Using Objective Methods to Measure the Underlying Mechanisms of Discomfort During Prolonged Standing

Prolonged standing is an occupational hazard that leads to higher likelihoods of joint and circulatory disorders. Existing measures of prolonged standing do not directly assess circulatory or joint responses. The goal of this research is to (Aim 1) identify novel weight transfer strategies, (Aim 2) investigate in vivo knee joint cartilage deformation, and (Aim 3) examine characteristics of lower extremity muscles during prolonged standing. Twenty-nine healthy adults were recruited in two body-mass index (BMI) subgroups, healthy weight (HW, 16 subjects, BMI29.9 kg/m2). Subjects stood for two hours on two different flooring surfaces. Radiographs of the knee and near infrared spectroscopy (NIRS) were used to measure joint and circulatory effects of prolonged standing, respectively. Subjective surveys, electromyography (EMG), and vertical reaction forces were also collected. A novel method was developed to determine weight transfer strategies, shifts and fidgets, based on force and temporal boundaries. Shifts and fidgets increased significantly over time, possibly related to increasing lower extremity circulatory measures. OB displayed more shifts and fidgets over time than HW. Tibiofemoral gap distance, determined using a fitted piecewise model, decreased over time. OB reached terminal tibiofemoral gap faster on a hard floor (HF) than mat (MT), indicating that the MT may have a beneficial effect on cartilage compression for OB. While little information was noted from EMG, NIRS measured significant changes in blood volume and flow over time. The MT decreased negative circulatory outcomes especially for OB. Development of circulatory pathologies related to prolonged standing are the result of repeated exposure to capillary and venous dilation from volume and pressure changes. As such, measures of HbT and flow may be important metrics relating circulatory effects to development of pathologies. This research has also shown that OB demonstrated different physiological responses to ergonomic interventions, providing evidence that it standing interventions may influence workers of different demographics differently. Future research should include human factors, such as BMI, age, gender, pregnancy, or disease, when researching occupational injuries associated with prolonged standing. These human factors should be considered when evaluating the effectiveness of ergonomic interventions and designing new interventions