OK, so maybe these high-impact exercises won't give you the ability to leap tall buildings in a single bound or run faster than a speeding bullet.
Yet athletes who incorporate them into their workouts say they can bring out athletic powers they didn't know they had, including adding an inch or more to vertical leaps.
But don't start sewing a big red "S" on your T-shirt just yet. This is not the latest fitness fad that any weekend in-line skater or morning jogger can leap into without risk of serious injury.
Plyometrics training is also called "shock training" because of the stresses it can place on the feet, legs, hips, and arms ? especially if done improperly. Some trainers say that only top-conditioned athletes should even attempt it.
"I would never do plyometrics with a client who has any kind of joint injuries," said Eileen Tessalone, group fitness coordinator and personal trainer at Gold's Gym in Paramus. "The impact is too great, there's too much compression on the spinal column and the hips."
Yet Tessalone does incorporate plyometrics at modified levels into her regular fitness classes, and doesn't believe it's only for athletes.
The exercises, she said, can help fitness programs mirror daily activities.
"Plyometrics can mimic something that happens in everyday situations," she said. Running after the kids, bending down quickly to pick up a dropped object, or running up the stairs all involve start-stop motions that can be mirrored with plyometrics, she said.
"You're asked to move and stop quickly, for the muscle to activate quickly and decelerate on a dime," Tessalone said.
Health club owner Pete Kremer also uses plyometrics with non-athletes.
"I like to include some of it with my clients. It's a change of pace and an excellent way to develop power," he said.
"I'll have somebody sit down and I'll toss a medicine ball over their head," Kremer said, describing a plyometric exercise. "As they catch the ball, they'll move their arms back with the ball and throw it back as fast as they can. The tricep muscle gets a stretch, it recoils like a spring."
It's the rapid muscle stretch and contraction that makes the exercise plyometric.
Kremer said that he uses plyometrics only with his more seasoned clients.
"You have to ease into it," he said. "It's ballistic, and it can be dangerous. You have to be conditioned to do it."
Even those who are in shape for plyometrics can do them only once or twice a week.
"If you over train, you put too much stress on the body," Kremer said. "There are cases of even elite athletes injuring themselves because of overwork."
Roy Hinchman, the strength and conditioning coach at Montclair State University, says athletes must be able to squat 1 1/2 times their body weight before he'll start them on plyometrics. He says the same rule can apply to non-athletes.
"Most plyometric work is done with the lower body," Hinchman said, explaining why the squat is a good indicator of whether a person is ready for plyometrics. People who can perform squats correctly can handle balance and stabilize their torso, he said.
Jumping is the exercise most often associated with plyometrics, but any movement that involves bounding up or down or on and off an object involves plyometrics, Tessalone said.
The routines aim to utilize all of the energy stored in the contraction to make the leap higher, the pivot faster, the swing stronger.
Kirk Vickers, trainer and owner of Triad Health & Fitness Corp in the Detroit area, explained plyometrics this way: "Take a rubber ball and drop it on the floor," Vickers said. "It flattens as it hits, but the energy springs it right back up."
With technically sound and mechanically correct form, the human body can react the same way, he said. It relies on an element of physiology called the stretch-shorten cycle, in which the muscle is rapidly stretched, then contracted, increasing the force applied on that muscle.
For athletes, plyometrics is an excellent component of an overall workout that can add speed, agility, and power to their game, whatever that game might be.
Rich Mejias, a 23-year-old soccer player and personal trainer at Gold's Gym in Paramus, uses plyometrics during 20-minute non-stop workouts that involve activities such as hopping on one foot, long jumps, and skipping.
"It's a complete lower body workout," said Mejias, who hopes to play one day for the MetroStars.
Plyometric activities for athletes are usually sport-specific. For example, a basketball player might bind up from a set position onto a bench and land on one leg, mimicking a layup. The player might also jump off the bench while throwing a medicine ball in the same motion. This imitates the act of grabbing a rebound and making a pass.
At Passaic High School, sprinters, hurdlers, and jumpers train before the season using plyometric activities that include jumping on, off, and between boxes and over hurdles.
"You think you can jump until you do this," said track coach Anthony Barbato, a firm believer in plyometrics.
"We'll have three boxes, 18, 24, and 36 inches," Barbato said. "You jump from box to box. The idea is not to land and stay there, but to jump from box to box to box continuously."
Barbato says plyometrics isn't used once the season begins because it's too draining on the athletes' bodies.
Passaic High senior Shanae Pritchett, 17, says plyometrics has helped her in the long jump, allowing her to practice technique while strengthening her muscles. "It makes you feel more confident," she said.
"You feel stronger."
Sarina Hunter, a 15-year-old sophomore hurdler, triple-jumper, and cross-country runner, agrees.
"It helps my legs get stronger when it comes to jumping," Hunter said. The exercises have helped improve her long-jump distance by 5 feet and her 400-meter hurdles time by 19 seconds.
Vickers said that although he can't guarantee people won't get injured during plyometrics training, it does help prevent game injuries.
"I've had parents of young athletes come back to me after their kids have gone off to college to tell me they are no longer plagued by nagging injuries," he said.
Once considered the secret Soviet training method, plyometrics caught the world's attention in the mid-1960s after successes with Russian and Eastern European track and field athletes.
However, the concept is believed to have been around much longer, perhaps starting with ancient Greeks. The word "plyometrics" is thought to be a derivation of the Greek words "pleythyein" and "metric," meaning to increase and measure, respectively.
During the 1972 Olympics, Russian sprinter Valeri Borzov brought it back into vogue when he credited plyometrics training to his winning a gold medal in the 100-meter event in 10 seconds. Six years earlier, his 100-meter times had hovered around 13 seconds, which did not indicate world-class potential.
Again, in the 1976 Olympic Games, after Dwight Stones won a gold medal in the high jump, his coach said plyometrics was a major factor.
Vickers said it was during that time some high school and professional trainers started using plyometrics techniques, but then they moved on to other methods.
During the first part of the 1990s, plyometrics resurfaced, becoming a buzzword in gyms and the subject of many health and fitness articles, which called it a controversial and sometimes dangerous form of exercise.
"It's gotten a bad rap, and there's been a move away from high-impact workouts, but in some situations it's desirable," Tessalone said.
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