Muscle strain injuries in sport
Why muscle strain injuries happen in sport is an interesting problem to solve because experiments have only been able to produce them by elongating muscles to extra-physiological lengths that are impossible to duplicate in real life because of the limits of the joint angle range of motion.
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#1. Muscles tear only when they are elongated to very long lengths
Muscles tear when they are elongated to the point of failure. It does not matter whether they are elongated passively or actively (in the context of an eccentric contraction). The muscle force produced does not matter. The only thing that matters is the extent to which the muscle is lengthened.
When muscles are pennated, they must be strained to extreme lengths before they will tear. These extreme lengths are clearly totally outside the scope of what is possible to achieve within the physiological constraints of a joint. This problem makes it very difficult to understand why muscles are strained during sporting activities.
#2. Muscles tear at shorter lengths if they have previously experienced stretch-induced injury
The only factor that has been shown to reduce the muscle length at which a muscle will rupture is the presence of previous stretch-induced injury. When muscles are strained to a point just before they would rupture, a subsequent elongation causes rupture to occur at a shorter muscle length. In other words, cumulative (minor) stretch-induced injuries without recovery likely lead to a complete rupture taking place at some point later on. This is almost certainly how muscle strains occur during sport.
Conclusions
Muscle strain injuries are tears that occur at the muscle-tendon junction (MTJ) in single eccentric contractions or passive stretches. Experimentally, muscles tear when they are elongated to the point of failure. It does not matter whether they are elongated passively or actively in an eccentric contraction, muscles still tear at the same length. Similarly, neither muscle force nor the activation level nor the presence of fatigue affect the muscle length at which a muscle tears. These findings demonstrate the importance of reaching a key threshold length for a muscle strain injury to occur. However, when muscles are torn in experimental settings, the lengths required to tear them are not within the bounds of what is physiologically possible in a joint movement. This makes it difficult to see how muscle strain injuries occur during sport. Even so, when muscles are elongated to a point just before they would normally rupture, a subsequent elongation causes rupture to occur at a shorter muscle length. Hence, cumulative (minor) stretch-induced injuries without recovery are likely responsible for a complete rupture taking place later on. This is probably how muscle strains occur during sport.
Comments (8)
Do you think hydration could play the key role in minor strains? Stiffer tendons leading to more muscle lengthening or just disrupted SSC?
Anything that causes a muscle to lengthen more than previously would be a factor. Not sure if we have any data on how much hydration levels alter tendon stiffness
Chris, if hipertrophy is fiber specific, how can i train biceps more than one time if i do a row, a pushdown and a bicep curl, just one set of each, but biceps its my biceps is gonna get fatigue?
I don't understand what you are asking. All exercise causes fatigue
If muscle needs to strain beyond the ROM allowed by joint structure, how do the minor stretch induced injuries that lead to the cumulative effects first happen?
Muscles only tear completely if taken to supraphysiological lengths. Less severe damage will occur at shorter lengths
interesting. but what exactly are those stretch induced injuries at the MTJ? Also an aspect i wondered: would stiffer tendons create a higher risk for the muscle strain injury, as for the same rom we would need more muscle length?
I agree. I think that there is a trade-off between tendon injury risk and muscle strain injury risk