A step towards understanding fatigue and the cost of walking in persons with Multiple Sclerosis and Rheumatoid Arthritis

Abstract

Elevated levels of fatigue have a major impact on daily functioning and heath related quality of life in persons with Multiple Sclerosis (MS) and Rheumatoid Arthritis (RA). Despite extensive research, factors contributing to fatigue remain poorly understood. Since both groups are also characterised by walking impairments, a comprehensive assessment of walking, as the most performed physical activity in daily life, could help understand whether this contributes to the elevated levels of fatigue. Gait alterations caused by disease characteristics such as muscle weakness or joint mobility restrictions could result in shorter step lengths and higher step frequencies. Given that the energetic cost of walking is primarily explained by the latter spatiotemporal parameters, gait alterations could lead to inefficient gait. In case energy is lost (during the step-to-step transition and collision), the cost of walking increases. Consequently, a higher energy demand during walking might contribute to higher levels of fatigue and even result in the inability to walk long distances. As reported by earlier studies, persons with RA and MS walk at a slower self-selected speed. Nonetheless, it can be determined if this slower speed incurs greater energetic cost by examining the U-shaped parabolic relationship between walking speed and the cost of walking. Conversely, it is possible that the walking pattern has been adapted to minimize energy expenditure, resulting in the self-selected pace being the most energy-efficient option. By including persons with MS which predominantly affects the neurological system and persons with RA the peripheral joints, assessing gait characteristic and the cost of walking will improve our understanding of the manifestation of fatigue. Therefore, the overall aim of this dissertation was to assess whether the self-reported fatigue is accompanied by differences in gait characteristics and the energetic cost of walking in persons with MS and RA. Chapter 1 introduces the rationale of this dissertation. First, disease characteristics of persons with MS and RA, the pathophysiology and most common symptoms were described. Then, in order to understand the different concepts of fatigue, a unified set of definitions of fatigue was explained. This also included several measurement instruments for assessing the different dimensions of fatigue. Consequently, disease-related gait alterations were described where after the determinants and concept of the energetic cost of walking were elaborated. Finally the scope, aims and outline are given to describe the focus and included chapters of this dissertation. Chapter 2 reviewed existing literature to assess whether the energetically optimal walking speed and cost of walking differed between persons with MS and healthy controls and whether this was different between overground and treadmill walking. Although the cost of walking was elevated in persons with MS, the energetically Chapter 7 118 optimal speed was similar compared to healthy controls. This indicated that even when walking at the similar energetically optimal speed, persons with MS require a higher energy demand. It was also found that the optimal cost of walking was similar between overground and treadmill walking with the latter required a higher walking speed. Chapter 3 examined whether fixed-paced and self-paced treadmill protocols yield differences in cost of walking and gait parameters to elucidate the effect of natural walking variability on the energetic demand as observed in walking protocols such as the 6-minute walk test. The lack of differences found in cost of walking, spatiotemporal and kinematic parameters validate the use of self-paced protocols Chapter 4 described whether persons with MS increased their perceived exertion and whether this was accompanied by changes in gait characteristics and cost of walking when subjected to a 6-minute walk test for provoking fatigue. This study revealed that although persons with MS increased their perceived exertion, gait characteristics did not deteriorate and this was not accompanied by changes in the cost of walking. Chapter 5 examined whether the level of trait fatigue and the self-selected walking speed in persons with RA differed from the walking speed with the lowest energetic cost and whether this was different from control subjects. In addition, the cost of walking and a comprehensive set of gait characteristics and kinematics at multiple fixed speeds was compared between groups to substantiate whether gait alterations contribute to the cost of walking. Also a relationship between self-selected speed and daily physical activity was assessed to determine whether persons with RA that walk at slower, energetically more costly self-selected speeds conserve energy by being physically less active in daily life. This study revealed that persons with RA report higher levels of trait fatigue and walk at slower, energetically more costly self-selected speeds. However, no differences were found in cost of walking, gait parameters and kinematics, compared to control subjects. Persons with RA with slower self-selected walking speeds, performed a less physical activity in daily life and vice versa. These findings indicate that walking at faster self-selected speeds is energetically less demanding for persons with RA which might also increase the level of physical activity in daily life. Chapter 6 synthesised the results of all chapters and discussed the different manifestations of fatigue. This was done by addressing walking characteristics in persons with MS and RA to further elaborate the understanding of the energy demand during walking. Finally, methodological considerations were provided and recommendations were given for future studies where after an overall conclusion was presented.