The 25-year-old has trimmed from his normal mid-90kgs playing weight, and is keeping up with some of the club's best-running talls on the track.
Riewoldt has been diligent in his rehabilitation from minor knee and hip surgery and looked strong in Friday's post-training running session.
Coach Damien Hardwick has already spoken of a desire to play Riewoldt further up the ground as "a traditional centre half-forward", which will be helped by the spearhead's improved fitness.
"I think he's had a real focus on what he's eating and also his training," captain Trent Cotchin said after the hit-out.
"He hasn't missed a beat with his rehab program and now he's joining into training.
"He looks fit, he's running with some of our better bigger blokes with their running capacity, so it's exciting - we'll just have to wait and see how he plays."
Riewoldt isn't the only one standing out. Across the group, 17 personal bests were recorded in the weekend's two-kilometre time-trial while pre-Christmas times also impressed.
Dustin Martin trained with the defenders on Friday in a session that lasted more than an hour at Punt Road and was held in searing heat for the fourth day running.
Cotchin said the midfielder was another who had applied himself across the summer months.
"He ran really well coming off a really solid Christmas break and his training has been outstanding," Cotchin said.
"He's playing a few different roles here and there so it will be exciting to see where he does line up and how he plays his game."
Alex Rance dominated the running at the end of the session that a handful of players had to endure to as part of their programs.
The rest of the group will run on Saturday morning, while Friday's will stick to cross training.
Cotchin said Rance was a strong example of the pre-season mentality at Richmond this year.
"He's a mean character when it comes to running, he's got that mental capacity to push himself and he and David Astbury are probably our big blokes who really dominate the running - and they push each other," he said.
"The great thing is they're willing to drive other guys and drag them along with them."
In his six seasons as a Tiger, Cotchin can't remember training in the extended 40-degree heat Melbourne has faced this week before.
He lost a kilo and a half in Friday's session, which came after Wednesday's huge day that many players described as the hardest pre-season hit-out they've ever done – a session instigated by Cotchin.
"We had our first real hit-out of match practice for the pre-season [on Wednesday] and from there we did a bit of conditioning mid-session and then finished off with a little bit more match practice," he said.
"Our day had actually been pushed back a little bit so I made the call that we did our cross-training straight off the track.
"The boys were a little bit flat with me without having lunch before going into cross-training but once we got through it, we worked out it was going to work out in our favour and we just had to relax and then do yoga."
Cotchin said players had pushed each other through the tough sessions and were keen to stick to pre-determined standards set at the start of pre-season.
While a number of players were kept from Friday's session, including Reece Conca, Ivan Maric, Daniel Jackson, Liam McBean, Jake King, Ty Vickery and Shaun Hampson, he expected the list to be nudging full strength next month.
"There's only a few guys who need to join training, a few are missing a session here and there to make sure their programs are still modified and they don't miss a beat once it does come to game time," he said.
"We're in pretty good condition at the moment. Hopefully we'll get a couple of guys back in joining training next week or the week after and have a really strong and fit side pre-season."
Conca, Dylan Grimes, Bachar Houli and Chris Knights didn't train with the main group on Friday but were put through their paces with running.
The Tigers play their first NAB Challenge match on Friday, February 14 against Melbourne at Etihad Stadium.