Preloading and range of motion effect on plantarflexor muscle performance

Objective: To determine the effects of maximal preloading and range of motion (ROM) on the mechanical parameters of the plantarflexor muscles obtained while using the isotonic mode of testing of a Biodex dynamometer.

Design: A convenience sample of healthy subjects in the context of a descriptive comparative study.

Setting: Research laboratory in Canada.

Subjects: Fifteen volunteered subjects without history of injury or disorder to the right lower extremity.

Measurements: Four maximal isotonic tests were performed against a selected load of 27Nm. For the first two tests, the movement at the ankle ranged from -12 degrees (dorsiflexion) to +32 degrees (plantarflexion); one of these tests was preceded by a 2-second maximal preloading contraction, while the other was performed without preloading. For the other two tests, the ROM at the ankle was increased by 15 degrees of plantarflexion and thus ranged from -12 degrees to +47 degrees; again one of these tests was executed with preloading and the other without preloading.

Results: The four tests showed differences in the mechanical parameters (MANOVA p < .05). At angles of -10 degrees and +5 degrees, subjects produced higher torque and power but lower velocity values for the two tests preceded by a maximal preloading. The effect of ROM was demonstrated at +20 degrees where tests performed in a small amplitude reached a lower velocity than the corresponding tests performed in a larger amplitude. Based on the velocity profiles, the results also revealed that maximal preloading changed the selected isotonic movement of the Biodex dynamometer to an isoaccelerative movement characterized by high torque and power production.

Conclusions: Isotonic assessment using the Biodex dynamometer provides different values of torque, velocity, and power depending on the testing conditions used. In clinical settings, it would be important to control these testing conditions.

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