At Pure we do a lot of plyometric drills. Here is a Spotlight post to tickle your curiosity regarding the subject.
Plyometric exercises are used to to increase the power of subsequent movements. We can practically define plyometric exercises as quick, powerful movements using a pre-stretch that involves the stretch-shortening cycle. More on that later.
Functional movements and athletic success require all muscles to function properly and at the correct speed. The relationship between strength (force) and speed is called power. When used correctly, plyometric exercise consistently shows increased power and muscle force production. Why does this matter? To understand how power, force production and plyometrics will make us faster and stronger endurance athletes, we need to take a peek at the physiology behind it all. There are two models of explanation, the mechanical and the neurophysiological.
Elastic energy is stored in the tendons of the muscles following a rapid stretch. When this eccentric movement (controlled lowering with gravity) is immediately followed by a concentric (controlled movement against gravity) muscle action, the stored energy in the tendons is released, increasing total force production. Visualize an elastic band being stretched; the faster and farther it is stretched from it’s original state, the more energy it will contain when it is released. However, unlike an elastic band, if a concentric muscle action does not occur immediately following the eccentric action, or if the eccentric phase is too long or requires too great a motion about the given joint, the stored energy dissipates and is lost as heat. As an example, imagine doing dumbbell thrusters with deep squats in a slow controlled motion; all energy from the hips is lost in the slow movement speed and large range of motion. The exercise adopts an entirely different purpose…and likely a drop in the amount of weight used.
This model involves the stretch reflex, which is the body’s involuntary response to an external stimulus that stretches the muscles. This reflexive component of plyometric exercise is primarily composed of muscle spindle activity. Muscle spindles are proprioceptive organs that react to the rate and magnitude of a stretch; when a quick stretch is detected, muscular activity reflexively increases. During plyometric exercises, the muscle spindles are stimulated by a rapid stretch, causing a reflexive muscle action. This reflexive response increases the activity in the primary muscle, thereby increasing the force the muscle produces. As in the mechanical model, if a concentric muscle action does not immediately follow a stretch (i.e., there is too long a time between stretch and concentric action or movement over too large a range), the reflexive ability of the stretch reflex is negated.
Putting It All Together: The Stretch Shortening Cycle
The stretch-shortening cycle combines mechanical and neurophysiological mechanisms and is the basis of plyometric exercise. A rapid eccentric muscle action stimulates the stretch reflex and storage of elastic energy, which increase the force produced during the subsequent concentric action. The efficiency of these subsystems is essential to the proper performance of plyometric exercises. All complexities aside, here are the three phases accompanied with an example of a runner.
1. Eccentric phase – preloading or stretch phase. The time from touchdown of the foot to the bottom of the movement is the eccentric phase.
2. Transition (amortization) phase – the time between the eccentric and concentric phases. If this phase lasts too long, the energy stored during the eccentric phase dissipates as heat, and the stretch reflex will not increase muscle activity during the concentric phase. Once the runner’s foot has touched down and movement has stopped, the amortization phase has begun. As soon as movement begins again, the amortization phase has ended.
3. Concentric phase – the body’s response to the eccentric and amortization phases. The energy stored in the tendons during the eccentric phase either is used to increase the force of the subsequent movement or is dissipated as heat. This stored elastic energy increases the force produced during the concentric phase. This phase includes entire push-off time of the runner’s foot.
Every step you take when running is a mini, unilateral plyometric exercise. The more efficiently we can activate the mechanical and neurophysiological components of the stretch shortening cycle, the stronger each stride will become! All the more true when we employ unilateral (single-leg or single-arm) drills, as this is the most sport specific to running.
At Pure, we commonly use complex training, which is the combination of high-intensity resistance training followed by plyometrics. Personally, my favourite combination is a cable single-leg deadlift closely followed by alternating box lunge jumps. The connection of these two exercises can be understood as a focused pre-strenthening followed by an explosive use of the stretch shortening cycle with the same muscle group.
Plyometric training increases power and muscle force production at a mechanical level using the same principles as an elastic band being stretched and released. At the neurophysiological level, it develops proprioceptive organs that are sensitive to rate and speed of stretch. Alongside a complete program including balance, resistance training, agility/speed drills and cardiovascular endurance, it is an important player in total body fitness. Common plyometric drills we use are: box jumps, all medicine ball tosses, squat jumps, skipping, bench lunge/lateral jumps and power push ups.
– Two to three sessions per week are common for track and field athletes during in-season, while during off-season, frequency can increase to two to four plyometric sessions per week.
– Drills should not be thought of as cardiorespiratory conditioning exercises but as power training.
– Lower body plyometric volume is normally given as the number of foot contacts but may also be expressed as distance. Upper body plyometric volume is typically expressed as the number of throws or catches.
– Vertical jump height improves as quickly as four weeks after the start of a plyometric training program.
– Besides providing the well-documented muscular power and bone strength adaptations, regular participation in an appropriately designed plyometric training program can better prepare young athletes for the demands of sport practice and competition by enhancing neuromuscular control and performance.
– Balance is important!! Many lower body plyometric drills require the athlete to move in nontraditional patterns or on a single leg. These types of drills necessitate a solid, stable base of support upon which the athlete can safely and correctly perform the exercises.
Feature image and content based on the NSCA’s Essentials of Strength Training and Conditioning (3rd edition).