Loading in an Upright Tilting Hospital Bed Elicits Minimal Muscle Activation in Healthy Adults

Abstract

Purpose: Upright tilting hospital beds (THB) are used during early rehabilitation of critically ill patients. Tilting patients in a THB to achieve weight-bearing or loading is purported to mitigate the response of prolonged immobility associated with critical illness. The primary aim of this study is to determine the level of muscle activation during loading in a THB and secondarily to assess whether safety straps influence the level of muscle activation. Methods: Quasi-experimental design in a musculoskeletal laboratory. Nineteen healthy community-dwelling adults with no prior neuromuscular disorder were included. Two groups, 10 subjects with straps-on and 9 subjects with straps-off, were tilted in a THB through 9 intervals of 10° (0°-80°). Muscle activation was recorded using surface electromyography in tibialis anterior, rectus femoris, gluteus medius, and lumbar erector spinae muscles. Raw and electromyography-normalized data were analyzed across angles and conditions. Loading (weight-bearing) was recorded using the THB footplate scale. Results: Electromyographic activity in the tibialis anterior, rectus femoris, gluteus medius, and lumbar erector spinae muscles was minimal as the angle of tilt and loading increased. No statistically significant increases compared with supine rest were observed, except rectus femoris muscle activation at 60° in the groups without straps (P = .023). Similarly, only muscle activation in the rectus femoris was higher in the group without straps from angles 40° to 80° than in the group with straps. Conclusion: Relaxed, gravity-facilitated loading in a THB elicits minimal muscle activation in healthy subjects and, therefore, passive loading's usefulness for enhancing muscle strength is questioned. Removal of safety straps did lead to increased muscle activation in the rectus femoris; this concept should be explored further to understand whether location of the straps, tightness of the straps, and/or the angle of the hip and knee joints during loading could hamper muscle activation.