Metabolic demand and muscle activation during different forms of bodyweight supported locomotion in men with incomplete SCI

Abstract

Body weight supported locomotor training uses neuroplasticity principles to improve recovery following a spinal cord injury (SCI). Steady state locomotion using the same body weight support (BWS) percent was compared in 7 males (42.6 ± 4.29 years) with incomplete SCI and matched (gender, age) noninjured controls (42.7 ± 5.4 years) using the Lokomat, Manual Treadmill, and ZeroG. The VO2000, Polar Heart Rate (HR) Monitor, and lower limb electromyography (EMG) electrodes were worn during the 2-minute sessions. Oxygen uptake (VO2) and HR were expressed as percentage of peak values obtained using progressive arm ergometry; VO2 was also expressed relative to resting metabolic equivalents (METS). Filtered EMG signals from tibialis anterior (TA), rectus femoris (RF), biceps femoris (BF), and medial gastrocnemius (MG) were normalized to ZeroG stepping. The Lokomat required 30% of VO2 peak (2METS) compared to ~54% (3METS) for Manual Treadmill and ZeroG sessions. HR was 67% of peak during Lokomat sessions compared to ~83% for Manual Treadmill and ZeroG. Muscle activation was higher in treadmill conditions compared to the ZeroG primarily due to increased BF activity. At the same level of BWS, locomotion using the Manual Treadmill or the ZeroG is more aerobically demanding than the Lokomat. Treadmill modalities encourage greater hip extensor activation compared to overground locomotion.

Figure 1

(a) Body weight supported training devices used during walking sessions; from left to right: Manual Treadmill, Lokomat, and ZeroG. All devices provided body weight support (BWS) through a harness. The Andago GmbH treadmill (Loko) was used for robotic assisted (Lokomat) and unassisted (Manual Treadmill) walking sessions. The ZeroG had a custom series elastic actuator that traveled along an overhead trolley, which provided dynamic BWS while individuals performed overground walking sessions. (b) Manual Treadmill sessions normally completed with therapist assistance (not provided in this study) at both legs. The Andago GmbH treadmill is used during these sessions without the robotic orthosis providing individuals with greater degrees of freedom during training.

Figure 2

VO₂ peak test variables for SCI and CON. Relative VO₂ peak (mL/kg/min), peak heart rate (HR) expressed in beats per minute (BPM), and maximum power achieved (Watts). Values are mean ± SE.

Figure 3

Relationship of the lower limb flexion: extension strength ratios (at the hip and knee) determined using LForce on the Lokomat with the percentage of body weight support (BWS) required for locomotion using the ZeroG in participants with SCI. Open circles and solid line indicate the relationship at the hip. Closed squares and dashed line indicate the relationship at the knee. P < 0.05 = ∗.

Figure 4

Metabolic equivalents (METS) for SCI and CON during locomotion with body weight support (BWS). Solid line indicates significance between device comparisons, and dashed line indicates significance between group comparisons. P < 0.05 = ∗, P < 0.01 = ∗∗, and P < 0.001 = ∗∗∗.

Figure 5

Cardiovascular measures ((a) VO₂, (b) HR) during locomotion with body weight support (BWS) expressed as percentage of peak values obtained from the arm ergometer test. Solid line indicates significance between device comparisons, and dashed line indicates significance between group comparisons. P < 0.05 = ∗, P < 0.01 = ∗∗, and P < 0.001 = ∗∗∗.

Figure 6

Muscle activity of independent muscle groups during treadmill locomotion with body weight support (BWS) normalized to ZeroG stepping with the same BWS. TA indicates tibialis anterior, RF indicates rectus femoris, BF indicates biceps femoris, MG indicates medial gastrocnemius, AVG indicates average muscle activity over a gait cycle, and 1GC indicates gait cycle completion time. Dashed line at 100 = value obtained while walking on the ZeroG. Statistically significant between group (SCI versus CON) comparisons P < 0.05 = ∗.

Figure 7

Ratio of root mean square (RMS) muscle activity across all muscle groups (μV) to oxygen uptake (%VO₂ peak) between devices for SCI and CON. Mean ± standard error.