Plyometric exercise was first used by athletes to enhance sport performance but more recently has been used in physical therapy for rehabilitation of injuries. It is a form of exercise that combines coordination, strength, and speed. Plyometrics largely involve the theory of stretch-shortening training. This means the muscles quickly move from a stretched position to a shortened position and back again. This cycle improves the ability of muscles to produce high levels of force over a short period of time.
A good way to visualize plyometrics is to think of jumping activities. There are a multiple phases throughout this movement, the first being the loading phase. During this time, the major muscles responsible for the movement are stretched. In jumping, the quads are put on stretch as you squat down in preparation for the jump. Envision yourself squatting down and then jumping as high as you can. Now, picture yourself standing up straight with your knees locked tight. Do you think you would jump as high from this position? The answer is no. Without the loading phase our bodies are unable to generate as much force because of failure to initiate the stretch-shortening cycle.
The second phase is the coupling phase. During this time, body position stays the same as the muscle force changes directions and you prepare to switch from squatting down to jumping up. Last is the unloading phase. In a jump, think of this phase as when you propel yourself off the ground. This is when the force generated by squatting down is put to use.
The timing of the coupling phase is very important. To be considered a plyometric exercise, the movement must be continuous. Higher forces are associated with a shorter coupling phase. If you stop to take a break between each jump, it is not a plyometric exercise. Think about multiple jumps in a row. The shorter amount of time you spend on your feet, the greater the force you will generate for each jump at a faster speed.
Who is appropriate for plyometric exercise?
This method of exercise puts high levels stress on the body and should be used only after significant healing has taken place. Traditional rehab exercises are often performed at slower speeds and moderate intensities. Plyometric exercises promote use of large muscle groups for strengthening and muscle endurance training. Though they may not be able to fully match the demands of paying a sport, plyometrics are a highly recommended middle ground between traditional rehab and return to sport.
Some examples of when to avoid plyometric exercise include acute inflammation or pain, joint instability, or immediately after surgery. Tendon injuries as well as joint issues like arthritis, bone bruises, or cartilage damage can be questionable and depend on the patient’s ability to tolerate the high forces involved in plyometric activities.
Before initiating a plyometric program, patients should first be able to tolerate activities of daily living without pain or swelling. They should also have nearly full range of motion and adequate strength and endurance to participate in the demanding exercises. In physical therapy, if a patient is unable to tolerate plyometrics, they are likely unable to tolerate returning to their sport.
How do you prescribe plyometric exercise?
There are 5 major variables to consider when starting a plyometric exercise program: frequency, intensity, volume, recovery, and progression. The frequency of exercise refers to how often an exercise is performed. High intensity plyometric exercises should be performed twice a week to allow 48-72 hours of rest between sessions. Intensity is the effort required to perform the exercise. You can change the intensity by changing the height of the platform the patient has to jump up to/down from. Intensity and frequency are inversely related. The higher the intensity of work, the lower the frequency of sessions.
Volume is the total work performed within one exercise session, including the number of sets and repetitions. For jumping exercises, volume is the amount of times your feet contact the floor. Low intensity/high volume is recommended initially to ensure that the patient performs the exercise with proper technique, then they can progress to high intensity/low volume.
Recovery is defined as the rest time between repetitions, sets, and sessions of plyometric exercise. The recovery time depends on the intensity of the activity. For high intensity exercise, a 1:5 to 1:10 ratio is recommended between sets. For example, with 1 second of explosive work, 5-10 seconds of rest may be allowed between attempts. However with low intensity exercise, a 1:1 or 1:2 ratio is recommended. For example, if you perform continuous jumps for 10 seconds, you get 10-20 seconds of rest.
Progression of any activity should occur only when activities are completed with proper form and without symptoms. The volume should progress first, while ensuring proper technique, then increasing the intensity and frequency should follow after. If any symptoms are present after a progression, the patient should recover until the symptoms stop. When they return to plyometric exercise it should be at the level before the exercise was progressed. A patient should tolerate 2-3 sessions at a particular intensity without symptoms before the intensity is progressed.
Correct and safe technique that will allow for peak performance is very important. When assisting a patient, a therapist should always correct improper technique that may be a result of their injury or a contributing factor that may have caused their injury. Continuous and immediate feedback is necessary early in treatment to reinforce proper technique and break any bad habits. If at any point throughout the exercise the patient fatigues to a point where they display improper or dangerous technique, the exercise should be stopped.
Support for plyometric exercise
Research shows that 6-15 week plyometric training programs generally improve performance in maximum vertical jump height, sprint times, golf club speed and driving distance, and overall running performance. Specifically for leg programs combined with weight lifting, a 90% increase in leg strength is reported after just 6 weeks of training. Females may also particularly benefit from plyometric leg exercises as they have proven to correct the muscle imbalance between the quads and the hamstrings that often makes female athletes more susceptible to injury.
While limited research is available on the benefits of an arm program for plyometric exercise, leg programs have been shown to improve postural stability and balance. Patients displayed better trunk control and stability when landing from a jump and landing forces were more equal between the 2 legs indicating a lower risk of injury.
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