Tendon Adaptation, Form Following Function and Sarcomerogenesis

In young and older adults trained at 60% of one repetition maximum, eccentric training increased fascicle length and concentric training increased pennation angle, yet the patellar tendon adapted the same way to both. The tendon seems blind to the direction of load and may respond once a strain threshold is reached. Links between architecture and function in living people are hard to prove because recruitment, calcium handling and connective tissue all play a part, so no single index predicts injury. Still, examples point to a link: steep pennation in highly trained individuals, fascicle length in sprinters, and rapid fascicle shortening after Achilles tendon rupture, which may help sarcomeres work at a useful length while the repaired tendon is compliant. Martino ends with sarcomerogenesis and Brenda Russell's idea that form follows function. In a Stanford study, three weeks of Nordic hamstring training lengthened distal biceps femoris long head fascicles, but through longer sarcomeres rather than more sarcomeres in series, possibly from a release of passive tension. Whether this holds long term is still being studied.