In the Amazon documentary All or Nothing: Arsenal, which followed the Premier League team during the 2021-22 campaign, viewers saw coach Mikel Arteta prepare his players for an away match at Liverpool by blasting out his opponent's anthem, "You'll Never Walk Alone," from loudspeakers on the side of the training field.

The purpose was to simulate the atmosphere his players encounter pre-game at Anfield before their most intimidating assignment of any season. Even if Arteta's method felt clunky, it is symbolic of a wider move across sports to uncover incremental gains in an increasingly competitive, well-funded and tech-savvy landscape.

Chris Lee is the managing director of Populous, the sports architects who have developed and built over 250 performance centers globally, including for the NFL's Buffalo Bills and the Australian women's soccer team, who opened a $57 million base in 2023. Populous is also now constructing the new Cleveland Clinic, which will be home for the NBA's Cleveland Cavaliers.

The purpose of any training center, Lee says, is most simply "about preparing players for the season or for games." But preparation has never been more innovative.

"There are really interesting concepts coming around the world. A lot of it is in the NBA, with immersive spaces preparing for predominantly away games," Lee explains. "Everyone saw Arteta trying to beam in Anfield ... but you're seeing that massively extended now in the NBA with the idea of fully immersive environments where you can recreate the arena you are about to go and play. There's a bunch of VR and immersive technologies coming into play."

The new Cavaliers facility, for example, will feature an immersive "shot lab" simulator that enables players to replicate the experience of playing in other NBA arenas. In golf, Rory Mcllroy revealed this week that the captain of Europe's Ryder Cup team had given his team-mates virtual reality headsets in which they hear abuse in order to prepare them psychologically for the rigours of playing in the event, having failed to win on American soil since 2012.

In 2025, a state-of-the-art training complex is obligatory. Manchester United last month opened a new £50 million ($67m) facility, while the NFL's Baltimore Ravens unveiled their new and improved center, having invested a further $20 million. Next year, the U.S. Soccer Federation will open a 200-acre National Training Center outside Atlanta, which will become the national home of the sport. For many sporting teams or institutions, it is increasingly the home of vast playing spaces, but also locker rooms, meeting rooms, front office headquarters and high-performances facilities.

It is the inner sanctum of any professional team; where coaches concoct masterplans, players pursue self-improvement and where the mood and culture of a team is established. When it is not up to scratch, superstars take note. Most memorably, Cristiano Ronaldo criticized United for their failure to upgrade the facilities between his departure from Manchester in 2009 and his return in 2021. "Nothing changed, surprisingly. Not only the pool, the jacuzzi, even the gym, even the kitchen," he told Piers Morgan Uncensored.

This explains the level of thought and consultation involved in construction. It also explains why cross-pollination between sports is increasingly common, as multi-sport ownerships and a globalized world inevitably lead to borrowings and learnings.

The Ravens' expansion, for example, involved initial discussions in early 2023, two-and-half years before completion. Simon Gelan, the team's senior vice president of operations, met with the general manager and head coach, as well as taking feedback from players, who have three to four meals per day at the training base. The revamped facilities include hot and cold tubs that can hold 20 players -- which means no more wait times for an open slot -- as well as a full lap pool for recovery and rehab.

The training floor will also have hi-tech equipment including anti-gravity treadmills and class 4 laser therapy, which can penetrate deep into tissues to enable faster regeneration and healing. They have also introduced blood flow restriction training, designed to strengthen muscles that surround joints without pounding injured areas during rehabilitation. There is even an on-site doctor's clinic, which includes an isolation room for sick athletes, as well as space for psychological and concussion evaluations.

"We take everybody's priorities very seriously," Gelan tells The Athletic. "It was about understanding the needs versus the wants. It may not be the Christmas-every-day version. But can we settle on a plan to get you the best functionality? It is a home at the end of the day, and you want to feel good about coming home. You want to feel you have everything you need to have the best opportunity to be successful."

That desire to create a home, and embody an ethos of a club, can be created in other ways. The Ravens grow their own vegetables on their rooftop garden, which then fuel the team in the canteen.

Atlanta United of MLS are the process of a $23 million expansion, and their base will likely host a national team during next summer's World Cup. Dimitrios Efstathiou, VP of soccer operations, tells The Athletic: "This is no joke. We spoke to every single leader of the department, going into very granular detail. How do you want the tables to look? Do you want them to be a certain colour? Do you want them to be a certain length?"

Adds Gelan: "The desire for natural light was highlighted across every department, including players. There's research that shows natural light helps create energy and enhance mood and performance." The team also believed that sight lines from the indoor rehabilitation or training rooms to the practice fields can improve a player's morale during rehabilitation. Architects and performance experts speak often about "connectivity," ensuring one shared space leads to another, or that a developing player has a visible sight line to the first-team training field from the gym.

Detailed consideration is given to how space is designed to improve a culture.

"There are lots of different ways of thinking about the nutrition and canteens," Lee says. "Are they all in together? Are they in adjacent rooms with kitchens in the middle, so that academy players can see and mingle with the senior players? Recently we've designed nutrition areas where there's a buffet in the middle, if you can imagine, and the first team is on one side and the academy are on the other side. They're selecting the same food, but there is still a subtle division. Increasingly we're beginning to see this concept of a 'street', these communal collision spaces where serendipitous moments happen, where a physio can meet a psychologist or players interact with key staff continually."

Where sporting centers include space for academies and children, consideration is also given to ensuring the safety of participants. At Atlanta, Efstathiou says glass is often used to create visible "safe spaces for minors to be interacting with adult coaches."

Before finalizing their own plans, the Ravens took inspiration from elsewhere, having stayed at Tottenham Hotspur's training base in 2023 ahead of their NFL regular season win against the Tennessee Titans. "I spent a lot of time asking questions. I had tours of their facilities, understood how everything worked," Gelan says. "We got a lot of great feedback. We went to see different facilities as well in the U.S. -- understanding the landscape and how we compared to other NFL, MLB, NHL and NBA facilities."

In some cities, this is leading to dual-sport performance centers, such as recently announced plans for NWSL's Portland Thorns FC and the city's new WNBA expansion franchise. The Bhathal family, who own both teams, are building a facility that will see the two have access to all the headline innovations of modern sport across as 12-acre center. This will include two basketball courts, two soccer fields and dedicated locker rooms but also shared access to a 5,000-square-foot strength training facility, a yoga room, recovery lounges, recovery pools, hyperbaric therapy and red-light therapy. Some leading soccer teams in Europe house both their men's and women's teams on one site.

"Some are looking at total gender parity between facilities, and everyone on one site," Lee says. "At the same time you have other clubs saying they get some feedback, particularly from the women's side, saying we don't really necessarily want to be on the single site. Despite having the opportunity to use facilities, there is some feeling that they may still always be second fiddle to a men's first team, regardless of the parity. So there's two interesting discussions which are very live at the moment on all in one site or women's only, men's only sites. Different clubs are taking different views. But there is, I would say, a broader trend to having all teams on a single site -- a 'whole club' philosophy."

He adds that exchanges between sports are now par for the course.

"What we're doing with the Cleveland Cavs absolutely affects what we're doing in the Premier League or Serie A. Basketball and NFL absolutely impacts in some way how we design for the Premier League and vice versa. We're engaged on a couple of Premier League club training facilities at the moment, and these clubs rightly want bespoke designs, but they also understand we can bring inspiration and ideas from the best training centers around the world. When we work with European football clubs, we work with the director football and head of performance but then we can bring in our global advisory group, mostly made up of ex professional athletes. ... That's important -- designing through the eyes of an athlete is really critical. It's not some architect coming in with some idea of how it should be."

As for why teams are prepared to invest so heavily in facilities, the answer is pretty clear. It is about attracting and developing talent and increasing the overall value of the business. Many facilities, such as Atlanta United's soon-to-be-improved base, will include on-site studios, enabling teams to produce content in-house. Before, they would need to go elsewhere across the city, sometimes to the stadium, or rented space further away, all of which took time away from their daily priorities.

In the NFL, players give annual assessments via the NFLPA report card that scores the facilities with a grade. In soccer, it can impact perceptions - and recruiting pitches.

"When this facility opens up, we will have a video and brochure for players when we're pitching to them," Efstathiou says. "It's important to us to say, 'Look what's happening here.' They're going to spend the majority of their life in the facility. They need to know we have a cafeteria that serves high-level clean protein, that we have a nutritionist, the gym, the treatment space, that's super important. You give that at almost the entry point of conversations with a player. I would love to say our reputation precedes us in terms of the league, but you do have to sell moving to the United States for soccer for a lot of players.

"Part of our pitch is saying it's not just the city; the facilities are state of the art, we can go up against any major club in the world to say, 'Take a look at what we have here.'"

The power and purpose of the elite modern training center