Exercise selection involves more considerations than just muscle lengths, but for many, having a grasp of them will already be a significant 'level-up' moment. If the rationale for your exercise selection doesn't extend beyond 'this exercise trains this muscle', you should keep reading.
Contractile Ranges
Our muscles can contract across 3 general ranges: short, mid, and lengthened. Though there can be significant overlap, these can generally be categorised into isolation exercises (short-range) and compound exercises (mid and lengthened range). We are quickest to fatigue in the short-range, and slowest to fatigue in the lengthened-range.
During contractions, protein filaments called actin and myosin that are housed in sarcomeres (contractile units of muscle) slide over each other, with the myosin cross-bridges attaching to the actin filaments. This pulls them inward and creates an overall shortening of the muscle (ie contraction). With this sliding filament theory in mind, you can imagine that the length of a muscle fiber can influence its ability to contract and generate peak force. If the sarcomere is too short, it can't generate high amounts of force as there is already overlap and insufficient space for myosin cross-bridges to form. Conversely, if the sarcomere is too long, the actin filaments are too spaced out for the myosin cross-bridges to reach and form attachments and create contractions. So, it stands to reason that when things are mid-range, this is the optimal length for these cross-bridges to form, meaning our ability to generate force is greatest. This is why you can bench press more than you can pec-fly.
Now that we have an idea of length-tension relationships, we can start to understand how that might influence our exercise selection. When putting together a programme, most people tend to gravitate towards the bread and butter exercises like the bench, squat, deadlift, and leg press. Our ability to generate force is highest with mid-range movements like these, which bodes well for goals involving strength and size. But it's also important to train the other ranges if we want to maximise our efforts to grow and improve.
Eliminating Superfluous Exercises
Arm training is the easiest example to use when looking at unnecessary exercises in most people's programmes. In one session, they'll have a barbell biceps curl, a dumbbell biceps curl, and a cable straight-bar biceps curl. All three exercises train the same contractile range (mid), which makes two of them unnecessary - the job can be done with one. A smarter approach in the context of this discussion would be to have standing dumbbell biceps curl (mid-range), a preacher curl (short-range), and a seated incline biceps curl (lengthened-range). Now the biceps have been trained by selecting specific exercises that favour a different portion of the muscle's length-tension relationship.
Eliminating unnecessary exercises from programmes opens up better progression opportunities. The same audit can be applied to any muscle group or training session. The results are often similar - far too many exercises achieving the same outcome, while the peripheries are neglected. Putting aside the valuable improvements in muscle hypertrophy, a lack of appropriate exercise diversity can also create problems with muscular imbalances and joint function. The joint position will influence muscle action and function, but part of training the entire contractile range is about utilising the joint's range of motion appropriately: the use it or lose it principle. If we don't place the joint in varying positions in a controlled setting such as a training session to improve its stability and strength, what happens when it is forced into it in an uncontrolled dynamic environment?
Introducing variety into your programmes can be a valuable strategy. Having a basic grasp of the length-tension relationship should be a factor in exercise selection if you want to continue your progress.
Live strong and prosper.
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