Evaluation of The Isometric and Dynamic Rates of Force Development in Multi-Joint Muscle Actions.

Area of Science:

• Biomechanics and Exercise Physiology
• Sports Science and Performance Analysis

Background:

• Rate of force development (RFD) is crucial for athletic performance, reflecting the ability to generate force rapidly.
• Assessing RFD across different movement types, such as isometric and dynamic actions, is essential for understanding explosive power.
• Previous research has explored RFD in various exercises, but direct comparisons between isometric leg press (ILP), countermovement jump (CMJ), and squat jump (SJ) require further investigation.

Purpose of the Study:

• To compare the rate of force development (RFD) during isometric leg press (ILP), countermovement jump (CMJ), and squat jump (SJ) in team sport athletes.
• To investigate differences in peak force (Fpeak) and RFD across various time epochs (0-200 ms) between these exercises.
• To determine if RFD normalized to Fpeak provides a comparable measure of explosive force production across different movement types and sexes.

Main Methods:

• Twenty-three team sport athletes (9 females, aged 21-24 years) participated in the study.
• Force-time data were collected during ILP, CMJ, and SJ to calculate Fpeak, RFDpeak, and RFD at specific time intervals (0-50, 50-100, 100-150, 150-200 ms).
• CMJ and SJ height, along with center of mass displacement, were also measured.

Main Results:

• Peak RFD and RFD at 0-150 ms were similar between CMJ and SJ, as was Fpeak.
• The isometric leg press (ILP) demonstrated significantly higher RFD at 50-100 ms and 100-150 ms compared to CMJ and SJ, even when normalized to body mass.
• RFD normalized to Fpeak was similar across ILP, CMJ, and SJ, and between males and females, particularly at the 50-100 ms interval.

Conclusions:

• The countermovement jump (CMJ) and squat jump (SJ) exhibit comparable explosive force production capabilities, suggesting they can be used interchangeably for assessing lower limb power.
• Rate of force development normalized to peak force serves as a robust, strength-independent metric for evaluating explosive power, facilitating comparisons across individuals and exercises.
• While ILP shows higher absolute RFD in later phases, normalized RFD highlights similarities in the initial explosive capacity between isometric and dynamic movements.