He has been leading boot-camp workouts since 2001. On Mondays, Wednesdays, and Fridays, he conducts the classes outdoors in Washington Square at 6 a.m., noon, 5 p.m., and 6 p.m. On Tuesdays, Thursdays, and Saturdays, the workouts take place at his indoor studio.
Griffin grew up in West Philadelphia and attended University City High. Although he's built like a football player, he ran track and did gymnastics. Today, at 5-foot-10 and 210 pounds, he's as solid as a concrete bridge abutment.
Griffin prides himself on offering an authentic boot-camp workout. "Too many boot-camp workouts don't conform to the boot-camp ethos, which is military fitness," he says. "That's what I guarantee."
The essence of the workout is Ranger-style endurance training (up to two miles of running during a typical one-hour session), and plenty of high-intensity calisthenics for strength and flexibility. He varies the workouts constantly, but always with a specific objective.
At the end of each monthly training cycle, Griffin gives a fitness test to measure progress, and he has taken some classes to the obstacle course at Fort Dix, nicknamed "The Beast of the East."
Another feature of Griffin's approach is keeping the classes small, usually no more than six clients. This lets him monitor each participant and tailor the exercises to those with needs or injuries. He calls it "personal training in a group setting."
"I love teaching and seeing people improve," Griffin says. "Some instructors teach classes with a 'puke factor.' That's OK if you have an emergency medical technician on hand and are equipped with a defibrillator."
Griffin also doesn't believe in "no pain, no gain."
"Pain signals the body's breakdown, either from lactic-acid buildup or serious injury," Griffin says. "I want people to hustle and work hard, but I won't sacrifice safety, and I won't push them past the breaking point."
Griffin, who has a congenial personality, does not bark orders or "chew people out." His criticisms are positive, constructive, and delivered softly. I actually heard him say to one female client, "Yes, that's it, dear. Outstanding!"
The other day, I watched Griffin lead a noon workout with his assistant instructor, Kalika Fail, 33, who is also a professional dancer.
"Fall in!" Griffin commanded as he began. On the back of his black shirt were the words: "Success Always! Hooah!!"
The first exercise involved running in place, lifting the knees high, then dropping to a push-up position.
"Go! Drop! Recover!" Griffin ordered.
Then he sent the class on a two-lap run of a quadrant of the square, about a half mile.
More exercises followed: Alternate arm raises from a push-up position, slow push-ups to increase strength, flying jackknifes, rower sit-ups, jumps-squats-and-drops (a.k.a., squat thrusts), bridges, and planks.
Interspersed were more runs of varying lengths. Griffin called this noon class his "elite performers." By and large, everyone was able to keep up, and afterward all were glistening with sweat in the midday sun.
"The group setting helps with motivation," said Mike Kennedy, 44, an editorial manager who has been taking the class for five years, during which he quit smoking and lost 30 pounds. "I've gone 180 degrees. I'm now running endurance races."
Ann-Marie Lewis, 53, a native of Trinidad who lives in Camden, has gained strength, flexibility and shed 23 pounds. "He makes sure you do the exercises with good form," she said appreciatively.
Mike Klinger, 31, a graphic arts designer from Clifton Heights, prefers Griffin's classes to going to the gym because "I don't have to figure out what to do. I know he'll tell us what to do, and it will be challenging and beneficial.
"My weight has dropped from 250 to 220, and I have more strength and sleep better."
To contact Sgt. Nate, go to www.sgtnate.com or call 484-410-8007.
"Well Being" appears every other week, alternating with Sandy Bauers' "GreenSpace" column. Contact Art Carey at email@example.com. Read his recent columns at www.philly.com/wellbeing.