2010年8月7日土曜日

ジャンプ・トレーニング

The power of
plyometrics
Michele Borboa, MS




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Plyometrics, also known as jump training, are fast, powerful movements often used by athletes to jump higher, run faster, throw farther, or hit harder, depending on the sport. You don't, however, need to be an athlete to benefit from these explosive moves. Incorporated into your weekly workouts, plyometrics are an efficient way to shred calories and boost your fitness. Continuing education coordinator for the American Council on Exercise (ACE), Jessica Matthews explains the effectiveness and execution of plyometrics and shares a plyometric workout to help you get the jump on improving your fitness.
Fitness benefits of plyometrics
According to Matthews, controlled impact and maximum power are the aims of plyometrics, which include jumps, bounds and other explosive movements. “Also known as jump training, plyometrics involve stretching the muscles prior to contracting them,” the fitness expert explains. “This type of training, when used safely and effectively, strengthens muscles, increases vertical jump and decreases impact forces on the joints.” Research suggests that plyometrics may also increase bone density in younger participants.

Though often part of the training protocols for athletes, plyometrics can add an element of fun while increasing the challenge and efficacy for any fitness enthusiast. Matthews says, “Plyometrics mimic the motions used in sports such as skiing, tennis and basketball. If you enjoy dodging moguls, chasing down ground strokes or charging the net, plyometrics might be an appropriate training option as these exercises are designed to increase muscular power and explosiveness.” Incorporating plyometrics into your workout program can also help you improve your cardiovascular fitness and burn calories.

These advanced explosive moves aren’t for everyone, however. Matthews warns that plyometrics are not appropriate for people who are in poor condition or have orthopedic limitations. If you haven’t worked out in a while, have joint problems or muscle strains, wait until you are on top of fitness game before including plyometrics in your fitness regimen.

Why do plyometrics boost fitness?
Plyometrics became a proven training protocol of choice for the Eastern Europeans in the 1970s to develop greater strength and power in their Olympic athletes. “They based their programs on scientific evidence that stretching muscles prior to contracting them recruits the ‘myotactic’ or stretch reflex of muscle to enhance the power of contraction,” explains Matthews. “This pre-stretching of muscles occurs when you perform jumps one after the other. For example, when you land from a jump, the quadriceps muscles at the front of your thigh stretch as your knee bends, and then quickly contract with the next leap. This pre-stretch enhances the power of the second jump.”

Proceed with caution
According to Matthews, plyometric training has received its share of criticism due to reported cases of injury following ''plyometric'' programs of depth jumping and drop jumping, which involve jumping up to, and down from, boxes or benches that are as high as 42 inches.

“The forces sustained from these types of jumps onto hard surfaces can be as much as seven times one's own body weight. However, carefully considering the type of jumps selected for the program, enlisting a coach or trainer for supervision, and gradually increasing to more difficult exercises can make a plyometric program both safe and effective.”

Matthews recommends: Jumps should always begin from ground level, off and onto padded surfaces such as grass or a gym mat over a wood gym floor. These types of jumps are both safe and easy to perform. Other training techniques include jumping over cones or foam barriers, and traveling bounding.

“One study found that participants in a well-designed program of stretching, plyometric training and weight training reduced their landing forces from a jump by 20 percent, and increased their hamstrings strength by 44 percent,” adds Matthews. “Both of these factors contribute to reducing an individual's potential risk of injury.”

Incorporate plyometrics wisely
If you are unfamiliar with plyometrics, Matthews suggests that you talk to a sports medicine physician or physical therapist to make sure this training technique is suitable for you. These experts may even help you get started, or recommend a fitness professional who can. She cautions, “But, if improving athletic performance is not a high priority, the additional risk associated with this activity may not be worth the potential benefits.”

“You will have a more rewarding training experience if you follow the recommendations outlined below. Please use only simple ground level jumps from soft surfaces, and train under proper supervision,” suggests Matthews. “Plyometric training can be a smart addition to a healthy individual's training program as long as it is used wisely.”

Plyometrics is about quality, not quantity
According to Matthews, a safe and effective plyometric program stresses quality, not quantity of jumps, as well as safe landing techniques. “Safe landing techniques, such as landing from toe to heel from a vertical jump, and using the entire foot as a rocker to dissipate landing forces over a greater surface area, are important to reduce impact forces.”

In addition, you can promote low-impact landings by using visualization cues, such as picturing yourself landing ''light as a feather'' and ''recoiling like a spring''.

Matthews also recommends that when landing, avoid excessive side-to-side motion at the knee. Landing forces can be absorbed through the knee musculature (quadriceps, hamstrings, gastrocnemius or calf muscle) more effectively when the knee is bending primarily in only one plane of motion.



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