I'd like to point out that the participants in the study had a caloric intake that would maintain their weight. Also, they were not allowed to move one bit from their bed. There was an exercising group and a non-exercising group. I'm sure the results aren't out yet. But what would happen to the participants' muscle mass in this scenario?
70 days of inactivity will have a muscle atrophy effect. There are measures to limit the extent to which muscle wanes, but still, without use, they will deteriorate.
I don't know what NASA is planning to do to counter these effects, but researchers have found that neuromuscular electrical stimulation can keep muscle protein synthesis active in comatose patients. While I'm not sure if NASA is braving these territories, it certainly provides a sense of what can be achieved. Especially since 70 days is quite limited compared to the time one can be comatose.