Author(s): JAEN-CARRILLO, D., LAWLEY, JUSTIN S; SANTOS, LUIS, Institution: UNIVERSITÄT INNSBRUCK, Country: AUSTRIA, Abstract-ID: 814

INTRODUCTION:
Trail runners develop biomechanical and neuromuscular adaptations to improve performance and reduce muscle damage due to the sport’s demands. Key factors include speed, ground contact time (GCT), cadence, and leg stiffness. Shorter GCT and increased leg stiffness enhance elastic energy return, with both reflecting the stretch-shortening cycle (SSC), crucial for running efficiency. Strength, particularly knee extensor strength and Achilles tendon adaptations, is essential for trail running performance. However, the impact of different resistance training loads on performance remains unclear, especially regarding how varying loads affect elastic energy utilization and force production in prolonged versus short efforts. This study aimed to assess the relationship between biomechanical and strength variables at various 1RM percentages in highly trained male trail runners.
METHODS:
Fifteen internationally competitive, injury-free trail runners participated in this study. To estimate their one-repetition maximum (1RM) in the half-squat, participants performed the exercise on a Smith Machine. Mean propulsive velocity and peak force were continuously measured at 1,000 Hz using a linear position transducer attached to the barbell. Participants then completed a running session consisting of a 9-minute and a 3-minute run, separated by a 30-minute rest. They refrained from vigorous activity for 24 hours before each test. Spatiotemporal variables and leg stiffness were recorded with a Stryd power meter.
RESULTS:
Pearson’s correlation analysis identified significant associations between relative load (%1RM) and leg stiffness across different running efforts. Specifically, leg stiffness correlated with loads of 30% (r=0.533) and 40% 1RM (r=0.33) during the 9-min run and with 40% 1RM (r=0.547) during the 3-min run. Regarding SDef, significant correlations were found between SDef at 50%, 60%, and 70% 1RM and leg stiffness during the 9-minute run (r = 0.539, r = 0.560, and r = 0.535, respectively). During the 3-minute run, SDef at 40%, 50%, 60%, and 70% 1RM correlated significantly with GCT (r=-0.559, r=-0.570, r=-0.565, and r=-0.527, respectively). Additionally, leg stiffness was significantly associated with SDef at 60% (r=0.544) and 70% (r=0.525) 1RM.
CONCLUSION:
Significant correlations between relative training loads (%1RM), leg stiffness, and GCT emphasized the role of the stretch-shortening cycle (SSC) in performance. Moderate loads (30–40% 1RM) influenced leg stiffness during prolonged running, while higher loads (50–70% 1RM) affected both stiffness and GCT in shorter efforts. These findings suggest that resistance training modulates SSC efficiency, impacting elastic energy utilization and force production. Tailoring resistance training loads to enhance stiffness and SSC function may optimize performance in trail running, providing valuable insights for coaches.