# What would the effect of variable gravity strength have on a developing child?

If a child grew up since being a toddler (2 to 3 years old) in an environment where the gravity levels fluctuated so they were sometimes stronger than earth gravity and sometimes weaker, how would this affect their physical development, particularly their bones, joints and muscles etc.?

For example, if they spent a few months to a year in an environment with moon like gravity (around 3 to 4 m/s²) then spent another few months in around 11-12 m/s².

With a maximum force of about 16 m/s² (slightly lower than humans can survive for 24 hours with no ill effects according to NASA) and a minimum of 1-2 m/s², what effect would the constant fluctuation specifically have on a growing and developing child, assuming optimum diet and exercise?

• Are you talking human beings, or a species which has adapted to this sort of thing? Commented Feb 27, 2017 at 2:40
• how drastic is the change, are we talking a slow transition from one to the other over a course of days or weeks?
– John
Commented Feb 27, 2017 at 3:23
• Wikipedia states that 16-gee can be "deadly", so I doubt your claim that the human body can tolerate it for 24 hours - except possibly in very special, very controlled positions. Since we haven't done (and won't do) this type of experiment, you'll have to wait until our understanding of our biology and the speed of our computers is orders of magnitude greater than what we have today. Only slightly related is an article in March Scientific American about how benign micro organisms turn pathological in space (on the ISS). My guess is that what you describe would either kill or maim the child, wi Commented Feb 27, 2017 at 8:23
• @LiZhi - Since 1g = 9.8 m/s^2, then 16 m/s^2 is less than 2g. Note your units carefully. Commented Feb 27, 2017 at 20:31

Experiments on the ISS have shown that objects growing in lower gravitational regions, i.e. the so–called microgravity or freefall during orbit in the ISS, exhibit several major differences from terrestrial life. These differences can be graded on a spectrum from 0 to 1 G.
Not all of these differences are the result of weaker gravitational forces felt.

• weaker heart muscles
This is why you see the astronauts spend so much time maintaining their physique nowadays. Their cardiac system needs to do less work to pump the blood around their body, quite simply, and so the heart and the sympathetic muscles which constrict the blood vessels atrophy. If the astronauts didn't do so, they'd require extensive recuperation periods when they returned to earth. Syncopation and blackouts would be frequent occurances.
• lengthened spinal column and weaker muscles of the back (erector spinae)
The discs of fluid which cushion and support the vertebrae would never need to accomodate the heavier forces that they experience on earth. Much like how swimming or sleeping extends your own height — except that the spinal column of someone grown on earth are usually stronger from their years of growing with those forces. So expect that your children would grow taller that they'd be able on earth, but would experience back problems and injuries galore.
• weaker bones and voluntary skeletal muscles
Moving around requires less work when you don't need to overcome a gravitational force. There are other factors that contribute to this comparative weakness, though: Trees which grow in the Biosphere 2 enclosure were noted to have weaker heartwood than trees of same kind outside the Biosphere; those trees never experienced any of the stresses due to wind and weathering, and so never needed to grow stronger for accomodatation.

In conclusion, your people would either need rigorous acclimation periods that would help transition them to the strength necessary for travel and tourism on earth, or they'd need to maintain such a regimen of strength–building activities during their entire lives.

https://en.wikipedia.org/wiki/Scientific_research_on_the_International_Space_Station#NASA.27s_ISS_research_and_science_activity