Kathy J. Simpson

Jump distance of dance landings influencing internal joint forces: II. Shear forces.

Little is known about shear loading patterns during dance movements. The purpose of the study was to investigate the effect of jumping distance (JD) on contributors of ankle and knee shear forces (SF) generated during the landing phase of traveling jumps. Six female dancers performed 10 trials each at 30, 60, and 90% maximum jump distance (JD) and 15 jumps ranging from 35 to 100% JD. A sagittal view of the right leg landing onto a force platform was filmed using a high-speed cine camera. Greater ankle and knee joint reaction shear forces (JRSF) and quadriceps SF (QuadSF) were observed (P < 0.05) at increased JD. Although the triceps surae SF (TriSurSF) also increased at greater JD for all but one participant, the effect on minimizing the increase in the ankle SF was minor. The peak QuadSF magnitude and rate of loading were always greater than the corresponding knee JRSF variables. However, the increased QuadSF that occurred at longer jumps led to increased knee SF for only half of the participants.

Kinematics and Energetics of Nut-Cracking in Wild Capuchin Monkeys (Cebus libidinosus) in Piaui´, Brazil

Wild bearded capuchins (Cebus libidinosus, quadrupedal, medium-sized monkeys) crack nuts using large stones. We examined the kinematics and energetics of the nut-cracking action of two adult males and two adult females. From a bipedal stance, the monkeys raised a heavy hammer stone (1.46 and 1.32 kg, from 33 to 77% of their body weight) to an average height of 0.33 m, 60% of body length. Then, they rapidly lowered the stone by flexing the lower extremities and the trunk until the stone contacted the nut. A hit consisting of an upward phase and a downward phase averaged 0.74 s in duration. The upward phase lasted 69% of hit duration. All subjects added discernable energy to the stone in the downward phase. The monkeys exhibited individualized kinematic strategies, similar to those of human weight lifters. Capuchins illustrate that human-like bipedal stance and large body size are unnecessary to break tough objects from a bipedal position. The phenomenon of bipedal nut-cracking by capuchins provides a new comparative reference point for discussions of percussive tool use and bipedality in primates.

Movement variability during single leg jump landings in individuals with and without chronic ankle instability

BACKGROUND Repeated episodes of giving way at the ankle may be related to alterations in movement variability. METHODS Eighty-eight recreational athletes (39 males, 49 females) were placed in 4 groups: mechanically unstable, functionally unstable, copers, and controls based on ankle injury history, episodes of giving way, and joint laxity. Lower extremity kinematics and ground reaction forces were measured during single leg landings from a 50% maximum vertical jump in the anterior, lateral, and medial directions. Ensemble curves of 10 trials were averaged and coefficients of variation were identified for ankle, knee, hip, and trunk motion in 3 planes. A log(e) (ln) transformation was performed on the data. Mixed model analyses of variance (ANOVAs) with Tukey post-hoc tests were utilized with Bonferroni corrections to α ≤ 0.008. FINDINGS At the knee, controls were more variable than functionally unstable and copers for knee rotation before initial contact, and were more variable during stance than functionally unstable in knee rotation (P ≤ 0.008). Interactions during stance revealed controls were more variable than functionally unstable in lateral jumps for hip flexion, and than mechanically and functionally unstable in hip abduction in the anterior direction (P≤0.008). Controls were more variable than all other groups in hip flexion and than mechanically unstable in hip abduction (P ≤0 .008). INTERPRETATION Individuals with ankle instability demonstrated less variability at the hip and knee compared to controls during single leg jump landings. Inability to effectively utilize proximal joints to perform landing strategies may influence episodes of instability.

Foot landing position during gait influences ground reaction forces

OBJECTIVE The purpose of this study was to determine how foot landing position influenced the ground reaction forces of two coordinate systems during gait. DESIGN Values of ground reaction forces components as expressed in two coordinate systems (room, foot) were used to compare ground reaction forces of different foot landing position. BACKGROUND Non-neutral foot landing position during gait could influence the mechanics of the whole body motion and/or the foot-ankle complex and produce different ground reaction forces patterns compared to a neutral foot landing position. METHODS Thirty females were assigned to a foot landing group: toe-out, toe-in or neutral. Each participant walked 10 trials across a force platform while three-dimensional motion was captured. RESULTS No differences were observed for vertical or anteroposterior ground reaction forces variables between groups for either coordinate system. For medio-lateral forces of both coordinate systems, toe-out participants exhibited greater first lateral and second medial maximum forces and exhibited greater impulses. CONCLUSION For toe-out participants, greater medio-lateral ground reaction forces of the room coordinate system indicate excessive forces are generated by toe-out participants that do not contribute to moving the participant forward. Furthermore, medio-lateral loading on the foot increases proportionally with the degree of toe-out. RELEVANCE Establishing norms for clinical populations requires understanding of factors that can influence ground reaction force (GRF). Foot landing position (FLP) only affects the medio-lateral forces. Excessive toe-out landing has been surmised to be related to injury. Greater forces acting medio-laterally to the foots long axis may have a relevant effect on in/eversion loading of the foot.

Biomechanical influence of TKA designs with varying radii on bilateral TKA patients during sit-to-stand

BackgroundCompared to the design of a traditional multi-radius (MR) total knee arthroplasty (TKA), the single-radius (SR) implant investigated has a fixed flexion/extension center of rotation. The biomechanical effectiveness of an SR for functional daily activities, i.e., sit-to-stand, is not well understood. The purpose of the study was to compare the biomechanics underlying functional performance of the sit-to-stand (STS) movement between the limbs containing an MR and an SR TKA of bilateral TKA participants.MethodsSagittal plane kinematics and kinetics, and EMG data for selected knee flexor and extensor muscles were analyzed for eight bilateral TKA patients, each with an SR and an MR TKA implant.ResultsCompared to the MR limb, the SR limb demonstrated greater peak antero-posterior (AP) ground reaction force, higher AP ground reaction impulse, less vastus lateralis and semitendinosus EMG during the forward-thrust phase of the STS movement. No significant difference of knee extensor moment was found between the two knees.ConclusionSome GRF and EMG differences were evident between the MR and SR limbs during STS movement. Compensatory adaptations may be used to perform the STS.

Difference in Hip Prosthesis Femoral Offset Affects Hip Abductor Strength and Gait Characteristics During Obstacle Crossing

The purpose of this article is to determine if individuals with high rather than low femoral offset of a total hip arthroplasty achieve improved hip abductor muscle strength and thus improved their ability to step over an obstacle safely. These outcomes will help surgeons decide whether increasing the femoral offset helps a patients physical function.

Factors influencing rearfoot kinematics during a rapid lateral braking movement.

Understanding the morphological, movement, and biomechanical characteristics that influence rearfoot motion during lateral movements is necessary for footwear design and for the determination of injury mechanisms. The purpose of this study was to identify factors related to rearfoot kinematics during a lateral braking movement. Seven highly skilled male tennis players performed 24 trials of side shuffle movements at various speeds. A rear view of the right leg performing a braking step onto a force platform was filmed. The neutral-O landing style was most commonly demonstrated. Average movement velocity, foot velocity at touchdown, and body mass were variables demonstrating weak or nonsignificant correlations with the rearfoot parameters. Although structural inversion was correlated significantly with the maximum rearfoot angle and velocity (r = -0.52 and -0.69), the results were affected by movement speed and sample size. The biomechanical characteristics displayed the greatest influence on the various rearfoot kinematic parameters. The magnitude of the significant (P less than 0.0001) correlations generally decreased in the following order: maximum horizontal and vertical force gradients, corresponding times to the maximum gradient values, maximum horizontal and vertical forces, and the corresponding times to maximum forces. In conclusion, the gradient-associated parameters were the most useful biomechanical parameters for predicting changes in rearfoot kinematics.

Lower Extremity Kinematics During a Drop Jump in Individuals With Patellar Tendinopathy.

Background: Patellar tendinopathy (PT) is a common degenerative condition in physically active populations. Knowledge regarding the biomechanics of landing in populations with symptomatic PT is limited, but altered mechanics may play a role in the development or perpetuation of PT. Purpose: To identify whether study participants with PT exhibited different landing kinematics compared with healthy controls. Study Design: Controlled laboratory study. Methods: Sixty recreationally active participants took part in this study; 30 had current signs and symptoms of PT, including self-reported pain within the patellar tendon during loading activities for at least 3 months and ≤80 on the Victorian Institute of Sport Assessment Scale–Patella (VISA-P). Thirty healthy participants with no history of PT or other knee joint pathology were matched by sex, age, height, and weight. Participants completed 5 trials of a 40-cm, 2-legged drop jump followed immediately by a 50% maximum vertical jump. Dependent variables of interest included hip, knee, and ankle joint angles at initial ground contact, peak angles, and maximum angular displacements during the landing phase in 3 planes. Independent-samples t tests (P ≤ .05) were utilized to compare the joint angles and angular displacements between PT and control participants. Results: Individuals with PT displayed significantly decreased peak hip (PT, 59.2° ± 14.6°; control, 67.2° ± 13.9°; P = .03) and knee flexion angles (PT, 74.8° ± 13.2°; control, 82.5° ± 9.0°; P = .01) compared with control subjects. The PT group displayed decreased maximum angular displacement in the sagittal plane at the hip (PT, 49.3° ± 10.8°; control, 55.2° ± 11.4°; P = .04) and knee (PT, 71.6° ± 8.4°; control, 79.7° ± 8.3°; P < .001) compared with the control group. Conclusion: Participants with PT displayed decreased maximum flexion and angular displacement in the sagittal plane, at both the knee and the hip. The altered movement patterns in those with PT may be perpetuating symptoms associated with PT and could be due to the contributions of the rectus femoris during dynamic movement. Clinical Relevance: Based on kinematic alterations in symptomatic participants, rehabilitation efforts may benefit from focusing on both the knee and the hip to treat symptoms associated with PT.

Kinematic and plantar pressure adjustments to downhill gradients during gait

Abstract The purpose of the study was to investigate the peak plantar pressure (PP) and kinematic adjustments to various negative gradients (−GR) and walking velocities (WV) during treadmill fitness walking. While filmed, plantar pressure data for seven sensors were collected for eight female subjects. Faster WV were associated with increased heel PP ( P

The effects of a lateral in-flight perturbation on lower extremity biomechanics during drop landings

One potential ACL injury situation is due to contact with another person or object during the flight phase, thereby causing the person to land improperly. Conversely, athletes often have flight-phase collisions but do land safely. Therefore, to better understand ACL injury causation and methods by which people typically land safely, the purpose of this study was to determine the effects of an in-flight perturbation on the lower extremity biomechanics displayed by females during typical drop landings. Seventeen collegiate female recreational athletes performed baseline landings, followed by either unexpected laterally-directed perturbation or sham (nonperturbation) drop landings. We compared baseline and perturbation trials using paired-samples t tests (P < .05) and 95% confidence intervals for lower-extremity joint kinematics and kinetics and GRF. The results demonstrated that perturbation landings compared with baseline landings exhibited more extended joint positions of the lower extremity at initial contact; and, during landing, greater magnitudes for knee abduction and hip adduction displacements; peak magnitudes of vertical and medial GRF; and maximum moments of ankle extensors, knee extensors, and adductor and hip adductors. We conclude that a lateral in-flight perturbation leads to abnormal GRF and angular motions and joint moments of the lower extremity.