Is the Leg Postural Switching Motion or the Change in Posture Responsible for Alleviating Low Limb Discomfort and Fatigue in Sedentary Sitting in Flight?

Abstract

Seated sleep during flight reduces the frequency of postural adjustment, which increases low limb fatigue and discomfort. The purpose of this study was to explore the mechanism by which leg postural adjustment relieves low limb fatigue and discomfort during sedentary sitting. Four postural tasks were set for the mechanism study (each lasted 40 min). Task 1: Bending the knee all through, quickly extending the knee once at the 20th minute. Task 2: Extending the knee all through, quickly flexing the knee once at the 20th minute. Task 3: Flexing the knee for 20 min, then switching to extension until the end. Task 4: Extending the knee for 20 min, then switching to flexion until the end. During tasks, electromyography, muscle oxygen, and subjective discomfort scores were recorded to assess the development of fatigue and discomfort in the lower limbs. The data from the first and latter halves of each task, and 4 min after the switch, were extracted, for a total of three periods of data. The results showed that continuous maintenance of one posture gradually increased fatigue and discomfort in the lower limbs, whereas posture changes relieved discomfort and fatigue. Under different leg postures, four leg muscles are in alternating passive stretch and fatigue development. Moreover, instantaneous switching behavior has a positive effect on reducing subjective discomfort. This study helps elucidate the mechanism by which leg posture adjustment relieves fatigue and subjective discomfort.