Core muscle characteristics during walking of patients with multiple sclerosis.

INTRODUCTION Multiple sclerosis (MS) is an inflammatory autoimmune disease of the central nervous system that affects up to 2 million people worldwide [1]. Lower-limb muscle weakness [2], with greater weakness on one side of the body [3-4], is a common symptom and may contribute to the walking difficulties frequently experienced by patients with MS [5]. Moreover, patients with MS have been shown to exhibit decreased postural and trunk control [6-7], although very little is known about core muscle activity during walking in this population. Traditionally, muscle activity is measured using electromyography (EMG). This technique provides high temporal resolution of surface muscle activity but is limited in its ability to evaluate deep muscles such as the quadratus lumborum (QL) and transversus abdominus (TA). Furthermore, data from surface EMG (sEMG) can be compromised due to interference or "crosstalk" from other muscles, and the equipment can experience environmental interference during dynamic tasks. Intramuscular EMG has limitations as well, most notably its invasive nature and that it only measures the activity of a very small portion of the muscle. Positron emission tomography (PET)/computed tomography (CT) imaging, with the glucose analog [[sup.18]F]-luorodeoxyglucose (FDG), can calculate cumulative muscle activity and skeletal muscle properties such as volume without the limitations commonly experienced with EMG. Previous studies have used FDG-PET/CT to measure entire muscle activity, muscle fiber activity, and muscle volume [4,8-12]. Muscle activity is quantified by the standardized uptake value (SUV), which directly represents the cumulative muscle activity of the performed task. Muscle fiber activity, or glucose uptake heterogeneity (GUh), is measured by the spatial distribution of FDG within the muscle [10-12]. Furthermore, muscle volume can be measured from CT imaging that is often performed just prior to PET imaging [10,12-13]. The activation of the core musculature has been suggested to serve a variety of purposes during walking. In nondisabled subjects, sEMG has been used to show that several core muscles are active throughout the gait cycle and that several, including the rectus abdominis (RA), external oblique (EO), and internal oblique (IO), can have increased activation during specific phases, such as midstance or foot-strike [14-15]. Swinnen et al. used sEMG to investigate the activity of the core muscles during treadmill walking with and without body weight support in patients with MS [15]. The authors found greater core muscle activation on one side of the body with increasing levels of body weight support than with no support. However, more- and less-affected sides of the patients were not defined, so it was difficult to determine whether weaker or stronger sides of the core were being activated. Furthermore, it is not clear which muscles are most active while walking with no body weight support. Despite the general lack of understanding of the importance of the core musculature to walking, core muscles have been targeted for intervention to improve gait and postural instability in patients with MS [16-18]. A further understanding of core muscle activity during walking is needed. Altered muscle activation strategies could lead to increased performance fatigability and contribute to the impaired balance and postural stability frequently experienced by patients with MS. Therefore, the purpose of this study was to investigate the characteristics of the core musculature in patients with MS and nondisabled controls while walking at a self-selected speed using the innovative approach of FDG-PET/CT. METHODS Eight mildly disabled patients with relapsing-remitting MS (4 men) and eight sex-matched nondisabled controls participated in the study. Recruitment was completed through the Rocky Mountain MS Center and University of Colorado Anschutz Medical Campus study announcement letter. …