When is the last time you jumped?
Not a light hop to grab a basketball while shooting hoops with friends, but really jumping -- pushing a large amount of force into the ground very quickly and flying into the air.
If you play a sport, you’ve probably jumped recently. If not, it’s probably been a while. And that’s OK. It’s not exactly socially acceptable to jump onto a dinner table out of the blue. The point is that most people quit jumping once they stop playing a sport.
For some people that’s a good decision. Maybe their joints are so worn out that jumping will only cause pain. For others, however, jumping is a legitimate strength-building option that can provide cardiovascular and performance benefits when executed correctly and safely.
Powermetrics vs. Plyometrics
What is plyometric training? You’ve likely heard the term before, but what does it really mean?
Since the 1970s, when plyometrics started gaining popularity in the United States, the term has grown in scope and lost much of its original meaning. It’s important to distinguish plyometric actions from plyometric training, because they encompass different concepts.
Plyometric actions include running, jumping, hurdling and any other type of rebounding activity that uses elastic energy to augment the working effect of muscle. In plain English, plyometric actions use a pre-stretch to make the muscle more explosive -- like pulling back and launching a rubber band. Almost all sports are plyometric in nature for that reason.
Plyometric training, on the other hand, is applying plyometric actions as a distinct method of exercising. The purpose is to challenge the body in a way that exceeds normal demands, forcing it to adapt and grow. It’s not just randomly jumping around and hoping for the best.
Due to the broad nature of the term “plyometric” and the common confusion over plyometric action and plyometric training, exercise physiologists have proposed the term “powermetrics” to describe plyometric training. So that’s what we’ll call it.
What Is Powermetrics?
Powermetrics is a way of training that utilizes kinetic energy, elastic energy and the stretch reflex.
For example, picture yourself standing on top of a small box. Drop off the box then jump up as high as you can as quickly as you can the instant your feet hit the ground. Here’s what your body is doing to make that happen.
As you drop from the box, gravity accelerates you toward the ground and you build up kinetic energy. When your feet make contact with the ground, your muscles and tendons undergo a brief, unexpected stretch.
At this point, three big things are happening:
1. Some of the kinetic energy you built up during free fall is being converted into elastic energy (think stretching a rubber band) and stored in your tendons and muscles.
2. A sensory receptor known as a muscle spindle experiences the same quick stretch and sends a message to the central nervous system.
3. Another sensory receptor known as the Golgi tendon organ experiences very high levels of muscular tension and inhibits the muscle to alleviate some of the stress and protect the joint.
After you’ve landed, you need to jump back up. The central nervous system receives the message from the muscle spindle and immediately sends a response back to the same place the original message came from, telling the muscle to contract. So the stretch results in a contraction to minimize the stretch. The muscle is being told to contract by the central nervous system and does so involuntarily, using the added benefit of the stored elastic energy (think releasing a stretched rubber band). Additionally, toward the end of this process, you begin voluntarily contracting your muscles, causing you to spring into the air.
Let’s briefly dig deeper into the role of the central nervous system, since it plays an important role in the stretch reflex. As you begin to jump up, some things are happening involuntarily -- this is known as the short-latency response. The muscle is being told what to do by impulses originating in the spinal cord and contracts before your brain has a say in the matter.
But right before you leave the ground, your conscious brain begins to play a more active role. This is the long-latency response. It’s more complex and appears to involve the motor cortex of the brain (in other words, you can consciously control what’s happening).
The involvement of the brain and central nervous system means the stretch reflex can be altered to meet the demands of a particular task. It’s adaptable, and you can get better at it.
Why Do Powermetrics?
Why should you do powermetric-type jumping? For starters, whenever a muscle shortens immediately after a stretch, as it does in this case, its power output increases while its energy expenditure decreases.
Both positives: You’re generating more force and power in less time and you use less energy. Your body is learning to develop explosive strength, the ability to generate large amounts of force quickly. In a study published in the “International Journal of Sports Medicine,” participants who completed 24 weeks of explosive-strength training experienced a far greater increase in strength than a group that completed 24 weeks of heavy resistance training.
In addition to improving performance, powermetrics serves as a learning process for your body and brain. Being able to absorb and generate force quickly is an important part of increasing athletic performance, but it must be learned. For example, during the stretch reflex, the Golgi tendon organ is considering inhibiting the muscle. It experiences a significant amount of tension so quickly that it wants to prevent being overloaded and becoming injured. From a performance standpoint, this is less than ideal because it decreases the amount of force the muscle can generate. Powermetric training, however, can alter the Golgi tendon organ response and allow you to maximize your muscles’ elastic energy.
Some Reasons to Avoid Powermetrics
Due to the intense nature of powermetrics, it has attracted its fair share of critics. One major concern is the force of impact with the ground that can equate to more than five times someone’s body weight. In comparison, activities like a slow jog can generate ground-reaction forces up to 2.5 times body weight.
Joints experience specific adaptations to imposed demands, so the body will adapt to repeated stressors. Depending on the stressor, joints have the ability to adapt like a muscle. For example, when subjected to increased stress, ligaments become stronger and stiffer, but weaker and less stiff with decreased stress.
And absent other joint injuries, exercise and weight-bearing activities can help prevent deteriorating cartilage and the onset of osteoarthritis.
So loading can improve the health and functionality of a joint -- as long as it’s performed correctly. Any action is inherently dangerous if it’s done the wrong way. If you have prior knee, back or hip issues; if you can’t jump and land in a safe position for your joints; if you are playing a sport that involves sprinting and jumping already; or if you simply haven’t done a lot of jumping in a few months, then doing intense jumping exercises is probably not a great idea.
Execution and Examples
One of the goals of powermetrics is to use the stretch reflex to your advantage. One of the most effective -- though advanced -- ways to retrain your stretch reflex is through depth jumps. You drop off one object -- usually a bench or box -- then jump back onto another object or jump as high as you can.
To do it properly, you need to spend as little time on the ground as possible, so your body effectively uses the stored elastic energy and stretch reflex. If you spend a lot of time on the ground, you’ll miss out on that and turn it into a normal jump.
In the beginning, you need to start by practicing the landing. Learn to drop off a small object, land in a safe position then gradually increase the height of the object over time. Once you can nail the landing, it’s time to start rebounding. Start with a low-level object and gradually increase the height as you get stronger.
Make sure you’re using proper form throughout the jump. Start with your feet resting flat on the box or bench, land with your knees and hips slightly bent but facing straight forward -- not bent inward -- and thrust arms upward and extend the body as you jump into the air.
Although these jumps may not seem that taxing, they take a major toll on your central nervous system and your joints if you perform them improperly. For this reason, the number of jumps needs to be closely monitored with respect to everything else in your program.
Here are some general guidelines:
1. Don’t exceed eight to 10 repetitions per set.
2. Don’t exceed 35 total jumps in one session.
3. Most people are better off sticking with two to three sets of five to eight jumps.
4. Rest a solid five minutes between sets.
5. Perform jumps at the very beginning of your training session.
6. Start off dropping from a six-inch elevation and progress from there. Most depth jumpers stay at about 18 inches.
7. Separate jumping sessions by 48 to 72 hours.
8. Limit the amount of heavy squats, deadlifts and sprints during a jumping-training phase.
There’s a lot more to powermetrics than hopping up and down, but give it a shot and let us know how it went. Are you new to jumping and have questions? Have you gotten great training results from jumping and have a story to share? Leave a comment below and let us know. Have fun jumping!
- The Encyclopaedia of Sports Medicine
- Practical Guidelines for Plyometric Intensity
- The Effects of a 6-Week Plyometric Training Program on Agility
- Effect of Plyometric Training on the Time-Course of Adaptations to the Elastic Properties of Tendons
- Quantification of Vertical Ground Reaction Forces of Popular Bilateral Plyometric Exercises