Comparing lower-limb asymmetries in NCAA D-I male and female athletes. This study is a hypothesis generating investigation of athletic asymmetries. Asymmetries can lead to poor sport performance, and injury. Evidence suggests that right and left side lower body asymmetries can lead to lower body pain and injury including increased back pain. Asymmetries appear to be dependent on factors such as neuromuscular, perceptual, kinesthetic requirements and the amount of experience in a specific event. It is possible that lower body symmetry can affect superior performance in many athletic tasks. PURPOSE: The purpose of this study was to investigate the strength characteristics and incidence of lower-limbs asymmetries in NCAA Division-I athletes. METHODS: Twenty-seven athletes (M = 19, F = 8) completed isometric mid-thigh pulls on a dual force plate as part of an on-going athlete monitoring program. Maximum strength was measured using an isometric pull from mid-thigh. Athletes performed isometric pulls (mid-thigh, knee angle 120° – 135°) in a custom designed force rack over a force plate (1000 Hz). Athletes' hands were attached to the bar using weightlifting straps and athletic tape and were explicitly instructed to perform the pull “as hard and fast as possible.” Pulls generally lasted 4 to 5 seconds and were terminated when peak force began to diminish. Two pulls were performed with two minutes rest between. Force values (IPF, force at 50, 90 and 250 ms) and rate of force development (RFD) values were obtained from the force-time curve. RFD was determined at 0-50ms, 0-90ms and 0-250ms. Previous work (several hundred trials) with this system has consistently resulted in test-retest reliability for IPF of ICCα ≥ 0.99 and RFD, ICCα ≥ 0.9. Statistical analysis using adjusted paired two-tailed t-Tests (p ≤ 0.016) were used to compare male and female asymmetries. RESULTS: Males exhibited no statistical difference in peak force (6%), force at different intervals 50 (6%), 90, (8%) and 250 ms (6%), or rate of force development at different intervals when comparing dominant versus non-dominant leg. However, when comparing dominant versus non-dominant leg in females, there was a significant difference in peak force (13%), and force at 50 (8%), 90 (8%), and 250 ms (10%). When comparing all subjects for left and right asymmetries, there was a significant difference in left versus right peak force (6%), force at all measured time intervals (50 (9%), 90 (8%), 250 ms (7%)), and RFD at 0-50 ms (18%). Males had no significant difference in left versus right leg RFD (19%); however there was a significant difference in peak force (11%), and force at 50 (9%) and 250 ms (7%). Females had a significant difference between right and left leg peak force at 50 (8%) and 90ms (7%), and rate of force development at 50ms (21%). CONCLUSIONS: The results show that as a collective group, the subjects had a degree of asymmetry in force measurements. When separated for sex, males had significant differences in right versus left force characteristics, but not dominant versus non-dominant, whereas females had significant differences in both left versus right and dominant versus non-dominant. PRACTICAL APPLICATION: Differences in right/left and dominate/non-dominant lower body strength characteristics could indicate potential concerns dealing with both performance and injury. This data also indicates that female athletes may be more vulnerable to performance aberrations and injury compared to males.