Plyometric training: how jump training can help athletes improve their performance in any sport

In many sports, good jumping ability is a prerequisite for superior performance. With that in mind, John Shepherd looks at the theory and practice of improving your jumping ability.

How far or high you can jump from a standing position two-footed position is often used as part of an assessment of sporting prowess (see table 1 – standing long jump standards). However, although you might think that standing jumps require nothing more than a swing of the arms and lots of power, technical ability plays a large role; for example, coaching can add as much as 10cm to a standing long jump in just one session.Table: Standards for standing long jump ability

% Rank	Females	Males
91-100	2.94 - 3.15 metres	3.40 - 3.75 metres
81 - 90	2.80 - 2.93 metres	3.10 - 3.39 metres
71 - 80	2.65 - 2.79 metres	2.95 - 3.09 metres
61 - 70	2.50 - 2.64 metres	2.80 - 2.94 metres
51 - 60	2.35 - 2.49 metres	2.65 - 2.79 metres
41 - 50	2.20 - 2.34 metres	2.50 - 2.64 metres
31 - 40	2.05 - 2.19 metres	2.35 - 2.49 metres
21 - 30	1.90 - 2.04 metres	2.20 - 2.34 metres
11 - 20	1.75 - 1.89 metres	2.05 - 2.19 metres
1 - 10	1.60 - 1.74 metres	1.90 - 2.04 metres

Source: D.A. Chu; ‘Explosive Power and Strength’; Human Kinetics; 1996

Studies have shown that jumping distance is a function of take off angle and speed; the best angle for maximum distance is around 19-27 degrees1. Any higher and forward momentum (and therefore distance covered) suffers. There also evidence that the arms play a major role in jumping, especially when taking off from one leg. A US study used computer modeling to show that when arm movements were restricted, average long jump speed was reduced by 15% and distance covered by 40cms compared to an ‘arms-free’ jump2. Meanwhile, a UK study on vertical velocities attained during high jumping showed that the arms have an even greater impact on performance than the free (non-jumping) leg3. This occurs because the arms can be driven downwards during take off, creating an upwards motion (Newton’s law of action and reaction), whereas the non-jumping leg cannot really exert any meaningful force once the jumping leg is ‘grounded’.

Role of the foot

The way the foot contacts the ground during a jump also affects the forces generated. A study on plyometric depth jump drills showed that jumps onto the balls of the feet generated 1.4 times more peak force during the subsequent spring upwards (and less than a third of the peak landing force) than jumps using flat feet4. More generally, the precise nature of any jumping exercise should closely mirror the demands of the sport for which the athlete is training. Sprinters for example should train using single leg forefoot-landing depth jumps because this most closely replicates the sprinting action. These jumping drills should also try to replicate the arm action (for reasons given above); high jumpers for example should try and use a double shift arm action during the single leg landing drills in order to mimic their actual event.

Leg muscle ‘stiffness’

Throw a hard rubber ball at a wall and it will bounce right back at you. Try the same thing with plasticine, and it will not rebound but drop straight to the ground. That’s because plasticine has no stiffness – it yields under force and absorbs all the energy in the process. To be a good jumper, you need muscles that are stiff enough not to yield, but to store energy and then return it during lift off, just like a rubber ball. A German study on athletic jumping performance collected data on optimum ‘leg stiffness’ for jumping5. The researchers concluded that there’s a minimum level of muscular stiffness require for effective jumping, but that increasing stiffness beyond that point did not lead to further gains in jumping ability.

As a rule of thumb, the faster the plyometric drill, the less time the foot is in contact with the ground. But coaches and athletes need to be aware that some jumping movements require more ground/foot contact time than others. For example, the optimum foot contact time in long jumping is significantly lower than in high jumping. If a high jumper tried to replicate foot long jumping contact times, performance would suffer because there’d be insufficient time to generate vertical lift. When performing plyometric drills to increase leg stiffness therefore, the drills also should aim to replicate the optimum foot contact times of the sport in question.

Putting it all together

How can athletes seeking to improve jumping ability best utilise the above information? Here is a summary:
•    Plyometric training should closely replicate the movement patterns and speed of the sport in question, and athletes should also ensure they’re fresh and rested before performing these drills;
•    Exercise drills should be performed on the same surface type as the sport; eg a field sport player should do drills on turf;
•    Some athletes may need extra practice to perfect the associated skills required in jumping such as coordination of arm movements, foot contact type when landing etc.;
•    Sportsmen and women who need to perform jumps when already fatigued (eg football and rugby players towards the end of a match) should perform some jump training under conditions of fatigue in order to help replicate match conditions;
•    Combining weights and plyometrics in a single session may be useful as research indicates that these methods are synergistic when it comes to building muscular power.

REFERENCES

1    J Sports Med Phys Fitness 1999 Dec;39(4):285-93
2    J Electromyogr Kinesiol 2001 Oct;11(5):365-72
3    Ergonomics 2000 Oct;43 (10):1622-36
4    Med Sci Sports Exerc, 1999 May; 31 (5) 708-16
5    J Biomech 1999 Dec;32(12):1259-67
6)    Dintimen G - Sports Speed (third edition) Human Kinetics 2002


Original article by John Shepherd; summary by Andrew Hamilton BSc Hons MRSC ACSM