Perhaps it means he resorted to fitness.

English term (edited): shortcut to fitness

A little more context would be helpful, but from what there is I would imagine that X believed it was possible to get fit quickly or with little effort (perhaps by taking some of these new "diet pills" etc., or by trying some new exercise programme), using methods requiring less effort than conventional ones, but "found himself on the road to nowhere", i.e. was not successful.

X took the short cut to fitness and found himself on the road to nowhere.

He tried some scheme, diet, training regime, patent medicine or something like that which promised quick results in restoring fitness, but it was no use, it didn't help him at all, maybe even made things worse.