The Effects of the Repetitive Use of a Position-Specific Loading Pattern on Lower Limb Asymmetry in NFL Offensive Tackles

American Football is a fast-paced, high-impact, collision sport associated with high frequency of injuries occurring through contact or non-contact, acute impact, or repeated stresses. This purpose of this short-term longitudinal study was to examine development of musculoskeletal asymmetries through a specific loading pattern used by the offensive tackle in the National Football League (NFL). Using both cross-sectional and longitudinal designs, strength and asymmetry changes in five NFL offensive tackles were analyzed pre- and post-training camp, with a focus on three key isometric strength tests: the Isometric Mid-Thigh Pull Test (IMTP), the Isometric Staggered Stance Pull Test (IMSSP), a Force Frame Test for isometric abduction and adduction strength, and a Countermovement Jump (CMJ) was employed to assess dynamic strength. Results displayed significant changes in isometric strength and asymmetry over the course of training camp, with IMSSP (p < 0.05) and CMJ (p < 0.05) revealing the greatest differences. Notably, post-leg dominance was observed in several athletes when testing isometric strength. Asymmetry percentages were most noticeable in CMJ tests, with substantial increases in post-training camp asymmetries for several athletes. These findings suggest that repetitive use of a staggered stance position during an NFL training camp can lead to musculoskeletal imbalances in strength between limbs. The results highlight the importance of monitoring isometric strength and asymmetry as part of a tailored strength and conditioning program to mitigate injury risks. Future research may wish to monitor the onset of asymmetry through other metrics such as eccentric hamstring strength and for a greater length of time. Recommendations for future training include alternating positions and incorporating exercises to balance strength across limbs.