Indeed Shatner says he ran and worked out frantically for TMP. Time well spent...
Although he didn't wax his body hair off the way he did in the TOS days, so you see his hairy arms in the short-sleeved shirt. Then you have Bones beaming aboard looking like a cross between a hippie and a pimp. TMP is the epitome of 70s leisure-suit sensibilities. No other live-action Trek has that 70s vibe to it, which is why I still like TMP, although I'm also glad they moved on afterwards. A little of that goes a long way.