Abstract
Background: This study compared the effects of performing different unilateral combined training interventions on diverse vertical and horizontal jumping performance parameters, change of direction, concentric and eccentric mean power, and their associated inter-limb asymmetries in young soccer players. Methods: Forty-seven young male soccer players (age: 15.5 ± 0.9 years) were distributed into three groups. Two groups performed the same training volume with both legs, beginning with the weaker leg (Stronger Volume Weaker leg group (SVW), n = 14) or with the stronger leg (Stronger Volume Stronger leg group, (SVS), n = 15). The third group executed double the volume with the weaker leg and also commenced with such leg (Double Volume Weaker leg group (DVW), n = 16) during a 10-week period. Pre- and post-intervention tests included a single-leg hop, single-leg lateral hop, triple hop, bilateral and unilateral countermovement jumps, a change of direction speed test, concentric and eccentric mean power during the lateral squat test, and their corresponding asymmetries. Results: Single-leg hop weaker leg, triple hop weaker leg, and bilateral countermovement jump improvements were achieved in the SVW (ES: 0.29 to 0.46) and DVW (ES: 0.55 to 0.73) groups. Between-groups analysis showed better results in single-leg hop in the SVW and DVW compared to group SVS. The DVW group achieved better improvements in countermovement jump in comparison to groups SVS and SVW. Conclusions: Groups that started with the weaker leg seemed to achieve a greater volume of significant changes than when starting with the stronger leg. Performing a double volume on the weaker limb does not guarantee further improved performance compared to other groups.
Highlights
Sprints, accelerations, decelerations, jumps, and kicks are some of the skills performed during multidirectional team sports and often occur in multiple planes of motion [1,2]
This study showed a substantial enhancement in unilateral jumping in those groups that started the training session with the weaker leg (ES: 0.31 to 0.82) and a significant reduction in between-limbs asymmetries in the triple hop when performing the double volume with the weaker leg (ES: 0.88) [20]
The main findings of the study were: (1) likely training effects in single-leg hop (SLH) were found in SVW group with the stronger and weaker leg; (2) likely improvements were found in SLH weaker leg in DVW group; (3) most and very likely improvements were found in single-leg lateral hop (SLLH) and triple hop (TH) with both stronger and weaker leg in those groups that started with the weaker leg; (4) substantial enhancement in countermovement jump (CMJ) bilateral and with both stronger and weaker leg in those groups that started the training programme with the weaker leg; (5) likely improvements in change of direction (COD) weaker were reached in those groups that performed the same volume in both legs; and (6) moderate and likely asymmetry reduction were achieved in TH and COD, respectively, in the DVW group
Summary
Accelerations, decelerations, jumps, and kicks are some of the skills performed during multidirectional team sports and often occur in multiple planes of motion [1,2] The execution of these skills often occur in differing volumes between limbs, resulting in the development of asymmetries between the limbs [3].Inter-limb asymmetries are defined as the distinction in execution or capacity of one leg comparative with the other [3], and recent literature has investigated this phenomenon across multiple physical qualities, such as change of direction (COD) speed, jumping, and strength [4,5]. Previous research has suggested that asymmetries > 15% may have higher possibility of lower extremity injury in comparison with scores beneath this cutoff [6] In conflict with this suggestion, asymmetries that are
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