COSTA MESA, Calif. — Brad Davidson teaches people how to get strong by bringing some of his childhood experiences on an Oregon dairy farm to his gym on in Costa Mesa, Calif.

Milking cows and carrying 50-pound sacks of powdered milk, as well as watching his grandfather and uncles perform grueling tasks every day, inspired a lifelong passion for studying the science of strength. His conclusion: The most effective techniques were invented between the end of the Civil War and the 1930s, many of them in Eastern Europe. Some of the exercises he uses in the parking lot of his gym, Synergy Training Centers, are borrowed straight from the farm, or a 19th-century logging camp: Clients tip over 475-pound tractor tires, swing sledgehammers or use a thick rope to pull slabs of weights stacked on a sled that grinds against the asphalt.

“We call it Country Strong or Farm Strong,” Davidson said. “That’s real-world strength.”

“You can’t beat what works,” he added. “Nothing great has been invented the last 70, 80 years. There’s been no new ideas. Just the same old ideas renamed or repackaged.”

Davidson, 34, who played football at Golden West College in Huntington Beach, Calif., and took a shot at making the U.S. Olympic bobsled team four years ago, is 5-foot-10 and 180 pounds. He pulls half a dozen books from his bookshelf in his office. They’re all thin and mostly old and obscure, loaded with black and white photos featuring barrel-chested men in too-tight shorts, hoisting massive weights straight out of a cartoon — matching cannonballs with a bar in between.

Their trailblazer is Arthur Saxon, the handlebar-mustachioed German billed as the world’s strongest man in the early 20th century. He is said to have been able to raise a plank carrying 12 men. And he once lifted a 315-pound barbell over his head, with one hand, and tossed it to the other hand.

“Look at this guy,” Davidson said, pointing to Saxon’s bulging biceps. “Every man wants to look like him, and every woman wants a man to look like him. He was unbelievably strong. No steroids, no supplements, just ate well and used training protocols. It’s just insane. He makes us look like a bunch of pansies these days.”

In his 1906 book “The Development of Physical Power,” Saxon wrote that “the usual idea about strength — I mean the idea of the average reader of health magazines — is generally a wrong one. Genuine strength should include not only momentary strength, as proved by the ability to lift a heavy weight once, but also the far more valuable kind of strength known as strength for endurance.”

Much of what Saxon and others preached has been vetted, tested and expanded on by research and by modern-day experts like Canadian Charles Poliquin, who has coached Olympic and professional athletes and is a mentor of Davidson’s. To get stronger without getting bigger, Davidson said, reduce repetitions, increase the weight and keep the “time under tension” below 20 seconds. “You have to be using 70 percent of your 1RM (one-rep maximum) or heavier to get a strength response.” He said deep squats (bending the knees so that the rear touches the heels) has proved far more effective at building strength and preventing injuries to lower legs than just going parallel.

While a quarter of Davidson’s clients are elite athletes, the rest are regular people who want to get stronger to live better lives — to be able to pick up their children or grandchildren without pain or make it through a workday without tiring out. Davidson does intensive assessment early on and develops workouts to suit whatever they want to achieve.

Saxon wrote that bicyclists should be able to “jump on your machine and ride 100 miles at any time without undue fatigue.” But in the real world, a “businessman” should be able to work “morning, afternoon and night with unflagging energy, holding tightly in his grasp the reins of business, retaining all the while a clear mind and untiring energy, both of body and brain.”

That notion appeals to Bert Selva, CEO of Shea Homes, the nation’s largest privately owned homebuilder. Selva, 48, who lives in Newport Beach, Calif., had back problems for years because of herniated discs. He has worked with Davidson for about five years and said “I’ve never felt better.”

“I run a big company, so I’ve got to have energy all day,” he said. “Now I don’t really feel a lapse in energy.”

Another Newport Beach client, Brian Barss, just likes the challenge of the farm gear out back. “I love taking a beating, so this is a good workout for me,” said Barss, 31. “It’s not for the meager or the timid, that’s for sure.”

Davidson said one reason for his obsessive emphasis on strength training is that his father, Mike, who is 54, has myotonic dystrophy, a disease that slowly attacks the muscles.

“He’s wasting away, and he falls multiple times a week,” Brad said. “If he gets in a car wreck, he’s not going to be able to prevent bones from breaking. He gets sick a lot. You and I, we get bronchitis, we get antibiotics and it’s gone in a week. He’s had it for three weeks and can’t get rid of it.

“So strength matters. The more muscle mass you have, the greater your chance to live long.”