Whether you are a weekend warrior, a high-level competitive athlete, or somewhere in between, every step you take begins from the ground up. Each person's most powerful muscles in the foot and ankle complex are the soleus and gastrocnemius, which have tendons that join together to form the common Achilles tendon.

Due to its structure, the soleus muscle has an incredible ability to produce force, especially during the eccentric phase of contraction, which is contraction as the muscle is lengthening. Every athlete's ability to run and jump and change direction quickly comes from their bodies' ability to control eccentric forces and utilize them for efficient movement.

This all starts with the foot and ankle. The calf and Achilles tendon must be able to control these large, repetitive eccentric forces, thereby acting as the first link in the force absorption pattern before transferring energy up the chain.

Below, we will go into more detail on why this mechanism is important and how you can use eccentric stretching of the Achilles tendon to increase your performance capacity.

The Importance Of Eccentric Stretching For The Achilles Tendon

As we mentioned before, eccentric stretching, or loading, of the Achilles happens as the soleus and gastrocnemius muscles are contracting while lengthening. This typically occurs during closed-chain dorsiflexion – when your knee passes over your foot and toes while in contact with the ground.

If you are a runner, how far your knee goes over your toes during each stance phase of the gait cycle is a direct indicator of some common pathologies. In the running population, "Achilles tendinopathy and medial tibial stress syndrome [commonly referred to as shin splints] had the highest incidence proportions" out of all other injuries (Kakouris et al., 2021).

During the stance phase of every step while running, your calves' ability to produce eccentric load is extremely important to reduce the shin angle or how far your knee goes over your toes.

If you are playing a sport involving much more multi-plane movement like basketball, soccer, etc., you likely do not have the same volume of repetitive movement as someone who runs 25+ miles a week.

But you sustain higher eccentric loads with quick accelerations, decelerations, and changes of direction. I'm sure you all know that the faster you can do these motions, the better you will perform and the higher level you will compete. Every step during these movements is an eccentric load, or stretch, on the Achilles tendon and calf musculature.

How To Train The Achilles Tendon With Eccentric Training

Since you know it is important now, how do you train it? And more importantly, how do you train it in a way that will actually transfer to your sport/activity and benefit you on the field, track, road, etc.

Well, the best way to train your body is to emulate the intensity of the load it will endure during your sport. This goes for eccentric load as well concentric.

The concept of eccentric overload, or using eccentric exercise with external loads that you can not produce concentrically, is known to "lead to greater increases in eccentric strength" and increased "cross-sectional area…of the type I and type II fibers" of your muscles, or in other words hypertrophy (Vinke et al., 2006).

Traditionally, we would use barbells, bands, dumbbells, kettlebells, etc., to produce these high eccentric loads. Now we are incorporating a newer and arguably more practical modality called flywheel, or inertial training, which means you have to eccentrically control how much force you concentrically produce with your own body.

Because it uses inertia to deliver this external load, the speed of concentric contraction can also increase the amount of load you must control eccentrically. To give you an idea of how this works, I will use a squat as an example.

With a flywheel, you will start at the bottom of the squat and concentrically push up to standing. Since there is very little to no external load acting on your body for the concentric motion, you are performing an air squat, so your speed, or acceleration, in this case, can be very high.

Once you reach the top of the squat, the crank of the flywheel reaches the end of the strap and begins to spin the opposite way pulling you back down into another squat.

As this happens, the acceleration force becomes inertia which is your body resisting the acceleration of your body getting closer and closer to the ground. In this case, inertia = eccentric load, and the faster you move concentrically, the greater force you must control eccentrically.

This allows you to work your way up to larger and larger eccentric loads while being safe and continuously progressing, ultimately resulting in an increased eccentric capacity.

There are two other key performance indicators that we see benefit from eccentric training: rate of force development & increased mobility through strength.

Since there is an abrupt and immediate change from light concentric to heavy eccentric activity, there is a large neural stimulus generating increased muscle recruitment and speed of contraction, resulting in a greater rate of force development (RFD).

Lastly, eccentric training will also increase muscle strength in greater ranges of motion. Keeping our bodies strong in stretched and awkward positions is extremely important for injury prevention. It is important to keep in mind here that this method of training is on the extreme side of the speed-strength continuum.

It is primarily training absolute strength and strength speed. That said, typically, the most athletic and injury-resilient individuals are those in the middle of the speed-strength continuum. It is necessary to periodize your training and ensure elements from both ends of the spectrum within your training phases.

Within a strength or max strength cycle, the Exerfly is a perfect tool for sport-specific eccentric training! It is closed-chain and provides an incredible amount of eccentric force necessary for re-creating the high loads that athletes sustain in their various sports and activities.

A few of my favorite exercises specifically for eccentrically loading the Achilles are Peterson’s Step Downs, ¼ Squat Calf Raises, and Straight Leg Deficit Calf Raises. Although Peterson's step-downs and ¼ squat calf raises are not your typical calf isolation exercises, they do a great job loading the Achilles while forcing the rest of the leg to communicate with it.

Your calf and Achilles tendon should never work completely alone in your sport or activity. It is important to train it this way in addition to your isolation exercises.

This method of training your calf and Achilles tendon is a great way to increase its eccentric capacity, RFD, and its strength in greater ranges of motion. These are important metrics for you, even if you are running a few miles a week, trying to ensure you don't injure yourself as you slowly increase mileage.

And additionally, if you are already competing at a high level, this is another tool in the toolbox to ensure you stay healthy and keep improving. It is important to note that this is an extreme side of the speed-strength continuum, and you should consider this aspect with the periodization of your training.

Because of the "stretching" aspect of eccentric exercise and the speed of contraction that happens, it results in your tendons becoming less stiff. We know that tendon stiffness and reactive strength are also important performance metrics, so remember, do not neglect your plyometrics!

To be a well-rounded and healthy athlete, you must continuously change the type of stimulus you use to train your body. So I encourage you to explore new areas of the speed-strength continuum, especially if you are used to only lifting heavy loads slowly or light/bodyweight loads very quickly.

References

Vinke , H., Refsnas, P. E., & Ekmark , M. (2006, October 1). Muscular performance after concentric and eccentric exercise in trained men. Europe PMC. Retrieved September 1, 2022, from https://europepmc.org/article/med/17019299

Kakouris, N., Yener, N., & Fong, D. T. P. (2021, April 20). A systematic review of running-related musculoskeletal injuries in Runners. Journal of Sport and Health Science. Retrieved September 1, 2022, from https://www.sciencedirect.com/science/article/pii/S2095254621000454