Do astronauts beef up their muscle mass before a mission on the ISS? Does it give a buffer of muscle mass they can lose? They don't look like strongmen, although NASA doesn't seem to discriminate size. Maybe they should in order to keep crews healthier.

Below an image of one of the strongest men in the world. Building an aqueduct or lifting Mars or something between the weightlifting exercises.

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  • $\begingroup$ The effects of zero gravity are very similar to the effects of enforced bed rest. It might be of interest to see if studies have been done as to a similar effect in the case of enforced bed rest. The number of astronauts is small, and it seems unlikely that one could do a controlled study with a sufficient sample size. $\endgroup$
    – user687
    Jun 6, 2017 at 23:11
  • $\begingroup$ Interesting question... I imagine that there are certain fitness and strength requirements for astronauts to be able to cope with the G-forces during launch. Would be good to know if there is any benefit to increased muscle mass in microgravity whether there is a trade off in terms of launch weight. $\endgroup$ Jun 7, 2017 at 12:53
  • $\begingroup$ Bodybuilding might be counterproductive: all that muscle uses energy (even at rest), so bodybuilders have a crazy metabolic rate. $\endgroup$
    – Hobbes
    Jun 7, 2017 at 20:07
  • $\begingroup$ @Hobbes But the dry food supply does not represent a significant mass for an ISS crew or even a crew to Mars. And muscle builders are used to supplement food with protein powder. High consumption of protein stimulates muscle building on Earth, wouldn't it help against atrophy in weightlessness? $\endgroup$
    – LocalFluff
    Jun 8, 2017 at 10:44

1 Answer 1


Current NASA standards for preflight physical training are:

  • To be selected it is not necessary to be a high performer in sports activities (some-times it can be even a “handicap” i.e. marathon runner / cardio-vascular status).
  • During their whole career they have to maintain a good physical shape (safe sports practice 2 – 3 times per week, = with minimum injury’ risk)
  • On NASA side, the sports practices are left on the initiative of each astronaut “self practice”, in Star City the sports’ practices are scheduled and managed in the training time-tables.

Preflight training includes strength training (using free weight exercises like the squat and deadlift). There doesn't seem to be a fixed regimen, just a set of tests for strength and agility the astronauts have to pass before flight.

During missions in the ISS, training is more structured:

astronauts are scheduled training sessions for the International Space Station (ISS) treadmill (TVIS) and cycle ergometer (CEVIS), as well as the Advanced Resistive Exercise Device (ARED). In-flight programs are designed to maintain or even improve the astronauts’ pre-flight levels of fitness, bone health, muscle strength, power and aerobic capacity. In-flight countermeasure sessions are scheduled in 2.5 h blocks, six days a week, which includes 1.5 h for resistive training and 1 h for aerobic exercise.

Loss of muscle is not the biggest concern.

After flight recovery within 1 - 6 weeks depending of the flight duration and after flight physical training intensity.

E.g. bone loss is a bigger problem (takes longer to recover from). Strength training helps increase bone density.

In conclusion, astronauts do a fair amount of strength training, just not to the level reached by bodybuilders and other strength athletes. At competition level, those athletes train several hours a day, every day. That would reduce the amount of time available for other aspects of training.

There's also the question, how much training is necessary? Competition athletes are several times stronger than average, but if there's only 10% muscle loss then you only need to have 110% of average strength at the start of a mission to come out okay.

  • $\begingroup$ Wouldn't big muscles help strength training that preserves bone density? I suppose that bone mass are better protected by weight lifting than by aerobics. And if you are strong enough to lift twice as much, in a strapped down microgravity gym, shouldn't that help the skeleton more per lift? $\endgroup$
    – LocalFluff
    Jun 8, 2017 at 10:50
  • $\begingroup$ Sure it'd help, but how much training is necessary? $\endgroup$
    – Hobbes
    Jun 8, 2017 at 11:13
  • $\begingroup$ If the astronaut starts out with twice the strength, half the training time in space should be needed. (Although it might be difficult to prevent these guys from habitually exercising obsessively anyway, which won't harm them, what else to do?). $\endgroup$
    – LocalFluff
    Jun 8, 2017 at 12:47
  • $\begingroup$ That might work for muscle and bone, but what about e.g. the heart? $\endgroup$
    – Hobbes
    Jun 8, 2017 at 15:14

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