Unbelievable part(s) (spoilers ahead)

Interesting. I hadn't read any of the books, so I didn't know that. It just stood out to me how defined Reacher's physique was in this series to the point where he was actually bodybuilding, and not just really strong. I suppose if they would have shown him doing sit ups, push ups, etc. during his down time, it could have been at least more plausible. Strangely, the series makes Finlay out to be the health-conscious weak guy, whereas Reacher is the junk food-eating ripped guy.

Actually, it's not necessarily unrealistic at all. There actually is a rare genetic "disorder" that causes this: myostatin-related muscle hypertrophy. The condition is characterized by reduced body fat and increased muscle size. Affected individuals have up to twice the usual amount of muscle mass in their bodies, though at least one study (done on mice) showed that there is not necessarily a commensurate increase in strength. This condition is not known to cause any medical problems. Mutations in the MSTN gene cause myostatin-related muscle hypertrophy. People with a mutation in both copies of the gene (because they inherited it from both parents) have significantly increased muscle mass. People with a mutation in one copy of the MSTN gene in each cell (i.e. inherited from a single parent) also have increased muscle bulk but to a lesser degree.

So if Reacher has this condition from both parents, he might indeed look at least fairly close to what Alan Ritchson looks like from working out the way he did for this role. The question is, would he then be as strong as Reacher is supposed to be? Reacher, after all, is supposed to be even stronger than his great size would suggest, and as I said,there was one study that showed no corresponding increase in strength (and that tendons are no stronger than normal, which is a limiting factor). On the other hand, there are real people with this condition (e.g. Liam Hoekstra) who apparently are unusually strong (and have to eat a lot to support all that extra muscle mass).

In the book Reacher was tall and well built. He did not absorb the blows of a crowbar in the book like he did in the TV series.

Yeah, that fight scene with repeated blows by a crowbar ... was so stupid and ridiculous it made me mad. I have a crowbar like that, I would not want to get hit by it once - it would do damage or kill someone. Not to mention the bad guy wielded it like it was made of styrofoam.

I'm not a big Tom Cruise fan, but I thought his first Jack Reacher movie was pretty good, and made more sense.