Sprinters and marathon runners. Does isokinetic knee extensor performance reflect muscle size and structure?

Area of Science:

• Sports Medicine
• Exercise Physiology
• Muscle Physiology

Background:

• Understanding the relationship between muscle structure and function is crucial for optimizing athletic performance.
• The quadriceps femoris muscle plays a key role in knee extension, vital for activities like sprinting and running.

Purpose of the Study:

• To investigate the correlations between quadriceps muscle structure and its concentric functional output in sprinters and marathon runners.
• To analyze how muscle cross-sectional area and fiber type composition influence isokinetic knee extensor performance at various velocities.

Main Methods:

• Isokinetic knee extensor output was measured at angular velocities from 30-180 degrees/second.
• Integrated electromyographic activity (iEMG), quadriceps cross-sectional area (CSA), and vastus lateralis fiber composition were analyzed.
• Comparisons were made between five sprinters and five marathon runners.

Main Results:

• Peak torque, instantaneous power, and contractional work were closely correlated with quadriceps CSA and type II fiber areas.
• When normalized for CSA, these relationships were only significant at 180 degrees/second and specifically for type IIA fiber area.
• Electromyography indicated the vastus lateralis muscle was representative of the total mechanical output.

Conclusions:

• Peak torque and instantaneous power at high angular velocities (e.g., 180 degrees/second) reflect intrinsic muscle structural characteristics.
• Optimal power output and efficiency occur at velocities exceeding the tested isokinetic dynamometer range, differing between sprinters and marathon runners.