'Proper pre-season flogging' didn't stop Grayson starring for Saints
For most mere mortals, doing any sort of physical activity the day after a tough gym session is a real struggle.
But how about playing a full 80 minutes, in an East Midlands derby, and steering your side to a huge victory over their local rivals?
That was what James Grayson delivered, having initially not been part of the 23-man matchday squad against Leicester Tigers in late November.
He went through all of the weekly work done by the men who are not involved, including what he labels 'a proper pre-season flogging' on the eve of the game.
But on the following morning, the call came for a weary Grayson as Dan Biggar was forced to withdraw.
And the rest, as they say, is history, as Grayson came up trumps to help mastermind a sensational 36-13 success against Tigers at a sold-out Franklin's Gardens.
"It was awesome," Grayson said.
"I didn't have much preparation time but it was a sold-out Franklin's Gardens and the first one I've played in - it was an awesome atmosphere.
"You see their team is full of England internationals and British & Irish Lions and to be able to go at them for 80 minutes and grind out a performance and blow them away a little bit in that second half was really positive.
"It was nice because it's always good to beat Leicester.
"I don't want Dan to be injured but to be able to step up and take my opportunity was nice."
When asked to outline the session he endured just a day before the big game, Grayson explained: "We had a second team conditioned games and high intensity training session.
"It's basically a minute and a half of rugby, 30 seconds rest, a minute and a half of rugby, 30 seconds rest and then you go into some running sessions, back into conditioned games, running sessions, back into conditioned games.
"It's about five or six kilometres we covered and it's a proper pre-season flogging.
"Then I was driving in to do training on the Saturday morning and I had a text from team manager Shieldsy (Paul Shields) saying 'can you ring me?'.
"I was going through my head - 'what have I done wrong?', 'what could it possibly be?' - and Dan had woken up with a sore foot so Shieldsy told me just to go home, try to prepare as if I was going to play.
"Dan had a fitness test and I was told I'd know the outcome about 12.30pm so I got the phone call and luckily enough I managed to play alright and not mess up."
Grayson certainly didn't mess up, delivering another mature display in the Saints No.10 shirt.
He kept going right to the end, even though he was really starting to feel the previous day's stresses and strains just 10 minutes into the second half.
"I wasn't sore, but I was tired and my legs were tired," the 21-year-old said.
"Around about 50 minutes in I cramped so for the last 30 or so I was just taking pickle juice that is supposed to stop you from cramping.
"It didn't really work so I was just holding on until the end."
Grayson landed four conversions and a penalty on the day, but it was his open-play action that really caught the eye.
He continues to go from strength to strength, having emerged from the Saints Academy, and the Northampton-born ace is now looking forward to his next assignment: a Champions Cup clash with Benetton at the Gardens on Sunday afternoon.
"It's been frustrating the past few weeks not being involved but we've been performing well so it's been nice to see," Grayson said.
"With Benetton coming, we need five points so to go out there and have that opportunity is really positive.
"We need to try to get as many points as we can out of these two games, and four or five out of this first one would put us in a great position.
"Benetton are a team that are slippery, there's always a chance to slip up against them.
"They're not like a French team where you might expect them to travel and not turn up.
"They'll travel and work their socks off so we've got to be prepared to roll our sleeves up and fight for 80 minutes.
"We went down by plenty of points there, fought back and then Dan rolled his sleeves up and knocked the winning kick over, which was never really in doubt.
"We've got to be prepared for them and we know they're not just going to lie down and roll over for us."
There has been a real buzz about Saints in recent times, with their away support at games such as Benetton and Wasps a crucial factor in helping to deliver dramatic late wins.
And Grayson said: "You start winning some games and you see some old faces coming back and starting to support.
"The home crowd gets a little bit bigger and the away fans start to travel a bit more because they're seeing you go away from home and getting positive results.
"Winning breeds support, you see that in any sport. If you start winning, people want to support you.
"If we can get the win this weekend, fingers crossed we can take it to Lyon next Saturday with some travelling support."