Plyometric exercise is a training technique that was designed specifically to improve an athlete’s ability to perform explosive power through manipulation of elastic properties of the muscle’s connective tissue and the muscle’s stretch reflex protective mechanism.
- Plyometric exercises are meant to be performed quickly and with high levels of force. In order to produce high levels of force very quickly we must recruit our most powerful motor units, the fast twitch. And which energy system do the fast twitch rely on? …the phosphagen (ATP/CP cycle). How long does this energy pathway last? ….5 – 10 seconds.
- As a result if a drill lasts longer than 5-10 seconds then this would not be training the ATP/CP energy pathway and the fast twitch motor units. Drills must NOT be considered cardiovascular conditioning, this is a big mistake I see in the gym. Plyometrics is an anaerobic exercise, so the individual must sufficiently recover between reps and sets to maximize power output: 5-10 seconds rest between repetitions (especially for depth jumps) and 2 – 3 minutes rest between sets.
Mechanics and Physiology of Plyometric Exercise.
1. Elastic Energy of Muscle: The connective tissue (endo, peri, epimysium) surrounding our muscle plus the tendons are like rubber bands. They stretch and rebound elastically. When you rapidly stretch and then rapidly follow the stretch with a concentric action it increases the force production. Think of stretching a rubber band and letting go of it.
2. The Stretch Reflex: deep inside the belly of a muscle we have special fibers called the muscle spindle that sense the rate and length of stretch. When you rapidly stretch a muscle these fibers send a signal to your central nervous system that the muscle has been rapidly overstretched and you must do something about it! So the CNS sends a signal back telling the muscle to contract. This neuro-muscular feedback loop is a protective mechanism called the stretch reflex.
Stretch-Shortening Cycle (SSC): lets say you are performing a vertical jump. In order to jump the highest you can you have to utilize the elastic components of the tissue, the stretch reflex, and recruit your FG motor units.
The SSC is composed of three parts:
- Eccentric: You first perform a counter movement where you squat down rapidly to stretch your agonist muscles (quads). By doing this you have stored elastic energy in the quads and have activated the muscle spindle (a sensory impulse is being sent to the CNS as this occurs).
- Amortization: the pause between eccentric and concentric. The CNS is sending a motor impulse back to the muscle telling it to explosively contract to prevent it from being stretched further. In plyometrics it is crucial that the amortization phase is as short as possible.
- Concentric: Your agonist muscle receives the instructions to contract forcefully and you release the elastic energy from the connective tissue as you leave the ground.
Here is an example of a single-leg push off: Single leg. This plyometric drill is a lower intensity drill designed to improve unilateral power in the lower limbs. Notice the 3 phases of the stretch-shorten cycle.
1. Lower Body Drills: these are great for almost any sport and any position. You can increase or decrease the intensity by manipulating the height of the drill, the speed of the drill, or using one or two legs.
- Low Intensity: two-foot ankle hops, skipping, squat jumps, vertical jump, push-off (single, alternate, lateral).
- High Intensity: single-leg vertical jump, zig-zag hop (hurdles), single-leg hops, box jumps, depth jumps.
2. Upper Body Drills: these are good for sports that require powerful upper body movements such as baseball, tennis, golf, shot put, discus, javelin.
- Low Intensity: chest pass throw, overhead throw, single-arm throw.
- High Intenisty: Power drop, clap push-ups, depth push-ups.
3. Trunk Plyometrics: I argue that the abdominal muscles are not designed for explosive power, so performing abdominal exercises rapidly (medicine ball sit-ups or leg-throws) is not actually improving power in the trunk. The trunk musculature is designed for posture and endurance; the purpose of these muscles are to stabilize the lumbar-pelvic area and transfer force up and down the kinetic chain. Also, the stretch reflex is not as effective because of the time it takes to go through the range of motion in the sit-up. ALSO, think about specificity and functionality; what skill in athletics or life requires you to explosively sit-up?
- Example 1: Medicine Ball Sit-Up – The stretch reflex is not as effective because of the time it takes to go through the range of motion in the sit-up. Also, since the abdominal muscles are designed to have more endurance then they have a higher percentage of slow twitch fibers than fast twitch. Less fast twitch fibers limits your ability to do explosive power.
- Example 2: Leg Throw Downs – this is more plyometric, but it is not targeting the abdominal muscles. When the leg is rising back up you are recruiting more hip flexor (rectus femoris and iliopsoas) than rectus abdominus.
National Strength & Conditioning Association (NSCA)
Criteria for Beginning Plyometric Training
It is important to NOT introduce plyometric training into an athlete’s or client’s program until the individual is strong enough and desires an improvement in muscular power. There is no reason to implement plyometric training if power is NOT the desired goal. The inappropriate application of plyometric training will lead to acute trauma or overuse injuries, and a decrease in performance.
Strength Criteria for Beginning Plyometrics
Lower Body Strength
- Athlete’s 1-RM squat should be at least 1.5 times her/his body weight.
Upper Body Strength
- Athlete’s bench press 1-RM should be at least 1.5 times the body weight.
- OR, for smaller athletes they should be able to do 5 clap push-ups in a row.
Lower Body Speed
- The athlete should be able to perform 5 reps of the squat with 60% body weight in 5 seconds or less.
Upper Body Speed
- Athlete should be able to perform 5 reps of bench press with 60% body weight in 5 seconds or less.
Each test position must be held for 30 seconds. Tests should be performed on the same surface used for drills. An athlete beginning plyometric training for the first time must stand on one leg for 30 seconds without falling. An athlete beginning an advanced plyometric program must maintain a single-leg half squat for 30 seconds without falling.
BALANCE TESTS: 30 seconds each on a stable surface.
- Standing on one leg
- Quarter squat on one leg
- Half Squat on one leg
Program Design for Plyometrics: first conduct a needs analysis of the athlete’s sport requirements to decide which plymetric drills are most appropriate. Lower body drills are appropriate for almost any sport! Remember plyometric training is supposed to develop explosive power NOT cardiovascular endurance so keep the intensity HIGH and the volume LOW.
1. Frequency – 1 day a week for beginners and up to 3 days for advanced. The athlete must have 48-72 hours recovery between sessions to allow full recovery of the nervous and muscular systems!
2. Recovery between reps and sets: 5-10 seconds between repetitions (especially for depth jumps) and 2 – 3 minutes between sets.
- Number of foot contacts with the ground per workout.
- For bounding or skipping volume can also be measured in distance covered.
- For upper body drills, volume can be expressed as the number of throws per workout.
- Beginner: 80-100 contacts
- Intermediate: 100-120 contacts
- Advanced: 120-140 contacts
4. Plyometric Program Length: 6 to 10 weeks as part of the power phase of the athlete’s periodization macrocycle and following the principle of progressive overload.
5. Planning and Periodization: Intensity should begin low and progress to moderate, while volume should begin high and progress to low.
Reference: Baechle TR, Earle RW. Essentials of Strength Training and Conditioning 3rd Edition. 2008.