Plyometrics.....What are they?

Speed and strength are without a doubt integral to any form of athlete from weight lifter to endurance, all require some form of power.  Over the years, coaches and trainers alike have sought for methods to improve speed and strength thus enhancing performance.

But what are plyometrics?

The definition of a plyometric exercise is: a movement which reaches maximal strength in the shortest amount of time possible. (Chu, 1998) But lets break this down further...

Skipping, hopping, jumping and bounding have all been been used in exercise for many years. In the early 60's it was noted that Russia and the Soviets used new training techniques with their Olympic Athletes, leading to their domination of certain Athletic events throughout this era. The Russians training consisted of foot speed skills, jumps, stretching and weight training which when combined resulted in increased speed. This is essentially the start of Plyometrics.

Today, the goal of Plyometric training is to enhance speed, power and explosive reaction of an individual through rapid, eccentric muscular contractions. This is accomplished by using a number of various techniques which we will discuss later.

Until recently, plyometrics have only been utilised at professional, Olympic and Collegiate level but it is becoming more and more popular in schools and amateur associations as speed and power are becoming increasingly more important at any level of sport.

Mechanics and Physiology of Plyometrics

To effectively use plyometrics as part of a training programme it is important to understand the mechanics and physiology of the exercise, this can be simply split up into; the mechanical model, neurophysiological model and the stretch-shortening cycle.

The mechanical model of plyometric training suggests that the elastic energy stored in muscles and tendons is increased with a rapid stretch like that of an eccentric muscle contraction, then stored for a short amount of time (Bosco et al 1982; Asmussen & Bonde-Peterson 1974.) Should a concentric muscle action follow immediately after, this stored energy is released providing a contribution to total force production. 
Mechanical model (Baechle & Earle)

SEC - The series elastic component stores elastic energy when stretched which then increases the force produced (Wilkie 1956; Hill 1970)
CC - The contractile component (i.e actin, myosin and cross-bridges) is the primary source of muscle force during concentric muscle contraction (Close 1972)
PEC - parallel elastic component (i.e epimysium, permysium and sarcolemma) exerts passive force with unstimulated muscle stretch. (Hill 1950)

Neurophysiological Model of Plyometric Exercise

This model involves potentiation (the change in force-velocity characteristics of a muscle, caused by stretch.) (Bliss & Collingridge, 1993) When a rapid stretch is detected, an involuntary, protective, response occurs to prevent over-stretching, this is known as the stretch reflex.
Stretch Reflex

(Wilk et al 1993)

When muscle spindles are stimulated due to the stretching of muscles, the stretch reflex is stimulated, sending input to the spinal cord via Type Ia nerve fibers.

After synapsing with the alpha motor neurons in the spinal cord, impulses travel to the agonist extrafusal fibers, causing an increase in the amount of muscle activity, allowing the muscle to act much more forcefully on the concentric phase producing a reflexive muscle action. (Guyton and Hall 1995; Bosco et al 1981; Bosco et al 1982)

Stretch-Shortening Cycle

The stretch-Shortening cycle (SSC) employs both the energy storage of the series elastic component and the stimulation of the stretch reflex to facilitate maximal increase in muscle power output over a minimal amount of time.

When a muscle is stretched (eccentric contraction) only some of the energy is stored in the elastic components of the muscle, as much of the energy is lost as heat. The energy stored is lost if the eccentric contraction (shortening of the muscle) does not follow the concentric contraction immediately. To express as great a force as possible, the muscle must contract in as short a time as possible. This process is called the stretch - shortening cycle. Reducing the time taken to complete this cycle can lead to increases of speed, strength and power.

The stretch-Shortening cycle consists of three phases: (Wilk et al, 2002)
• The eccentric phase - The rapid lengthening of the muscle.
• The amortization phase - A brief resting period.
• The concentric phase - An explosive muscle shortening movement

The stretch-shortening cycle combines mechanical and neurophysiological mechanisms and provides the underpinning basis of plyometric exercise. (Fleck 2004)

Plyometric Training Techniques

Plyometric training can be used across the whole body and there are a number of different techniques available.

Lower Body Plyometrics

For the majority of sports or athletic events, speed and power from the legs are essential in making lower body plyometrics appropriate for virtually any athlete or performer. Whilst direction of movement varies by sport, many sports require athletes to produce some form of maximal effort, be it vertical or lateral movement in a short amount of time. There are a wide variety of lower body drills with varying levels of intensity and direction of movement.

Lower body plyometric drills include:

• Bounds
• Standing jumps
• Box drills
• Depth jump
• Jumps in place

All of these have their advantages but we will take a more in depth look at jumps in place.

Jumping in place drills involve jumping and landing in the same spot. The emphasis is on the vertical component of jumping and are performed repeatedly with no rest between jumps keeping ground contact time as low as possible. The time between jumps is the stretch-shortening cycle's amortisation phase. Examples of jumps in place include the squat jump and tuck jump.

Tuck Jump

There are a number of key positions and phases when performing jumps in place such as a tuck jump:

1. Stand with feet shoulder-width apart, knees slightly flexed, with arms with elbows flexed at 90 degrees to the waist.

2. Flex knees further into a half squat

3. Jump straight up in the air bringing knees up to the chest.

4. Return to a soft landing, landing on balls of feet and repeat immediately.

5. Reduce ground contact time by landing soft on feet, flexing knees slightly and springing into air.

Upper Body Plyometrics

Whilst Upper body Plyometrics are less commonly practised than Lower Body Plyometrics they are still a very effective training technique, paticularly for sports requiring explosive upper body power. Racket sports such as tennis, badminton and squash,throwing events in athletics  as well as a number of invasion games including; basketball, rugby, and football can all benefit from upper body plyometrics.

Upper body plyometric drills usually involve the use of a medicine ball. Drills include:
• over head throws
• side throws
• over back throws
• slams
• explosive start throws
• squat throws

Some also consider Plyometric push ups as a drill but it has been argued that the ground contact time taken when performing plyometric push ups is too long to be considered plyometric. As a result we will look at one of the throwing and catching medicing ball drills in further detail.

Side throws

1. Stand facing a wall or partner, throwing distance away with feet shoulder width apart; place left foot forward.

2. Hold medicine ball with both hands, with arms slightly flexed.

3. Swing the ball over to the right hip/chesy before forcefully throwing ball forward to a partner or wall by extending the right arm and shoulder forward. Inhale to draw stomach in, maximising usage of muscle.

4. Catch the ball on the bounce from your partner or wall, recoiling the ball to the right of the body and repeat immediately.


Trunk Plyometrics

A strong core is essential in all sports or athletic events. A strong core provides solid balance and stability to the body. This allows for the transfer energy to perform powerful movements. As power is generated from the core outwards, the greater the stability of the core, the more powerfully muscles can contract. A solid core not only helps generate force and power for sport but improves posture, reducing strain on the spine and helping reduce the likelihood of injury. For any performer or athlete seeking to improve explosive speed and power, a strong core training regime is essential.

Exercises for the trunk can be performed plyometrically, but modifications must be made to make the exercises shorter and quicker, ensuring stimulation of the stretch reflex. Many plyometric trunk exercises utilize only the performers body weight (known as Body weight exercises) whilst others again make good use of weighted objects such as a medicine ball.

Examples of trunk plyometric drills include:

• Trunk rotations
• Side-lying leg lifts
• Sitting toe touch
• Pullover crunches
• Alternative to touches
• Sit up toss

Again all of these have their advantages but lets delve deeper into the sit up toss.

 Sit-up Toss

Figure 1 shows the un-adapted version of a sit-up toss, this movement has a large range of motion and the time needed to complete the exercise negate the abdominal stretch reflex.

Figure 1. Un-adapted Sit-up toss

Figure 2 however, shows the adapted version of a sit-up toss, it now has a relatively small range of motion allowing quick movement which increases abdominal muscle activity through use of the stretch reflex.

Figure 2. Adapted Sit-up toss

1. Sit about 2-3 feet away from a partner with feet planted and knees flexed at a 90 degree angle.

2. Extend arms towards partner allowing for slight flexion at the elbow, waiting to receive the medicine ball from a partner.

3. When the ball is thrown, catch the ball flexing elbows and bringing the ball into the chest, rocking back slightly. (Do not allow yourself to fall into a full sit up)

4. Sit up, extending the arms to powerfully chest pass the ball back to a partner, before repeating as quickly as possible.

Programme Guidelines and Exercise Prescription

When developing a programme for any athlete or performer whether they are a complete novice or a seasoned pro, there are a number of things to assess:

1. Intensity - This relates to the amount of stress placed on muscles, connective tissues, and joints. As a general rule, as intensity increases, volume decreases.
2. Frequency - The typical recovery guidline for prescribing plyometrics is 48 to 72 hours, if following this guidline, the recommended training guideline would be between 2 and 4 plyometric sessions per week.
3. Recovery - Drills should be considered as a form of power training rather than cardio conditioning and so sufficient rest should be granted between sets. The time between sets is determined by varied work-to-rest ratio (i.e 1:5 or 1:10), this is specific to the type and volume of the drill being performed and if training on consecutive days, different muscle groups should be targeted.
4. Volume - In lower body plyometrics, volume is expressed as 'contacts per workout' (the number of times feet are in contact with the floor per set). In upper body plyometrics, volume is shown as catches per work out. Again, volume relates closely to intensity, decreasing as intensity increases.

5. Programme Length - The majority of programmes tend to last between 6 and 10 weeks, with improvements in explosive techniques such as max vertical height notable as quickly as 4 weeks in.
6. Progression & Regression - Plyometrics is a form of resistance training and so the principles of progressive overload must be followed. Volume, Intensity, Overtraining and Periodization must all be altered throughout the programme to ensure maximal gains. Should the technique be flawed when progressed or an athlete pick up an injury, it is important to be able to regress back a stage or two as technique is the most important part of plyometrics.
7. Health and safety

• Warm up & Cool downs - As plyometrics involves rapid stretching of muscles, warm ups and cool downs are essential in preventing injury. The warm up should consist of general stretching followed by low intensity dynamic movements comprising of lunges, marching, skipping and jogging. The cool down should consist of roughly 5 minutes of general stretches.
• Age consideration - Physical and emotional maturity should be taken into account, gradually progressing from simple to more complex plyometrics, ensuring enough rest days to avoid injury or burn out
• Equipment - The correct footwear must be warn to preven stress injuries to bones and injuries to joints. If jumping from boxes it is also important to make sure boxes are secured correctly.

So there we have it, Plyometrics in 2000 words....If you have any questions feel free to comment.

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