Ricardo Montalbán was in near-constant pain due to an injury on his back .
There were some questions initially as to whether Montalbán had had prosthetic muscles applied to his chest during filming of Star Trek II to make him appear more muscular ; director Nicholas Meyer replied that even in his sixties and despite his back injury which left him in near constant pain , Montalbán had a vigorous training regimen , was `` one strong cookie '' and that his real chest was seen on film ; Khan 's costume was specifically designed to display Montalbán 's physique .