The length-tension relationship shows that our muscles have an ideal joint angle where they produce the greatest tension. The type of tension that contributes almost entirely to bigger muscles (active) occurs at the midpoint of the range of motion for any normal movement. This happens when the weight’s line of action lies perpendicular, or at a 90° angle, to the body part serving as the lever. For an exercise to best build size and strength, it must train a muscle in a range close to this length.
Fewer connections form when the filaments that bind together to create tension operate too closely or too far apart. At long lengths, less overlap of these parts occur as they fail to reach each other which reduces the number of sites. At short lengths, too much overlap occurs and this also fails to allow most sites to form.
Tension, or the squeeze you feel when your muscles contract, is the main reason that muscles grow. This relationship clearly has important effects on proper training then. Unfortunately, many trainees choose exercises and ways of training that defy the length-tension relationship.
Our own physical body possesses a wisdom which we who inhabit the body lack. We give it orders which make no sense.
– Henry Miller
- Muscles have active and passive tension.
Active tension is the force created purely by the contractile elements of a muscle. Think of this as occurring when you flex your arm. Muscles also store energy when stretched and this creates passive tension. Think of this as the tension you store when you perform a counter-movement and release when jumping into the air.
A muscle operates most strongly at resting length with the highest active tension, but due to passive tension, it creates more total force at about 110-120% resting length total. Active tension is most important for stimulating muscle growth, but passive can play a role too.
Passive tension allows a pre-stretch or stretch-shorten cycle. A pre-stretch occurs as a stretch of a muscle followed by a subsequent concentric contraction in a short time frame. It helps the muscle to produce more force.
- The optimal joint angle depends on all of the muscle’s insertion points.
Multi-joint muscles attach to multiple joints. They change length depending upon the positions of all their joints. Many major muscles throughout the body act on more than one joint.
The body will attempt to lengthen at one joint before shortening at another joint or vice versa. This keeps you at that middle length that works best for tension. When you take a step, your hip flexes while your knee extends. When you pull something, your shoulder extends while your elbows flexes. When you push something, your elbow extends while your shoulder flexes.
When you isolate a joint, your muscles fail to keep the ideal middle length since they move at only one joint and thus stretch and shorten too much.
- Multi-joint muscles possess passive and active insufficiencies.
Passive insufficiency occurs when a multi-joint muscle fails to extend at all its joints. This happens since a full stretch at multiple joints cannot occur. This position represents the longest possible length of a muscle. The muscle will not generate much active tension but will generate high passive tension. Anytime you feel a deep stretch in the muscles, such when reaching to touch your toes, you feel passive insufficiency.
Active insufficiency occurs when the multi-joint muscle fails to shorten at all its joints. You may feel this as a cramping sensation. This results in little active or passive tension. While sitting on a chair, extend your legs fully while also bending forward at the waist. When touching the front of your thighs, you will notice the inability to intensely contract the long band of muscle located between the outer part of the quads (vastus lateralis) and the inside of your leg (adductors). This muscle you touched, known as the rectus femoris, enters active insufficiency since it shortens at both the hip and the knee. You would never perform this motion in daily life, unless using a leg extension machine.
Active and passive insufficiencies highlight that muscles grow weaker as they move further away from an ideal position. Proper lifting should never expose you to these portions of the range of motion. This can only occur when doing a purposely unnatural exercise.
The Length-Tension Relationship Favors Compound Exercises
Boil things down to their fundamental truths and reason up from there.
– Elon Musk
We know with overwhelming evidence that the length-tension relationship is true. Despite being one of the lone basic truths in the exercise world, it seems surprising that many exercises ignore this concept. The length-tension relationship gives us one of the strongest pieces of evidence that our bodies are designed for compound movements when dealing with heavy weights.
Compounds allow the muscle to form more tension throughout the range of motion, which means better results for strength and size. They also avoid active and passive insufficiencies. I also suggest not performing exercises too slowly (or too quickly).
If you do any movement that either stretches or shortens a muscle too much, you have a very poor exercise. This occurs through every isolation exercise. In fact, the big three alone seem to optimize length-tension for all the muscles involved, even for compounds. Any deviation away from these, and you have a less effective (and less safe) exercise.