We know that prolonged zero gravity is bad for human health; bone demineralisation and the like. However, Skylab was big enough for astronauts to run around the internal wall.

Was the "artificial gravity" experienced sufficient to reduce the experienced health problems?

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    $\begingroup$ Was it even commonly practiced? These kinds of activities tend to have some very dangerous effects on the station. There's, for example, a training bicycle rigidly attached to the Zvezda module, which the cosmonauts don't use because when used, the entire Russian segment enters harmonic oscillations and everything starts shaking, risking damaging the seals and joints between modules. Other training devices, including the treadmill, are only stabilized using flexible bands so training astronauts don't transfer body oscillations to the station. $\endgroup$
    – SF.
    May 25, 2020 at 11:18
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    $\begingroup$ Weren't the station designers aware that that would happen? They had experience of over 6000 manned days across 6 space stations by the time Zvezda was launched. Why such an amateur screwup with putting a useless bike on it? The russian experience of manned longterm flight was quite extensive at that time. $\endgroup$
    – Innovine
    May 25, 2020 at 20:50
  • $\begingroup$ People have been building bridges for a long time @Innovine, yet they still experience resonance, the Tacoma Narrows Bridge collapse is a good example of that, more recently the London Milleneum bridge had to be closed for weeks because of it. It's very hard to model resonance on a structure in microgravity. $\endgroup$
    – GdD
    May 25, 2020 at 21:59
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    $\begingroup$ Surely they knew of potential resonance problems, so a few bungie cords or other shock absorbing mounting instead of a fixed mount would have been an obvious choice? I don't think the designers of either of the bridges you mentioned were working on the most expensive object ever built, with a cost of tens of thousands of dollars per kilo just to get things to it. $\endgroup$
    – Innovine
    May 26, 2020 at 5:58
  • $\begingroup$ Worth noting that rats or mice do this on their cages when exposed to microgravity for extended periods. $\endgroup$
    – ikrase
    May 26, 2020 at 10:36

2 Answers 2


The Skylab crew exercised using a bicycle ergometer, not by running around the ring of storage lockers.

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Image credit - NASA

Per the answer to this question Did NASA tell the Skylab astronauts to "Stop running around!"? the crew was directed to not run around the ring of storage lockers any more.

They experienced the usual loss of bone minerals.

The mineral balance study, while imperfect, showed a clear trend. In space, all crewmen excreted more calcium in their urine, along with a high level of hydroxyproline, an amino acid whose loss is associated with metabolic turnover of bone. This confirmed what had been found during Gemini and indicated a loss of structural material in weight-bearing bones that are subjected to compressive loads in normal gravity. Pre- and postflight x-rays of heel and wrist bones corroborated the mineral balance study. In spite of the third crew's increased exercise, loss of calcium and nitrogen-the latter indicating a loss of muscle mass- continued throughout the mission. The actual amount of bone mineral lost, even after 84 days, was not serious; but that depletion continued unabated implied that longer missions entailed risk. Comparison of the Skylab results with studies on bedridden patients-the nearest one-g analog-indicated the possibility of irreversible damage to leg bones on missions lasting a year or more. Another hazard was kidney stones formed as a result of high concentrations of calcium in the urine.

Living and Working in Space, A History of Skylab p. 341 (emphasis mine)

  • $\begingroup$ Accepted as answer, because there can be no health impact if they don't do it. $\endgroup$ May 26, 2020 at 15:52

Short answer: No, for several reasons.

Longer answer: the apparent gravity from centripetal acceleration was low, and the astronauts likely didn't have enough exposure to get any real benefit. I'm going to have to dig up long unused physics knowledge here. The formula for centripetal acceleration is ac = v2 / r, in other words centripetal acceleration is equal to velocity squared divided by the radius of the movement.

I'm going to plug in some educated guesswork figures here, I don't expect them to be exact but they should be good enough. Velocity is a tough one, but from my memories of the videos the it seems to be a slow running pace, kind of a jog, so I'm going to say it's 3m/s. I have no figures on the ring the astronauts ran on, the outer diameter was about 7 meters, so I'm going to say 6 meters, or 3 meters radius. Plugging that into the formula I get 3m/s2. That's less than 1/3 earth gravity. Remember this is not exact, but an estimate, the real figure could be more or less.

While that is a significant acceleration it seems to have been more of a curiosity than a serious form of exercise, so their exposure to it was only a few minutes over the mission. Although we have very limited knowledge on the effects of low gravity on the human body it's very unlikely it would have been measurable.

Lastly, there was nothing to compare to. Skylab was the first US space station, and the first time the US astronauts could spend extended time in space where there was room to move around, before they were in small capsules with limited exercise opportunities. Skylab had a gym which the astronauts used, so differences in bone density would be attributable to exercise.


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