Dom Sibley has admitted he became "self-conscious" about his weight and fitness after seeing more experienced members of the England squad training.

Sibley, the England opening batsman, has emerged from lockdown having shed around 12kg - more than 26lbs - through improved diet and fitness regimes. And, although he conceded he had long been told to consider losing some weight, he revealed there was a moment on the curtailed tour of Sri Lanka in March which provided the "wake-up call" required to make him turn words into action.

Exhausted after a training session on a hot and humid day, he watched in awe as a group of senior players - Joe Root, Ben Stokes and Jos Buttler - embarked on another fitness session. It brought home to Sibley the need to improve his fitness.

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"In Sri Lanka, for the first time in my career, I felt a little bit self-conscious about my physique and my weight," Sibley said. "I just remember sitting on the plane and thinking 'I need to do something'.

"You look at the guys who have been in the system a long time. Just seeing how fit some of the senior guys are and how impressive they are in training… I remember being in Sri Lanka, especially with that heat, and seeing a few of the lads running after a big session and that was an eye opener for me. Ben Stokes is a bit of a freak when it comes to his training.

"Actually it was seeing him, Root and Buttler running after a session in Colombo. I remember being absolutely spent so that was a real eye opener. Seeing these guys and the graft they put in to stay at this level for the amount of time they have done, is something that I want to do.

"It was an opportunity for me to improve that side of my game and I'm glad to have been able to stick to it. I needed to do it. It's great to have all the support from the backroom staff, the support's been great and the information I've been given and all that has been really helpful."

While Sibley has long been, by the standards of modern international cricket, a little thicker set than most, there was no evidence that it was holding him back in South Africa earlier this year. After registering a maiden Test century in Cape Town - an unbeaten effort that lasted well over eight hours - he finished with an average of 54.00 and having faced more balls (784) than any other batsman on either side.

"I've never felt tired batting," Sibley said. "My fitness has never affected my batting. It's not necessarily going to improve my batting. But it might help my agility in the field. And carrying less weight might keep me on the park for longer with fewer niggles.

"I've always been someone who hasn't necessarily been the fittest in the squad. I've always, whether at Surrey or Warwickshire, been coasting in that aspect.

"I have always prided myself in training really hard on my batting but maybe that side has not been something I have done to the best of my ability. I've had taps on the shoulder before and haven't really done anything about it.

"I think it was overdue having that wake-up call and a good lesson for me, regardless of whether it leads to runs. If I'd done nothing during lockdown I think I'd have got to here and thought 'I haven't quite ticked every box'. But I feel I've trained hard and I'm ready for the series. Success or failure, I feel like I've left no stone unturned."

It was noticeable in last week's warm-up match that England's quick bowlers - Jofra Archer and Mark Wood - appeared to target Sibley's ribcage with a leg slip and short leg in place. He survived one tough chance off such a delivery in the first innings, but was caught down leg off a similar delivery a little while later as he attempted a clip off the hip; a shot that has proved hugely productive for him in county cricket. He fully expects West Indies to deliver a similar line of attack.

"It was interesting in the practice match that they went with that as well so it was a good experience," Sibley said. "In the second innings I dealt with it a bit better.

"South Africa put a fielder round there [leg slip] for me. It's somewhere I've scored a lot of runs in county cricket but that's the great thing about Test cricket: you've always got new challenges and suddenly my strength is being turned into a way to get me out.

"I've played the pull shot since a young age. But in South Africa, with the bouncy wickets, I didn't feel in control of it so I chose to get out of the way of the ball. But it's a case of managing risk and knowing when to play and not play. You've got to find ways to deal with it."