Dr Mel Siff Blog

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<Any thoughts on this [squat jumps]? I would like some advice as I have a
friend who insists on doing this potentially harmful movement with heavy
weights to increase his “explosiveness”.>

*** You do not necessarily have to jump off the floor when doing “jump
squats”. You can try to produce as much vertical force as possible so that
you may rise high onto your toes without leaving the platform. Explosiveness
is not a quality which is best developed by producing large forces under very
heavy loading, but with less heavy weights which allow one to produce high
RFD (Rate of Force Development) and peak power. This means executing
stretch-shortening or prestretching exercises which have a short coupling Read more…

There are few sports which offer as many variations of upper and lower body
plyometric action as gymnastics, a fact that tends to be obscured by the
proliferation of texts on so-called plyometric drills like hopping, depth
jumping and ball throwing.

Gymnastics involves complex jumps, depth landings from certain apparatus,
depth jumps, plyometric rebounds, ballistic actions in three dimensions,
training of reaction time, short sprints, explosive trunk activities and Read more…

The latest issue of the Journal of Strength & Conditioning Research (Aug
2000, 295-301) contained the following article:

Rimmer E & Sleivert G ‘Effects of a Plyometrics Intervention Program on
Sprint Performance’

It compared the training effects of two different training programs on a
group of 32 male rugby and touch rugby players of average age 24 years. One
group trained with sprint training, while the other group performed
“sprint-specific plyometric exercises.” While the plyometrics group decreased
their ground contact time at 37m distance by 4.4%, the authors concluded that
a sprint specific plyometrics program can improve 40m sprint performance to
the same extent as standard sprint training, possibly by shortening ground
contact time.

The article also noted that the plyometrics intervention appears to have had
the greatest effect on sprint performance during the initial acceleration
stage. This findings concurs with what Young (Sprint bounding and the sprint
bound index Nat Strength Cond Assoc J 1992, 14: 18-21) suggested, namely
that bounding may be considered a specific exercise for the development of
acceleration because of the similar contact times of bounding and sprinting
during the initial acceleration phase.

The authors end the article by stating that coaches and participants should
“consider a plyometrics training program that incorporates sprint-specific
exercises as part of the overall training program.”

And that returns us to where we began! This is precisely the sort of
conclusion that Verkhoshansky and others reached when they did the pioneering
work of plyometric training about 40 years ago. They stressed the importance
of using plyometrics (actually, ’shock method’) as a part of the overall
training program integrated with other forms of strength training in a
suitable sequence of training ‘complexes’ (e.g. see Siff & Verhkoshansky
“Supertraining” 1999, Ch 5.3).

Dr Mel C Siff

The following appeared in a newsletter by Ian King, an Australian fitness
professional who often tours the world market
(http://www.kingsports.net/bs18-askthemaster.htm)

Someone asked him in his column which he calls “Ask the Master” :

JUMP WITHOUT PLANTARFLEXION

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<In the seminar you did near Boston you mentioned during jump training, to
jump without plantar flexing the feet. What is the purpose of that? . . .
. . . >

King’s reply was as follows:

<< The technique of actually dorsi flexing in the jump has a number of
purposes, including:

* decreasing ground contact time
* therefore increasing elastic energy utilization
* teaches focus on air time, not toe time
* greater specificity with the sprint technique I teach
* reduces hamstring flex in sprint leg cycle >>

—————————-

INTRODUCTORY COMMENTS

Issues such as the following immediately spring to mind:

1. If one really wishes to jump without plantarflexion, one has to begin
from a static start way back on the heels, with no contact whatsoever between
any other part of the foot and the ground. After you have read this, try it
for yourself and experience how one needs to balance on the tip of the heel
before one even attempts this drill. Any ground contact with other parts of
the sole besides the heel will elicit a reflex tendency to plantarflex the
ankle.

2. One needs to stress that there can be dorsiflexion of the toes, as well
as the ankle. The correct phasing of contributions from each is central to
all jumping and running efficiency.

3. In referring to elastic energy utilization, it is essential to identify
in which exact tissues the elastic energy storage and release is occurring.
Regarding increased utilisation of elastic energy processes in the all of the
soft tissues involved in jumping and running, it is essential to understand
the central role played by plantarflexion.

Anyway, no scientists have yet managed to determine how much of rebounding
efficiency is due to contributions from stored elastic energy and how much is
due to facilitation of stretch and related nervous processes. To claim that
any training method will increase elastic energy usage in isolation from
other mechanisms implies that one knows the answer to a problem that science
has not yet managed to resolve.

4. Once you left the ground, air time is unaffected by anything that your
driving leg can do. Long jumpers use specific running techniques in the air
before they land, but the ability to execute them depends on a very powerful
take-off facilitated by processes including ankle and toe plantarflexion.

5. Whatever exact meaning is attributed to the obscure phrase, “reduces
hamstring flex in sprint leg cycle”, it needs to be pointed out that the
hamstrings do not “flex”. Muscles contract and relax, while joints flex or
extend. The deflection of bones under the effect of strong transverse
loading might also be regarded as a form of flexion, but “hamstring flex” is
a new one to me.

Would anyone be interested in commenting further on the validity and accuracy
of these statements, regarding either the biomechanics or the practical
issues involved?

Dr Mel C Siff
Denver, USA

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.

—————————————-

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 0.28
m 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