Tibial Shear Force Research Articles

Relationship Between Tibial Acceleration and Proximal Anterior Tibia Shear Force Across Increasing Jump Distance

Proximal anterior tibia shear force is a direct loading mechanism of the anterior cruciate ligament (ACL) and is a contributor to ACL strain during injury. Measurement of this force during competition may provide insight into risk factors for ACL injury. Accelerometers may be capable of measuring tibial acceleration during competition. The purpose of this study was to examine the relationship between acceleration measured by a tibia-mounted accelerometer and proximal anterior tibia shear force as measured through inverse dynamics and peak posterior ground reaction forces during two leg stop-jump tasks. Nineteen healthy male subjects performed stop-jump tasks across increasing jump distances. Correlation coefficients were calculated to determine if a relationship exists between accelerometer data and proximal anterior tibia shear force and peak posterior ground reaction force. An analysis of variance was performed to compare these variables across jump distance. Significant correlations were observed between accelerometer data and peak posterior ground reaction force, but none between accelerometer data and proximal anterior tibia shear force. All variables except peak proximal anterior tibia shear force increased significantly as jump distance increased. Overall, results of this study provide initial, positive support for the use of accelerometers as a useful tool for future injury prevention research.

Associations between lower limb muscle activation strategies and resultant multi-planar knee kinetics during single leg landings

Anterior cruciate ligament injury prevention programs purportedly improve knee joint loading through beneficial modification of lower limb neuromuscular control strategies and joint biomechanics, but little is known about how these factors relate during single-legged landings. Thus, we examined the relationship between explicit lower limb muscular pre-activity patterns and knee joint biomechanics elicited during such landings. Randomized controlled trial. Thirty-five female athletes had 3D knee joint biomechanics and lower limb EMG data recorded during a series of single-leg landings. Regression analysis assessed the relationship between pre-activity of vastus lateralis, lateral hamstring and rectus femoris with peak knee flexion angle and moment, and external anterior tibial shear force. Vastus lateralis, lateral hamstring and vastus lateralis:lateral hasmtring co-contraction assessed the relationship with knee abduction angle and moment. Greater pre-activity of rectus femoris predicted increased peak anterior tibial shear force (R(2)=0.235, b=2.41 and P=0.003) and reduced knee flexion moment (R(2)=0.131, b=-0.591, and P=0.032), while greater lateral hamstring predicted decreased peak knee flexion angle (R(2)=0.113, b=8.96 and P=0.048). No EMG pre-activity parameters were predictors (P>0.05) for knee abduction angle and moment. Current outcomes suggest reducing reliance on quadriceps activation may be beneficial during single-legged landings. It also, however, may be required for adequate joint stability during such maneuvers. Further research is needed to determine if inadequate hamstring activation, rather than elevated quadriceps activation, leads to hazardous loading during single-legged landings.

Hamstrings Stiffness and Landing Biomechanics Linked to Anterior Cruciate Ligament Loading.

Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks. To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury. Cross-sectional study. Research laboratory. A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg). Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests. Hamstrings stiffness was normalized to body mass (N/m·kg-1). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height. Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t22 range = 1.729-2.224, P < .05). Greater hamstrings stiffness was associated with landing biomechanics consistent with less ACL loading and injury risk. Musculotendinous stiffness is a modifiable characteristic; thus exercises that enhance hamstrings stiffness may be important additions to ACL injury-prevention programs.

Preferential Loading of the ACL Compared to the MCL during Landing: A Novel In Sim Approach Yields the Multi-Planar Mechanism of Dynamic Valgus during ACL Injury

Objectives:Strong biomechanical and epidemiologic evidence associates knee valgus collapse with isolated non-contact ACL injury. However, the predominance of isolated non-contact anterior cruciate ligament (ACL) injuries is challenging for clinicians and researchers to explain, as the medial collateral ligament (MCL) has been reported to be the primary restraint against knee valgus. The purpose of this study was to investigate the relative ACL to MCL strain patterns during physiologic simulations of a wide range of high-risk dynamic landing scenarios. We hypothesized that both knee abduction and internal tibial rotation moments would generate a disproportionate increase in ACL strain relative to MCL strain. However, the physiologic range of knee abduction and internal tibial rotation moments that produce ACL injuries would not be of sufficient magnitude to consistently compromise MCL integrity.Methods:A novel in sim approach was used to test our hypotheses. 17 cadaveric lower extremities (45 ± 7 years, 9 female & 8 male) were tested to simulate a broad range of landing conditions following a jump under anterior tibial shear, knee abduction and internal tibial rotation. Specimens were oriented to simulate lower extremity posture during ground strike while landing from a jump. Landing was simulated by applying an impulsive axial impact load (simulating ground reaction forces) under simulated muscle forces. ACL and MCL strains were quantified using DVRT displacement transducers arthroscopically placed across the ACL AM-bundle and sutured to the anterior/middle/posterior aspects of superficial MCL across the joint line. Specimens were tested until failure. Multiple paired and independent t-tests along with general linear models were used to investigate the changes in strain levels under each modes of loading. An extensively validated, detailed finite element model of the lower extremity was used to better interpret experimental findings.Results:ACL failure was generated in 15 of 17 specimens (88%). Increased anterior tibial shear force, and knee abduction and internal tibial rotation moments resulted in significantly higher ACL: MCL strain ratios (p<0.05) compared to landing under no applied external loads. Under all modes of single- and multi-planar loading, ACL: MCL strain ratio remained greater than 1.7, and relative ACL strain was significantly higher than relative MCL strain (p<0.003, Figure 1). Relative change in ACL strain was significantly greater under combined multi-planar loading compared to ACL strain under anterior tibial shear force (p=0.016), knee abduction (p=0.018) and internal tibial rotation (p<0.0005) moments alone.Conclusion:The tibiofemoral frontal plane loading mechanism has become a recent topic of debate as a contributing factor to non-contact ACL injuries. Both in vivo and video analyses studies indicate that increased knee abduction is associated with increased risk for ACL injury. The current findings demonstrates that while both the ACL and MCL resist knee valgus during landing, physiological magnitudes of the applied loads that lead to high ACL strain levels and injury were not sufficient to compromise MCL integrity. Further, these findings support multi-planar knee valgus collapse as a primary mechanism of non-contact ACL injury. This enhances our understanding of the non-contact ACL injury mechanism, and provides insight that can improve current risk screening and injury prevention strategies.

Clinically Relevant Injury Patterns After an Anterior Cruciate Ligament Injury Provide Insight Into Injury Mechanisms

Background: The functional disability and high costs of treating anterior cruciate ligament (ACL) injuries have generated a great deal of interest in understanding the mechanism of noncontact ACL injuries. Secondary bone bruises have been reported in over 80% of partial and complete ACL ruptures. Purpose: The objectives of this study were (1) to quantify ACL strain under a range of physiologically relevant loading conditions and (2) to evaluate soft tissue and bony injury patterns associated with applied loading conditions thought to be responsible for many noncontact ACL injuries. Study Design: Controlled laboratory study. Methods: Seventeen cadaveric legs (age, 45 ± 7 years; 9 female and 8 male) were tested utilizing a custom-designed drop stand to simulate landing. Specimens were randomly assigned between 2 loading groups that evaluated ACL strain under either knee abduction or internal tibial rotation moments. In each group, combinations of anterior tibial shear force, and knee abduction and internal tibial rotation moments under axial impact loading were applied sequentially until failure. Specimens were tested at 25° of flexion under simulated 1200-N quadriceps and 800-N hamstring loads. A differential variable reluctance transducer was used to calculate ACL strain across the anteromedial bundle. A general linear model was used to compare peak ACL strain at failure. Correlations between simulated knee injury patterns and loading conditions were evaluated by the χ2 test for independence. Results: Anterior cruciate ligament failure was generated in 15 of 17 specimens (88%). A clinically relevant distribution of failure patterns was observed including medial collateral ligament tears and damage to the menisci, cartilage, and subchondral bone. Only abduction significantly contributed to calculated peak ACL strain at failure (P = .002). While ACL disruption patterns were independent of the loading mechanism, tibial plateau injury patterns (locations) were significantly (P = .002) dependent on the applied loading conditions. Damage to the articular cartilage along with depression of the midlateral tibial plateau was primarily associated with knee abduction moments, while cartilage damage with depression of the posterolateral tibial plateau was primarily associated with internal tibial rotation moments. Conclusion: The current findings demonstrate the relationship between the location of the tibial plateau injury and ACL injury mechanisms. The resultant injury locations were similar to the clinically observed bone bruises across the tibial plateau during a noncontact ACL injury. These findings indicate that abduction combined with other modes of loading (multiplanar loading) may act to produce ACL injuries. Clinical Relevance: A better understanding of ACL injury mechanisms and associated risk factors may improve current preventive, surgical, and rehabilitation strategies and limit the risk of ACL and secondary injuries, which may in turn minimize the future development of posttraumatic osteoarthritis of the knee.

Quantification of Tibiofemoral Shear and Compressive Loads Using an MRI-Based EMG-Driven Knee Model

The purpose of this study is to describe an MRI-based EMG-driven knee model to quantify tibiofemoral compressive and shear forces. Twelve healthy females participated. Subjects underwent 2 phases of data collection: (1) MRI assessment of the lower extremity to quantify muscle volumes and patella tendon orientation and (2) biomechanical evaluation of a drop-jump task. A subject-specific EMG-driven knee model that incorporated lower extremity kinematics, EMG, and muscle volumes and patella tendon orientation estimated from MRI was developed to quantify tibiofemoral shear and compressive forces. A resultant anterior tibial shear force generated from the ground reaction force (GRF) and muscle forces was observed during the first 30% of the stance phase of the drop-jump task. All of the muscle forces and GRF resulted in tibiofemoral compression, with the quadriceps force being the primary contributor. Acquiring subject-specific muscle volumes and patella tendon orientation for use in an EMG-driven knee model may be useful to quantify tibiofemoral forces in persons with altered patella position or muscle atrophy following knee injury or pathology.

Quadriceps and Hamstrings Coactivation During Common Therapeutic Exercises

Anterior tibial shear force and knee valgus moment increase anterior cruciate ligament (ACL) loading. Muscle coactivation of the quadriceps and hamstrings influences anterior tibial shear force and knee valgus moment, thus potentially influencing ACL loading and injury risk. Therefore, identifying exercises that facilitate balanced activation of the quadriceps and hamstrings might be beneficial in ACL injury rehabilitation and prevention. To quantify and compare quadriceps with hamstrings coactivation electromyographic (EMG) ratios during commonly used closed kinetic chain exercises. Cross-sectional study. Research laboratory. Twenty-seven healthy, physically active volunteers (12 men, 15 women; age = 22.1 ± 3.1 years, height = 171.4 ± 10 cm, mass = 72.4 ± 16.7 kg). Participants completed 9 separate closed chain therapeutic exercises in a randomized order. Surface electromyography quantified the activity level of the vastus medialis (VM), vastus lateralis (VL), medial hamstrings (MH), and biceps femoris (BF) muscles. The quadriceps-to-hamstrings (Q:H) coactivation ratio was computed as the sum of average quadriceps (VM, VL) EMG amplitude divided by the sum of average hamstrings (MH, BF) EMG amplitude for each trial. We used repeated-measures analyses of variance to compare Q:H ratios and individual muscle contributions across exercises (α = .05), then used post hoc Tukey analyses. We observed a main effect for exercise (F(3,79) = 22.6, P< .001). The post hoc Tukey analyses revealed smaller Q:H ratios during the single-limb dead lift (2.87 ± 1.77) than the single-limb squat (5.52 ± 2.89) exercise. The largest Q:H ratios were observed during the transverse-lunge (7.78 ± 5.51, P< .001), lateral-lunge (9.30 ± 5.53, P< .001), and forward-lunge (9.70 ± 5.90, P< .001) exercises. The most balanced (smallest) coactivation ratios were observed during the single-limb dead-lift, lateral-hop, transverse-hop, and lateral band-walk exercises. These exercises potentially could facilitate balanced activation in ACL rehabilitation and injury-prevention programs. They also could be used in postinjury rehabilitation programs in a safe and progressive manner.

Changing sagittal plane body position during single-leg landings influences the risk of non-contact anterior cruciate ligament injury

To examine the effects of different sagittal plane body positions during single-leg landings on biomechanics and muscle activation parameters associated with risk for anterior cruciate ligament (ACL) injury. Twenty participants performed single-leg drop landings onto a force plate using the following landing styles: self-selected, leaning forward (LFL) and upright (URL). Lower extremity and trunk 3D biomechanics and lower extremity muscle activities were recorded using motion analysis and surface electromyography, respectively. Differences in landing styles were examined using 2-way Repeated-measures ANOVAs (sex × landing conditions) followed by Bonferroni pairwise comparisons. Participants demonstrated greater peak vertical ground reaction force, greater peak knee extensor moment, lesser plantar flexion, lesser or no hip extensor moments, and lesser medial and lateral gastrocnemius and lateral quadriceps muscle activations during URL than during LFL. These modifications of lower extremity biomechanics across landing conditions were similar between men and women. Leaning forward while landing appears to protect the ACL by increasing the shock absorption capacity and knee flexion angles and decreasing anterior shear force due to the knee joint compression force and quadriceps muscle activation. Conversely, landing upright appears to be ACL harmful by increasing the post-impact force of landing and quadriceps muscle activity while decreasing knee flexion angles, all of which lead to a greater tibial anterior shear force and ACL loading. ACL injury prevention programmes should include exercise regimens to improve sagittal plane body position control during landing motions.

The effect of dietary calcium concentration and particle size on performance, eggshell quality, bone mechanical properties and tibia mineral contents in moulted laying hens

1. A total of 72 H&N Brown Nick laying hens, 76 weeks of age (moulted at 60 weeks of age), were randomly assigned into a 3 × 3 factorial arrangement with three limestone particle sizes and three dietary Ca concentrations (30, 36 and 42 g/kg Ca); with 8 replicates per treatments, and one hen (individual) per experimental unit. 2. Particle sizes of the limestone were: distributions smaller than 2 mm (Fine), between 2 to 5 mm (Medium), and larger than 5 mm (Large). The fine, medium and large limestone particles were all obtained from the same source, and sieve sizes used had screen sizes 2 mm and 5 mm. 3. The different concentrations of dietary Ca, particle size or interactions had no significant effect on egg production, egg weight, egg mass, feed intake or feed conversion ratio. 4. The concentrations of dietary Ca and particle sizes had no significant effect on egg breaking strength, eggshell as % by weight of whole egg or eggshell thickness. The interactions between Ca concentrations and particle sizes had a significant effect on eggshell breaking strength, but not on other parameters. 5. Different dietary particle sizes had no significant effect on the Ca, P and Mg mineral contents of eggshell. While the different concentrations of Ca in diets had a significant effect on the P content of eggshell, they had no significant effect on Ca and Mg contents. 6. Different dietary concentrations of Ca had a significant effect on shear stress, and Ca and Mg contents of tibiae, but not other parameters. Also, dietary particle sizes had a significant effect on shear stress and Ca contents of tibiae. The interaction between Ca concentrations and particle sizes had a significant effect on tibia shear force and Ca content. 7. According to the results of this study, moulted brown laying hens should be fed 36 g/kg Ca and a medium limestone particle size (2–5 mm) in the diet to maintain performance, eggshell and bone quality.

Trunk Neuromuscular Control is Associated with ACL Loading Mechanisms During an Athletic Cutting Task

Trunk position and postural control influence lower extremity biomechanics during athletic tasks. Triplanar loading of the knee results in high levels of stress in the anterior cruciate ligament (ACL). Excessive trunk motion has been reported during movements resulting in ACL injury. However, the relationship between trunk neuromuscular control (NMC) and triplanar knee loads during an athletic cutting task (ACT) has not been examined. PURPOSE: To investigate the relationship between a laboratory measure of trunk NMC during unstable-sitting (UST) and triplanar knee loads during an ACT. METHODS: 30 physically active subjects (15 male, 15 female, age: 20.5 ± 2.5 yrs, mass: 67.50 ± 11.39 Kg, height: 173.78 ± 9.28 cm) from the university setting participated in this study. During each 1-minute UST trial subjects were required to maintain balance atop a rigid hemisphere with their arms crossed at the chest and with their feet in contact with a footrest fixed to the unstable-sitting device. Center of pressure (CoP) sway data were collected during the UST using a forceplate. For the ACT subjects were instructed to take 3 running steps, jump over a 17 cm hurdle, and cut at 60° in the opposite direction of their dominant plant leg. Peak triplanar trunk angles and knee loads were collected using an infrared motion capture system and forceplate during the first 50% of stance time during the side-step ACT. Pearson product-moment correlation coefficients were calculated among CoP sway data and external knee loads. RESULTS: CoP sway velocity (1.34 ± 0.23 cm/s) was directly associated with anterior tibial shear force (0.114 ± 0.092) (r = 0.382, p = 0.049), and tibial external rotation moment (0.032 ±.013) (r = 0.451, p = 0.018). CoP sway area (50.29 ± 18.50 cm2) was positively associated (r = 0.548, p = 0.006) with knee flexion moment (0.115 ± 0.032). CoP sway path (81.02 ± 14.44 cm) was positively associated with knee flexion moment (r = 0.407, p = 0.032) and tibial external rotation moment (r = 0.474, p = 0.011). CONCLUSION: The results of this study provide evidence of a relationship between trunk NMC and triplanar knee loading associated with ACL injury. These relationships suggest that poor NMC of the trunk is associated with increased triplanar loading at the knee joint. Interventions with a focus on improving trunk NMC may decrease ACL injury risk.

Sagittal plane body positions influence tibial anteror shear force during single-leg landing

BackgroundExcessive tibiofemoral compression has been shown to rupture the Anterior Cruciate Ligament (ACL) as axial tibia load may produce an anterior shear force to the proximal lateral tibial plateau.ObjectiveTo quantify...

Effect of posterior tibial slope on knee biomechanics during functional activity

Treatment of medial compartment knee osteoarthritis with high tibial osteotomy can produce an unintended change in the slope of the tibial plateau in the sagittal plane. The effect of changing posterior tibial slope (PTS) on cruciate ligament forces has not been quantified for knee loading in activities of daily living. The purpose of this study was to determine how changes in PTS affect tibial shear force, anterior tibial translation (ATT), and knee-ligament loading during daily physical activity. We hypothesized that tibial shear force, ATT, and ACL force all increase as PTS increases. A previously validated computer model was used to calculate ATT, tibial shear force, and cruciate-ligament forces for the normal knee during three common load-bearing tasks: standing, squatting, and walking. The model calculations were repeated with PTS altered in 1° increments up to a maximum change in tibial slope of 10°. Tibial shear force and ATT increased as PTS was increased. For standing and walking, ACL force increased as tibial slope was increased; for squatting, PCL force decreased as tibial slope was increased. The effect of changing PTS on ACL force was greatest for walking. The true effect of changing tibial slope on knee-joint biomechanics may only be evident under physiologic loading conditions which include muscle forces.

The association between lower extremity energy absorption and biomechanical factors related to anterior cruciate ligament injury

Background Greater total energy absorption by the lower extremity musculature during landing may reduce stresses placed on capsuloligamentous tissues with differences in joint contributions to energy absorption potentially affecting anterior cruciate ligament injury risk. However, the relationships between energy absorption and prospectively identified biomechanical factors associated with non-contact anterior cruciate ligament injury have yet to be demonstrated. Methods Sagittal plane total, hip, knee and ankle energy absorption, and peak vertical ground reaction force, anterior tibial shear force, knee flexion and knee valgus angles, and internal hip extension and knee varus moments were measured in 27 individuals (14 females, 13 males) performing double leg jump landings. Correlation coefficients assessed the relationships between energy absorption during three time intervals (initial impact phase, terminal phase, and total landing) and biomechanical factors related to anterior cruciate ligament injury. Findings More favorable values of biomechanical factors related to non-contact anterior cruciate ligament injury were associated with: 1) Lesser total ( R 2 = 0.178–0.558), hip ( R 2 = 0.229–0.651) and ankle ( R 2 = 0.280), but greater knee ( R 2 = 0.147) energy absorption during the initial impact phase; 2) Greater total ( R 2 = 0.170–0.845), hip ( R 2 = 0.599), knee ( R 2 = 0.236–0.834), and ankle ( R 2 = 0.276) energy absorption during the terminal phase of landing; and 3) Greater knee ( R 2 = 0.158–0.709), but lesser hip ( R 2 = 0.309) and ankle ( R 2 = 0.210–0.319) energy absorption during the total landing period. Interpretation These results suggest that biomechanical factors related to anterior cruciate ligament injury are influenced by both the magnitude and timing of lower extremity energy absorption during landing.

Alterations to movement mechanics can greatly reduce anterior cruciate ligament loading without reducing performance

Anterior cruciate ligament (ACL) injuries are one of the most common and potentially debilitating sports injuries. Approximately 70% of ACL injuries occur without contact and are believed to be preventable. Jump stop movements are associated with many non-contact ACL injuries. It was hypothesized that an athlete performing a jump stop movement can reduce their peak tibial shear force (PTSF), a measure of ACL loading, without compromising performance, by modifying their knee flexion angle, shank angle, and foot contact location during landing. PTSF was calculated for fourteen female basketball players performing jump stops using their normal mechanics and mechanics modified to increase their knee flexion angle, decrease their shank angle relative to vertical and land more on their toes during landing. Every subject tested experienced drastic reductions in their PTSF (average reduction=56.4%) using modified movement mechanics. The athletes maintained or improved their jump height with the modified movement mechanics (an average increase in jump height of 2.5cm). The hypothesis was supported: modifications to jump stop movement mechanics greatly reduced PTSF and therefore ACL loading without compromising performance. The results from this study identify crucial biomechanical quantities that athletes can easily modify to reduce ACL loading and therefore should be targeted in any physical activity training programs designed to reduce non-contact ACL injuries.

Significant Correlation between Tibial Acceleration and Proximal Anterior Tibia Shear Force across Increasing Jump Distance

Proximal anterior tibia shear force (PATSF) is the most direct loading mechanism of the anterior cruciate ligament (ACL) and is likely a significant contributor to ACL strain during noncontact ACL injuries. Measurement of PATSF during actual athletic competition may provide insight into risk factors for the mechanism of noncontact ACL injury. Unfortunately, the methods to accurately measure and calculate PATSF during actual athletic competition have not been developed and may not be feasible. But, accelerometers are simple to use, relatively inexpensive, and may be capable of measuring tibial acceleration in vivo during actual competition. PURPOSE: To determine if data from an accelerometer mounted on the proximal tibia correlates with PATSF as measured through inverse dynamics and to determine if peak tibial acceleration (PTA) and PATSF increase with jump distance. METHODS: A total of 10 healthy subjects participated in the study (Age=24.8±3.9 yrs; Ht=176.3±5.4 cm; Wt=77.9±6.9 kg). Subjects were fitted with 16 retro-reflective markers and a small, wireless, triaxial accelerometer was affixed to the proximal tibia. 3D coordinate data and force plate data were combined with anthropometric data to calculate PATSF through inverse dynamics. Subjects performed a series of stop-jump tasks with initial jump distances ranging from 20% to 80% of the subject's height. The stop-jump task began with a broad jump to two force-plates followed by an immediate maximal jump. A Pearson product-moment correlation coefficient was conducted to determine if a relationship exists between PTA and PATSF. A one-way ANOVA was performed to compare PTA and PATSF across jump distances. RESULTS: The Pearson product-moment correlations revealed significant correlations between PATSF and PTA as measured by the accelerometer (r=0.56; p=0.0048). Both PATSF and PTA increased as jump distance increased, but the one-way ANOVA was not significant. CONCLUSIONS: Significant correlations between PATSF and PTA indicate that an accelerometer can provide in vivo tibia accelerations that correspond to PATSF. The lack of significant increases in both variables relative to jump distance appears to be due to the small sample size based on post-hoc power analysis. Overall, the accelerometer may be a useful tool for future injury prevention research.

Thigh strength and activation as predictors of knee biomechanics during a drop jump task.

To examine whether normalized quadriceps and hamstring strength would predict quadriceps and hamstring muscle activation amplitudes and whether these neuromuscular factors would predict knee kinematics and kinetics during a drop jump task. Thirty-nine females and 39 males were measured for isometric quadriceps and hamstring strength and were instrumented to obtain surface electromyography, kinematic, and kinetic measures during the initial landing of a drop jump. Multiple linear regressions first examined the relationship between thigh strength and activation then examined whether these neuromuscular variables were predictive of hip and knee flexion excursions, knee extensor moments (KEM), and anterior knee shear forces during the deceleration phase of the drop jump. Females versus males produced lower normalized thigh strength and demonstrated greater quadriceps and hamstring activation amplitudes during the drop jump. Lower thigh muscle strength was a weak (males) to moderate (females) predictor of greater quadriceps activation amplitudes. However, thigh strength and activation were poor predictors of hip and knee joint excursions and KEM. Regardless of sex and thigh strength, anterior shear forces were greater in individuals who demonstrated less hip flexion and greater knee flexion excursions and greater peak quadriceps activation and internal KEM during the landing. Although thigh muscle strength explained some of the variance in quadriceps and hamstring activation levels as measured with surface electromyography, we failed to support the hypothesis that these neuromuscular factors are strong predictors of sagittal plane hip and knee flexion excursions or KEM. Although greater quadriceps activation amplitude was a significant predictor of greater anterior tibial shear forces, its contribution was relatively small compared with kinematic and kinetic variables.

Sagittal Plane Knee Biomechanics and Vertical Ground Reaction Forces Are Modified Following ACL Injury Prevention Programs: A Systematic Review

Context:Injuries to the anterior cruciate ligament (ACL) occur because of excessive loading on the knee. ACL injury prevention programs can influence sagittal plane ACL loading factors and vertical ground reaction force (VGRF).Objective:To determine the influence of ACL injury prevention programs on sagittal plane knee biomechanics (anterior tibial shear force, knee flexion angle/moments) and VGRF.Data Sources:The PubMed database was searched for studies published between January 1988 and June 2008. Reference lists of selected articles were also reviewed.Study Selection:Studies were included that evaluated healthy participants for knee flexion angle, sagittal plane knee kinetics, or VGRF after performing a multisession training program. Two individuals reviewed all articles and determined which articles met the selection criteria. Approximately 4% of the articles fulfilled the selection criteria.Data Extraction:Data were extracted regarding each program’s duration, frequency, exercise type, population, supervision, and testing procedures. Means and variability measures were recorded to calculate effect sizes. One reviewer extracted all data and assessed study quality using PEDro (Physiotherapy Evidence Database). A second reviewer (blinded) verified all information.Results:There is moderate evidence to indicate that knee flexion angle, external knee flexion moment, and VGRF can be successfully modified by an ACL injury prevention program. Programs utilizing multiple exercises (ie, integrated training) appear to produce the most improvement, in comparison to that of single-exercise programs. Knee flexion angle was improved following integrated training (combined balance and strength exercises or combined plyometric and strength exercises). Similarly, external knee flexion moment was improved following integrated training consisting of balance, plyometric, and strength exercises. VGRF was improved when incorporating supervision with instruction and feedback on proper technique.Conclusion:ACL injury prevention programs that are aimed at modifying sagittal plane knee biomechanics and VGRF should use an integrated training approach that incorporates instruction and feedback on proper movement technique.

The relationship between anterior tibial shear force during a jump landing task and quadriceps and hamstring strength

Background Eccentric quadriceps contraction during landing and the resulting anterior tibial shear force are anterior cruciate ligament injury risk factors, while hamstring contraction limits anterior cruciate ligament loading. Anterior tibial shear force is derived from quadriceps and hamstring co-contraction, and a greater quadriceps/hamstring strength ratio has been associated with heightened lower extremity injury risk. The purpose of this investigation was to evaluate relationships between anterior tibial shear force during landing and quadriceps and hamstring strength. Methods Anterior tibial shear force was calculated during a jump landing task in 26 healthy females. Isokinetic eccentric quadriceps strength and concentric hamstrings strength were assessed at 60°/s, 180°/s, and 300°/s. Correlational analyses were conducted to evaluate relationships between lower extremity strength and anterior tibial shear force. Findings Quadriceps ( r = 0.126 to 0.302, P > 0.05) and hamstrings strength ( r = −0.019 to 0.058, P > 0.05) and the quadriceps/hamstring ratio ( r = 0.036 to 0.127, P > 0.05) were not significant predictors of anterior tibial shear force. Interpretation Quadriceps and hamstring strength are not indicative of sagittal-plane knee loading during landing. Contractile force resulting from maximal strength testing may not represent that produced during landing, as it is unlikely that landing requires maximal effort. Additionally, peak anterior tibial shear force, quadriceps torque, and hamstrings torque are generated at different points in the knee flexion/extension range of motion. Therefore, peak anterior tibial shear force is a function of the available strength at a given point in the range of motion rather than of peak strength. These findings illustrate the limitations of peak strength values in predicting dynamic loading during landing.

Single-Day Reliability of Kinetics During a Jump-Landing Task

Oftentimes while conducting biomechanical analyses in attempts to understand injury (e.g., ACL and ankle) risk factors mean scores of several trials are utilized to evaluate individual movement patterns; yet, analysis of inter-trial variability within a single session merits further consideration. PURPOSE: The purpose of this study was to analyze inter-trial reliability within one session of performing a jump-landing task from a box. The study aimed to evaluate inter-trial reliability on the kinetic variables (vertical ground reaction force and proximal tibial anterior shear force) at three instants (maximum vertical ground reaction force (MVGRF), maximum knee flexion (MKF), and maximum proximal tibial anterior shear force (MPTASF) in a jump-landing task across gender. METHODS: Twenty-five males (24±2.3yrs, 178.6±7.2cm, and 84.1±13.1kg) and twenty-five females (23±2.5yrs, 167.2±7.4cm, and 62.8±8.5kg) were selected from a sample of convenience from a university student population. 3-D electromagnetic motion analysis sensors sampling at 1 00Hz and two Bertec force plates sampling at 1000 Hz were used for data collection. Five trials were conducted and each trial was considered as a separate data point and evaluated using an intraclass correlation coefficient model (ICC 2,k) to analyze the reliability of each variable at different time instants. RESULTS: All variables were significant different at p<0.05. Moderate to poor reliability was shown for vertical ground reaction force (0.67) and proximal tibial anterior shear force (0.32) at MVGRF across gender with minimal differences between males (0.62, 0.24) and females (0.73, 0.44), respectively. The maximum kinetic values also revealed poor reliability (MVGRF 0.35 and MPTASF 0.38) across gender with minimal differences between genders (females=0.28, vs. males=0.42). Fair reliability was found for vertical ground reaction force at MKF (0.71), with females showing better reliability (0.84) as compared to their male counterparts (0.63). CONCLUSION: Five trials during a single-session jump landing task showed poor to fair reliability within ground reaction force and proximal tibial anterior shear force across gender. Future studies should focus on evaluating the inter-trial variability of kinetic data across multiple sessions.

Neuromuscular and biomechanical characteristics do not vary across the menstrual cycle

Research examining the menstrual cycle and its relationship to ACL injury has focused on determining the incidence of ACL injury during the different phases of the menstrual cycle and assessing the changes in neuromuscular and biomechanical characteristics between these phases. Conflicting results warrant further investigation to determine if neuromuscular and biomechanical characteristics respond in a similar pattern to the fluctuating estradiol and progesterone. The purpose of this study was to determine if changes in the levels of estradiol and progesterone significantly altered fine motor coordination, postural stability, knee strength, and knee joint kinematics and kinetics between the menses, post-ovulatory, and mid-luteal phases of the menstrual cycle. Ten healthy and physically active females (Age: 21.4 +/- 1.4 years, Height: 1.67 +/- 0.06 m, Mass: 59.9 +/- 7.4 kg), who did not use oral contraceptives, were recruited from the local university population. Single-leg postural stability, fine motor coordination, knee strength, knee biomechanics, and serum estradiol and progesterone were assessed at the menses, post-ovulatory, and mid-luteal phases of the menstrual cycle. Levels of estradiol were significantly higher during the post-ovulatory (P = 0.016) and mid-luteal phases (P < 0.001) compared to the menses phase. Levels of progesterone were significantly lower during the menses (P < 0.001) and post-ovulatory phases (P < 0.001) compared to the mid-luteal phase. No significant differences existed between phases of the menstrual cycle for fine motor coordination (P = 0.474), postural stability (P = 0.707), hamstring - quadriceps strength ratio at 60 degrees s(-1) (P = 0.748) or 180 degrees s(-1) (P = 0.789), knee flexion excursion (P = 0.6), knee valgus excursion (P = 0.899), peak proximal tibial anterior shear force (P = 0.797), flexion moment at peak proximal tibial anterior shear force (P = 0.698), or valgus moment at peak proximal tibial anterior shear force (P = 0.924). The results of the current study suggest neuromuscular and biomechanical characteristics are not influenced by estradiol and progesterone fluctuations. All neuromuscular and biomechanical characteristics remained invariable between testing sessions despite concentration changes in estradiol and progesterone.