[inamberclad]

EMS = electro muscular stimulation? No, not 100%. Astronauts have very good resistance training onboard the ISS at this point. Some of them come back to earth stronger than they left. However, it turns out that your body also needs skeletal loading in order to produce strong bones. That kind of loading comes from having large forces distributed through the entire body. NASA tried a variety of shortcuts around resistance training, but none of them were satisfactory.

A spinning drum is probably the best method short of artificial gravity, but it has a couple problems. A rotating reference frame creates some pretty non-intuitive effects (https://www.youtube.com/watch?v=bJ_seXo-Enc). Research is ongoing about just how fast a human can be spun for a long duration, although data is hard to come by. We also don't know how low of a gravity a human can stay healthy in without intervention like serious exercise. If it turns out that you need 1G, that involves a much larger spinning drum than a G/3 (Mars) or G/6 (Moon) environment. The problem is that we really have no way to simulate those environments for a human.

[mealkh]

What about flywheel training? You can do deadlifts, squats etc with it that will produce large spinal/skeletal load even in the absence of planetary gravity due to the inertia. Something like https://exerflysport.com/ or https://exxentric.com/store/kbox/

[RetroTechie]

Given the travel time, any visit to Mars would probably not be short-stay like 1 day. More likely weeks, months or longer.

So you'd have Mars G for time on the surface anyway.

And besides: a few astronauts have already done long duration microgravity, returned to Earth & lived to tell.

[inamberclad]

Sure, but NASA is concerned about an emergency landing scenario on Mars. Astronauts that crash land while physically incapacitated from long duration microgravity will face near certain death.