Novel Plyometrics

Written by Dr. Mel Siff

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. 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.

***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.