Preloading and range of motion effect on plantarflexor muscle performance

Area of Science:

• Biomechanics
• Human Movement Science
• Exercise Physiology

Background:

• Isotonic testing on dynamometers is common for assessing muscle function.
• Understanding the influence of preloading and range of motion (ROM) is vital for accurate interpretation of results.
• The Biodex dynamometer is frequently used in clinical and research settings.

Purpose of the Study:

• To investigate the impact of maximal preloading and varying range of motion (ROM) on plantarflexor muscle mechanical parameters.
• To analyze how these testing variations affect torque, velocity, and power measurements using a Biodex dynamometer in isotonic mode.

Main Methods:

• A descriptive comparative study involving 15 healthy subjects.
• Four maximal isotonic tests were conducted on the Biodex dynamometer with a 27Nm load.
• Tests involved two ROMs ( -12° to +32° and -12° to +47°), with and without a 2-second maximal preloading contraction.

Main Results:

• Significant differences in mechanical parameters were observed across the four testing conditions (MANOVA p < .05).
• Maximal preloading increased torque and power while decreasing velocity at specific angles (-10°, +5°).
• Increased ROM enhanced velocity at +20°, and preloading shifted isotonic testing towards isoaccelerative characteristics.

Conclusions:

• Isotonic assessment parameters (torque, velocity, power) on the Biodex dynamometer are sensitive to testing conditions.
• Maximal preloading and range of motion significantly influence mechanical output.
• Standardizing preloading and ROM is essential for reliable and reproducible clinical assessments of plantarflexor function.