Research on dynamic comfort maintenance by measuring lower limb edema and seat pressure during simulated seated sleep in flight

Objectives. Seated sleep during flight can bring significant discomfort to passengers. The objective of this research was to study passengers' dynamic comfort maintenance strategies in lower limb postural shifting during seated sleep in flight. Methods. Studies on seated sleep postures and sitting comfort were conducted. First, 40 participants were recruited to the observational research for collecting typical leg postures during seated sleep. Then, an experiment was conducted with the participants simulating seated sleep in the aircraft seat. The changes in lower limb edema and seat pressure in different postures were measured with a bioelectrical impedance device, near-infrared spectroscopy device and pressure mapping device. Results. Six postures were selected through the observational research. The experiment showed that tissues of the thighs and buttocks suffer alternate higher compression by shifting between the six postures. Lower limb edema is higher when the shanks are forward, while the tissue under the ischial tuberosity suffers higher compression when the shanks are neutral. Conclusion. Six motivations for passengers to shift each sitting posture to achieve dynamic comfort were summarized, which helps obtain alternating rest in different body parts. The suggestion of a leg position adjustment system was also proposed.

Perceptual Thresholds for Vibration Transmitted to Road Cyclists

OBJECTIVES

In this article, we seek to determine how sensitive road cyclists are to vertical vibration transmitted while riding a road bicycle and to propose metrics for the evaluation of dynamic comfort.

BACKGROUND

Road cyclists are exposed to random-type excitation due to road roughness. Vibration transmitted affects dynamic comfort. But how sensitive are cyclists to vibration level? What are the best metrics to measure the amount of vibration transmitted to cyclists? Previous studies used sinusoidal excitation with participants on rigid seats and measured acceleration.

METHODS

We use a psychophysical estimation of Just Noticeable Differences in Level (JNDL) for vertical vibration transmitted to cyclists on a road simulator. In Experiment 1, we estimate the JNDL for whole-body vibration using vertical excitation on both wheels simultaneously (20 male cyclists). In Experiment 2, we estimate the JNDL at two different points of contact by applying the same signal to only the hands or the buttocks (9 male cyclists).

RESULTS

The JNDLs are expressed in terms of acceleration and power transmitted to the cyclist. We compare the JNDLs expressed with these 2 metrics and measured at different points of contact.

CONCLUSION

Using these two metrics and at all points of contact, vibration magnitude needs to be reduced by at least 15%, for the change to be detectable by road cyclists.

APPLICATION

A road bicycle needs to transmit at least 15% less vibration for male cyclists to detect an improvement in dynamic comfort. Dynamic bicycle comfort can be measured in terms of a new metric: power transmitted to the cyclist.