Explosiveness and speed are two of the most sought after training attributes in sports (Rhea 2009). Historically, these attributes have been thought of as genetically predetermined (Bourne 2009). However, as coaches and scientists better understand how training changes athletes at a cellular level, athletes have greater capacity to adopt improvements from all areas of training (speed, strength, endurance).
A study published in 2000 (Abe et al.) comparing muscle architecture of elite sprinters vs. elite long-distance runners showed that sprinters had longer muscle fascicles (bundles of muscle fibers). Muscle architecture refers to the shape and structure of muscles. The two main components of muscle architecture are pennation angle and fascicle length. Both components are important for fast movements and until recently were thought to be genetically determined and not trainable. Pennation angle- Refers to the angle that the muscle fibers run across the Y-axis. Smaller pennation angles are better for explosive movements. The biceps brachii and gastrocnemius (calf muscle) have opposite pennation angles due to the nearly zero degree angle of biceps and large pennation angle of the gastrocnemius.
Think of the hip joint. A large pennation angle of the gluteus maximus muscle will run horizontally across the hip joint. A small pennation angle will run vertically with the hip joint. If you are still having difficulty imaging this refer to the pictures below.
As demonstrated above, you see that a smaller pennation angle has a larger Y-axis component. This larger Y-axis component applied to the hip produces more hip extension (propulsion)/unit of concentric contraction. This small pennation angle means an athlete will move their leg faster no matter the muscle fiber type.
With any type of resistance training an increase in pennation angle will happen. This is good for strength but not good for speed. Eccentric training has been shown to minimally increase pennation angle while simultaneously increase strength (Douglas 2017). Concentric training has been shown to increase pennation angle to a high degree when also improving strength (Franchi 2014).
What does this mean in the real world?
It means that concentric training is really good for powerlifters who lift a lot weight very slow, but at a certain point may impede speed adaptations. Understand this does not mean you should not train concentrically. This is where the art of coaching comes into play.
The other component of muscle architecture is fascicle length. Fascicle length is the length of a bundle of muscle fibers. Short muscle fascicles are slower and long muscle fascicles are fast. The more contractile units (sarcomeres) you have in a fascicle the longer it becomes, thus improving speed. Eccentric training can increase the number of sarcomeres in a muscle fascicle and therefore, increase the speed a muscle can move.
More Eccentric Benefits
Eccentric training increases leg stiffness which is the ability of the legs to act like springs. This ability improves vertical impulse forces and ground contact times, both are critical for sprinting ability (Douglas 2017). Motor unit firing speed also increases after eccentric training, this allows an athlete to use fast twitch muscles faster (Douglas 2017).
How to train eccentrically
Understand heavier loaded eccentric lifts will require assistance; band assisted lifts are useful with these highly stressful workloads. Plyometric movements also count as eccentric training and can be used with lighter weights such as medicine balls or body weight plyometrics. Do not go overboard with plyometrics. Many coaches end up using them as conditioning, this is not the purpose of plyometrics and is counterproductive in developing explosiveness.
When to train eccentrically?
This is where the art of coaching comes into play. Considering these two things it’s up to you. Your team or athlete needs to have enough time in between competition and eccentric training session in order to recover and compete at a high level. It may be up to 5-6 months before the benefits of eccentric training are completely realized your athlete needs to be at a high enough training level in order to tolerate and improve from eccentric training.
Key paper on this topic: