Trevor Anderson calls it a "lightbulb" moment for Jordan Spieth.
Anderson, a performance coach with 27 years' experience, was guiding the three-time major winner through a series of exercises for a photoshoot back in 2014 when he saw something click.
The pair were using a "rip trainer" -- a resistance cord and weighted bar designed to mimic the action of a swing.
"He went: 'Oh, I love how that feels,'" Anderson recalls. "There are pictures and images from that photo shoot and you can see him in this great position."
Anderson has been coaching amateur and professional golfers since 2004 and, in that time, has seen how fitness conditioning can help to sharpen a player's game -- even if that means tweaking a major winner's swing with a one-off piece of advice.
"For elite players, it's always about that one little nugget, that one little feeling, that one little thing that they're able to put together," Anderson tells .
"When you start being able to tap into the athleticism that you already possess and utilize that to your advantage on the golf course ... you get some consistent results."
Anderson trains athletes across a range of disciplines, including American football, baseball and general fitness, but it's golf where he has seen the biggest shift in mindset towards conditioning.
On today's PGA Tour, the majority of players are lean, muscular, and athletic -- equally at home in the gym as they are on the golf course.
"I think I've learned to love it (the gym)," world No. 7 Rory McIlroy said in an interview with . "You start off and you hate it, you're like, 'Do I have to do this?' But once you start to see results and you start to get stronger ... I think that's where the enjoyment comes from."
The same attitude is found in the women's game. LPGA Tour star Lexi Thompson that she is "addicted" to working out, something she said created "dramatic changes in my golf swinging distance."
Anderson, who calls himself "a complete nerd" when it comes to the biomechanics of the golf swing, has closely observed how fitness has become a crucial component of the modern game.
"Twenty years ago, a meat head trainer guy like me trying to talk about the golf swing was taboo," he says, adding that physical conditioning was previously seen as "no big deal -- a guy might have a dad bod or a little belly."
Today, however, he finds himself working closely with golfers to improve physical aspects of their games: stability, mobility, coordination, speed and explosiveness.
"The golf swing is one of the most violent, athletic movements in the world of sport ... standing in place and moving as fast as you can," Anderson says.
Rather than helping players to get stronger, Anderson's emphasis is on durability and withstanding the rigours of swinging a golf club time and time again.
To do that, he uses exercises like TRX -- a suspension training tool that uses your body weight to build strength, balance and core stability -- squat and lunge routines, a plank series, deadlift repetitions and sets of sprints and jumps.
Anderson also views a varied sporting background as a benefit to golfers.
He points to the likes of 2019 US Open champion and former college basketball player Gary Woodland, two-time major winner Dustin Johnson -- "he could dunk a basketball right now," says Anderson -- and 2017 Masters winner and keen footballer Sergio Garcia.
"What I've found is that competitors on the golf course, they have a competitive advantage if they played team sports or individual sports that require all those aspects of athleticism, speed, agility, reaction," Anderson continues.
"Different types of pressure situations that you experience through general sport ... These are worldwide the vein that runs through all these sports and, from the competition perspective, you can really tap into them on the golf course."
WOODS' WORKOUTS
Golf's relationship with fitness training is not a phenomenon unique to the past two or three decades. Gary Player, a nine-time major winner who still regularly works out well into his 80s, has frequently extolled the advantages of exercise and a healthy lifestyle.
But it's Tiger Woods who's often credited with revolutionizing the sport's attitude towards the gym.
Aged 24, Woods said his daily routine would involve a four-mile run, a weightlifting workout, several hours of hitting balls and putting practice, another four-mile run, then an evening playing basketball or tennis if he fancied it.
"The work that he put in is what made him a great player," says Anderson.
"Now, when you look at today, a lot of the young, athletic, very good players that are out there, Tiger was their idol.
"When they wanted to know what it was like, what it takes to be successful on the golf course, they were looking at somebody like Tiger; you've got to be fast, you got to be athletic, you've got to be powerful, you've got to be balanced. And they were adopting that mentality."
DECHAMBEAU'S 'SCIENTIFIC APPROACH'
One of the most striking approaches to physical conditioning in the game of golf today has been Bryson DeChambeau, the 2020 US Open champion and former world No. 1 who piled on 40 pounds during the COVID-19 pandemic.
It was an approach that reaped rewards when tournaments returned, with DeChambeau recording four top-10 finishes in the June and July of 2020.
"It's a little emotional for me because I did do something a little different; I changed my body, I changed my mindset in the game and I was able to accomplish a win while playing a completely different style of golf," he told reporters .
But Anderson doesn't think DeChambeau's blueprint -- which involved putting on muscle to drive the ball huge distances -- will change golf moving forward. He says the window of opportunity offered by the pandemic makes DeChambeau an "anomaly."
"What really helped him be able to do that is he has this one plane swing," Anderson adds.
"All of his irons are the same length and all this type of stuff. He has a very cerebral kind of analytical, scientific approach that he takes to the game. He can keep everything right on that same plane and come down just with more power and speed."
DeChambeau is currently absent from the PGA Tour having undergone surgery for a fractured bone in his left hand.
It means he will miss the upcoming PGA Championship at Southern Hills Country Club in Tulsa, Okla., where newly-crowned Masters champion Scottie Scheffler, world No. 2 Jon Rahm and four-time major winner McIlroy will be among the favourites.
As for Spieth, who Anderson has worked with on several occasions through a shared sponsor, the American could join an elite circle by completing a career grand slam at the PGA Championship.
He'll no doubt be hoping for another lightbulb moment as he bids to win his first major title in five years.
