FATIGUE is a funny thing.
You can get exhausted just hearing about it, especially when the tired old excuses are trotted out by men employed to display their fitness.
But, within the confines of the Celtic dressing room, there is not a murmur, not a moan.
The Green Machine is powering towards the finishing line in the title race, turbocharged by victories like the 3-0 dismantling of St Mirren.
Having surpassed last season's points total of 79, with eight games remaining, now it might require just one, perhaps two, more surges to see the trophy retained.
By the end of the week, it should be safely secured in the Parkhead board room for another season - at least.
A campaign which has encompassed four competitions and 45 games over the last eight months is about to see its reward reaped.
Not surprisingly, having the league trophy come within touching distance has added a spring to the step of players who, hitherto, might have been feeling the pace of this marathon.
For Neil Lennon, the manner of their most recent victories confirms a new lease of life is being enjoyed by the Bhoys in green and white.
The power plays have seen them beat Inverness 5-0, with three of their goals coming after the break.
At Kilmarnock next time out, all three counters were delivered in the second half.
And, again, against St Mirren, following Stefan Johansen putting them ahead a minute before the interval, they came back out to step up the pace and add two more from Leigh Griffiths and Anthony Stokes to finish off Danny Lennon's strugglers.
Little wonder the Hoops boss is buzzing like an electricity sub-station.
The hard work put in during pre-season really comes into its own at this stage, and Celtic show no signs of running out of juice as they make their final charge.
Lennon said: "I'm not aware of any real tiredness showing among the players. Scott Brown and Stefan Johansen looked really strong against St Mirren.
"Leigh Griffiths came off, but he has had a little ankle sprain, so he's not trained as much as we would have liked.
"We kept checking on him to make sure he was okay to continue because the game might have caught up with him a little bit. But playing matches will do him the world of good.
"Anthony Stokes was another who looked really strong, and my back four looked really good, too. So, there are no real concerns from me in terms of fatigue at the minute."
Considering his side have played a dozen European matches, the vast majority of them high-intensity, while the bulk of the team have also been heavily involved on international duty in tandem with their club commitments, the freshness being shown is testimony to their conditioning.
Lennon said: "The boys are fit, and we have backroom staff who monitor each individual on their performance in games.
"So, we keep abreast of that. And, obviously, we try to use this to avoid injuries, as well."
They work on the theory prevention is better than cure, and players will be given time out if it is felt their workload has put them anywhere near the danger zone for picking up a strain - or worse.
Mentally, too, they are constantly assessed, to gauge when they might benefit from a break from the front line.
Efe Ambrose came into that category at the weekend.
The Nigerian was left on the bench while Charlie Mulgrew partnered Virgil van Dijk - just back from a three-week break as a result of suspension - at the heart of the defence which kept yet another clean sheet against a Saints side which huffed and puffed - Paul McGowan was particularly effective behind the main striker - but rarely threatened Fraser Forster's goal.
Lennon explained: "We just gave Efe a rest, exactly because of what I have been talking about. We also wanted to give Liam Henderson his home debut, and so Charlie stayed in defence.
"We have not really seen Charlie and Virgil van Dijk play together, and we felt it was a home game in which we would have enough possession of the ball to allow Liam to express himself. We have also got three games in a week."
Even before the title is won, Lennon is thinking ahead, and taking the opportunity to check out how certain players might interact, and how different systems can be effected.
However, he is not losing sight of what has given this team its core strength this season, and what has carried it to the brink of three-in-a-row.
"Efe and Virgil have been the mainstays of the team, but this just gives me an indication of what else we have," he said of the elective changes.
"It might take a bit of time to forge a different partnership. But that was not at the forefront of our thinking on Saturday, and Efe will start against Partick Thistle on Wednesday."
Whichever personnel and system he starts with at Firhill, Lennon wants them to pick up where they left off against St Mirren.
A contended manager reflected: "In the second half, we were terrific and dominated the game.
"We played some really great, attacking football.
"My only criticism is we were a bit wasteful in front of goal, otherwise the score would have been a lot more impressive.
"St Mirren pressed us with quite a high line, but we always felt that Leigh and Anthony would eventually get behind them.
"Stefan got us going after a great ball in from Leigh, and that was just the bit of quality we were looking for because we were counter-attacking very, very well."
Lennon continued: "At half- time, I just asked them to pick it up again, like they did against Kilmarnock. We had been a bit sloppy in periods in the first half, But, in the second, I got the response I wanted.
"Now we're all looking forward to Wednesday. It's a bubbly dressing room at the minute, and we just want to keep going and really enjoy it."