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Resistance Training/Periodization

(56) INTRA-INDIVIDUAL RESPONSES FROM ADDITIONAL SPRINT OR NORDIC HAMSTRING EXERCISE TRAINING.

Saturday, July 15, 2023
10:00 AM – 11:30 AM East Coast USA Time
Location: Milano III-IV
Abstract Details:

Introduction: Sprint training (SPT) has been defined as a potential vaccine for hamstring strain injuries (HSI). However, eccentric load placed on the hamstrings during the gait cycle is influenced by running velocity, which could impact the adaptive response. The nordic hamstring exercise (NHE) is also frequently implemented, however, its effectiveness could be impacted by initial eccentric hamstring strength (EHS), being unable to move through muscle action types.

Purpose: To determine intra-individual variation based on sprint and EHS ability on modifiable risk factors of HSIs.

Methods: 28 Collegiate athletes were randomly assigned to either NHE (n = 15, 21.4±2.6 years, 1.70±0.04 m, 76.9±14.2 kg) or SPT (n = 13, 22.2±2.5 years, 1.71±0.05 m, 70.6±7.8 kg) groups. Both groups performed identical resistance training programs twice per week for seven weeks, with either additional NHE or SPT. Pre- and post-intervention testing of Bicep femoris fascicle length (BFL) ultrasound images were taken at the hamstring muscle belly. EHS was assessed by participants performing three NHE repetitions on the Nordbord. BFL analyzed using ImageJ software and the following equation OFL+(h¸SIN(PA)), where OFL is the observed fascicle, h is the perpendicular distance between aponeurosis and BF end point and PA is the pennation angle. Peak EHS was analyzed using custom designed Excel spreadsheets. 20m sprint performance and EHS was used to determine between “fast” and “slow” and “strong” and “weak” based on the median values. Two-way AVOVAS with Bonferroni post-hoc analysis and Hedge’s g effect sizes were used to determine the significance and magnitude of differences. An a priori alpha level was set at p≤0.05. Hedge’s g effect sizes were interpreted as trivial (≤0.19), small (0.20–0.59), moderate (0.60–1.19) and large ( >1.20).

Results: Significant increases in BF FL and EHS were observed for both training groups (p< 0.001). The median values for EHS and 20m sprint performance was 303.15 N and 3.39 seconds, respectively. Weak participants had the greatest increase in BFL and EHS with the NHE (p< 0.001, g = 1.94-4.57). Strong participants had similar increases in EHS for both the NHE and SPT (p< 0.001, g = 1.57-1.60), with SPT having the greatest increase in BFL (p< 0.001, g = 1.24) in comparison to the NHE (p< 0.001, g = 0.73). Fast participants had the greatest increase in BF FL and EHS via SPT (p< 0.001, g = 1.63-1.61), in contrast to NHE (p< 0.001, g = 1.19-1.29). Slow participants had the greatest increase in BF FL and EHS via NHE (p< 0.001, g = 1.72-2.09), in contrast to SPT (p< 0.001, g = 1.16-1.35).  

Conclusions: Weaker individuals had greater adaptations from the NHE, while strong participants had similar increases in EHS for both training modalities, while SPT had a greater effect on BFL. Fast participants had greater increases in BFL and EHS using sprint training, whereas slow participants had the greatest adaptations through NHE. Demonstrating initial EHS and sprint performance impacts the potential adaptations that can be realised. Practical Applications: The prescription of training with the goal of decreasing HSI incidence should consider initial training status, including strength and speed performance as they can both impact the magnitude of adaptations independently. Although training should not rely on a single modality, especially when weak.

Acknowledgements:



This research was funded by the National Strength and Conditioning Association (NSCA) Foundation Doctoral research grant.