Two-time British and Irish Lions tourist Phil Vickery believes the condition of Warren Gatland's forwards going into the first Test will be central to their chances of success in New Zealand.
Former England prop Vickery - a veteran of 78 Test caps - represented the Lions in 2001 and 2009, either side of their last visit to New Zealand in 2005.
Much has been made of the gruelling schedule the current squad face before taking on the All Blacks, with Saturday's tour opener against the Provincial Barbarians the first of six pre-Test warm-up matches.
"I think the key for me is that first Test", Vickery told Omnisport. "And it will be how they arrive at that first Test for me, particularly the forward pack.
"[Brodie] Retallick and [Sam] Whitelock in that second row [for New Zealand] - my God, they are two unbelievable players. They don't get pushed around at scrum time, they don't get messed around at the lineout, they're ball-carriers, their work rate is good, they tackle, they're on their feet, back in the game and doing the right things.
"This Lions forward pack will have to front up - and not just front up in scrummages and mauls and the lineout, they've got to out-energise them and out-work them.
"Something I know from my experience of Warren [Gatland] on the '09 tour, the conditioning staff are the most important people. The physios and the medical team are the most important people on tour. He will be guided by that, he will understand how much rugby the guys have played."
While the importance of a Lions tour for fans of England, Scotland, Wales and Ireland can hardly be underestimated, Vickery knows the southern hemisphere nations also relish the occasion.
"It's such a special thing," he added. "For us it's every four years, but for those countries it's every 12 years. You can be a 100-cap All Black, a World Cup winner and not play the Lions, so it's such a big deal for them.
"The Lions to me brings together that amateur spirit. The tour is very professional - probably the most professional tour there can be - but the basis and the roots and foundation of it are thousands and thousands of people who save up for four years and make sacrifices to go and watch a Lions tour. What a fantastic thing to be involved in.
"We sometimes take it for granted. When the Lions come to town and bring all those supporters, it's amazing."
Phil Vickery was talking at an 'Ingredients for Success' event for Robert Walters, a specialist professional recruitment firm and official sponsor of The British & Irish Lions. They have recently recruited the Ultimate Lions Fan, view the video @RobertWaltersPR.