Abstract
Background: Training programmes incorporate a range of exercises aimed at improving power and overall athletic performance. However, the effects of varying loading modes in commonly used explosive jump protocols – namely the countermovement jump (CMJ) and squat jump (SJ) – remain inconclusive in the literature, with potential implications for optimising training specificity and effectiveness.
Aims/objectives: The main aim of this study was to investigate how different jump types and external loading conditions (25 kg) independently and interactively influence concentric jump performance metrics and their associated asymmetries during repeated vertical jump trials. The first objective aimed to examine the main and interaction effects of jump type (CMJ and SJ) and 25 kg external loading modes – weighted vest (WV), handheld dumbbell (DB), rear loaded straight barbell (BB), and hexagonal (trap) bar (HB) – with body weight (BW) as a control, by comparing key kinetic variables: mean concentric force (MForcecon), mean concentric impulse (MImpulsecon), mean concentric rate of force development (MRFDcon), mean concentric power (MPowercon), mean concentric velocity (MVelocitycon), and jump height (JH). The second objective aimed to examine the main and interaction effects of these same jump types and external loading modes on asymmetries in temporal concentric force characteristics, specifically mean concentric force asymmetry (ASY-Forcecon), mean concentric impulse asymmetry (ASY-Impulsecon), and mean concentric rate of force development asymmetry (ASY-RFDcon).
Methods: Thirty-one male rugby players (mean age: 19.15± 1.68 years; mean stature: 185.11 ± 7.43 cm; mean body mass: 89.28 ±14.34 kg), actively competing at the university level, volunteered to participate in this study. These athletes performed a total of 30 explosive jumps, consisting of two commonly used jump modalities: the CMJ and the SJ. All jumps were executed on a calibrated dual uniaxial force plate (VALD ForceDecks) to ensure precise measurement of kinetic variables, such as MForcecon, MImpulsecon, MRFDcon, MPowercon, MVelocitycon, JH, ASY-Forcecon, ASY-Impulsecon, and ASY-RFDcon. Baseline trials were performed at BW, followed by external loading modalities (WV, DB, BB, HB), each adding 25 kg. To minimise fatigue, leaning, and adaptation effects, jump type and loading mode were randomised in blocks, with three trials per condition (averaged), 30-s rest between trials, and 10-min rest between blocks. For the SJ, a ~3-s static hold preceded take-off to remove SSC influence...