Comparison of Rate of Force Development between Explosive Sustained Contractions and Ballistic Pulse-like Contractions during Isometric Ankle and Knee Extension Tasks

Abstract

Background: The rate of force development (RFD) is a measure of explosive strength, commonly evaluated within the same repetition as peak force/torque, by instructing the participants to produce “fast” and “hard” contraction. Previous studies have indicated that attempting to achieve the maximal RFD and maximal force/torque within the same contraction may not be optimal. Methods: This study assessed the differences between explosive sustained (“fast-and-hard”) and ballistic (pulse-like) contractions on the RFD during isometric ankle and knee extensions in young, recreationally active participants (n = 33; age: 23.4 ± 5.6 years). The participants performed both contraction types for isometric ankle and knee extension tasks. The RFD was calculated for time intervals 50, 100, 150 and 200 ms from the contraction onset and also in between these time points (50–100, 100–150 and 150–200 ms). Findings: The results of this study showed a higher RFD in the ballistic contractions in later time intervals (100–150 and 150–200 ms) compared to that of the explosive sustained contractions (effect size (Hedge’s g) = 0.51–0.73). The differences between explosive sustained and ballistics contractions were larger and occurred for more outcome variables in females than males. Peak RFD was also larger in ballistic contractions, both for females (p = 0.010; Hedge’s g = 0.54) and males (p = 0.003; Hedge’s g = 0.78). The intra-session reliability of the RFD was similar for both contraction types, increasing from moderate to excellent with longer time intervals. Conclusion: Our results suggest that ballistic contractions should be used when the assessment of the RFD is the primary goal. When the aim is to assess both the RFD and peak force, it is suggested to use the combination of separate explosive sustained contractions and ballistic contractions in the protocol.