Purpose: This study aimed to examine changes in sagittal (AP LAX), frontal (VV LAX), and transverse (IER LAX) plane knee laxity in men and women during an intermittent exercise protocol (IEP) simulating the intensity and duration of a soccer match.
Methods: Intercollegiate/club athletes (29 females and 30 males) were measured on AP LAX (-90 to 130 N) before and after warm-up and every 15 min during and for 1 h after the IEP. VV LAX (± 10 N · m) and IER LAX (± 5 N · m) were measured before and after warm-up, at the end of each 45-min half, and at 30 min after exercise. Values were compared to a control (no exercise) condition.
Results: Compared to control condition, females increased AP LAX and VV LAX during the IEP, whereas males did not (P < 0.037). AP LAX increased within 15 min of exercise (9.5 ± 2.1 mm), and peak values obtained at the end of the first (10.1 ± 2.0 mm) and second half (10.1 ± 2.1 mm) were 12% greater than before warm-up values (9.0 ± 1.8 mm). VV LAX increased before warm-up (9.5° ± 3.4°) to the end of each half (both 10.4° ± 3.2°; 10% increase) and remained elevated 30 min after exercise (10.5° ± 2.9°). Both sexes increased IER LAX from before warm-up (25.5° ± 6.1°) to all time points (after warm-up = 26.6° ± 6.0°, first half = 27.0° ± 6.6°, second half = 27.3° ± 6.5°, 30 min after exercise = 26.95° ± 5.7°; P = 0.007). Changes in AP LAX (-0.10 to 5.9 mm), VV LAX (-1.7° to 5.7°), and IER LAX (-4.1° to 13.3°) during exercise varied considerably among individuals in both sexes, with a larger proportion of females experiencing substantial changes in AP LAX and VV LAX.
Conclusions: Although exercise-related knee laxity changes were more pronounced in females, there was a subset of both males and females who experienced substantial knee laxity increases during exercise. Whether these individuals are more susceptible to higher-risk lower extremity biomechanics and injury risk later in a game or practice is currently under investigation.