Plyometric exercises use explosive movements to create muscular power, which is the time it takes to convert strength into speed. Hopping, bounding and jumping are plyometric exercises. Even jumping rope.

Done correctly, they can improve coordination, agility and performance.

"Plyometrics much of the time are referred to as jumping exercises," said personal trainer Brad Krzykowski, owner of Beyond Fitness Hawaii. "They have to do with a stretch in the muscle followed by a forceful contraction. The pre-stretch enables a person to get a stronger contraction, such as jumping off a step onto the ground and immediately jumping after landing."

Krzykowski has a client who sometimes jumps up stairs on one leg — and sometimes sideways.

Such jumps are considered advanced exercises, he said. A more basic but still very useful drill involves jumping side to side over a line with both feet. A variation: forward and backward over the same line. And still another variation: Jump back and forth in either direction but over a cone instead of a line.

Plyometrics are high-intensity training and not for everyone. They should be used by well-conditioned athletes with good leg strength. Wear good footwear and try to land softly, on your toes. Use cushioned surfaces.

A good warm-up and stretch are essential to preventing injury during plyometrics, Krzykowski said. "You need to make sure your body has transitioned into exercise, lubricated the joints, got your body heat up and your heart rate up."

Krzykowski recommends two sessions a week.

Reach Mike Gordon at mgordon@honoluluadvertiser.com.