Repetitive work is common in the workplace and can lead to the development of muscle fatigue. The purpose of this thesis was to improve our understanding of muscular and kinematic adaptation strategies of the shoulder complex throughout the process of fatigue and recovery. To achieve this I completed 6 studies, three studies investigating various aspects of repetitive work and fatigue and three methodological studies that were needed to interpret results. The muscular and kinematic effects of repetitive work were first investigated by incorporating a fatigue protocol between pre- and post-fatigue, simulated, repetitive work (Chapter 2). Fatigue is a complex process and how fatigue develops has been shown to influence its effects. To address this, Chapter 6 and 7 respectively, investigated the response to dynamic and static, fatiguing, repetitive work performed until participants reached termination criteria. Electromyography (EMG) was used throughout this thesis to assess muscle activity, which presented challenges because of its time consuming MVE protocols, the effects of myoelectric fatigue on its interpretation and between participants, fatigue developed in different muscles and at different rates, making comparisons between individuals challenging. For more efficient data collection, a method was developed to reduce the number of maximum voluntary exertions (MVE) required to elicit repeatable, maximum shoulder muscle activity, without eliciting muscle fatigue (Chapter 3). Methods were developed (Chapters 4 and 5) to mitigate the effects of myoelectric fatigue on EMG data and to calculate a multi-muscle fatigue score. This improved interpretation of how prolonged repetitive work impacted load sharing in the shoulder muscles and allowed the calculation of a multi-muscle fatigue score. Overall, this thesis found that the response to repetitive work is complex, multi-faceted and varies between individuals. Repetitive work impacts kinematics, muscle activity, muscle fatigue, strength, affective valence and perceived mental and physical fatigue in both static and dynamic work tasks (Chapters 2, 6, 7). Participants utilized the degrees of freedom in the shoulder complex and use coordinated compensation strategies to maintain their task performance, both following muscle fatigue (Chapter 2) and while developing muscle fatigue (Chapter 6, 7). These responses changed over time, as different muscles fatigued and recovered and were variable between individuals (Chapters 2, 6, 7). Removing fatigue artifacts from the EMG showed that muscle activity changes observed are due to load sharing between the musculature of the shoulder complex (Chapter 6, 7). Participants can adapt to the challenge of fatiguing, repetitive work and individuals will use different, coordinated strategies to maintain task performance. / Thesis / Doctor of Philosophy (PhD)

Abstract The objectives of the study were to evaluate factors associated with work ability and musculoskeletal symptoms among food industry workers, to evaluate thermal and neuromuscular responses during repetitive work in the cold and to find out whether cold-induced deterioration in neuromuscular function can be prevented by using additional torso heating or altering work intensity during repetitive work at 4 °C. A questionnaire study (1,117 respondents) and measurements of physical work strain (18 subjects) were performed among workers in food-processing industry. The impact of changes of ambient temperature (16 subjects) and work intensity (8 subjects) on thermal responses and neuromuscular function was evaluated during repetitive work in laboratory conditions. The results from the questionnaire study indicated that self-assessed poor work ability and musculoskeletal symptoms were associated with impaired individual health resources and work-related factors, including higher number of years working in the cold, experience of draught and body cooling at work. Measurements during repetitive work in cold food-processing facilities showed that muscular strain was localized in forearm muscles. Laboratory studies showed that compared with 19 °C, repetitive work at 4 °C increased muscular strain in forearm and upper arm extensors significantly only in men, although the level of muscular strain remained lower and mean skin temperature higher compared with women. Working at 4 °C indicated more continuous activation of the working muscles compared with work at 19 °C. By intermittently increasing the workload at 4 °C the more continuous activation could be counteracted, thus leading to lower strain and fatigue of the working muscles. Additional torso heating did not affect muscular strain of the working muscles at 4 °C. In conclusion, the results indicate a multifactorial feature of work ability and musculoskeletal symptoms among workers in food-processing industry. Gender affects both thermal and neuromuscular responses, which should be considered in the area of work demands and work organization in cold conditions. Altering work intensity could be considered beneficial for reducing muscular strain during repetitive work in cold conditions.

Construction machines use quick couplers to rapidly change the attached tool. The gear lets the machine operator control the hooking and unhooking of the tool from inside of the cabin. This saves time and makes construction work much easier for the workers. The quick coupler is most commonly used on excavators, placed at the outer end of the excavator arm. The tool which the quick coupler connects to needs to have an adapter welded on it for the coupling process to work. Both quick coupler and adapter are equipped with hydraulic quick couplings, the female halves in the quick coupler and the male halves in the adapter. They connect the distribution of hydraulic fluid from the machine to the tool. This master thesis, in industrial design engineering, is focusing on developing a test equipment that can ensure the quality of hydraulic quick couplings. The project is done in collaboration with the company Steelwrist, which requests that the equipment can detect if the couplings are leaking, in both connected and unconnected state, as well as, measuring the internal friction and spring forces that occur during the connection and disconnection.  The project was carried out through a design process with four phases, inspired by ‘the double diamond process’. The used process consists of three sessions of diverging and converging in the form of first widely exploring followed by taking focused actions. The focus in the first phase was to discover information about safety, quality, measurements and instruments, along with conducting interviews and observations in order to understand the current state at the company. In the second phase was the specification and workflow of the new test equipment defined. In the following phase the development of the test equipment started. First by generating hundreds of potential solutions to partial functions, which could be divided into five concepts that were parallely developed and evaluated. In the last phase was the best of the five concepts finalized and constructed in CAD, in order to deliver models and drawings on the final design.  The main focus in the developing and evaluating process has been to create a as safe product as possible. The positions needed to be performed by the operator were extensively investigated and the ergonomics were highly prioritized. Another important factor was the simplicity of the machine components of the test equipment. The project resulted in a complete solution for a new testing station, consisting of storage for adapters, spare parts and documents, along with the test equipment in the shape of a floor standing machine. The test equipment seals the hydraulic quick coupling half, which is meant to be tested, towards an adapter with a pneumatic cylinder. A servo motor then moves the opposite quick coupling half in order to enable the connection and disconnection. The last mentioned coupling half is attached to a load cell which measures the force. The existing leak detection instrument is connected to the test equipment in order to fill the test object with air in the different states. / Byggmaskiner använder snabbfästen för att snabbt byta det fastsittande verktyget. Redskapet låter maskinföraren styra på- och avkopplingen av verktyget från insidan av hytten. Detta sparar tid och gör konstruktionsarbetet mycket enklare för dem som jobbar. Snabbfästet används oftast på grävmaskiner, placerade längst ut på grävmaskinsarmen. Verktyget som snabbfästet ansluter till måste vara utrustad med en fastsvetsad grind för att kopplingsprocessen ska fungera. Både snabbfästet och grinden är utrustade med hydrauliska snabbkopplingar, honhalvorna i snabbfästet och hanhalvorna i grinden. De ansluter hydrauliken från maskinen till verktyget. Detta examensarbete inom teknisk design fokuserar på att utveckla en testutrustning som kan säkerställa kvaliteten på hydrauliska snabbkopplingar. Projektet utförs i samarbete med företaget Steelwrist, som begär att utrustningen ska upptäcka läckage i kopplingarna, både i anslutet och ej anslutet tillstånd, samt att mäta de interna friktion- och fjäderkrafter som uppstår under anslutning och frånkoppling. Projektet bestod av fyra faser, inspirerad av design processen 'the double diamond process'. De fyra faserna omfattar totalt tre sekvenser innehållande en divergerande del och sedan en konvergerande del i form av att först utforska brett, följt av att smalna av med mer fokuserat besluttagande. Fokus i den första fasen var att ta reda på information om säkerhet, kvalitet, mätningar och instrument, tillsammans med intervjuer och observationer för att förstå det aktuella tillståndet på företaget. I den andra fasen definierades specifikationer och arbetsflödet för den nya testutrustningen. I följande fas inleddes utvecklingen av testutrustningen. Först genom att generera hundratals potentiella lösningar på delfunktioner, som sedan kunde delas in i fem koncept som parallellt utvecklades och utvärderades. I den sista fasen färdigställdes det bästa av de fem koncepten och konstruerades i CAD så modeller och ritningar på den slutliga designen kunde levereras. Huvudfokuset i utvecklings- och utvärderingsprocessen har varit att skapa en så säker produkt som möjligt. De positioner som utförs av operatören undersöktes grundligt och ergonomin prioriterades högt. En annan viktig faktor var enkelheten i testutrustningens olika komponenter. Projektet resulterade i en komplett lösning för en ny teststation, bestående av lager för adaptrar, reservdelar och dokument, tillsammans med testutrustningen i form av en markplacerad maskin. Testutrustningen försluter den hydrauliska snabbkopplingshalvan, som är tänkt att testas, mot en adapter med en pneumatisk cylinder. En servomotor flyttar sedan motsatt snabbkopplingshalva för att möjliggöra anslutning och frånkoppling. Den sistnämnda kopplingshalvan är fäst på en lastcell som mäter krafterna som uppstår. Det befintliga läckagedetekteringsinstrumentet är anslutet till testutrustningen för att fylla testobjektet med luft i dem olika tillstånden.