Comparison of Oxygen Demands and Muscle Activity Patterns During Different Forms of Body Weight Supported Locomotion in Individuals With Incomplete SCI

Abstract

<p>Body weight supported devices available to enhance locomotor recovery following an incomplete spinal cord injury (SCI) include treadmills with (Lokomat^TM) and without (Manual Treadmill) robotic assistance, and the overground ZeroG^TM system. Cardiovascular and muscular demands of these devices were compared during steady-state locomotion at the <em>same</em> level of body weight support (BWS) in 7 individuals with incomplete SCI (42.6±4.29 years) and matched able-bodied controls (CON). Questionnaires evaluated consumer preference based on walking experience. Oxygen uptake (VO₂), heart rate (HR) and ratings of perceived exertion (RPE) were expressed as percentage of peak values obtained using arm ergometry. Additionally, VO₂ was expressed relative to resting metabolic equivalents (METS). Filtered electromyography (EMG) signals from tibialis anterior (TA), rectus femoris (RF), biceps femoris (BF) and medial gastrocnemius (MG) were normalized to ZeroG^TMstepping. Lokomat^TM sessions were the least demanding in terms of oxygen uptake compared to the Manual Treadmill and ZeroG^TM, and considered the least appropriate device for the SCI group’s current level of function. For SCI, the a) ZeroG^TM required 3.0 METS, 54.7% of VO₂peak, 84.7% of peak HR, b) Manual Treadmill required 2.8 METS, 52.9% of VO₂peak, 80.8% of peak HR and c) Lokomat^TM required 1.7 METS, 30.1% of VO₂peak, 67.3% of peak HR. Central RPEs were 3.8, 3.7, 0.5 and peripheral RPEs were 5.1, 4.1, 0.7 for the ZeroG^TM, Manual Treadmill and Lokomat^TM respectively. For CON, walking required minimal effort (at most 31.5% of VO₂ peak), with ZeroG^TM sessions requiring greater muscle activation. For SCI, muscle activation was higher in treadmill conditions compared to the ZeroG^TM due to increases in TA and BF activity. The Manual Treadmill and ZeroG^TM should be considered progressions following Lokomat^TM training where hip extension can be encouraged using the treadmill and additional components of gait (e.g. balance, torso stability) can be focused on using the ZeroG^TM.</p>