Sex-dimorphic landing mechanics and their role within the noncontact ACL injury mechanism: evidence, limitations and directions

Abstract Anterior cruciate ligament (ACL) injuries continue to present in epidemic-like proportions, carrying significant short- and longer-term debilitative effects. With females suffering these injuries at a higher rate than males, an abundance of research focuses on delineating the sex-specific nature of the underlying injury mechanism. Examinations of sex-dimorphic lower-limb landing mechanics are common since such factors are readily screenable and modifiable. The purpose of this paper was to critically review the published literature that currently exists in this area to gain greater insight into the aetiology of ACL injuries in females and males. Using strict search criteria, 31 articles investigating sex-based differences in explicit knee and/or hip landing biomechanical variables exhibited during vertical landings were selected and subsequently examined. Study outcomes did not support the generally accepted view that significant sex-based differences exist in lower-limb landing mechanics. In fact, a lack of agreement was evident in the literature for the majority of variables examined, with no sex differences evident when consensus was reached. The one exception was that women were typically found to land with greater peak knee abduction angles than males. Considering knee abduction increases ACL loading and prospectively predicts female ACL injury risk, its contribution to sex-specific injury mechanisms and resultant injury rates seems plausible. As for the lack of consensus observed for most variables, it may arise from study-based variations in test populations and landing tasks, in conjunction with the limited ability to accurately measure lower-limb mechanics via standard motion capture methods. Regardless, laboratory-based comparisons of male and female landing mechanics do not appear sufficient to elucidate causes of injury and their potential sex-specificity. Sex-specific in vivo joint mechanical data, if collected accurately, may be more beneficial when used to drive models (e.g., cadaveric and computational) that can additionally quantify the resultant ACL load response. Without these steps, sex-dimorphic landing mechanics data will play a limited role in identifying the aetiology of ACL injuries in women and men.http://deepblue.lib.umich.edu/bitstream/2027.42/112577/1/13102_2011_Article_99.pd

The Effectiveness of the Critical Power Model on Prescribing Elements of Intermittent Exercise

Intermittent exercise is a valuable method of training, consisting of numerous interrelated factors. The critical power model has been used to administer interval training programs; however, it has not been used to accurately prescribe elements of intermittent exercise. PURPOSE: This study aimed to use individual critical power models to prescribe elements of intermittent exercise. METHODS: Ten male athletes, mean (sd) age and mass 19.6 (1.4) years and 77.8 (8.1) kg performed three phases of testing on a cycle ergometer: 1) familiarization, one learning trial to establish a starting point for subsequent tests; 2) establishment of individual W/t relationship from [Eq 1], i.e. t = W’ / (W – WCP), 4 bouts of exercise designed to elicit fatigue in 2-15 minutes; 3) intermittent exercise, 3 bouts of work with predicted number of work/recovery cycles (n = 5) of 60/60 s, 120/60 s, and 60/120 s. The elements of these bouts were prescribed using [Eq 2], i.e. n = W’ / ((Ww – WCP)tw – (WCP – Wr)tr) and estimates of W’ and CP from phase 2 of testing. One sample t-tests were used to compare the number of cycles actually completed to the predicted value of 5 cycles for each intermittent exercise bout. A repeated-measures ANOVA was used to compare the effect of intermittent exercise on the number of work/recovery cycles completed across conditions. RESULTS: The mean (sd) completed work/recovery cycles were 4.64 (0.47), 4.65 (1.10), and 3.70 (0.80), for the 60/60 s, 120/60 s, and 60/120 s trials, respectively. Results of the t-tests suggested that actual values were not significantly different from predicted for 60/60 s and 120/60 s (t(9) = -2.39, p = 0.04; t(9) = -1.01, p = 0.34), but were for 60/120 s (t(9) = -5.14, p \u3c 0.01). Results of the rANOVA suggested that the mean completed work/recovery cycles was significantly different across conditions (F(2,18) = 3.99, p = 0.04). DISCUSSION: These data suggest that using [Eq 2], with estimates of W’ and CP from [Eq 1], to prescribe elements of intermittent exercise can be successful for trials with short recovery periods

The Effect of Cardiovascular Drift on the Efficacy of Exercise Prescription

TACSM Abstract – The Effect of Cardiovascular Drift on the Efficacy of Exercise Prescription KATHERINE FORESTER, JIMMY SMITH, Ph.D., and SCOTT MCLEAN, Ph.D. Kinesiology; Southwestern University; Georgetown, TX Category: Undergraduate ABSTRACT Due to the difficulty in measuring metabolic cost in the field, heart rate (HR) is often used to prescribe exercise intensity. Purpose: To examine the effect of cardiovascular drift (CVdrift) on the efficacy of exercise prescription (ExRx). Methods: Eight women with a mean (sd) age 21.6(2.0) years, body mass 70.9(11.0) kg, height 163.7(6.0) cm, and VO2max of 33.7(4.2) mL/kg/min, each performed two cycling trials for 30 to 45min at work rates that elicited 50% and 70% of VO2max. HR (bpm) and VO2 (mL/kg/min) were recorded throughout each trial and values at the beginning, middle, and end of exercise across both intensities were compared using 3 x 2 two-way repeated measures ANOVAs. Repeated measures ANOVAs were used to compare responses across time within each exercise intensity. Results: Estimated work rates accurately elicited 50% and 70% of HRmax and VO2max at 5 min of exercise. For HR, there was a significant effect of both time (F (1,2) = 124.8, p \u3c .001) and intensity (F (1,1) = 312.0, p \u3c .001), and a significant interaction between time and intensity (F (1,2) = 6.14, p = 0.012). There was a significant effect of time on HR at both the 50% intensity (F (1,2) = 40.74, p \u3c .001) and 70% intensity (F(1,2) = 101.9, p \u3c .001). VO2 increased significantly due to both time (F (1,2) = 6.63, p = .009) and intensity (F (1,1) = 312.0, p \u3c .001) but there was no interaction, and the significant effect of time was only at the 70% intensity (F (1,2) = 3.90, p = .05). Discussion: The main finding of this study was that HR and metabolic demand became increasingly dissociated across time at both intensities. This dissociation was more pronounced at an intensity of 70% of VO2max than 50% of VO2max. This finding implies that during prolonged exercise at a steady work rate, HR becomes increasingly less valid as a surrogate for metabolic demand of exercise. Key words: Cardiovascular drift, exercise prescription, metabolic drift

ACL Injuries: Do We Know the Mechanisms?

Injuries of the anterior cruciate ligament (ACL) remain a frequent occurrence in many sports activities. Recent research has identified risk factors, and prevention strategies are being developed based on these findings. There is, however, still a limited understanding of the actual injury mechanisms. In this presentation we will review the current knowledge on ACL injury mechanisms, and identify needs and opportunities for further research

Quantification of in Vivo ACL Elongation During Dynamic Joint Movements: A New Methodology

Anterior cruciate ligament (ACL) injuries are common in movement tasks incorporating sudden changes in velocity, such as sidtestepping. Current techniques adopted to quantify ACL strain are invasive as well as limited to slow, quasi-static move- ments. This paper presents a method for non-invasive measurement of ACL elongation during dynamic movement tasks, validation of the method, and demonstrates its applicability to the analysis of sidestep movement

Studies Related to Nutrients Entering Groundwater From the Heber Valley Sewer Farm and Dairies

Foreword: This report includes the results from a two year study in the Heber Valley to determine amounts of nutrients that are entering the groundwaters of the Heber Valley, and might ultimately enter Deer Creek Reservoir. Since Deer Creek Reservoir in Heber Valley, Utah supplies approximately 65 percent of the water distributed to Salt Lake County, the maintenance of its quality is of considerable importance. To maintain the quality of this reservoir and limit its eutrophication best management practices for surface water have been implemented gradually during the past decade in Heber Valley. These practices have significantly improved the qualities of surface streams flowing into the reservoir. However, data for amounts of phosphorus and nitrogen in groundwater inflows to the reservoir are several times larger than predicted from 1967 data. Concern has been voiced that perhaps cleaning up the surface inflows by spreading treated sewage on land, retaining dairy wastes in lagoon, etc, have only delayed the arrival time of nutrients into Deer Creek Reservoir, and that their transmission through gruondwaters into the reservoir will result in eutrophication unless other measures are implemented. To provide data for better understanding of the processes assocaited with soil sorption and transmission of chemicals (with a focus on phosphorus and nitrogen) into the saturated groundwater and ultimately into Deer Creek Reservoir, a three pronged research program was initiated by Utah State University during the Spring of 1989. This program consisted of: 1. Installation of unsaturated zone (Vandose zone) samples that extract water from the partially saturated soil at 6 sites (with two samplers at different depths at each site) within the land disposal area of the Heber Valley Special Service District (referred to as the sewer farm hereafter), and adjacent to two liquid manure lagoons at dairy farms. 2. Laboratory sorption studies on soil columns that were acquired in an undistrubed state from the 6 sites in the above sewer farm , and 3. Development of computer solutions to estimate the transmission of nutrients through the unsaturated top soil into the groundwater. An earlier 1990 preliminary report Interim Report for Studies related to Nutrients Entering Groundwater from the Heber Valley Sewer Farm and Dairies provided information related to the results of the laboratory sorption studies, and tentative results from the field studies based on the data collected during the summer of 1989. Since the field data given in the earlier report covered only a portion of ayear, and the study was continued for a second year that report is superceded by this report. This report provides the data collected over the two year period of the study, 1989-1990. Included in this report are field data obtained from the most critical spring period of 1990 when the surface soils recieve the relatively large quantities of snow melt water. The 1990 water year was again a dry year in which precipitation was considerably below normal. Thus the field collection period did not include a truly wet condition as will undoubtedly occur during years of above normal precipitation. Above normal rainfall did occur during the months of April and May, 1991. However this was not anticipated and the field samplers were unfortunately removed prior to these occurences to allow more easy working of the farm area. Since only a few copies of the above mentioned interim report were reproduced, this report duplicates the description of the field instrumentation, and the laboratory sorption studies. The data tables contained in that report have been updated to include field data from the second year through 1990. The results from the computer solutions that were contained in the interim report as Appendix A are not included herein, however. That report must be consulted for this detail. Field data collected from the first year indicated that larger quantities of nitrogen in the form of nitrate (NO3) than phophorus were within the unsaturated surface soils of the farm irrigated by the treated sewage, and by the dairy lagoons. Based on this information an additional research program, or changing the emphasis of the research, was directed to studying the nitrogen cycle in the groundwater system of Heber Valley to determine in natural processes reduce the amount of NO3- reaching Deer Creek Reservoir through the Heber Valley aquifers. More specifically the additional emphasis was deirected to determine whether conditions exist that favor denitrification and the extent by which such process might be reducing the amounts of NO3- input to Deer Creek Reservoir from the irrigated farm of the Heber Valley Special Service District, and two dairy lagoons. Denitrification is a process whereby bacteria transfer electrons from compounds, known as electron donors, to NO3-, an electron acceptor. The end products of this reduction are gases of N2O and N2, both of which escape to the atmosphere and thus reduce the amount of nitrogen in the water. The results of this sadditional research will be reported in a forthcoming project report consisting of the Ph.D. dissertation by Scott F. Korom Denitrification in the Unconsolidated Deposits of the Heber Valley Aquifer. This dissertation is being written in the format now allowed by Utah State University where different sections are designed as separate papers for submission to professional journals. Therefore the results of the denitrification phases of the research should also be available in future professional journal papers

Investigating Isolated Neuromuscular Control Contributions to Non-Contact Anterior Cruciate Ligament Injury Risk via Computer Simulation Methods

Background Despite the ongoing evolution of anterior cruciate ligament injury prevention methods, injury rates and the associated sex-disparity remain. Strategies capable of successfully countering key control parameters existent within the injury mechanism thus remain elusive. Forward dynamics model simulations afford an expedited means to study realistic injury causing scenarios, while controlling all facets of the movement control strategy. Utilizing these methods, the current study examined the potential for perturbations in key initial contact neuromuscular parameters to injure the anterior cruciate ligament during the stance phase of sidestep cutting maneuvers. Methods Controlled experiments were performed on optimized and validated subject-specific forward dynamic musculoskeletal sidestep models generated from 10 male and 10 female data sets. Random perturbations (n=5000) were applied to initial contact kinematic and muscle activation parameters in these baseline models and then to those with prescribed systematic modifications in initial hip and knee flexion, hip internal rotation and hip internal rotation velocity postures. The number of injuries via an isolated anterior tibial shear (\u3e2000N) or knee valgus load (\u3e125Nm) mechanism was determined for each of the seven model conditions and subsequently compared. Findings Neuromuscular control perturbations produced peak stance phase (0–100ms) knee valgus loads large enough to induce anterior cruciate ligament injury. Decreases and increases in combined initial contact hip and knee flexion postures and hip internal rotation velocity produced significant increases and decreases in these valgus-induced ACL injury rates respectively. Interpretation Anterior cruciate ligament injury via a valgus load mechanism is more likely during sidestepping when landing in a more extended posture, or with increased hip external rotation velocity. The fact that injury rates are reduced when these control parameters are reversed suggests they should be central to ongoing prevention strategy developments

Development and Validation of a 3-D Model to Predict Knee Joint Loading During Dynamic Movement

The purpose of this study was to develop a subject-specific 3-D model of the lowerextremity to predict neuromuscular control effects on 3-D knee joint loading during movements that can potentially cause injury to the anterior cruciate ligament (ACL) in the knee. The simulation consisted of a forward dynamic 3-D musculoskeletal model of the lower extremity, scaled to represent a specific subject. Inputs of the model were the initial position and velocity of the skeletal elements, and the muscle stimulation patterns. Outputs of the model were movement and ground reaction forces, as well as resultant 3-D forces and moments acting across the knee joint. An optimization method was established to find muscle stimulation patterns that best reproduced the subject’s movement and ground reaction forces during a sidestepping task. The optimized model produced movements and forces that were generally within one standard deviation of the measured subject data. Resultant knee joint loading variables extracted from the optimized model were comparable to those reported in the literature. The ability of the model to successfully predict the subject’s response to altered initial conditions was quantified and found acceptable for use of the model to investigate the effect of altered neuromuscular control on knee joint loading during sidestepping. Monte Carlo simulations (N5100,000) using randomly perturbed initial kinematic conditions, based on the subject’s variability, resultedin peak anterior force, valgus torque and internal torque values of 378 N, 94 Nmand 71 Nm, respectively, large enough to cause ACL rupture. We conclude that the procedures described in this paper were successful in creating valid simulations of normal movement, and in simulating injuries that are caused by perturbed neuromuscular control

Effect of Gender and Defensive Opponent on the Biomechanics of Sidestep Cutting

Purpose: Anterior cruciate ligament (ACL) injuries often occur in women during cutting maneuvers to evade a defensive player. Gender differences in knee kinematics have been observed, but it is not known to what extent these are linked to abnormal neuromuscular control elsewhere in the kinetic chain. Responses to defense players, which may be gender-dependent, have not been included in previous studies. This study determined the effects of gender and defense player on entire lower extremity biomechanics during sidestepping. Methods: Eight male and eight female subjects performed sidestep cuts with and without a static defensive opponent while 3D motion and ground reaction force data were recorded. Peak values of eight selected motion and force variables were, as well as their between-trial variabilities, submitted to a two-way (defense × gender) ANOVA. A Bonferroni-corrected alpha level of 0.003 denoted statistical significance. Results: Females had less hip and knee flexion, hip and knee internal rotation, and hip abduction. Females had higher knee valgus and foot pronation angles, and increased variability in knee valgus and internal rotation. Increased medial ground reaction forces and flexion and abduction in the hip and knee occurred with the defensive player for both genders. Conclusions: A simulated defense player causes increased lower limb movements and forces, and should be a useful addition to laboratory protocols for sidestepping. Gender differences in the joint kinematics suggest that increased knee valgus may contribute to ACL injury risk in women, and that the hip and ankle may play an important role in controlling knee valgus during sidestepping. Consideration of the entire lower extremity contributes to an understanding of injury mechanisms and may lead to better training programs for injury prevention