Author(s): Garett Lesa
Mentor(s): A. Wayne Johnson, Malorie Wilwand
Institution BYU
In American football, all player positions depend on hamstring muscle strength and tendon resilience to successfully complete plays and assigned tasks. Tendons play a crucial role in force transmission from muscles to bones, and enable movements such as sprinting, jumping, and changing direction which are critical to success in American football. Gaining a deeper understanding of eccentric hamstring strength (EHS) and its relationship to tendon length may enable coaches, players, and trainers to tailor training strategies such as stretching interventions to enhance performance and possibly reduce injury. We hypothesize that shorter or excessive tendon lengths may produce less EHS. For example, if a short tendon produces less strength, then stretching along with strengthening may improve this relationship and thus improve performance. Purpose: This study investigates the relationship between 3 of the hamstring tendon lengths (semitendinosus (ST), semimembranosus (SM), and biceps femoris (BF)) accounting for player height (tendon length/height (cm)) and EHS. Methods: This secondary analysis of HAMIR data involved 102 (Ht: 186.51 ± 6.22 cm; Wt: 102.41 ± 19.22 kg) uninjured, actively rostered collegiate American football players. Participants underwent MRI scans to measure tendon length, and their height was recorded. Maximum EHS was assessed by having each athlete perform three Nordic curls on a Nordbord device, recording force exertion from each leg across all three trials for data analysis. Results: The ratio of total tendon length of ST, SM, BF to player’s height was found to be weakly correlated with EHS. Specifically, a significant negative correlation was seen between EHS and ST and BF ( r = -0.15, p = 0.01; r = -0.25, p = 0.01 respectively). And a positive non-significant correlation was seen between EHS and SM (r = 0.06, p = 0.56). Average peak EHS was 439.5 ± 82.04 N. Conclusion: The ratio of tendon length to height of 2 hamstring muscles, ST and BF significantly influenced EHS, although weakly. The lower the ratio the greater the force production. This supports our hypothesis that longer tendons would generate less force. Thus, hamstring stretching to increase strength is not recommended. This collaborates with previous research indicating that static stretching decreases performance metrics such as vertical jump. This project was made possible through the efforts of individuals affiliated with the HAMIR study with funding from the National Football League (NFL). The NFL had no role in the study design, collection, analysis, nor interpretation of the data presented, and was not involved in the writing of the manuscript, nor the decision to submit the manuscript for publication.