Sometimes stretching makes connective tissues denser and more resistant to extension. Other times, it promotes growth. If I do heavy curls every other day, the tendons in my arms won’t stretch; they’ll get thicker with more collagen fibers.
Stretching with lighter weights probably causes less of an inflammatory response than stretching with heavier weights. A lower inflammatory response may reduce proliferation of collagen fibers and prevent the tissue from strengthening.
The body apparently has a negative feedback system for resisting the sudden stretch of connective tissue. You can stretch a little, but then the body tries to compensate by strengthening.
However, one way to beat the system may be to “convince” the tissues that the stresses they see are normal.
The answer may be slow and steady loading. The body may be programmed to be more compliant to slow and steady loads. When you gain weight, your tissues need to stretch. Without this ability, weight gain would be limited, which could, I suppose, lead to starvation in times of famine.
One could also use the example of normal growth during maturation. Think about your ligaments. As the bones grow, so do the ligaments. How do the ligaments “know” they’re supposed to grow, rather than strengthen and resist further growth? The answer, perhaps, is slow and steady loading.
Perhaps the body’s response to slow and steady loading is to comply with the applied forces, whereas its response to rapid and heavy loading is to resist.
The mechanism for strengthening appears to be inflammation and consequent proliferation of collagen. What about the mechanism for lengthening? I mentioned the piezo-electric properties of collagen in my earlier post because it’s been found that certain tissues (nerve and bone) grow when placed in an electric field. If stretching connective tissue causes it to generate an electric field, then perhaps that field, if maintained over time, will promote extension of the connective tissue through normal growth.
