• Plyometrics

• Definition

• Activities that enable a muscle to reach maximal force in the shortest possible time.

– Incorporates a pre-stretch or countermovement to elicit a quick, powerful response

• Models of Plyometrics

• Mechanical Model

– Based upon the elastic property of musculoskeletal tissue

• When muscle put on stretch, it contributes stored elastic energy to subsequent muscle contraction

– The series elastic component (SEC) is primary factor made up mostly of the tendon

– If concentric contraction does not occur immediately after muscle stretch, the stored elastic energy will dissipate as heat

• Models of Plyometrics

• Neurophysiological Model

– Based upon the characteristics of the muscle’s contractile components

• When muscle put on stretch, it initiates the stretch reflex

• Stretch reflex responds to muscle spindle activity

– Muscle spindle is proprioceptive organ that senses muscle stretch resulting in greater neural input to make the muscle contract concentrically

– Too long of a stretch will negate the neurophysiological effect

• Stretch-Shortening Cycle

• The combination of elastic energy and stretch reflex facilitate a maximal increase in muscle recruitment

– Occurs in 3 phases:

• Eccentric Phase

• Amortization or Transition Phase

• Concentric Phase

• Phase 1 – Eccentric Phase

• During this phase:

– SEC stores elastic energy

– Muscle spindles are stimulated

• As spindles are stretched, type 1a afferent nerve fiber sends signal to spinal cord for response

• Visualize the time of foot contact with ground until the bottom of the movement in the long jump

• Phase 2 – Amortization Phase

• During this phase:

– There is a pause from end of eccentric stretch of muscle & initiation of concentric muscle contraction

– Upon stretch of spindles, signal sent via type 1a afferent nerve fiber to spinal cord for response

• Visualize the time foot stoppage right before beginning leap of the long jump

• Phase 3 – Concentric Phase

• During this phase:

– Energy stored in SEC is utilized to enhance force of muscle contraction or it is dissipated as heat

– Signal from spinal cord is transported via alpha motor neuron to the muscle resulting in a reflex concentric contraction

• Visualize the foot leaving the ground to propel the long jumper forward and upward toward the pit

• Example of Phase Importance

• Vertical Jump (3 different starting positions)

• If starting from a squatting position (hip and knee joints at 90o flexion), then jumping upward; virtually no eccentric phase so height attained is not optimal

• If starting from a partial squat, followed by a further flexion of hip and knee, and then moving immediately into the jump upward (countermovement), this allows for some eccentric energy and some stimulation of the stretch reflex; jumper goes higher than the squatted static position

• If starting with a run up to the pit, all phases will be incorporated resulting in highest jump upward

• Plyometric Program Design

• Based upon the components of:

– Mode

– Intensity

– Frequency

– Duration

– Recovery

– Progression

– Warm-up

• Mode

• Determined by body region performing the plyometric action

v Lower-body plyometrics

vGood for all movement sports

vMost are jumping drills

v Upper-body plyometrics

vGood for throwing sports

vExamples include medicine-ball throws, catches, and several variations of the push-up

v Trunk Plyometrics

vDifficult to perform true plyometrics in the trunk musculature

vMovements must be shorter and quicker in this region to get any eccentric energy and the stretch-reflex

• Intensity

• Dependent on the drill utilized

– Examples:

• Skipping is relatively low intensity

– Minimal stress on muscles and joints

• Depth jumping is relatively high intensity

– Great stress on muscles and joints

– Note: as intensity increases, volume should decrease

• Frequency

• Number of plyometric sessions/week

– Typically ranges from one to three depending on sport and time of year

• Athletes often utilize 2-4 sessions per week

– During in-season

» one session per week is appropriate for football players

» 2-3 sessions per week is appropriate for track and field athletes

– During off-season:

» 2-3 sessions per week are appropriate for football players

» 3-4 sessions per week are appropriate for track and field athletes

• Recovery

• Primary determinant to effectiveness of plyometric program since maximal anaerobic efforts are involved

– 48 to 72 hours (avg) between plyometric sessions shoul be allowed

– During exercise sessions:

• Depth jumps

– 5-10 seconds between reps

– 2-3 minutes between sets

• Time between sets should be based upon 1:5 to 1:10 work-to-rest ratios and are specific to volume and types of drills used

• Drills for same body area should not be performed on successive days

• Volume

• Defined as number of repetitions and sets performed during a training session

– Lower-body plyometric volumes

• Based on # of foot contacts per workout

• Also could be based upon distance, as with bounding drills

– Beginner (no experience)- start with 80-100 feet

– Intermediate (some experience)- start with 100-120 feet

– Advanced (considerate experience)- start with 120-140 feet

– Upper-body plyometric volumes

• Based upon # of throws or catches per workout

• Program Length

• Typical programs are 6-10 weeks

– However, vertical jump height can improve in 4 weeks

• Plyometrics can be utilized for both resistance and aerobic training

• For quick, powerful movements, should incorporate plyometrics throughout the entire macrocycle

– Intensity and volume should vary with sport and time of season

• Progression

• Should follow the principle of progressive overload

– Typically, as intensity increases, volume should decrease

• That is,

– Start with low to moderate volumes of low intensity

– Progress to low to moderate volumes of moderate intensity

– Then to low to moderate volumes of high intensity

• Warm-up

• Should consist of low-intensity, dynamic movements

• Typical warm-up drills:

– Marching (prep for running, posture emphasis)

– Jogging (prep for impact and high-intensity drills)

• Toe jogging, straight leg jog, butt-kicks

– Skipping (prep for reciprocal coordination between upper and lower body movements; quick landings)

– Footwork (prep for change of directions)

– Lunging (prep for lunge and multi-directions)

• Plyometrics and Other Exercises

• Plyometrics and Resistance Training

– Guidelines:

• Combine lower-body resistance training with upper-body plyometrics and vice versa

• Performing heavy resistance and plyometrics on same day is not recommended

– Complex training (heavy resistance followed by plyometrics) can be performed with adequate recovery in-between

• Traditional resistance training can be combined with plyometrics to enhance muscle power

– Example: (only for advanced plyometric person)

» Performing squat jump with 30% of one’s squat 1RM utilizing an external resistance

• Plyometrics and Other Exercises

• Plyometrics and Aerobic Exercise

– May consider combining these 2 training components for intermittent sports, i.e. soccer, basketball, etc.

– Aerobic exercise may have negative effect on power production

• Advisable to perform plyometric exercise before aerobic endurance training if incorporating both components

• Safety Considerations

• Generally, injuries from plyometrics, occur due to:

– Insufficient strength and conditioning base

– Inadequate warm-up

– Improper progression of lead-up drills

– Inappropriate volume or intensity for phase of training

– Poor shoes or surface

– Lack of skill

• Safety Considerations

• Pretraining Evaluation of Athlete

– Important for reducing potential for injury and facilitating performance

– Components of evaluation:

• Technique

• Strength

• Speed

• Balance

• Age

• Physical Characteristics

• Components of Evaluation

• Technique

– Learning proper landing technique for lower-body plyometrics is essential, i.e. depth jumps

• Center of gravity cannot be offset from base of support, otherwise injury can occur

• Shoulders should be over knees during landing while flexion of ankles, knees, and hips occurs

• Components of Evaluation

• Strength

– Must have a base of strength

• For lower body plyometrics, 1 RM squat should be at least 1.5 times his/her body weight

• For upper body plyometrics, 1 RM bench press should be:

- at least 1.0 times athlete’s body weight if weight is

over 220 pounds

- at least 1.5 times athlete’s body weight if weight is

less than 220 pounds

- alternative measure:

-ability to perform 5 clap push-ups in a row

Note: If athlete doesn’t possess minimum

strength, plyometrics should be delayed

• Components of Evaluation

• Speed

– For lower body plyometrics, athlete should be able to perform 5 repetitions of the squat with 60% body wt in 5 sec or less

• At same time, it is recommended that athlete participate in sprint training and speed-specific resistance training

– For upper body plyometrics, athlete should be able to perform 5 repetitions of the bench press with 60% body wt in 5 sec or less

• Components of Evaluation

• Balance

– Having the ability to maintain a position without moving for a given period of time is an important “basic” for plyometrics

• 3 balance tests for evaluation

– Beginners

» Standing – double-, then single-leg hold for 30 seconds

– Some experience

» Quarter-squat – double-, then single-leg hold for 30 seconds

– Advanced

» Half-squat – double-, then single-leg hold for 30 seconds

• Components of Evaluation

• Age

– High-intensity (e.g. depth jumps) plyometric drills are not recommended for prepubescent-aged children due to potential damage to growth plates

– Psychological maturity is also required prior to initiating high-intensity plyometrics. It is important to be able to follow coach’s or trainer’s instructions.

• Components of Evaluation

• Physical Characteristics

– High-volume, high-intensity plyometrics not recommended for individuals who are more than 220 lbs; increased risk for injury due to weight.

• These individuals should not perform depth jumps from heights greater than 18 in (46 cm)

– Individuals with previous injuries to spine and other body areas that take significant stress from plyometrics should refrain from these exercises

• Equipment and Facility Considerations

• Landing surface

– Should have adequate shock-absorbing properties

• Good surfaces – grass field, suspended floor, rubber mats

• Poor surfaces – concrete, tile, hardwood floor

– Excessively thick (6 in or more) exercise mats not good since these could extend the amortization phase and not let stretch-reflex occur effectively

– Mini-trampolines also not effective for plyometrics due to extended amortization phase

• Equipment and Facility Considerations

• Training area

– Bounding and running drills should be a minimum of 33 yds and up to 109 yds for straightaway

– Standing, box, and depth jumps only need a minimal area but height of 9.8 to 13.1 ft (3-4 meters) is required

• Equipment and Facility Considerations

• Equipment

– Boxes should be sturdy with non-slip top

– Box heights should range from 6 to 42 inches with landing surfaces of at least 18 by 24 inches

– Box should be constructed of sturdy wood (3/4 in plywood or heavy-gauge metal)

– Landing surface must be non-slip

• May use nonslip treads, mixing sand into paint, rubberized flooring

• Equipment and Facility Considerations

• Proper footwear

– Footwear with good ankle and arch support, good lateral stability, and wide non-slip soles

• Supervision

– Need close monitoring to avoid injury

• Depth Jumping

– Maximum height of 48 inches can be used but not increased possibility of injury

– Recommended heights:

• 16-42 inches with 30-32 inches being the norm

• 20-30 inches for athletes weighing over 220 pounds

• Summary

• Plyometric exercise has been proven to increase muscular power

• Sufficient base of strength, speed, aerobic and flexibility training, and nutrition are important for plyometrics to be effective

• Progression is important to incorporate in order to avoid injury and maximize performance