The notions analog and model are simultaneously used with microgravity. Microgravity analogs only replicate microgravity effects on physiological responses, while a microgravity model is a platform used as a prototype or to imitate microgravity. These analogs are mostly used to conduct experiments for long duration of time. Ground microgravity analogs are:
long-duration bedrest
water immersion
Long-duration bedrest is an analog to microgravity that grants an easier access for hours to weeks in which human subjects are possible to study. It is mostly employed to simulate microgravity effects on various physiological systems, particularly on bone-studies, muscle and the cardio-vascular system of humans. Initially, the investigations of bone-loss used horizontal bedrest, and later on head-down tilt (HDT) bedrest was used for a better result that has similar effects on spaceflight. There are various HDT angles that could be used; it varies from 6⁰ through 12⁰ and 18⁰. The limitation of this platform is that subjects rarely (if ever), develop motion sickness during or after; which constitute a great discrepancy between this analog and spaceflight.
Figure 1. Types of Long Duration Bedrest
Water immersion is a model of microgravity that makes it possible to carry out bones and cardio-vascular studies on human subjects for days, and possibly months. This platform is an easier access to microgravity analog. Immersion reproduces microgravity induced changes in human body’s motor and cardio-vascular systems, and affects other physiological functions. A challenge to water immersion is that there is discomfort and possible risks of long-term skin contact with the liquid environment. Therefore dry immersion was developed that constitutes of head-out water immersion with subjects kept dry with the use of a waterproof, highly elastic fabric that creates artificial conditions similar to microgravity via floatation (Figure 2). Immersion is the main model for training of working operations in weightlessness. The limitation to the use of water immersion is that there is discomfort and possible risks of long-term skin contact with the liquid environment. The limitation to both water and dry immersion is that subjects do not develop motion sickness.
Figure 2. Types of Water Immersion
From comparison of data, similarity has been observed in the HDT bedrest and dry immersion, although it is also suggested that dry immersion has an influence that is stronger than HDT bedrest. The microgravity analog platforms make it possible to have human subjects for experimental purposes, without the need to travel to space!
Further reading
Abdulrashid, F.A., Oluwafemi, F.A., Hussaini, S.J., Daniel, I.B., Isah, B., Ademu, A., Otum, A.O., Polok, A.C., Dumbiri, C.O., 2020. Possible solutions to the effects of space environment on astronauts’ physiology, London Journals Press, LJER 20 (5).
Oluwafemi, F.A., Neduncheran, A., 2022. Analog and simulated microgravity platforms for life sciences research: Their individual capacities, benefits and limitations. Advances in Space Research. https://doi.org/10.1016/j.asr.2022.01.007.
