Energy flow throughout the body during a sport specific movement is like water running through a garden hose. If you have a bunch of holes in the hose, you will lose water pressure. Similarly, if you have unstable or injured areas in the body, you will have energy leaks and reduced power during movement. The final product at the end of the hose is less than ideal. When it comes to your body, the final product is reduced athletic performance and a higher risk of injury.
Energy flow is the movement of energy within the body. Energy is either generated, transferred, or absorbed by a joint or body segment. Mechanical energy is generated from the ground up, starting from the lower limbs and trunk. This energy flows into the upper limbs and is eventually transferred to an object, such as a tennis ball or baseball. If an athlete has an existing injury or poor technique, some energy will be absorbed by that area and can no longer be used to generate force in tasks such as a tennis serve or baseball pitch. If there is an energy leak anywhere along the way, adjacent joints will generate more energy in order to compensate for this loss. If the energy generated is beyond the physiological capability of that tissue, overuse injuries can occur.
In simpler terms, if energy is not transferred then it is absorbed. Normally energy will flow throughout the body like a hot potato – it is passed quickly and efficiently without risk of injury (ie: a burn if you’re playing hot potato). But if one area is not prepared to take the flow of energy (due to an injury, lack of strength or endurance, or a lack of proper technique), some energy will be partially absorbed by the surrounding area or body tissue. If you’re still following the hot potato analogy, that one person forgot to pass on the potato and has absorbed all the energy, likely sustaining a 2nd degree burn. Passing the hot potato to the proper person is like transferring all the energy to the proper object. In the case of tennis or baseball, the ball will be that object.
A recent study looking at energy flow in the upper body showed a possible link between the tennis serve, ball velocity, and overuse injuries. In this study, researchers analyzed the serves of 19 elite male tennis players, with a mean age of 25 years. To establish baseline values, they placed retroreflective markers on various anatomical landmarks and used high resolution 3D motion capture cameras to analyze a trial of five tennis serves for each athlete. After a period of two competitive tennis seasons, the athletes completed an injury questionnaire and underwent further energy flow analyses. Eleven athletes had sustained overuse injuries over two seasons. Energy flow values were then calculated and compared between injured and non-injured athletes.
The results showed differences in energy flow throughout the kinetic chain and differences in rates of energy generation or absorption by joint torques in the injured versus non-injured groups.
The energy transferred from the ground to the tennis racket was different between injured and non-injured players. Injured players had an energy transfer efficiency of 71% from the trunk to the racket, whereas healthy athletes had an 88% efficiency. Therefore, injured athletes absorbed roughly 17% more energy during a tennis serve. Over multiple competitive seasons, it is not difficult to imagine how this can lead to overuse injuries and reduced performance.
Energy Generation or Absorption
When observing each phase of the tennis serve, we see that a joint either generates or absorbs varying degrees of energy. The following is a breakdown of the group differences based on the specific phase of a tennis serve:
|Trunk||Higher energy output during preparation phase||Higher energy output during late cocking phase|
|Shoulder||Energy generation during cocking phase||Energy absorption during cocking phase|
|Elbow||Energy generation during acceleration phase||Energy absorption during acceleration phase|
|Wrist||Energy absorption during cocking phase||Energy absorption during loading and cocking phase|
The trunk generates power during the initial stages of a tennis serve in healthy players. This provides sufficient energy up the kinetic chain in order to increase the speed of the ball when it contacts the racket. In injured players, the trunk plays “catch-up” just before the acceleration phase in order to generate sufficient power. This can impact ball speed and can also lead to compensation patterns and injury, such as an abdominal muscle tear.
Here is a video showing how the entire kinetic chain contributes to the generation and transfer of energy in a tennis serve.
The findings in tennis have led to more research into baseball players. A 2015 studyshowed the energy flow differences in high velocity versus low velocity pitchers. As in tennis, power generated from the trunk was vital in generating sufficient energy and ball speed during a pitch. In high velocity pitchers, the trunk generated more power in the earlier phases of the pitch (arm cocking phase). Greater energy flow out of the trunk led to higher rates of energy into the forearm, hand, and ball.
As evident above, the higher the output of energy from the trunk, the greater the energy input into the forearm and hand during the arm cocking phase. The end result is increased ball speed. Although this study didn’t analyze injured players, the impact of energy flow on performance is clearly shown. For any athlete wondering about how proper technique and previous injury can impact performance and future injury rates, consider the energy generation, absorption, and flow within the human body.