The purpose of the study was to investigate the effects of fatigue on lower extremity joint kinematics, and kinetics during repetitive drop jumps. Twelve recreationally active males (n = 6) and females (n = 6) (nine used for analysis) performed repetitive drop jumps until they could no longer reach 80% of their initial drop jump height. Kinematic and kinetic variables were assessed during the impact phase (100 ms) of all jumps. Fatigued landings were performed with increased knee extension, and ankle plantar flexion at initial contact, as well as increased ankle range of motion during the impact phase. Fatigue also resulted in increased peak ankle power absorption and increased energy absorption at the ankle. This was accompanied by an approximately equal reduction in energy absorption at the knee. While the knee extensors were the muscle group primarily responsible for absorbing the impact, individuals compensated for increased knee extension when fatigued by an increased use of the ankle plantar flexors to help absorb the forces during impact. Thus, as fatigue set in and individuals landed with more extended lower extremities, they adopted a landing strategy that shifted a greater burden to the ankle for absorbing the kinetic energy of the impact.
Joshua T. Weinhandl, Jeremy D. Smith and Eric L. Dugan
Joshua T. Weinhandl, Mukta Joshi and Kristian M. O’Connor
The increased number of women participating in sports has led to a higher knee injury rate in women compared with men. Among these injuries, those occurring to the ACL are commonly observed during landing maneuvers. The purpose of this study was to determine gender differences in landing strategies during unilateral and bilateral landings. Sixteen male and 17 female recreational athletes were recruited to perform unilateral and bilateral landings from a raised platform, scaled to match their individual jumping abilities. Three-dimensional kinematics and kinetics of the dominant leg were calculated during the landing phase and reported as initial ground contact angle, ranges of motion (ROM) and peak moments. Lower extremity energy absorption was also calculated for the duration of the landing phase. Results showed that gender differences were only observed in sagittal plane hip and knee ROM, potentially due to the use of a relative drop height versus the commonly used absolute drop height. Unilateral landings were characterized by significant differences in hip and knee kinematics that have been linked to increased injury risk and would best be classified as “stiff” landings. The ankle musculature was used more for impact absorption during unilateral landing, which required increased joint extension at touchdown and may increase injury risk during an unbalanced landing. In addition, there was only an 11% increase in total energy absorption during unilateral landings, suggesting that there was a substantial amount of passive energy transfer during unilateral landings.
Michael A. Samaan, Matthew C. Hoch, Stacie I. Ringleb, Sebastian Bawab and Joshua T. Weinhandl
The aim of this study was to determine the effects of hamstrings fatigue on lower extremity joint coordination variability during a sidestep cutting maneuver. Twenty female recreational athletes performed five successful trials of a sidestep cutting task preand postfatigue. Each participant completed an isolated hamstrings fatigue protocol consisting of isokinetic maximum effort knee flexion and passive extension contractions. Vector coding was used to examine hip and knee joint couplings (consisting of various planar motions) during the impact and weight acceptance phases of the sidestep cut stance phase. Paired t tests were used to analyze differences of each phase as an effect of fatigue, where alpha was set a priori at .05. The hip rotation/knee rotation coupling exhibited a significant decrease in coordination variability as a function of fatigue in both the impact (P = .015) and weight acceptance phases (P = .043). Similarly, the hip adduction-abduction/knee rotation coupling exhibited a significant decrease in coordination variability in the weight acceptance phase (P = .038). Hamstrings fatigue significantly decreased coordination variability within specific lower extremity joint couplings that included knee rotation. Future studies should be conducted to determine if this decrease in coordination variability is related to lower extremity injury mechanisms.
Shelby A. Peel, Lauren E. Schroeder, Zachary A. Sievert and Joshua T. Weinhandl
To examine the relationship between anterior cruciate ligament injury risk factors in unanticipated cutting and decelerating. Three-dimensional kinematics and ground reaction forces were collected on 11 females (22  y, 1.67 [0.08] m, and 68.5 [9.8] kg) during 2 unanticipated tasks. Paired samples t tests were performed to compare dependent variables between tasks. Spearman rank correlation coefficients were calculated to analyze the relationship between peak internal knee adduction moment and peak anterior tibial shear force (ASF) during 2 unanticipated tasks. Significantly greater knee abduction angles, peak knee adduction moments, and peak ASFs were observed during cutting (P ≤ .05). A strong positive correlation existed between decelerating ASF and cutting ASF (ρ = .67), while correlations between decelerating knee adduction moment and cutting knee adduction moment and decelerating ASF and cutting knee adduction moment were not significant. In situations where time management is a necessity and only one task can be evaluated, it may be more appropriate to utilize an unanticipated cutting task rather than an unanticipated deceleration task because of the increased knee adduction moment and ASF. These data can help future clinicians in better designing more effective anterior cruciate ligament injury risk screening methods.
Michael A. Samaan, Eric K. Greska, Matthew C. Hoch, Joshua T. Weinhandl, Sebastian Y. Bawab and Stacie I. Ringleb
ACL injury may cause a lack of knee joint proprioception and motor control due to knee joint instability. ACL reconstruction restores knee joint stability, yet dynamic postural control may still be affected while performing dynamic tasks.
To examine the effects of ACL injury and reconstruction on dynamic postural control using the Star Excursion Balance Test (SEBT) and single leg hop (SLH).
One Division I female athlete.
Main Outcome Measure:
The athlete’s dynamic postural control, both pre- and postreconstruction, was compared with preinjury data using the method of minimal detectable change using reach distances obtained from the SEBT and hop distances from the SLH.
ACL injury and reconstruction affected the anterior, posteromedial, and posterolateral reach distances of the SEBT. Despite restoration of joint stability, anterior reach distance in the SEBT did not return to preinjury levels 27 months after ACL reconstruction. SLH distances decreased following injury but returned to preinjury levels 27 months after ACL reconstruction.
Dynamic postural control and performance during the SEBT and SLH were affected by ACL injury and for extended periods of time after ACL reconstruction. Quadriceps inhibition and muscle strength of the involved limb may affect dynamic postural control both after ACL injury and reconstruction while performing the SEBT. Compensatory mechanisms at the hip and ankle may aid in performance of the SLH after reconstruction. Using baseline measurements, where possible, may help researchers better understand the effects of ACL injury and reconstruction on dynamic postural control.