THE SUBSTITUTE rule introduced into the AFL this season is rapidly turning into one of the most crucial tactical moves on game days, according to Sydney Swans veteran Ryan O'Keefe.

As the role of the substitute continues to evolve, O'Keefe believes the pressure is now increasing on the nominated player to have an instant impact on matches.

The Swans are one club that quickly had to change their philosophy after coach John Longmire used ruckman Mark Seaby as his substitute player in their round one draw with Melbourne.

The move didn't work and most clubs, including the Swans, are now using speedy midfielders off the bench to take advantage of tiring opposition late in games.

The back-up ruckman tactic was scrapped immediately, with the Swans using Lewis Jetta to great effect in last week's one-point victory over North Melbourne.

With the game on the line, Jetta helped set up two vital last-quarter goals with blistering runs down the wing, while he also helped regain possession with a great tackle on Kangaroo Michael Firrito.

"They're very much an impact player. You saw how 'Jets' did it on the weekend," O'Keefe told reporters in Sydney on Tuesday.

"We're all stuck in second gear and they're flying out there.

"It's an important thing, too, they have to come on and make an impact. When they do, you can see they're fresh and flying and making us all look pretty pedestrian really.

"I don't bother trying to catch them.

"But it's important subs realise they have a really important role in the game now and they've got to come on and make an impact because they're fresh and zippy and have to capitalise on that."

O'Keefe also feels it is next to impossible for players to be nursed through the season now carrying injuries.

The 30-year-old himself struggled mightily with an ongoing groin problem in 2010 that required surgery as soon as the Swans were knocked out of the finals.

But the 2006 All Australian is fully fit and relatively pleased with his contribution in helping the Swans to sixth on the AFL ladder ahead of Saturday's away game against the Brisbane Lions.

"Obviously the game is really hard on the body now and it's getting harder," he said.

"It's harder to play with injuries. If you're carrying something it's noticeable, there's a clear difference between a player fully fit to one 60 or 70 per cent.

"I think I'm doing my job. We've got a lot of young players that need a lot of helping and encouragement and I think I'm doing that.

"You have to keep performing and playing consistent footy and be a constant in the team."

One area O'Keefe isn't pleased with is his goalkicking.

A regular in the midfield, O'Keefe has been used in the forward line at times throughout his career and is usually very solid with set shots.

But he has managed just 4.9 from nine games so far in a Swans side that has the third worst attacking record in the league this season.

"We're all not contributing that well to the scoreboard," he said.

"I've missed a few sitters and that's something I have to try to work through."

Ryan O'Keefe and fellow 2005 premiership team-mate Jared Crouch are teaming up again to lead a 15-day cycling trip through southern China in the 'Wild China Challenge'. You can find full details here.

The views in this story are those of the author and not necessarily those of the clubs or the AFL