# Impact of unilateral single-mode balance training vs. combined balance and plyometric training on soccer players’ interlimb asymmetry in balance and neuromuscular performance

## TL;DR

This study compares two training methods to reduce leg imbalance in soccer players, finding that single-mode balance training is more effective for improving balance in the non-dominant leg.

## Contribution

The study provides new evidence that unilateral single-mode balance training is more effective than combined balance and plyometric training for reducing interlimb asymmetry in elite youth soccer players.

## Key findings

- Unilateral single-mode balance training significantly reduced the limb symmetry index in the Y Balance Test anterior reach.
- Both training methods showed high attendance rates, indicating feasibility for implementation in soccer training programs.
- Combined balance and plyometric training did not show significant improvements in interlimb asymmetry compared to single-mode balance training.

## Abstract

It has been shown that unilateral balance training (BT) enhances balance and neuromuscular performance in the trained and untrained leg and thus has the potential to reduce side-to-side differences. However, it is unresolved how effective unilateral single-mode BT compared to unilateral combined balance and plyometric training (BT + PT) is in reducing interlimb asymmetry. Thus, we examined the impact of both training modalities on soccer players’ interlimb asymmetry in balance and neuromuscular performance.

Sixty male elite youth soccer players were randomly assigned to a unilateral single-mode BT group (n = 20), a unilateral combined BT + PT group (n = 22) or an active control group (n = 22). All groups trained for nine weeks (2 sessions/week) with their non-dominant leg. The interventions included balance exercises for the single-mode BT group, balance and plyometric exercises for the combined BT + PT group and stretching exercises for the active control group. Training progression was achieved by manipulating sensory input (balance exercises), the number of floor contacts (plyometric exercises), or the duration of the stretching exercises. Before and after the intervention period, performance in the Y Balance Test – Lower Quarter (YBT–LQ) and the single leg drop landing (SLDL) test as well as leg muscle activity were assessed. The magnitude of interlimb differences was quantified by calculating the limb symmetry index (LSI) and compared using repeated measures analysis of variance (significance level: p < .05).

The analysis revealed significant main effects of test (pre vs. post) for the LSI values of the YBT–LQ (anterior reach: ηp2 = .07; posterolateral reach: ηp2 = .11) and activity of the gastrocnemius muscle (ηp2 = .33) but not for the SLDL test. Further, a significant test×group interaction was detected for the LSI value of the anterior reach (ηp2 = .10) and post-hoc analyses yielded a significant LSI reduction for the unilateral single-mode BT group (d = .79) only.

Nine weeks of unilateral single-mode BT and combined BT + PT proved to be effective and feasible (attendance rates of ≈ 99%–100%). In particular, unilateral single-mode BT appears to be suitable for reducing the LSI value of the YBT–LQ anterior reach, which is a predictor for time loss non-contact lower limb injuries.