Relationship between hip and knee strength and peak knee valgus and its associated knee flexion angle during single leg squat

Physiotherapy ◽  
2015 ◽  
Vol 101 ◽  
pp. e149-e150
Author(s):  
A. Bin Hussein
Keyword(s):  
Knee Flexion ◽  
Flexion Angle ◽  
Knee Valgus ◽  
Knee Flexion Angle ◽  
Knee Strength ◽  
Peak Knee ◽  
Single Leg Squat

scholarly journals Knee Proprioception and Strength and Landing Kinematics During a Single-Leg Stop-Jump Task

2013 ◽  
Vol 48 (1) ◽  
pp. 31-38 ◽  
Author(s):  
Takashi Nagai ◽  
Timothy C. Sell ◽  
Anthony J. House ◽  
John P. Abt ◽  
Scott M. Lephart
Keyword(s):  
Knee Joint ◽  
Knee Flexion ◽  
Muscular Strength ◽  
Biomechanical Analysis ◽  
Flexion Angle ◽  
Knee Flexion Angle ◽  
Knee Strength ◽  
Peak Knee ◽  
The Relationship ◽  
Flexion And Extension

Context The importance of the sensorimotor system in maintaining a stable knee joint has been recognized. As individual entities, knee-joint proprioception, landing kinematics, and knee muscles play important roles in functional joint stability. Preventing knee injuries during dynamic tasks requires accurate proprioceptive information and adequate muscular strength. Few investigators have evaluated the relationship between knee proprioception and strength and landing kinematics. Objective To examine the relationship between knee proprioception and strength and landing kinematics. Design Cross-sectional study. Setting University research laboratory. Patients or Other Participants Fifty physically active men (age = 26.4 ± 5.8 years, height = 176.5 ± 8.0 cm, mass = 79.8 ± 16.6 kg). Intervention(s) Three tests were performed. Knee conscious proprioception was evaluated via threshold to detect passive motion (TTDPM). Knee strength was evaluated with a dynamometer. A 3-dimensional biomechanical analysis of a single-legged stop-jump task was used to calculate initial contact (IC) knee-flexion angle and knee-flexion excursion. Main Outcome Measure(s) The TTDPM toward knee flexion and extension, peak knee flexion and extension torque, and IC knee-flexion angle and knee flexion excursion. Linear correlation and stepwise multiple linear regression analyses were used to evaluate the relationships of both proprioception and strength against landing kinematics. The α level was set a priori at .05. Results Enhanced TTDPM and greater knee strength were positively correlated with greater IC knee-flexion angle (r range = 0.281–0.479, P range = .001–.048). The regression analysis revealed that 27.4% of the variance in IC knee-flexion angle could be accounted for by knee-flexion peak torque and TTDPM toward flexion (P = .001). Conclusions The current research highlighted the relationship between knee proprioception and strength and landing kinematics. Individuals with enhanced proprioception and muscular strength had better control of IC knee-flexion angle during a dynamic task.

scholarly journals Kinematic Comparison between Medially Congruent and Posterior-Stabilized Third-Generation TKA Designs

2021 ◽  
Vol 6 (1) ◽  
pp. 27
Author(s):  
Stefano Ghirardelli ◽  
Jessica L. Asay ◽  
Erika A. Leonardi ◽  
Tommaso Amoroso ◽  
Thomas P. Andriacchi ◽  
...  
Keyword(s):  
Knee Flexion ◽  
Knee Kinematics ◽  
Primary Total Knee Arthroplasty ◽  
Flexion Angle ◽  
Heel Strike ◽  
Third Generation ◽  
Knee Flexion Angle ◽  
Posterior Stabilized ◽  
Rotational Angle ◽  
Peak Knee

Background: This study compares knee kinematics in two groups of patients who have undergone primary total knee arthroplasty (TKA) using two different modern designs: medially congruent (MC) and posterior-stabilized (PS). The aim of the study is to demonstrate only minimal differences between the groups. Methods: Ten TKA patients (4 PS, 6 MC) with successful clinical outcomes were evaluated through 3D knee kinematics analysis performed using a multicamera optoelectronic system and a force platform. Extracted kinematic data included knee flexion angle at heel-strike (KFH), peak midstance knee flexion angle (MSKFA), maximum and minimum knee adduction angle (KAA), and knee rotational angle at heel-strike. Data were compared with a group of healthy controls. Results: There were no differences in preferred walking speed between MC and PS groups, but we found consistent differences in knee function. At heel-strike, the knee tended to be more flexed in the PS group compared to the MC group; the MSKFA tended to be higher in the PS group compared to the MC group. There was a significant fluctuation in KAA during the swing phase in the PS group compared to the MC group, PS patients showed a higher peak knee flexion moment compared to MC patients, and the PS group had significantly less peak internal rotation moments than the MC group. Conclusions: Modern, third-generation TKA designs failed to reproduce normal knee kinematics. MC knees tended to reproduce a more natural kinematic pattern at heel-strike and during axial rotation, while PS knees showed better kinematics during mid-flexion.

scholarly journals Quadriceps Strength Symmetry Does Not Modify Gait Mechanics After Anterior Cruciate Ligament Reconstruction, Rehabilitation, and Return-to-Sport Training

2020 ◽  
pp. 036354652098007
Author(s):  
Elanna K. Arhos ◽  
Jacob J. Capin ◽  
Thomas S. Buchanan ◽  
Lynn Snyder-Mackler
Keyword(s):  
Knee Flexion ◽  
Cruciate Ligament ◽  
Return To Sport ◽  
Quadriceps Muscle ◽  
Quadriceps Strength ◽  
Flexion Angle ◽  
Knee Flexion Angle ◽  
Sport Training ◽  
Gait Biomechanics ◽  
Peak Knee

Background: After anterior cruciate ligament (ACL) reconstruction (ACLR), biomechanical asymmetries during gait are highly prevalent, persistent, and linked to posttraumatic knee osteoarthritis. Quadriceps strength is an important clinical measure associated with preoperative gait asymmetries and postoperative function and is a primary criterion for return-to-sport clearance. Evidence relating symmetry in quadriceps strength with gait biomechanics is limited to preoperative and early rehabilitation time points before return-to-sport training. Purpose/Hypothesis: The purpose was to determine the relationship between symmetry in isometric quadriceps strength and gait biomechanics after return-to-sport training in athletes after ACLR. We hypothesized that as quadriceps strength symmetry increases, athletes will demonstrate more symmetric knee joint biomechanics, including tibiofemoral joint loading during gait. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Of 79 athletes enrolled in the ACL-SPORTS Trial, 76 were participants in this study after completing postoperative rehabilitation and 10 return-to-sport training sessions (mean ± SD, 7.1 ± 2.0 months after ACLR). All participants completed biomechanical walking gait analysis and isometric quadriceps strength assessment using an electromechanical dynamometer. Quadriceps strength was calculated using a limb symmetry index (involved limb value / uninvolved limb value × 100). The biomechanical variables of interest included peak knee flexion angle, peak knee internal extension moment, sagittal plane knee excursion at weight acceptance and midstance, quadriceps muscle force at peak knee flexion angle, and peak medial compartment contact force. Spearman rank correlation (ρ) coefficients were used to determine the relationship between limb symmetry indexes in quadriceps strength and each biomechanical variable; alpha was set to .05. Results: Of the 76 participants, 27 (35%) demonstrated asymmetries in quadriceps strength, defined by quadriceps strength symmetry <90% (n = 23) or >110% (n = 4) (range, 56.9%-131.7%). For the biomechanical variables of interest, 67% demonstrated asymmetry in peak knee flexion angle; 68% and 83% in knee excursion during weight acceptance and midstance, respectively; 74% in internal peak knee extension moment; 57% in medial compartment contact force; and 74% in quadriceps muscle force. There were no significant correlations between quadriceps strength index and limb symmetry indexes for any biomechanical variable after return-to-sport training ( P > .129). Conclusion: Among those who completed return-to-sport training after ACLR, subsequent quadriceps strength symmetry was not correlated with the persistent asymmetries in gait biomechanics. After a threshold of quadriceps strength is reached, restoring strength alone may not ameliorate gait asymmetries, and current clinical interventions and return-to-sport training may not adequately target gait.

Patellofemoral Joint Stress during Running with Added Load in Females

2020 ◽  
Vol 41 (06) ◽  
pp. 412-418
Author(s):  
Molly Kujawa ◽  
Aleyna Goerlitz ◽  
Drew Rutherford ◽  
Thomas W. Kernozek
Keyword(s):  
Knee Flexion ◽  
Patellofemoral Joint ◽  
Reaction Force ◽  
Step Length ◽  
Force Platform ◽  
Flexion Angle ◽  
Knee Flexion Angle ◽  
Peak Knee ◽  
Foot Strike ◽  
Quadriceps Force

AbstractPatellofemoral joint (PFJ) pain syndrome is a commonly reported form of pain in female runners and military personnel. Increased PFJ stress may be a contributing factor. Few studies have examined PFJ stress running with added load. Our purpose was to analyze PFJ stress, PFJ reaction force, quadriceps force, knee flexion angle, and other kinematic and temporospatial variables running with and without a 9 kg load. Nineteen females ran across a force platform with no added load and 9.0 kg weight vest. Kinematic data were collected using 3D motion capture and kinetic data with a force platform. Muscle forces were estimated using a musculoskeletal model, and peak PFJ loading variables were calculated during stance. Multivariate analyses were run on PFJ loading variables and on cadence, step length and foot strike index. Differences were shown in PFJ stress, PFJ reaction force, peak knee flexion angle and quadriceps force. Joint specific kinetic variables increased between 5–16% with added load. PFJ loading variables increased with 9 kg of added load without changes in cadence, step length, or foot strike index compared to no load. Added load appears to increase the PFJ loading variables associated with PFJ pain in running.

scholarly journals Progressive Changes in Walking Kinematics and Kinetics After Anterior Cruciate Ligament Injury and Reconstruction: A Review and Meta-Analysis

2017 ◽  
Vol 52 (9) ◽  
pp. 847-860 ◽  
Author(s):  
Lindsay V. Slater ◽  
Joseph M. Hart ◽  
Adam R. Kelly ◽  
Christopher M. Kuenze
Keyword(s):  
Lower Extremity ◽  
Knee Flexion ◽  
Cruciate Ligament ◽  
Knee Extensor ◽  
Flexion Angle ◽  
Knee Adduction Moment ◽  
Control Group ◽  
Knee Flexion Angle ◽  
Peak Knee ◽  
Healthy Control

Context:  Anterior cruciate ligament (ACL) injury and ACL reconstruction (ACLR) result in persistent alterations in lower extremity movement patterns. The progression of lower extremity biomechanics from the time of injury has not been described. Objective:  To compare the 3-dimensional (3D) lower extremity kinematics and kinetics of walking among individuals with ACL deficiency (ACLD), individuals with ACLR, and healthy control participants from 3 to 64 months after ACLR. Data Sources:  We searched PubMed and Web of Science from 1970 through 2013. Study Selection and Data Extraction:  We selected only articles that provided peak kinematic and kinetic values during walking in individuals with ACLD or ACLR and comparison with a healthy control group or the contralateral uninjured limb. Data Synthesis:  A total of 27 of 511 identified studies were included. Weighted means, pooled standard deviations, and 95% confidence intervals were calculated for the healthy control, ACLD, and ACLR groups at each reported time since surgery. The magnitude of between-groups (ACLR versus ACLD, control, or contralateral limb) differences at each time point was evaluated using Cohen d effect sizes and associated 95% confidence intervals. Peak knee-flexion angle (Cohen d = −0.41) and external knee-extensor moment (Cohen d = −0.68) were smaller in the ACLD than in the healthy control group. Peak knee-flexion angle (Cohen d range = −0.78 to −1.23) and external knee-extensor moment (Cohen d range = −1.39 to −2.16) were smaller in the ACLR group from 10 to 40 months after ACLR. Reductions in external knee-adduction moment (Cohen d range = −0.50 to −1.23) were present from 9 to 42 months after ACLR. Conclusions:  Reductions in peak knee-flexion angle, external knee-flexion moment, and external knee-adduction moment were present in the ACLD and ACLR groups. This movement profile during the loading phase of gait has been linked to knee-cartilage degeneration and may contribute to the development of osteoarthritis after ACLR.

scholarly journals Change of Direction Biomechanics in a 180-Degree Pivot Turn and the Risk for Noncontact Knee Injuries in Youth Basketball and Floorball Players

2021 ◽  
pp. 036354652110269
Author(s):  
Mari Leppänen ◽  
Jari Parkkari ◽  
Tommi Vasankari ◽  
Sami Äyrämö ◽  
Juha-Pekka Kulmala ◽  
...  
Keyword(s):  
Knee Flexion ◽  
Injury Risk ◽  
Knee Injury ◽  
Reaction Force ◽  
Knee Injuries ◽  
Flexion Angle ◽  
Knee Valgus ◽  
Change Of Direction ◽  
Increased Risk ◽  
Peak Knee

Background: Studies investigating biomechanical risk factors for knee injuries in sport-specific tasks are needed. Purpose: To investigate the association between change of direction (COD) biomechanics in a 180-degree pivot turn and knee injury risk among youth team sport players. Study Design: Cohort study; Level of evidence, 2. Methods: A total of 258 female and male basketball and floorball players (age range, 12-21 years) participated in the baseline COD test and follow-up. Complete data were obtained from 489 player-legs. Injuries, practice, and game exposure were registered for 12 months. The COD test consisted of a quick ball pass before and after a high-speed 180-degree pivot turn on the force plates. The following variables were analyzed: peak vertical ground-reaction force (N/kg); peak trunk lateral flexion angle (degree); peak knee flexion angle (degree); peak knee valgus angle (degree); peak knee flexion moment (N·m/kg); peak knee abduction moment (N·m/kg); and peak knee internal and external rotation moments (N·m/kg). Legs were analyzed separately and the mean of 3 trials was used in the analysis. Main outcome measure was a new acute noncontact knee injury. Results: A total of 18 new noncontact knee injuries were registered (0.3 injuries/1000 hours of exposure). Female players sustained 14 knee injuries and male players 4. A higher rate of knee injuries was observed in female players compared with male players (incidence rate ratio, 6.2; 95% CI, 2.1-21.7). Of all knee injuries, 8 were anterior cruciate ligament (ACL) injuries, all in female players. Female players displayed significantly larger peak knee valgus angles compared with male players (mean for female and male players, respectively: 13.9°± 9.4° and 2.0°± 8.5°). No significant associations between biomechanical variables and knee injury risk were found. Conclusion: Female players were at increased risk of knee and ACL injury compared with male players. Female players performed the 180-degree pivot turn with significantly larger knee valgus compared with male players. However, none of the investigated variables was associated with knee injury risk in youth basketball and floorball players.

scholarly journals Quadriceps Neuromuscular Function and Jump-Landing Sagittal-Plane Knee Biomechanics After Anterior Cruciate Ligament Reconstruction

2018 ◽  
Vol 53 (2) ◽  
pp. 135-143 ◽  
Author(s):  
Sarah H. Ward ◽  
J. Troy Blackburn ◽  
Darin A. Padua ◽  
Laura E. Stanley ◽  
Matthew S. Harkey ◽  
...  
Keyword(s):  
Knee Flexion ◽  
Sagittal Plane ◽  
Neuromuscular Function ◽  
Knee Extension ◽  
Spinal Reflex ◽  
Flexion Angle ◽  
Voluntary Activation ◽  
Knee Flexion Angle ◽  
Jump Landing ◽  
Peak Knee

Context:  Aberrant biomechanics may affect force attenuation at the knee during dynamic activities, potentially increasing the risk of sustaining a knee injury or hastening the development of osteoarthritis after anterior cruciate ligament reconstruction (ACLR). Impaired quadriceps neuromuscular function has been hypothesized to influence the development of aberrant biomechanics. Objective:  To determine the association between quadriceps neuromuscular function (strength, voluntary activation, and spinal-reflex and corticomotor excitability) and sagittal-plane knee biomechanics during jump landings in individuals with ACLR. Design:  Cross-sectional study. Setting:  Research laboratory. Patients or Other Participants:  Twenty-eight individuals with unilateral ACLR (7 men, 21 women; age = 22.4 ± 3.7 years, height = 1.69 ± 0.10 m, mass = 69.4 ± 10.1 kg, time postsurgery = 52 ± 42 months). Main Outcome Measure(s):  We quantified quadriceps spinal-reflex excitability via the Hoffmann reflex normalized to maximal muscle response (H : M ratio), corticomotor excitability via active motor threshold, strength as knee-extension maximal voluntary isometric contraction (MVIC), and voluntary activation using the central activation ratio (CAR). In a separate session, sagittal-plane kinetics (peak vertical ground reaction force [vGRF] and peak internal knee-extension moment) and kinematics (knee-flexion angle at initial contact, peak knee-flexion angle, and knee-flexion excursion) were collected during the loading phase of a jump-landing task. Separate bivariate associations were performed between the neuromuscular and biomechanical variables. Results:  In the ACLR limb, greater MVIC was associated with greater peak knee-flexion angle (r = 0.38, P = .045) and less peak vGRF (r = −0.41, P = .03). Greater CAR was associated with greater peak internal knee-extension moment (ρ = −0.38, P = .045), and greater H : M ratios were associated with greater peak vGRF (r = 0.45, P = .02). Conclusions:  Greater quadriceps MVIC and CAR may provide better energy attenuation during a jump-landing task. Individuals with greater peak vGRF in the ACLR limb possibly require greater spinal-reflex excitability to attenuate greater loading during dynamic movements.

Joint Torques and Patellofemoral Force During Single-Leg Assisted and Unassisted Cycling

2016 ◽  
Vol 25 (1) ◽  
pp. 40-47 ◽  
Author(s):  
Rodrigo R. Bini ◽  
Tiago C. Jacques ◽  
Marco A. Vaz
Keyword(s):  
Outcome Measures ◽  
Lower Limb ◽  
Knee Flexion ◽  
Compressive Force ◽  
Flexion Angle ◽  
Knee Flexion Angle ◽  
Joint Torques ◽  
Custom Made ◽  
Peak Knee ◽  
Leg Cycling

Context:Unassisted single-leg cycling should be replaced by assisted single-leg cycling, given that this last approach has potential to mimic joint kinetics and kinematics from double-leg cycling. However, there is need to test if assisting devices during pedaling effectively replicate joint forces and torque from double-leg cycling.Objectives:To compare double-leg, single-leg assisted, and unassisted cycling in terms of lower-limb kinetics and kinematics.Design:Cross-sectional crossover.Setting:Laboratory.Participants:14 healthy nonathletes.Interventions:Two double-leg cycling trials (240 ± 23 W) and 2 single-leg trials (120 ± 11 W) at 90 rpm were performed for 2 min using a bicycle attached to a cycle trainer. Measurements of pedal force and joint kinematics of participants’ right lower limb were performed during double- and single-leg trials. For the single-leg assisted trial, a custom-made adaptor was used to attach 10 kg of weight to the contralateral crank.Main Outcome Measures:Peak hip, knee, and ankle torques (flexors and extensors) along with knee-flexion angle and peak patellofemoral compressive force.Results:Reduced peak hip-extensor torque (10%) and increased peak knee-flexor torque (157%) were observed at the single-leg assisted cycling compared with the double-leg cycling. No differences were found for peak patellofemoral compressive force or knee-flexion angle comparing double-leg with single-leg assisted cycling. However, single-leg unassisted cycling resulted in larger peak patellofemoral compressive force (28%) and lower knee-flexion angle (3%) than double-leg cycling.Conclusions:These results suggest that although single-leg assisted cycling differs for joint torques, it replicates knee loads from double-leg cycling.

scholarly journals Stiff Landings Are Associated With Increased ACL Injury Risk in Young Female Basketball and Floorball Players

2016 ◽  
Vol 45 (2) ◽  
pp. 386-393 ◽  
Author(s):  
Mari Leppänen ◽  
Kati Pasanen ◽  
Urho M. Kujala ◽  
Tommi Vasankari ◽  
Pekka Kannus ◽  
...  
Keyword(s):  
Knee Flexion ◽  
Injury Risk ◽  
Acl Injury ◽  
Young Female ◽  
Flexion Angle ◽  
Knee Flexion Angle ◽  
Acl Injuries ◽  
Increased Risk ◽  
Peak Knee ◽  
Acl Injury Risk

Background: Few prospective studies have investigated the biomechanical risk factors of anterior cruciate ligament (ACL) injury. Purpose: To investigate the relationship between biomechanical characteristics of vertical drop jump (VDJ) performance and the risk of ACL injury in young female basketball and floorball players. Study Design: Cohort study; Level of evidence, 3. Methods: At baseline, a total of 171 female basketball and floorball players (age range, 12-21 years) participated in a VDJ test using 3-dimensional motion analysis. The following biomechanical variables were analyzed: (1) knee valgus angle at initial contact (IC), (2) peak knee abduction moment, (3) knee flexion angle at IC, (4) peak knee flexion angle, (5) peak vertical ground-reaction force (vGRF), and (6) medial knee displacement. All new ACL injuries, as well as match and training exposure, were then recorded for 1 to 3 years. Cox regression models were used to calculate hazard ratios (HRs) and 95% CIs. Results: Fifteen new ACL injuries occurred during the study period (0.2 injuries/1000 player-hours). Of the 6 factors considered, lower peak knee flexion angle (HR for each 10° increase in knee flexion angle, 0.55; 95% CI, 0.34-0.88) and higher peak vGRF (HR for each 100-N increase in vGRF, 1.26; 95% CI, 1.09-1.45) were the only factors associated with increased risk of ACL injury. A receiver operating characteristic (ROC) curve analysis showed an area under the curve of 0.6 for peak knee flexion and 0.7 for vGRF, indicating a failed-to-fair combined sensitivity and specificity of the test. Conclusions: Stiff landings, with less knee flexion and greater vGRF, in a VDJ test were associated with increased risk of ACL injury among young female basketball and floorball players. However, although 2 factors (decreased peak knee flexion and increased vGRF) had significant associations with ACL injury risk, the ROC curve analyses revealed that these variables cannot be used for screening of athletes.

scholarly journals Lower Extremity Muscle Activation and Knee Flexion During a Jump-Landing Task

2012 ◽  
Vol 47 (4) ◽  
pp. 406-413 ◽  
Author(s):  
Meghan Walsh ◽  
Michelle C. Boling ◽  
Melanie McGrath ◽  
J. Troy Blackburn ◽  
Darin A. Padua
Keyword(s):  
Lower Extremity ◽  
Muscle Activity ◽  
Knee Flexion ◽  
Flexion Angle ◽  
Initial Contact ◽  
Knee Flexion Angle ◽  
Jump Landing ◽  
Lower Extremity Muscle ◽  
Peak Knee ◽  
The Relationship

Context: Decreased sagittal-plane motion at the knee during dynamic tasks has been reported to increase impact forces during landing, potentially leading to knee injuries such as anterior cruciate ligament rupture. Objective: To describe the relationship between lower extremity muscle activity and knee-flexion angle during a jump-landing task. Design: Cross-sectional study. Setting: Research laboratory. Patients or Other Participants: Thirty recreationally active volunteers (15 men, 15 women: age = 21.63 ± 2.01 years, height = 173.95 ± 11.88 cm, mass = 72.57 ± 14.25 kg). Intervention(s): Knee-flexion angle and lower extremity muscle activity were collected during 10 trials of a jump-landing task. Main Outcome Measure(s): Simple correlation analyses were performed to determine the relationship between each knee-flexion variable (initial contact, peak, and displacement) and electromyographic amplitude of the gluteus maximus (GMAX), quadriceps (VMO and VL), hamstrings, gastrocnemius, and quadriceps : hamstring (Q : H) ratio. Separate forward stepwise multiple regressions were conducted to determine which combination of muscle activity variables predicted each knee-flexion variable. Results: During preactivation, VMO and GMAX activity and the Q : H ratio were negatively correlated with knee-flexion angle at initial contact (VMO: r = −0.382, P = .045; GMAX: r = −0.385, P = .043; Q : H ratio: r = −0.442, P = .018). The VMO, VL, and GMAX deceleration values were negatively correlated with peak knee-flexion angle (VMO: r = −0.687, P = .001; VL: r = −0.467, P = .011; GMAX: r = −0.386, P = .043). The VMO and VL deceleration values were negatively correlated with knee-flexion displacement (VMO: r = −0.631, P = .001; VL: r = −0.453, P = .014). The Q : H ratio and GM activity predicted 34.7% of the variance in knee-flexion angle at initial contact (P = .006). The VMO activity predicted 47.1% of the variance in peak knee-flexion angle (P = .001). The VMO and VL activity predicted 49.5% of the variance in knee-flexion displacement (P = .001). Conclusions: Greater quadriceps and GMAX activation and less hamstrings and gastrocnemius activation were correlated with smaller knee-flexion angles. This landing strategy may predispose an individual to increased impact forces due to the negative influence on knee-flexion position.

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