Presented with an opportunity to move past Fremantle and return to the top four, the Power fumbled their way to a six-point loss at the MCG – their fourth defeat in five games.
Hinkley said the team was being challenged not to completely fade away this season having sat atop the ladder just five games ago.
The coach said he had full faith in the fitness program that had made Port Adelaide the toughest team to keep pace with late in games during the first half of this year.
"I don't think we're running out of steam, I think it's a long season," Hinkley said on Sunday night.
"You lose your confidence and once your confidence disappears so does some of the outward stuff you can do … the run, the kick, the handball, the mark, the conversion.
"It's just what the game does to you at this stage … it's hard work and we've got lots of work to do."
Hinkley said next Saturday night's clash against the Sydney Swans at Adelaide Oval could be the challenge his players need to rediscover their best football.
"You need something to get you over that little bit of a hill that we're facing right now," he said.
"Maybe it is an opportunity to play against Sydney and have a bit of a go at them as best we can and see what happens.
"It was only six or seven weeks ago we played Sydney on their home ground and we gave a really strong performance.
"There's no bigger challenge than next week for us, which is a good thing."
Hinkley was critical of his big-bodied midfielders, with Collingwood gaining a clear advantage in the middle of the ground, winning the clearances 24-12 in the first half.
At full time the centre clearances were 13-5 in the Magpies' favour.
"We've lost in tight … you know what we've done? We've fumbled in tight," Hinkley said.
"That's a reflection of us not being strong enough and hard enough at AFL level for a whole season.
"That's the challenge for us, to get that right.
"We've got some big-bodied midfielders who play in there and they haven't been able to handle the heat now for 4-6 weeks."
Collingwood midfielder Dayne Beams racked up 20 possessions and eight clearances in the first half and Hinkley conceded the Power had not paid close enough attention to the ball-winner.
He praised run-with specialist Kane Cornes for limiting his impact in the second half.
