The Impact of Eccentric or Isometric Training on Strength, Architecture, and Sprinting across an Australian Football Season

Abstract

ABSTRACT Purpose Investigate impact of an isometric (ISO) or Nordic hamstring exercise (NHE) intervention, alongside a sprint training program on hamstring strength, architecture and sprinting performance in Australian Footballers. Methods Twenty-five male athletes undertook NHE (n = 13) or ISO (n = 12) training across a 38-week period (including pre-season and in-season). Biceps femoris long head (BFlh) architecture, isometric and eccentric knee flexor strength were assessed at baseline, end of pre-season (14-weeks) and at the conclusion of the intervention. Sprint times and force-velocity profiles were determined at baseline and at the end of pre-season. Results Following the intervention both groups had significant improvements in BFlh fascicle length (NHE: 1.16 cm, 95%CI 0.68 to 1.63 cm, d = 1.88, p < 0.001; ISO: 0.82 cm, 95%CI 0.57 to 1.06 cm, d = 1.70, p < 0.001), muscle thickness (NHE: 0.11 cm, 95%CI 0.01 to 0.21 cm, d = 0.51, p = 0.032; ISO: 0.21 cm, 95%CI 0.10 to 0.32 cm, d = 0.86, p = 0.002) and eccentric strength (NHE: 83 N, 95%CI 53 to 114 N, d = 1.79, p < 0.001; ISO: 83 N, 95%CI 17 to 151 N, d = 1.17, p = 0.018). Both groups also finished the intervention weaker isometrically than they started (NHE: -45 N, 95%CI -81 to -8 N, d = -1.03, p = 0.022; ISO: -80 N, 95%CI -104 to -56 N, d = -3.35, p < 0.001). At the end of pre-season the NHE group had improved their 5 m sprint time by 3.3% (±2.0%) and their maximum horizontal velocity was 3% (±2.1) greater than the ISO group who saw no changes. Conclusion Both ISO and NHE training with a periodised sprinting program can increase BFlh fascicle length, thickness, and eccentric strength in Australian Footballers. NHE training also improves 5 m sprint time and maximum velocity. However, both interventions reduced isometric strength. These findings provide unique, contextually relevant insights into the adaptations possible in semi-professional athletes.