. prolonged kneeling is common and viewed as a problematic and demanding task (Haslegrave, 1997). Kneeling for a prolonged period of time can be physically demanding for the muscles, and by flexing the knee and applying pressure the blood flow to the supporting muscles is suspended. Even though kneeling is generally perceived as a static task, it induces muscle fatigue in the knee flexors and extensors (Sharrard, 1964), but analysis of this affect has been done primarily through electromyography. Hortobagyi et al. (2000) has reported that after immobilization and restraining, eccentric, concentric, and isometric strength is reduced by 47%. The aim of this study was to measure and quantify the changes, if any, in knee strength and in muscle oxygenation in the leg muscles during prolonged kneeling. It was hypothesized that prolong kneeling will reduce the isometric strength of the knee joint. It was also hypothesized that a decrease in rSO 2 levels will be observed due to the reduction in blood flow to the knee flexors and extensors. An association between muscle oxygenation loss and time will be investigated to help determine when to stop kneeling to minimize knee strength reductions, if any are present. 2. Methods 2.1 Subjects Eight subjects (7 males and 1 female) between the ages of 18-30 years were recruited for this study. All subjects had no history of knee or back injuries, and had the ability to kneel and move through their full knee and ankle range of motion with no pain. This research was approved by the UWM Institutional Review Board (Protocol #13.321-UWM).