Increasing passive stiffness
In our bodies, the biochemical elements of the muscle-spring system are the protein titin (in muscle tissue) and collagen (in tendon tissue). The stiffness of these proteins determines the passive stiffness of our muscles and tendons, respectively.
The long-term objectives of ‘spring training’, should be to create shorter titin molecules and more cross-linked collagen to increase the passive stiffness of the muscles and tendons that make up our springs. For athletes and coaches, the important question is ‘can training produce these changes?’ The answer to this question is ‘yes’.
For example, training basketball players for eight weeks results in approximately 10% improvement in two measures of passive stiffness, which in turn translates into better jumping performance. This tells us that our springs can be stiffened with the appropriate training.
Increasing active stiffness
Increasing the passive stiffness of muscles and tendons is all well and good, but to gain a performance advantage, you need to translate that passive stiffness into speed. Turning passive stiffness into speed involves activating the muscles within the spring at the right time (increasing active stiffness).