Most people know someone who is a little off, strange, or just downright eccentric. Now I'm not here to talk about your aunt (or uncle), but I do want to talk about the other thing that is eccentric: muscle contraction.
Our muscles utilize three different types of muscle contractions in locomotion (moving). Concentric, isometric, and eccentric muscle contractions produce varying forces in our everyday movement to create, hold, and absorb force. A concentric contraction happens when the muscle fibers shorten to produce force. This accounts for a large portion of the actions we perform in a day. Isometric contractions happen in a static state. The muscle fibers don't lengthen or shorten during this type of contraction, rather they hold like a chain holding something in place.
Eccentric muscle contractions happen like a braking system however. The muscle lengthens and produces immense force to slow down the actions of the joints to keep them safe. In training, eccentric muscle contractions tend to be something that many neglect or just don't know they need to add to their training.
Eccentric contractions happen when you walk, run, jump, land, and even sit down. However, the forces that occur in these actions happen in different capacities. While simple eccentric actions such as sitting and walking happen every day, they require significant less force than jumping, landing, and running. Eccentric muscle actions have the ability to create more force than concentric actions, largely in part of necessity of preventing injury.
So what does this look like in training? In order to cover the broad spectrum of forces and the rate at which they occur, you need to train eccentric capabilities across a broad spectrum. This means a control in tempo or simply the environment by which the action occurs.
If you've never done any type of eccentric training, I suggest starting with tempo movements. Controlling the lowering of a movement (i.e. lowering a deadlift or a bench press) for a set number of seconds. The longer the tempo, the more sustained force you output. Then, you can progress to do what are called fast eccentrics. Depth drops and catches can be a great tool to use (i.e. stepping off of a box and landing in an athletic position). The tricky thing with this is to make sure the height or intensity isn't too high in order to not get injured, because even as you build a tolerance to fast eccentric movements there is a threshold you shouldn't cross.
Two additional considerations when implementing the above eccentric training practices into your workouts are overall volume and DOMS (Delayed Onset Muscle Soreness). The DOMS is due to the amount of force produced in eccentric contraction, so being aware of extensive soreness as you begin to use eccentrics should be considered. Easing into frequency of use with eccentrics will help accommodate that soreness. The other consideration of volume is to make sure that you do not exceed what is known as Maximal Recoverable Volume (MRV) in efforts to drive adaptation. Again, the body has a threshold, and your MRV will determine what is best. With eccentrics, it is best to air on the side of less. Personally, when considering the need and training status of an individual I like to start around 20 reps per exercise. With the fast eccentrics, sometimes this is even lower in order to promote recovery and not over do the training stimulus.
If you have never done eccentrics in your training, it wouldn't be a crazy idea (pun definitely intended) to start implementing them. Start slow (literally, use a slow tempo) and build up. Increasing this capacity can not only make for a benefit in performance, but also in your day to day life.