Stretching: Can it make a muscle longer?

[Tyciol]

Note, this is not about muscle attachment sites. Nor is it about tendon lengths. It is about the length of muscular tissue. The length of a muscle varies based on the position of its ends in space already. It is about a longer muscle belly, something that wouldn't change the space between the bulge and the joint while flexing (that's tendon-determined I think) but would change the distance while relaxed since the muscle could hang loosely and the tendon would not be taut.

Changes in human skeletal muscle induced by long-term eccentric exercise

muscular work of high tension can induce fine-structural alterations. When repeated over a long period of time, extreme tension demands seem to initiate reorganization in the muscle fibres, predominantly in the, ultrastructurally defined, Type-2 fibres. This adaptation probably results in a better stretchability of the muscle fibres

Thomas Kurz references this in one of his Q and As on how perhaps isometric as well as eccentric contractions (isometrics stray both into concentric and eccentric territory as nothing is perfectly immobile) could result in muscle lengthening.

To use the hamstring as an example, this isn't about changing where it attaches on the back of the lower leg or on the pelvis, but about the length of the muscle itself and where it can contract from, the amount of actin/myosin units along the length of the fibers. Could it multiply along the length as well as expanding the myofibrils laterally when it hypertrophies?

Eccentric training does not increase sarcomere number in rabbit dorsiflexor muscles

Eccentric training of rabbit dorsiflexor muscles (50 maximal contractions, 2 times per week, for 12 weeks) increased sarcomere number by only 3% in superficial fascicles of the tibialis anterior (TA) and did not change sarcomere number in deep fascicles of the TA nor in proximal or distal fascicles of extensor digitorum longus. Thus eccentric training had little or no effect on sarcomere number. These results do not support previous speculation that eccentric training produces increases in sarcomere number.

This study seems to clash, but looking past the conclusion, we do notice that the amount of sarcomeres increased 3%. While small, this shows that it actually DOES lengthen. That it failed to do so in other muscles doesn't matter, the experiment may not have properly targetted or stretched them. The problem with "eccentric training" is that it doesn't necessarily specify through what range of motion it was trained, since it probably needs to, beyond being concentric, also involve a big stretch of the muscle.

We also have to keep in mind that one discusses sarcomere length and the other number.

[gomez26]

perhaps related to serial sarcomere addition?

http://www.thefreelibrary.com/Applic...ers-a070695084
http://www.goju.com/index2.php?optio...do_pdf=1&id=93
http://jan.ucc.nau.edu/~pe/exs490web...leadaptUSE.htm

[Tyciol]

Yeah something like that. I'm wondering if maybe it's something like how our fat cells multiply when they get too big. In this case, are there fluctuations in the length of sarcomere and do they perhaps divide into 2 sarcomere when they get too long? Are new sarcomere formed near the ends near the tendons or in the middle or something like that?

[gomez26]

apparently there is a region of transition cells at the end of muscles (where muscle turns to tendon), these cells can turn into muscle cells if exposed to enough stretching load. but .... it would take many hrs a day of stretching to induce noticeable changes in healthy muscle. this mechanism was investigated more for rehab of injured muscles to increase mobility etc rather than any reasonable training applications for sport or recreation. i.e. limbs strapped into certain positions for many, many hrs as part of rehab schedule. nevertheless the mechanism for both lengthening & shortening a muscle does exist.

[Tyciol]

I imagine targetting stuff like this might be easier with biaxial muscles like the hamstring, rectus femoris or gastrocnemius. Single-joint muscles like the soleus or short head or triceps would be problematic since you're limited by the overall joint mobility (plantar/elbow flexion).

The biceps everyone fixates on do have a limitation in regards to the amount of pronation/elbow extension/shoulder hyperextension one can do, but I'm wondering if people combine all 3 of these to the maximum.

I'm thinking you'd probably want the resistance pulling along the length of the forearm (wrist directly below elbow) so that the traction is kind of along the length rather than in a preacher curl type position where it is stretched with the resistance perpendicular. Relaxing too much is dangerous like that since the elbow could hyperextend, seems like there would be greater ligament strain that way. There's still ligament straight when we lock out in line with gravity, but I dunno, it just doesn't seem like it'd be as bad. Like consider how we adopt that locked-out position with a deadlift yet can support huge weights that way.

Come to think of it, the "skinning the cat" exercise could get that exact combination of hyperextension/supination/elbow extension under traction that the bicep would need to be maximally stretched wouldn't it?


Another thing is, if the shortest a muscle can contract to is limited by the max overlap (when the H-band is zero link and the actin fils touch each other) this means if muscle got longer, it limits how short they could become. This, in addition to the whole "the bicep is so big it impedes elbow flexion" could explain the (literal) lack of flexibility in certain joints. That said, the opposite is difficult to imagine, could someone stretch their tricep to the degree where they could no longer lock out their elbow?

I'm going to say no, because you probably couldn't stretch the short heads that far due to limitations of elbow flexion. Possibly the long head since it is biaxial and you could stretch it via hyperflexion of the shoulder. So, maybe the long head of the triceps can become more over-active insufficient in shoulder-extended movements (like kickbacks or dips) if it is stretched?

Beyond the lower resting tonus, this is also an explanation for why spinal contortionists have such difficulty maintaining a neutral posture. Perhaps the muscles that stabilize the core are lengthened and limited to how much they can contract? It's difficult to imagine this though and I think it's unlikely because while I could see it limiting the max contraction (curl, hyperextension) I don't think it would be so long as to prevent simply attaining a neutral posture, so I think the low tonus explanation is better for why they often need a back brace.