Comparative effects of isometric and plyometric training on neuromuscular performance and postural balance in male soccer players (U-19): A randomized controlled trial

Purpose This study investigated the effects of an 8-week isometric strength training at multiple joint angles (IST) vs. loaded plyometric training (PT) on physical and balance performances in youth soccer players (U19). Methods Forty-five male players (age: 18.06 ± 0.78 years) were randomly assigned to either IST (n = 15), PT (n = 15) or a control (n = 15) group. In addition to soccer-specific regular training (i.e., control group), IST and PT trained 2×/week for 8 weeks. Athletes were assessed using the squat jump (SJ), countermovement jump (CMJ), horizontal jump (HJ), 30-m sprint (30 m), 5-m sprint (5 m), change of direction ability (4 × 5 m sprint test [S 4 × 5 m]), 5 m shuttle run test (5 m SRT) and static balance (stork balance test) one week before and after training. Results Significant time × group interactions showed higher performances with IST and PT compared to CG for jump tests (SJ: p < 0.001, η p 2 = 0.70, CMJ: p < 0.001, η p 2 = 0.65 and HJ: p < 0.001, η p 2 = 0.65), sprint tests (30m: p < 0.001, η p 2 = 0.85 and 5m: p < 0.001, η p 2 = 0.68), change of direction (4 × 5mS: p < 0.001, η p 2 = 0.83), 5 m shuttle run test (5 m SRT: p = 0.001, η p 2 = 0.80) and static balance tests (Right leg: p < 0.001, η p 2 = 0.86 and Left leg: p < 0.001, η p 2 = 0.91). Conclusion Physical and balance performances were improved after both training (IST and PT). Thus, coaches and fitness conditioners may incorporate IST and PT in training routine of soccer players during the in-season period.