Context: Noncontact anterior cruciate ligament injury has been reported to occur during the later stages of a game when fatigue is most likely present. Few researchers have focused on progressive changes in lower extremity biomechanics that occur throughout fatiguing.Objective: To evaluate the effects of a sequential fatigue protocol on lower extremity biomechanics during a sidestepcutting task (SS).Design: Controlled laboratory study. Setting: Laboratory.Patients or Other Participants: Eighteen uninjured female collegiate soccer players (age ¼ 19.2 6 0.9 years, height ¼ 1.66 6 0.5 m, mass ¼ 61.6 6 5.1 kg) volunteered.Intervention(s): The independent variable was fatigue level, with 3 levels (prefatigue, 50% fatigue, and 100% fatigue). Using 3-dimensional motion capture, we assessed lower extremity biomechanics during the SS. Participants alternated between a fatigue protocol that solicited different muscle groups and mimicked actual sport situations and unanticipated SS trials. The process was repeated until fatigue was attained.Main Outcome Measure(s): Dependent variables were hipand knee-flexion and abduction angles and internal moments measured at initial contact and peak stance and defined as measures obtained between 0% and 50% of stance phase.Results: Knee-flexion angle decreased from prefatigue (À178 6 58) to 50% fatigue (À168 6 68) and to 100% fatigue (À148 6 48) (F 2,34 ¼ 5.112, P ¼ .004). Knee flexion at peak stance increased from prefatigue (À52.98 6 5.68) to 50% fatigue (À56.18 6 7.28) but decreased from 50% to 100% fatigue (À50.58 6 7.18) (F 2,34 ¼ 8.282, P ¼ 001). Knee-adduction moment at peak stance increased from prefatigue (0.49 6 0.23 Nm/kgm) to 50% fatigue (0.55 6 0.25 Nm/kgm) but decreased from 50% to 100% fatigue (0.37 6 0.24) (F 2,34 ¼ 3.755, P ¼ 03). Hip-flexion angle increased from prefatigue (45.48 6 10.98) to 50% fatigue (46.28 6 11.28) but decreased from 50% to 100% fatigue (40.98 6 11.38) (F 2,34 ¼ 6.542, P ¼ .004). Hip flexion at peak stance increased from prefatigue (49.88 6 9.98) to 50% fatigue (52.98 6 12.18) but decreased from 50% to 100% fatigue (46.38 6 12.98) (F 2,34 ¼ 8.639, P ¼ 001). Hip-abduction angle at initial contact decreased from prefatigue (À13.88 6 6.68) to 50% fatigue (À9.18 6 6.58) and to 100% fatigue (À7.88 6 6.58) (F 2,34 ¼ 11.228, P , .001). Hip-adduction moment decreased from prefatigue (0.14 6 0.13 Nm/kgm) to 50% fatigue (0.08 6 0.13 Nm/kgm) and to 100% fatigue (0.06 6 0.05 Nm/kg) (F 2,34 ¼ 5.767, P ¼ .007).Conclusions: The detrimental effects of fatigue on sagittal and frontal mechanics of the hip and knee were visible at 50% of the participants' maximal fatigue and became more marked at 100% fatigue. Anterior cruciate ligament injury-prevention programs should emphasize feedback on proper mechanics throughout an entire practice and not only at the beginning of practice.Key Words: anterior cruciate ligament, knee, fatiguing, kinematics, kinetics
Key PointsA progressive change in lower extremity mechanics occurred for knee-flexion angle, hip-abduction angle,...