A recent study by the University of Koblenz clearly shows that the fitness of the calf muscles plays a decisive role in maximising strength production in the entire muscle architecture of the lower extremities. This is most evident in sports that rely on rapid or spontaneous force development.

Koblenz, September, 18th 2024 The Latin word for „feather“ is „penna“, which translates as „pennation“ or „pinnation“ and gives the muscular development of this complexly organised area of the lower muscle architecture its apt name. The fact that these pinnate muscle fibres are arranged at an angle to the tendon appears to be an ingenious evolutionary solution for maximum force development.

Pinnately arranged muscles can accommodate more muscle fibres in a comparable volume. These are therefore shorter, but the cross-sectional area can increase, which has an effect on force production. This is known as the physiological cross-sectional area (PCSA) and is an indicator of the muscle’s ability to generate force. The more muscle fibres next to each other, the greater the maximum force effect, which has the effect of an optically large muscle when viewed from the outside. However, the development of rapid strength always comes at the expense of endurance.

Another criterion of the study became clear in muscle contraction in relation to speed. While muscles contract telescopically, in fast-twitch muscle fibres these telescopes are shortened and therefore not long enough to produce efficient speed. The fibres and thus the force are distributed over the parallelism of the fibres.

However, the researchers were able to show that for a given ratio of length to thickness, there is an optimum fibre angle to enable maximum force production. They called this phenomenon the pennation mechanical advantage (PMA).

The calf muscle is short and therefore not ideal for a feathered design. The extensors of the leg only cross over one joint, the ankle, knee and hip. Only at these points do the fibres have the angle required for optimum force development and therefore have the highest PMA. In this related relationship, the muscle architecture can generate the maximum required force and thus six times the contraction force. The gluteal muscle is responsible for motor control and rapid movement in the system.

The future of muscle research is leading to biomechanics and robotics, where the pinna has new approaches to offer. One could think about better training methods for athletes, improved rehabilitation techniques for injuries and even more efficient designs for robots and prostheses that mimic human movements, provided they utilise artificial muscle actuators. While research into muscle architecture continues, it turns out that nature has optimised our muscles in ways that are both sophisticated and efficient. The clever, feathered design of some of the leg muscles is a natural engineering feat that has been perfected over millions of years.

Originalpublication:

DOI: 10.1098/rsos.240037

PictureSource: Karolina Kaboompics Pexels