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SAN FRANCISCO — Let’s begin where the process so often ends.

“We’re actually going to go into the bathroom, of all places,” said Geoff Head, the Giants sports science specialist.

It’s almost five hours before the first pitch at AT&T Park last September, so we’re free to barge unannounced into the Giants’ clubhouse restroom. The players have yet to trickle in.

Head selected this lonely hour to provide an extended look at a largely unknown part of the Giants’ late-season success. Now in its third full season, the sports science program takes a high-tech approach to assessing health and fitness by looking at what Head calls “the physiological biomarkers of fatigue and performance.”

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SF Giants Gameday podcast: Are unlikely contributions a sign Giants can sustain success? Depending on the results of player testing, Head might have a turmeric-spiced shake or sodium-infused water at the ready. Each of his concoctions are custom-made for the player’s individual molecular needs. It gives team chemistry a whole new meaning.

“Players are looking for every legal advantage, every edge,” Head said. “That’s why the game has started to evolve. You can’t take steroids. They test ALL the time — I feel like that there are testers here every day.

“And that’s a good thing. You want the sport to be clean. But now the question is, ‘OK, how do I adjust and still play 162 games without getting hurt?'”

That explains why we are here, in this ghost town of a clubhouse bathroom, examining the blue paper cups stacked atop each of the five urinals.

“An area we’re really focused on is hydration. And one of the ways we check players’ hydration daily is through what’s called USG — a urine specific gravity machine,” Head explains.

The Giants value these readings so much that they’ve turned urination into a competition. To be eligible to win the coveted Hydration Domination contest, players must post their best scores before batting practice. The best hydrated player after each series wins an award shaped like a golden urinal. Think of it as the M-V-Pee trophy.

These tests are 100 percent voluntary. The Major League Baseball Players Association is explicit in its medical privacy guidelines regarding the results of such body monitoring. Not even Manager Bruce Bochy nor General Manager Bobby Evans are privy to the individual test results.

These hydration checks are akin to the ones that helped get former NFL coach Chip Kelly bounced out of Philadelphia a few years ago. Some Eagles players found them to be an invasion of privacy and just plain weird.

But the Giants players, led by some key veterans, embraced the testing in earnest last year, quietly launching a clubhouse revolution.

“Definitely,” catcher Buster Posey said. “Geoff has worked his tail off the last year or two in trying to find anything he can to give us an edge.

“Maybe it’s as simple as paying attention to guys weight and keeping enough calories in their system to help them maintain weight. Or maybe it’s different types of recovery. He’s constantly soaking up information and trying to figure out ways we can benefit.”

Hunter Pence, the outfielder and noted kale muncher, said: “It’s all very powerful information. It’s something that I’m tremendously grateful for.”

The Giants are one of a handful of major league teams to employ full-time sports science specialists, although that number keeps growing. In 2015, two teams had an official sports scientist. This year, the number is 11 — and likely higher than that, since some teams still keep their program a secret.

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Two years ago, the Giants put their program in the hands of Head, a former oft-injured defensive back at Northern Arizona University. He got his master’s degree in kinesiology and sports conditioning at A.T. Still University before working as a trainer at the acclaimed Fischer Institute facility in Scottsdale, Arizona.

The Giants brought him aboard to work in conjunction with head athletic trainer Dave Groeschner. Injuries are unavoidable, but together they take aim at some of the preventable pulls and strains that can clutter up a disabled list.

During this clubhouse tour last Sept. 16, it’s about 2:30 p.m. and there are still no players in sight. Players would usually be here by now, but Bochy, as a nod to toward the team’s widespread fatigue, canceled batting practice and issued mandatory late reporting times.

Later that night, looking energized, the Giants beat the Cardinals 8-2. Posey hit his first home run since July 16.

“I think that throughout the course of a season as long as ours — we play 162 games in 180 days — any way you can feel a little bit fresher or bounce back a little quicker is a huge, huge positive,” reliever George Kontos said.

As he walked around before the game, Head pointed to the iPads in every locker. He grabbed one belonging to a starting pitcher and started clicking away to demonstrate a new Giants ritual known as the “Daily Wellness Questionnaire.”

Using the iPad, a player can begin by tapping a photo of his avatar. Then he answers questions designed to give Head feedback on various aspects of recovery. An injured player, for example, can also click anywhere on a body graphic to open a window for typing in more details.

“So if a player has had a hamstring injury in the past, the player might touch his hamstring and say, ‘It’s like a 3,”’ Head says. “That area will light up and basically remind me that, ‘Hey, this player had an injury in that area in the past.'”

These iPad conversations, like the hydration tests, are voluntary and private. Head does not relay the information to Bochy, nor does he ever suggest to the manager that the player needs a day off.

The privacy allows players to be honest. That’s the key.

“We’re all in this together,” said reliever Hunter Strickland, who said he fills out the questionnaire every day. “You can obviously go in there and be dishonest about it and write, ‘Oh, excellent!’ every day. But that’s only hurting yourself and the team.”

# # #

Here in the Giants kitchen, team chefs Joe Day and Matt Shepard are whipping up pregame meals. The special of the day? Well, that depends on the latest readouts regarding vitamins and minerals from the sports science testing.

The chefs never get to see individual player data, but Head keeps them apprised of teamwide gaps. A day earlier, for example, tests revealed that a number of players were Vitamin B-12 deficient. So Day and Shepard spent this day adding crab, shrimp and clam chowder to the menu.

It’s a welcome challenge for the chefs, who embrace the nutrition revolution.

“In the past, it was even worse: Philly cheesesteak sandwiches, hot dogs, a sundae machine — it was like a 7-Eleven in here,” Day said. “Nobody had really any kind of a concept or effort to make everything clean. From then to now, it’s night and day.”

A look around cabinets and refrigerators reveals that this former convenience store is now more like a farmers market. There are pre-made kale juice packs, as well as bins full of ginger and turmeric, which have been shown to help reduce inflammation.

Besides the meals from the chefs, Head will whip up recovery shakes using only certified ingredients. The shakes are individualized based on testing: Posey gets a different shake than Pence, who gets a different one from Madison Bumgarner.

“I have a big spread sheet, and it looks like a football play list,” Head said. “Every day I go in and I make these drinks, and it’s based on this environment, the type of game, the intensity.”

# # #

Posey is grateful for the numbers. But just as with the back of his baseball card, the numbers don’t tell the whole story. Coming off a season in which he caught a career-high 123 games, the four-time All-Star said there are times when he doesn’t bother looking at the lab-rat readouts.

“I’ve had this conversation with Geoff: Regardless of what the machine tells me, I need to be ready to play every day,” Posey said. “And I don’t want to come in with the pre-notion that I’m sub-par or deficient in a certain area.

“So I’m a little bit cautious. It’s not like I can say, ‘Oh, I’m going to take the day off because I’m not in the green today.’ I don’t think fans would understand.”

Head understands, too. He said the goal of his program isn’t to have all the answers. It’s to have the odds forever in the Giants’ favor.

“Injuries are a part of baseball. It is a combat sport at high intensity, and injuries will happen, unfortunately,” he said. “We are not saying that our sports science program will stop all injuries from happening. But we are doing everything we can as a sports medicine department to help prevent the injuries that can be preventable.”

With that, Head had to end the interview. Players were starting to file in, already flush with excitement.