As Bristol Bears celebrated and dissected their impressive PREM win over reigning champions Northampton earlier this month, one surprising feature stood out in the mixed zone – Louis Rees-Zammit’s socks.

While scrum-half Harry Randall went topless in Bristol's new post-match media area, Rees-Zammit – who has made a flying start this season with four tries in three matches – had taken off his boots. In doing so, he revealed one of the latest secrets to his success.

On top of his usual long Bears match socks, Rees-Zammit now wears an extra pair of specially designed, shorter grip socks. Many other players, especially backs, do this. But as usual, Rees-Zammit has a point of difference in that on the end of his are individual holes for each of his toes.

‘I don’t know if they make me faster, but I feel a bit more control on my feet,’ Rees-Zammit said. ‘I feel being able to spread my toes within my boot helps me change direction and do what I do on the field. It’s a bit of a weird one to see, I can imagine!'

It has now been 14 months since Rees-Zammit returned to rugby from his stint playing American Football, first with the Kansas City Chiefs and then the Jacksonville Jaguars. In his first season with Bristol, the now 25-year-old – by his own admission – took a while to adjust back to the sport he grew up playing. That was understandable.

Rugby and NFL are two very different sports in terms of their physical demands, even if they share a common theme of physicality. Rees-Zammit was certainly not poor last season, but on the evidence of what we’ve seen this term, he looks back to his best.

The Wales flier certainly hasn’t lost any of his trademark speed. But it is in other areas of his game that his development has been significant. His performance against Northampton was notable not only for two trademark tries and copying opposition flanker and friend Henry Pollock's 'pulse check' celebration, but a 50:22 kick and strong physicality both in the carry and at the contact area. His defensive work has improved, too.

‘What I love about all players, including Louis, is that if they put the work in, they get the reward,’ said Bristol director of rugby Pat Lam. ‘He’s kicking really well and has put a lot of time and effort into hitting 50:22s. Jordan Crane, our defence coach, does extra tackling work with our backs and Louis has been in for that.

‘He’s in such a great place mentally. He’s got a smile on his face, he’s enjoying the company of the boys here, the way we’re trying to play, and what we’re trying to do. You see the finishing stuff from him, but he’s banging into contact. He’s clearing players out at the ruck. There’s a lot of stuff in his game that I value as a coach.’

One of professional sport’s most genetically gifted athletes, Rees-Zammit’s point of difference has always been – and always will be – his speed. He once hit an eye-popping 24.2mph during a rugby match, which as it happens is faster than anyone has ever been recorded during an NFL game. But one of the biggest factors in his fine form has been his physical work.

When trying to make it as a wide receiver or running back in the USA, Rees-Zammit upped his weight to fit NFL requirements, weighing in at about 16st 8lb. Now, he’s down to 15st 6lb, close to his weight from his first rugby stint. It is not a massive difference, but it has allowed Rees-Zammit to maintain his trademark pace with impressive power and explosivity.

Jake Gillies, Bristol’s sports scientist, told Daily Mail Sport that in pre-season, Rees-Zammit was recorded running at 10.77 metres per second, again just over 24mph. He once raced Welsh Olympic sprinter Jeremiah Azu at Bristol’s training ground over 40 metres and was only just pipped to the post, clocking in at 4.59 seconds to Azu’s 4.54. Combined with his new power – Rees-Zammit can squat 200kg  – it is little wonder that opposition defences are struggling to haul him in.

‘When everyone thinks about Louis, they think about his peak speed and rightly so because he's a freak,’ Gillies added. ‘But what impresses me most about him is how quickly he gets to that peak. His acceleration from a standing start is silly. He got to 10.77 metres per second in just over 4.5 seconds in training.

'But he's also strong in contact because the faster you are going into it, the harder you are to stop. At his weight, the momentum he carries into every contact, if he's running at full speed, is significant. He’s a really unique player.’

Last season, Rees-Zammit spent long periods playing full-back for both club and country. Now, he is back in his favoured wing position. Being dropped to the bench by a struggling Wales side in the summer was a reflection that Rees-Zammit wasn’t firing on all cylinders, and he acted upon it.

In the off-season, he headed to Marbella with former Bristol team-mate Rich Lane and England women’s No10 Holly Aitchison to ensure he was fighting fit. 

‘I was joking with him when I saw he was on holiday with Rich,’ said Lam. ‘Rich was very good at those kicks as well. I saw the video he posted from that trip online and I laughed and said: “Did you only put the good ones in there?” He said he didn’t and after he hit the 50:22 against Northampton, I said: “Fair play. You’re getting your reward for that."' 

In a World Cup season, Rees-Zammit looks determined to impress, and that can only be good news for Bristol as well as Wales, who named him in their 39-man Nations Championship squad for their autumn games on Tuesday. Dragons backs Aneurin Owen and Che Hope and Cardiff prop Rhys Barrett are the uncapped players in head coach Steve Tandy’s party, while Leicester flanker Tommy Reffell is absent due to a knee injury. His Tigers team-mate Olly Cracknell also misses out, as does No8 great Taulupe Faletau and young Scarlets centre Macs Page.

Against Northampton, Rees-Zammit made 81 metres with ball in hand, beat six defenders and scored twice – and was only denied a hat-trick by a Tommy Freeman block. The more unseen parts of his game were just as good.

Rees-Zammit also scored twice at Sale, showing a scintillating turn of foot to track escaping Sharks wing Arron Reed. He was then rested, like most of Bristol’s key men, for last weekend’s European trip to South Africa where the Bears were thumped 49-12 by the Stormers, but will return to face Exeter on Saturday.

‘In his first couple of months here, he was still getting used to being back in a stop-start game that isn't quite as stop-start as NFL,’ Gillies said of Rees-Zammit. ‘I don't think we saw his speed capabilities last year. I think we had a couple of times where he went 10.2, 10.3 and 10.4 metres a second, but you could see there was still room for him to develop that more. Now, he’s just lean mass. He’s so strong – one of our strongest backs.

‘He’ll squat the same as some of the forwards and that means he has the ability to produce an impressive amount of force which underpins his speed. Louis is very relaxed when he runs. His technical model of sprinting is brilliant, so smooth. It’s just poetry.

‘We never want our players to stand still, so we’re looking at how we can get Louis’ peak velocity higher but also how we can get him there quicker. Our programme allows players to run fast often in training. I would love to see him over a longer track. 

'I think if he had 80 metres to run into, he could get to 11 metres per second. He’s definitely the fastest I’ve worked with by some distance. But there’s not a lot of room on pitches in today’s game, so the fact he can also evade people, go round people, and use his physicality really makes him stand out. He can kick and chip, too.’

Even in a disappointing defeat by Saracens, Rees-Zammit showed flashes of promise.

‘I’m loving playing with this team,’ said the 25-year-old, who has two specific sprint training sessions each week and has called for a ban on rugby being played on artificial pitches after suffering horrid leg burns at Saracens.

‘We had a really good pre-season. Last season, we obviously didn’t make the top four in the PREM (Bristol finished sixth) and that was a bit painful. I’m working hard every day in training. If I can add more strings to my bow, that’s only going to help me be a better player.’