One of the causes of work-related Musculoskeletal Disorders (MSDs) is the manual handling of heavy objects. To reduce the risk of such injuries, workers are instructed to follow general guidelines on how to lift and carry objects depending on their mass. Current ergonomic assessments using wearable sensors can differentiate correct from incorrect body postures but are limited. Being able to estimate the mass of an object during ergonomic assessment would be a great improvement. This work investigates a combination of Inertial Measurement Units (IMUs) and Electromyography (EMG) sensors for offline estimation of an object’s mass for different movements. 10 participants performed 26 lifting and carrying trials with loads from 0 to 19 kg, while wearing a 17IMU motion capture system and EMG sensors on both biceps brachii and both erector spinae. Two methods were considered to estimate the carried mass: (1) supervised machine learning and (2) musculoskeletal modeling. First, the data was used to select features, train, and compare regression models. The lowest Mean Squared Error (MSE) for 10-fold cross-validation for lifting and carrying combined was 5.8113 for a Gaussian Process Regression (GPR) model with an exponential kernel function. Then, a MSE of 4.42 and a Mean Absolute Error (MAE) of 1.63 kg were obtained also with a GPR for Leave-One-Subject-Out Cross-Validation (LOSOCV) only for lifting and frontal carrying trials. For the same trials, the upper-extremity musculoskeletal model, scaled to each participant, estimated the mass with a MSE of 1.78 and a MAE of 0.95 kg. The study was restricted to lifting and frontal carrying, but the combination of the two technologies showed great potential for object mass estimation.

Localized muscle fatigue (LMF) has been proposed as a surrogate measure to injury, since the onset of fatigue is rapid rather than months or years required to the onset of work related musculoskeletal disorders (WMSDs). The objectives of this study were to estimate LMF and quantify muscle activity of select forearm muscles during simulations of high pressure cleaning lance tasks common in the chemical production industry. Twenty participants, twelve males and eight females, with no musculoskeletal injuries and meeting criteria for upper extremity fitness, performed the simulated task. Independent variables studied include work height (shoulder, waist, and knuckle), lance orientation (parallel to the operator and parallel to the ground), and duty cycle (33, 50, and 67%) based on task analyses of actual work tasks. Dependent variables included mean RMS and rates of change in mean RMS, mean and median power frequency, MVE, and subjective ratings of fatigue. Repeated measures ANOVA was used to test the main effects of the independent variables and appropriate interactions. In general it was found that working at waist height, at higher duty cycles, and with the lance oriented parallel to the operator resulted in higher fatigue measures. Subjective ratings of fatigue were not well correlated with objective measures, similar to findings in previous studies. The simulated task was found to be extremely fatiguing and modifications to task design or job rotation schedules are required to reduce risk associated with injury development. / Master of Science

Magister Chirurgiae Dentium (MChD) / Occupational hazards are common among many professions and dentistry is no exception. Occupational hazards include percutaneous injuries, inhalation of noxious chemicals, noise and musculoskeletal disorders (MSD). Despite the fact that MSD have been documented to be very prevalent among dentists in various countries, there is a paucity of literature from South Africa. Aim The aim of the present study was to determine the prevalence of musculoskeletal disorders among the dentists in KwaZulu-Natal (KZN), South Africa and to identify risk factors associated with it. The study was a cross-sectional, descriptive one and questionnaires were used to elicit information regarding socio-demographic details, medical history, work history and work-related posture information from dentists based in KwaZulu-Natal. A convenience sample of all qualified dentists in this region who were registered members of the South African Dental Association (SADA) was used. Results One hundred and nine dentists responded to the questionnaire. The response rate was 31%. The majority were male; a third aged between 30 - 39 years and the ratio of females to males was 1:3. Almost all the dentists reported pain in the neck, lower back and shoulder. Less than a quarter of the dentists in KZN reported hand pain, numbness in the hands and a tingling sensation in the hands. More than three quarters reported that they had no negative effects when performing restorative work and scaling and polishing, but 3.1% reported having extreme levels of pain. The most common working position reported was the 2 0' clock position. Nearly three quarters rotated their necks while performing clinical dentistry and a third tilted their shoulders towards their dominant hand. There was no relationship between Body Mass Index (BMI) and whether respondents treated patients while seated or standing and neither was there a relationship between pain in the lower back and BMI. There was a strong association between pain in the neck while performing clinical work and the number of years in practice confounded by age. When compared to other countries the prevalence of MSD is very high. The highest occurrence was for neck, back and shoulder pain. Avoiding these injuries is critical and self-recognition is important in either preventing further injuries or in increasing severity of the condition. The findings of this study suggests that it may be valuable to include ergonomic work practice in the training of dentists and dentists should be involved in a proper exercise routine which should include stretching and weight training to prevent injuries. Regular breaks should be taken to perform stretching exercises in-between the management of patients in order to reduce the risk of MSD.