Specific Changes in Young Soccer Player's Fitness After Traditional Bilateral vs. Unilateral Combined Strength and Plyometric Training

Abstract

The aim of this study was to compare changes in young soccer player's fitness after traditional bilateral vs. unilateral combined plyometric and strength training. Male athletes were randomly divided in two groups; both received the same training, including strength training for knee extensors and flexors, in addition to horizontal plyometric training drills. The only difference between groups was the mode of drills technique: unilateral (UG; n = 9; age, 17.3 ± 1.1 years) vs. bilateral (TG; n = 9; age, 17.6 ± 0.5 years). One repetition maximum bilateral strength of knee muscle extensors (1RM_KE) and flexors (1RM_KF), change of direction ability (COD), horizontal and vertical jump ability with one (unilateral) and two (bilateral) legs, and limb symmetry index were measured before and after an 8-week in-season intervention period. Some regular soccer drills were replaced by combination of plyometric and strength training drills. Magnitude-based inference statistics were used for between-group and within-group comparisons. Beneficial effects (p < 0.05) in 1RM_KE, COD, and several test of jumping performance were found in both groups in comparison to pre-test values. The limb symmetry index was not affected in either group. The beneficial changes in 1RM_KE (8.1%; p = 0.074) and 1RM_KF (6.7%; p = 0.004), COD (3.1%; p = 0.149), and bilateral jump performance (from 2.7% [p = 0.535] to 10.5% [p = 0.002]) were possible to most likely beneficial in the TG than in the UG. However, unilateral jump performance measures achieved likely to most likely beneficial changes in the UG compared to the TG (from 4.5% [p = 0.090] to 8.6% [p = 0.018]). The improvements in jumping ability were specific to the type of jump performed, with greater improvements in unilateral jump performance in the UG and bilateral jump performance in the TG. Therefore, bilateral strength and plyometric training should be complemented with unilateral drills, in order to maximize adaptations.

Limb symmetry index in competitive alpine ski racers: Reference values and injury risk identification according to age-related performance levels

“…Additionally, as is done in youth soccer, unilateral drills should be implemented in the training process of young athletes to maximize (neuronal) adaptations. 53 …”

Effects of Combined Strength and Power Training on Physical Performance and Interlimb Asymmetries in Adolescent Female Soccer Players

“…Additionally, inter-limb asymmetries might also play a role in performance (e.g., greater symmetrical team-sports players seem to be faster that their asymmetrical counterparts) 18,19 . In this regard, strength training is amongst the most frequently used strategies to improve soccer performance and high-intensity actions, as well as to decrease asymmetries 12,14,[20][21][22] .…”

“…Therefore, training programs should focus on combined bilateral and unilateral strength training to decrease inter-limb asymmetries and to increase performance during F o r P e e r R e v i e w 4 competition. However, relatively few studies have addressed this issue in young soccer players 22,23 . In addition, to the authors´ knowledge, no studies have analyzed the effect of an intervention on inter-limb asymmetry in youth female soccer players, hence, more studies for this population are warranted.…”

Bilateral Deficit and Bilateral Performance: Relationship with Sprinting and Change of Direction in Elite Youth Soccer Players

“…The relationship between UL strength training and COD in soccer has been largely investigated [40][41][42][43]. Recently, Núnez et al [39] demonstrated that UL strength training seems to be more effective in improving COD abilities performance than the BL modalities.…”