Kristian M. O’Connor

Resistance training is accompanied by increases in hip strength and changes in lower extremity biomechanics during running

BACKGROUND Movement and muscle activity of the hip have been shown to affect movement of the lower extremity, and been related to injury. The purpose of this study was to determine if increased hip strength affects lower extremity mechanics during running. METHODS Within subject, repeated measures design. Fifteen healthy women volunteered. Hip abduction and external rotation strength were measured using a hand-held dynamometer. Three-dimensional biomechanical data of the lower extremity were collected during running using a high-speed motion capture system. Measurements were made before, at the mid-point, and after a 6-week strengthening program using closed-chain hip rotation exercises. Joint range of motion (rearfoot eversion, knee abduction, hip adduction, and internal rotation), eversion velocity, eversion angle at heel strike, and peak joint moments (rearfoot inversion, knee abduction, hip abduction, and external rotation) were analyzed using repeated measures analysis of variance (P <or= 0.05). The independent variable was time (pre-, week 3, and week 6). A separate analysis of variance was conducted with the dependent variables of peak hip abduction and external rotation strength. FINDINGS Hip abduction (P=0.009) and external rotation strength (P<0.0005) increased by 13% and 23%, respectively. Eversion range of motion decreased (P=0.05), hip adduction range of motion increased (P=0.05), and a trend of decreased hip internal rotation range of motion (P=0.08) were found. Rearfoot inversion moment (P=0.02) and knee abduction moment (P=0.05) decreased by 57% and 10%, respectively. INTERPRETATION The hip abductors and external rotators were strengthened, leading to an alteration of lower extremity joint loading which may reduce injury risk. These exercises could be used in the rehabilitation, or prevention, of lower extremity injuries.

Fatigue-related changes in stance leg mechanics during sidestep cutting maneuvers

BACKGROUND The increased number of women participating in sports has been paralleled by a greater knee injury rate in women compared to men. Among these injuries, those occurring to the anterior cruciate ligament are commonly observed during sidestep cutting maneuvers. In addition, general fatigue appears to correlate with injuries to the passive structures during a game. The purpose of the study was to examine the fatigue-related changes in lower limb mechanics during a cutting maneuver in female athletes. METHODS Twelve college female soccer players were recruited. Sidestep cutting maneuvers were performed prior to, and after a fatiguing exercise (60-min shuttle run). Fatigue state was evaluated by calculating power output from countermovement jumps performed before and after the shuttle run. Three-dimensional stance leg hip, knee and ankle kinematics and kinetics during the cutting task were calculated and reported as initial ground contact angle, ranges of motion and peak moments of the stance phase. Cutting maneuver stance leg mechanics were analyzed through repeated measures two-way ANOVAs (P<0.05). FINDINGS Jumping power output decrements suggested fatigue was induced. Sagittal and frontal planes kinematics and kinetics of the cutting task did not change after fatigue. In the transverse plane, the hip, knee and ankle joints were more externally rotated at touchdown, and during stance the knee underwent greater internal rotation. INTERPRETATION Increased knee internal rotation has potentially important implication for increased injury risk when combined with unexpected perturbation faced in a game. Also, the fact that the sub-maximal level of fatigue did not lead to greater dynamic changes suggests a possible threshold of fatigue before function is dramatically affected.

Assessment of a greater trochanter-based method of locating the hip joint center

An alternative, yet unverified, predictive method that places the hip joint center (HJC) at one-quarter of the distance from the ipsolateral to the contralateral greater trochanter (GT method) is currently widely used in the biomechanics community. Therefore, the objective of this study was to confirm that this method is a viable option for estimating HJC coordinates. To accomplish this, HJC coordinates in the pelvic anatomical coordinate system were estimated via the GT method, a functional method, and the regression equations proposed by Bell et al. (1990). The HJC coordinated estimated by the functional method served as a baseline measurement. The results of this study demonstrate that all three methods evaluated offer repeatable estimates of HJC location. In comparison to the functional method, the GT method yielded a HJC estimate that was 7.6mm medial, 12.2mm posterior, and 4.8mm proximal. On the other hand, the Bell regression equations estimated the HJC to be 2.6mm medial, 7.2mm posterior, and 21.7mm proximal relative to the functional method. Additionally, the total 3D difference between the GT and functional methods was 23.5mm compared to the 30.8mm difference between the Bell and functional methods. These results suggest that the GT method is a viable option for estimating HJC coordinates.

Effect of Patellofemoral Pain on Strength and Mechanics after an Exhaustive Run

PURPOSE To investigate the effects of an exhaustive run on trunk and lower extremity strength and mechanics in patients with and without patellofemoral pain (PFP), we hypothesized that strength would decrease and mechanics would change after the exhaustive run. METHODS Nineteen subjects with PFP and 19 controls participated (10 men and 9 women per group). Lower extremity and trunk mechanics during running, body mass-normalized strength, and pain assessments before and after an exhaustive run were quantified. A repeated-measures ANOVA was used to assess group differences and exhaustion-related changes (P < 0.05), with t-test post hoc analyses performed when significant interactions were identified (P < 0.0125). RESULTS Pain significantly increased with the exhaustive run in the PFP group (P = 0.021). Hip strength was reduced after the exhaustive run, more so in those with PFP (abduction: before = 0.384 ± 0.08, after = 0.314 ± 0.08, P < 0.001; external rotation: before = 0.113 ± 0.02, after = 0.090 ± 0.02, P < 0.001). Persons with PFP also demonstrated increased knee flexion (before = 41.6° ± 5.5°, after = 46.9° ± 7.5°, P < 0.001), hip flexion (before = 30.4° ± 6.8°, after = 42.5° ± 9.7°, P < 0.001), and anterior pelvic tilt (before = 7.2° ± 5.1°, after = 13.3° ± 6.7°, P = 0.001) after the exhaustive run compared to controls. Trunk flexion increased in both PFP (before = 13.09° ± 6.2°, after = 16.31° ± 5.3°, P < 0.001) and control (before = 1393° ± 4.7°, after = 15.99° ± 5.9°, P < 0.001) groups. Hip extension (before = -2.09 ± 0.49 N · m · kg(-1), after = -2.49 ± 0.54 N · m · kg(-1), P = 0.002) moments increased only in subjects with PFP. CONCLUSIONS Exhaustive running results in reduced hip strength in subjects with PFP; however, this did not result in changes to hip internal rotation or adduction kinematics. Kinematic and kinetic changes after the exhaustive run are more indicative of compensatory changes to reduce pain. Increasing trunk flexion during running might provide pain relief during running; however, reducing anterior pelvic tilt may also warrant attention during treatment.

Validation of a single camera three-dimensional motion tracking system ☆

The ability to analyze human movement is an essential tool of biomechanical analysis for both sport and clinical applications. Traditional 3D motion capture technology limits the feasibility of large scale data collections and therefore the ability to address clinical questions. Ideally, the measurement system/protocol should be non-invasive, mobile, generate nearly instantaneous feedback to the clinician and athlete, and be relatively inexpensive. The retro-grate reflector (RGR) is a new technology that allows for three-dimensional motion capture using a single camera. Previous studies have shown that orientation and position information recorded by the RGR system has high measurement precision and is strongly correlated with a traditional multi-camera system across a series of static poses. The technology has since been refined to record moving pose information from multiple RGR targets at sampling rates adequate for assessment of athletic movements. The purpose of this study was to compare motion data for a standard athletic movement recorded simultaneously with the RGR and multi-camera (Motion Analysis Eagle) systems. Nine subjects performed three single-leg land-and-cut maneuvers. Thigh and shank three-dimensional kinematics were collected with the RGR and Eagle camera systems simultaneously at 100Hz. Results showed a strong agreement between the two systems in all three planes, which demonstrates the ability of the RGR system to record moving pose information from multiple RGR targets at a sampling rate adequate for assessment of human movement and supports the ability to use the RGR technology as a valid 3D motion capture system.

Effects of physical exertion on trans-tibial prosthesis users' ability to accommodate alignment perturbations

Background: It has long been reported that a range of prosthesis alignments is acceptable in trans-tibial prosthetics. This range was shown to be smaller when walking on uneven surfaces. It has also been argued that findings on gait with prostheses that were obtained under laboratory conditions are limited in their applicability to real-life environments. Objectives: This study investigated the hypothesis that efforts to compensate for suboptimal alignments by active users of trans-tibial prostheses become less effective when levels of physical exertion increase. Study design: A 2 × 2 repeated-measures analysis of variance was conducted to compare the effects of physical exertion and subtle alignment perturbations on gait with trans-tibial prostheses. Methods: The gait of eight subjects with trans-tibial amputation was analyzed when walking with two different prosthesis alignments and two different physical exertion levels. The main and interaction effects were statistically evaluated. Results: Bilateral step length symmetry and measures of step variability within the same leg were found to be affected by the intervention. There was no significant effect on index variables that combined kinematic or kinetic measures. Conclusion: Findings showed that persons with trans-tibial prostheses responded heterogeneously to the interventions. For most variables, the research hypothesis could not be confirmed. Clinical relevance Findings support the practice of allotting several sessions to the alignment of trans-tibial prostheses, as users’ gait responds differently to perturbations when external factors (e.g. exertion) change. Furthermore, the found inhomogeneity in the population of persons with trans-tibial amputation supports the use of technical gait assessment methods in clinical practice.

Influence of ground reaction force perturbations on anterior cruciate ligament loading during sidestep cutting

Abstract Anterior cruciate ligament (ACL) injury risk is likely increased under unexpected loading conditions. Such situations may arise from mid-air contact with another athlete, or misjudgments in landing height, stride length or surface compliance resulting in an unbalanced landing and unexpected changes in the ground reaction forces (GRFs). The purpose this study was to identify how GRF perturbations influence ACL loading during sidestep cutting. Muscle-actuated simulations of sidestep cutting were generated and analyzed for 20 subjects. Perturbations of 20, 40 and 60% of the nominal value were applied to the posterior, vertical, and medial GRF. Open-loop, forward dynamics simulations were run with no feedback or correction mechanism which allowed deviations from the experimentally measured kinematics as a result of the GRF perturbations. Posterior and vertical GRF perturbations significantly increased ACL loading, although the change was more pronounced with posterior perturbations. These changes were primarily due to the sagittal plane component of ACL loading regardless of perturbation direction. Peak ACL loading occurred almost immediately after initial ground contact, and was thus predicated on initial joint configuration. The results of this study give merit to including knee flexion angle at initial ground contact in the evolving neuromuscular training modalities aimed at preventing non-contact ACL injury.

Extrinsic foot muscle forces when running in varus, valgus and neutral wedged shoes

Excessive pronation, although ill-defined, is often cited as a cause of many types of running injuries particularly at the knee (e.g., James et al. 1978). The extrinsic foot muscles have been reported to act in controlling rearfoot motion (O’Connor et al. 2006). The extrinsic muscles are: tibialis anterior (TA) and posterior (TP), gastrocnemius (GA), peroneals (PER), soleus (SOL) and extensor digitorum longus (EDL). The TA, TP, GA and SOL act as rearfoot invertors and are generally considered to act to resist eversion during the initial portion of support. It has been suggested that the activation patterns of these muscles may change in order to maintain a preferred movement pattern (Nigg 2001). O’Connor and Hamill (2004) reported that perturbing foot inversion/eversion in varus and valgus posted shoes did not alter the EMG patterns of the GA, SOL, TA and TP although a valgus perturbation of the foot increased the eversion angle and the internal inversion moment. O’Connor et al. (2006) used mfMRI to examine the relative metabolic activity of the extrinsic foot muscles when running in varus, valgus and neutral wedged shoes. The results of this study did not support the theory that muscle activity would increase as the degree of eversion increased. The purpose of this study was, therefore, to examine the role of the extrinsic foot muscles when the frontal plane motion of the foot was perturbed by varus, valgus and neutral wedged footwear. We hypothesized that we would confirm the results of the O’Connor et al. (2006) study by showing that the role of the extrinsic foot muscles would not change with a significant eversion perturbation.