"We've got very good fitness. We'd compete with anyone in the league," Merrick said. "It helps us in the last 10-15 minutes of a game."
There has been no silver bullet this season but Merrick's training sessions - in conjunction with assistant Chris Greenacre and interim goalkeeping coach Des Buckingham - have been conducted at a high tempo.
"We get fitness through playing with the ball all the time," Merrick said. "You've never seen our boys run without the ball, so it's every training session; it's ball-centred and it's very intense."
Wellington's strength and conditioning coach Lee Spence said he took pleasure from seeing the Phoenix still running at full flight late in games.
Spence said they gathered data during the pre-season, where they had GPS monitors on their players, which focused on a metres-per-minute target. Heart rates were also recorded.
"You can get really, really in-depth and collect as many numbers as you want but it's how it affects your training on a day-to-day basis," Spence said.
Phoenix skipper Andrew Durante is a doubt for today's game against Adelaide United in Lower Hutt because of a calf problem.
Durante was sent for scans yesterday and was set to undergo a late fitness test this morning to determine his availability.
Merrick also has to juggle his backline because of the suspension of Manny Muscat, who picked up his fifth yellow card of the season during last week's win over the Victory.
Michael Boxall, who has filled in admirably for right back Louis Fenton (concussion), should retain his spot, while the fit-again Fenton could muscle his way in to the side.
