Why animals have different muscle fibre types.

Area of Science:

• Animal physiology
• Biomechanics
• Muscle fiber research

Background:

• Animals possess distinct muscle fiber types: slow-twitch with low maximum shortening velocity (Vmax) and fast-twitch with high Vmax.
• Previous research suggested advantages of different fiber types during locomotion based on in vitro properties.
• Optimal force, power, and efficiency in muscles depend on the ratio of shortening velocity (V) to Vmax.

Purpose of the Study:

• To investigate if animals utilize different muscle fiber types at velocities optimal for mechanical power and efficiency during actual locomotion.
• To compare the in vivo shortening velocity (V) of muscle fibers with their maximum shortening velocity (Vmax).

Main Methods:

• Comparative analysis of muscle fiber shortening velocity (V) during locomotion against their maximum shortening velocity (Vmax).

Main Results:

• During slow locomotion, slow muscle fibers operate at velocities yielding peak mechanical power and efficiency.
• Fast muscle fibers are utilized at their optimal shortening velocity during maximal movements.
• Maximal movements are unachievable without fast fibers due to the insufficient shortening speed of slow fibers.

Conclusions:

• Muscle fiber recruitment during locomotion is matched to their intrinsic properties for optimal performance.
• Fast muscle fibers are critical for achieving high speeds and powerful movements in animals.
• The study elucidates the functional significance of different muscle fiber types in vivo.