Too often in fitness and specifically exercise selection, the terms “stretched” and “lengthened” are used interchangeably. This is a mistake, in my opinion. Words matter, and how you define them even more so. Let’s differentiate between them:
“Stretched” is used to refer to a position in an exercise, when the eccentric is completed and the concentric contraction is about to be initiated. This is completely separate from the anatomical length of a muscle. Let’s look at two different examples to illustrate this. In a preacher curl, at the bottom of the rep when the elbow is almost locked, this is termed the stretched position of the exercise. It is not lengthened in an absolute sense, but it is experiencing the maximal stretch possible within the constraints of that exercise being done correctly. Another example is a seated quad extension. When the knee is bent and the hamstring is almost touching the calf (before the weight hits the rest of the stack), this is the stretched position of the exercise. Again, this is not a lengthened quad–this is a position in the exercise in which the muscle worked (quads) is being stretched before a concentric contraction. Note that isometric exercises like a plank do not have eccentrics or concentrics, and thus no “stretched position”.
“Lengthened” is used to refer to the anatomical length of a muscle. Anatomical length typically involves three different positions: fully shortened, mid range, and fully lengthened. The muscle is weakest in its fully shortened position, strongest in its mid range, and weaker in its fully lengthened position (it follows a normal distribution, illustrated by a bell curve). We can go about ascertaining the shortened, midrange, and lengthened positions by first understanding the building blocks of the language of training: anatomy. By understanding where muscles originate and insert and which joints they cross, we can understand their anatomical length positions. Let’s use the example of the bicep from earlier with the preacher curl: it is commonly known as an elbow flexor (it performs a curling motion). However, one of the biceps muscles, the biceps brachii, crosses the shoulder joint as well. This means that it performs shoulder flexion in addition to elbow flexion and supination. In order to fully shorten it, we need to have it shorten over both of the joints it crosses: both the elbow and the shoulder must be flexed. This position can be seen in a high cable bicep curl. In order to find its lengthened range, the inverse is true: both the shoulder and the elbow must be extended. This position can be replicated in a lengthened cable curl. The midrange is easiest to find: it is where you are strongest. Both the elbow and shoulder are between flexion and extension. This can be found in a standing curl, like a normal dumbbell curl.
This comes with a necessary question: does this matter to my training? The answer is yes… sort of. Research has shown that training muscles in the lengthened positions can lead to a greater hypertrophy stimulus. Then again, so do externally stabilized modalities because they allow for more output, and training the lengthened range using an externally stabilized modality is not always an option. However, training in the shortened position can be more effective for proprioception and stability, like in the case of the high cable curl. And of course, none of this matters without effort…
This is not a silver bullet that will be a Band-Aid for other aspects of your training if they are lacking. This is simply yet another variable to give some thought to. This principle takes practice to understand a certain degree of study in order to understand the positions. But perhaps more importantly, if you want to really understand the concept, go out and try to apply these yourself: only then will you gain a firsthand understanding of how those ranges feel. Try certain exercises over time and see how you respond–track hypertrophy/strength as well as stability and see if there is a noticeable difference in how you move in those ranges. No matter what you do, just try.