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Dr. Siff discusses ways of implementing plyometrics and common
mistakes
Drop jumps and various standing drills are so widely used as a means of plyometric training that we often seem to forget that they classically may be
done in many other ways, such as using the common children's swing that we all
used to play upon in public parks. With the latter, you simply arrange a swing
near a wall so that you can swing to different heights and strike the wall with your feet to provide the rebound. For those who have our textbook,
"Supertraining" (Siff & Verkhoshansky 1999), see p275 for diagrams
of this exercise.
In this way you do not have to buy a big supply of costly "plyo" boxes
- all that you need is some rope, wood and something to hang your swing from and
you have a very controllable plyometric training device. With a little
ingenuity, you can even arrange a wooden wall at hand height that will allow you
to shove off with the hands, as well. ("Supertraining" p275 for
diagrams.)
Of course, you can make these devices more sophisticated and technical so that
you can carry out accurate biomechanical measurements with them. For those who
have our textbook, "Supertraining", page 219, you will see a diagram
of a special plyometric bench that my senior engineering students constructed at
the University of the Witwatersrand (South Africa) in 1992. The same students
also constructed various upper and lower body swings with built in load cells or
force plates to measure the forces exerted during impact.
Quite recently I came across the following research article that carried out
much the same sort of work that my engineers had been doing. I think that many
of you will find the results interesting.
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Fowler NE, Lees A & Reilly T Changes in stature following plyometric
drop-jump and pendulum exercises. Ergonomics 1997 Dec; 40(12):1279-86
The aim of this study was to compare the changes in stature following the
performance of plyometric exercises using drop-jumps and a pendulum swing. Eight
male participants aged 21.7 +/- 1.8 years with experience of plyometric training
gave their informed consent to act as subjects. Participants undertook two
exercise regimens and a 15-min standing test in a random order. The exercises
entailed the performance of 50 drop-jumps from a height of 0.28m or 50 pendulum
rebounds (off a wall).
Participants were instructed to perform maximal jumps or rebounds using a
'bounce' style. Measurements of stature were performed after a 20-min period of
standing (pre-exercise), 2-min after exercise (post-exercise) and after a
20-min standing recovery (recovery). Back pain and muscle soreness were assessed
using an analogue-visual scale, at each of the above times and also 24 hours and
36 hours after the test. Peak torque during isokinetic knee extension at 1.04
rad per sec was measured immediately before and after the exercise bouts, to
assess the degree of muscular fatigue.
Ground/wall reaction force data were recorded using a Kistler force platform
mounted in the floor for drop-jumps and vertically on the rebound wall for
pendulum exercises. Drop-jumps resulted in the greatest change in stature (-2.71
mm), compared to pendulum exercises (-1.77 mm) and standing (-0.39mm). Both
exercise regimens resulted in a significant decrease in stature when compared to
the standing condition. Drop-jumps resulted in significantly greater peak impact
forces (p < 0.05) than pendulum exercises (drop-jumps = 3.2 x body weight,
pendulum = 2.6 x body weight).
The two exercise conditions both invoked a small degree of muscle soreness but
there were no significant differences between either. Both exercise regimens
resulted in a non-significant decrease in peak torque, indicating a similar
degree of muscular fatigue. Based on the lower in height and lower peak forces,
it can be concluded that pendulum exercises pose a lower injury potential to the
lower back than drop-jumps performed from a height of 28 cm.
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***What does this mean for the coach? Well, first of all, it stresses that there
is a very real place for use of the PLYOMETRIC SWING as a safe and effective
form of explosive training. Secondly, it shows that the *potential* for injury
is greater with drop jumps, because of the greater impact forces exerted on the
whole body.
However, it needs to be pointed out that the body can adapt to such stresses,
but this potential for injury is a good reason why any drop jumps should be
prescribed carefully and intelligently, especially among novices whose
musculoskeletal system has not adequately adapted to the impulsive loading.
Regarding the experiment, it should also be pointed out that, if 50 repetitions
are to be done, then it is essential that they be done in limited sets of a few
repetitions at a time, not like some sort of endurance exercise. In the USA many
coaches tend to prescribe far too many plyometric repetitions at a time. More is
not necessarily better. In the case of plyometrics, quality is definitely more
important than quantity.
Dr Mel C Siff
Denver, USA
mcsiff@a...
http://www.egroups.com/group/supertraining
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