Different Lower-Limb Setup Positions Do Not Consistently Change Backstroke Start Time to 10 m

Backstroke starts involve the athlete starting from a flexed position with their feet against the pool wall and then extending their ankles, knees, hips and back to push off; however, swimmers can start in different positions. The purpose of this study was to evaluate the performance impact of different knee extension angles in the setup position for a backstroke start. Ten backstroke swimmers completed maximum-effort starts in each of two setup positions: one with the knees maximally flexed, and one with the knees less flexed. The start handles and touchpad were instrumented with multi-axial force sensors. Activity of major hip and knee extensors was measured using surface electromyography. Body position in the sagittal plane was recorded using high-speed cameras. There was no overall difference in time to 10 m between the two conditions (p = 0.36, dz = 0.12), but some participants showed differences as large as 0.12 s in time to 10 m between start conditions. We observed that starts performed from a setup position with less knee flexion had an average 0.07 m greater head entry distance (p = 0.07, dz = 0.53), while starts from a setup position with maximal knee flexion had an average 0.2 m/s greater takeoff velocity (p = 0.02, dz = 0.78). Both head entry distance and takeoff velocity are related to start performance, suggesting each position may optimize different aspects of the backstroke start. Coaches should assess athletes individually to determine which position is optimal.

Download Full-text

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

Journal of Athletic Training ◽

10.4085/1062-6050-306-16 ◽

2018 ◽

Vol 53 (2) ◽

pp. 135-143 ◽

Cited By ~ 18

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.

Download Full-text

Modeling the Angle-Specific Isokinetic Hamstring to Quadriceps Ratio Using Multilevel Generalized Additive Models

Medicina ◽

10.3390/medicina55080411 ◽

2019 ◽

Vol 55 (8) ◽

pp. 411

Author(s):

Sousa ◽

Soares ◽

Lima ◽

Paes ◽

Nakamura ◽

...

Keyword(s):

Knee Flexion ◽

Multilevel Model ◽

Joint Angle ◽

Knee Extension ◽

Additive Models ◽

Knee Extensors ◽

Strength Development ◽

Present Sample ◽

Non Linear ◽

H:Q Ratio

Background and Objectives: This study considered the use of a generalized additive multilevel model to describe the joint-angle-specific functional hamstring to quadriceps ratio (H:Q ratio) in the knee, using all of the available truly isokinetic data within the range. Materials and Methods: Thirty healthy male basketball players aged 15.0 (1.4) years (average stature = 180.0 cm, SD = 11.1 cm; average body mass = 71.2, SD = 14.9 kg) years were considered. All players considered had no history of lower extremity musculoskeletal injury at the time of testing or during the 6 months before testing, and had been engaged in formal basketball training and competition for 5.9 (2.4) years. Moments of force of the reciprocal concentric and eccentric muscular actions for the knee extensors and flexors assessed by isokinetic dynamometry at 60°∙s−1 were used. Results: Maximum moments of force were attained at different angle positions for knee extension. For knee flexion, it was apparent that there was an ability to maintain high levels of moment of force between 30° and 60° in the concentric muscular action, corresponding to the concentric action of the hamstrings. However, for the eccentric knee flexion, corresponding to the quadriceps action, there was a marked peak of moment of force at about 55°. The functional H:Q ratio for the knee extension was non-linear, remaining higher than 1.0 (i.e., point of equality) from the beginning of the extension until approximately 40° of the knee extension, leveling off below the point of equality thereafter. On average, the functional H:Q ratio for the knee flexion did not attain 1.0 across the range of motion. The functional H:Q ratio for the knee in the present sample peaked at 20° and 80°, declining between these angle positions to below 0.50 at about 0.54. Conclusions: Estimating the form of the non-linear relationship on-the-fly using a generalized additive multilevel model provides joint-angle-specific curves and joint-angle-specific functional H:Q ratio patterns, allowing the identification and monitoring of strength development, with potential implications for injury and performance.

Download Full-text

Determining the Force-Length-Velocity Relations of the Quadriceps Muscles: II. Maximum Muscle Stress

Journal of Applied Biomechanics ◽

10.1123/jab.15.2.191 ◽

1999 ◽

Vol 15 (2) ◽

pp. 191-199 ◽

Cited By ~ 11

Author(s):

John W. Chow ◽

Warren G. Darling ◽

James C. Ehrhardt

Keyword(s):

Knee Flexion ◽

Isometric Force ◽

Muscle Length ◽

Gravitational Effect ◽

Knee Extension ◽

Cross Sectional ◽

Average Value ◽

Isometric Knee Extension ◽

Maximum Effort ◽

Muscle Stress

The purpose of this study was to determine the maximum muscle stress (σ), defined as the maximum isometric force divided by the physiological cross-sectional area, of the quadriceps muscles for a pilot study involving musculoskeletal modeling. One female subject performed maximum effort isometric knee extension exercises on an isokinetic dynamometer at different attachment arm angles. The gravitational effect was taken into consideration when determining the isometric resultant knee torques at different knee flexion angles. The anatomical and geometric parameters of the quadriceps muscles were obtained from radiography and magnetic resonance imaging taken from the subject. The σ value was computed using me measured knee torques, musculoskeletal parameters data, and information reported in the literature. The computation procedures used in this study represented the first attempt to incorporate the concept of optimal muscle length in the determination of maximum muscle stress. The σ values obtained from the data for nine different knee flexion angles ranged from 21.4 to 30.5 N/cm2. The average value of 25.6 ± 2.6 N/cm2 is notably smaller than the human σ values reported in the literature, but is comparable to the σ values obtained from isolated muscles.

Download Full-text

Skeletal muscle fatigue, strength, and quality in the elderly: the Health ABC Study

Journal of Applied Physiology ◽

10.1152/japplphysiol.01276.2004 ◽

2005 ◽

Vol 99 (1) ◽

pp. 210-216 ◽

Cited By ~ 64

Author(s):

Andreas Katsiaras ◽

Anne B. Newman ◽

Andrea Kriska ◽

Jennifer Brach ◽

Shanthi Krishnaswami ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Fatigue ◽

Knee Flexion ◽

Peak Torque ◽

Older Men ◽

Knee Extension ◽

Muscle Quality ◽

Knee Extensors ◽

Men And Women ◽

Skeletal Muscle Fatigue

We examined the muscle fatigue characteristics in older men and women and determined whether these were related to the size, strength, or quality of muscle. A total of 1,512 men and women aged 70–79 yr from the Health, Aging, and Body Composition Study participated in this study. Muscle cross-sectional area and attenuation were determined with computed tomography. Skeletal muscle fatigue and strength (peak torque) of the knee extensors and flexors were measured using isokinetic dynamometry. Men were more fatigue resistant than women for both knee extension (fatigue index: 70.4 ± 15.3 vs. 66.9 ± 14.3%; P < 0.05) and knee flexion (67.9 ± 16.4 vs. 64.9 ± 17.6%; P < 0.05). Peak torque and muscle quality (specific torque) were higher in men than women for knee extension (99.6 ± 28.2 vs. 63.0 ± 16.8 N·m and 1.62 ± 0.43 vs. 1.51 ± 0.39 N·m/cm2; both P < 0.05) and for knee flexion (74.0 ± 26.4 vs. 49.6 ± 15.9 N·m and 2.47 ± 1.29 vs. 2.22 ± 0.78 N·m/cm2; both P < 0.05). Total work and power output was greater in men compared with women for both the quadriceps (1,353 ± 451 vs. 832 ± 264 J and 87.7 ± 33.5 vs. 53.3 ± 19.2 W; both P < 0.05) and the hamstrings (741 ± 244 vs. 510 ± 141 J and 35.4 ± 16.0 vs. 23.7 ± 10.2 W; both P < 0.05). In both genders, the quadriceps was able to perform more work with greater power compared with the hamstrings. Those who were stronger actually had greater fatigue after adjusting for age, race, physical activity, and total body fat. In conclusion, older men were more fatigue resistant than women, although in both men and women greater fatigue was not related to muscle weakness.

Download Full-text

Preparatory Knee Flexion-Extension Movements Enhance Rapid Sidestepping Performance in Collegiate Basketball Players

Frontiers in Sports and Active Living ◽

10.3389/fspor.2021.670649 ◽

2021 ◽

Vol 3 ◽

Author(s):

Masahiro Fujimoto ◽

Eri Uchida ◽

Akinori Nagano ◽

Mark W. Rogers ◽

Tadao Isaka

Keyword(s):

Lower Limb ◽

Knee Flexion ◽

Knee Extension ◽

Movement Initiation ◽

Basketball Players ◽

Step Initiation ◽

Limb Loading ◽

Flexion Extension ◽

Collegiate Basketball ◽

Lift Off

Lower-limb weight-bearing load distribution in stationary standing influences the timing of rapid first step initiation of importance for functional movement activities and agility performance in sports. This study investigated the effect of pre-step lower-limb loading and unloading with preparatory knee flexion-extension movements on sidestepping performance in fifteen male collegiate basketball players. Participants performed two-choice (step limb) reaction time sidestepping under two conditions: without preparatory movements before the go cue (no-prep–NP) and with continuous alternating knee extension and flexion movements (prep–P). The reaction signal was provided at the beginning of knee extension and flexion and during these movements which corresponded with the largest and smallest loading instants and the transition states between those instants. Sidestepping performance was assessed with three-dimensional kinematic data and ground reaction forces. Step initiation onset time was significantly faster by 13–15% than the NP condition when initiated in the knee flexion phase (p ≤ 0.028, r ≥ 0.70), whereas step-limb unloading interval from step initiation to step lift-off was significantly faster by 12–15% in the knee extension phase (p ≤ 0.01, r ≥ 0.74). The preparatory movements significantly shortened step lift-off by 10–12% (p ≤ 0.013, r ≥ 0.73) and step duration by 17–21% (p < 0.001, r ≥ 0.85) with 19–22% faster step velocity (p < 0.001, r ≥ 0.84), which resulted in 14–15% shorter overall time to step landing (p < 0.001, r ≥ 0.84), irrespective of the loading phases. These results indicated that lower-limb loading with pre-step knee flexion facilitated faster step initiation, while lower-limb unloading with knee extension facilitated faster step-limb unloading, both resulting in faster step lift-off. Bilateral knee flexion-extension movements as a preparatory action could be utilized by invasion sports players to facilitate reactive stepping performance for more effective movement initiation.

Download Full-text

Runners Adapt Different Lower-Limb Movement Patterns With Respect to Different Speeds and Downhill Slopes

Frontiers in Sports and Active Living ◽

10.3389/fspor.2021.682401 ◽

2021 ◽

Vol 3 ◽

Author(s):

David Sundström ◽

Markus Kurz ◽

Glenn Björklund

Keyword(s):

Lower Limb ◽

Energy Cost ◽

Degrees Of Freedom ◽

Stance Phase ◽

Sagittal Plane ◽

Three Dimensional ◽

Movement Pattern ◽

Knee Extension ◽

Generic Model ◽

Energy Cost Of Running

The aim of this study was to investigate the influence of slope and speed on lower-limb kinematics and energy cost of running. Six well-trained runners (VO2max 72 ± 6 mL·kg−1·min−1) were recruited for the study and performed (1) VO2max and energy cost tests and (2) an experimental running protocol at two speeds, 12 km·h−1 and a speed corresponding to 80% of VO2max (V80, 15.8 ± 1.3 km·h−1) on three different slopes (0°, −5°, and −10°), totaling six 5-min workload conditions. The workload conditions were randomly ordered and performed continuously. The tests lasted 30 min in total. All testing was performed on a large treadmill (3 × 5 m) that offered control over both speed and slope. Three-dimensional kinematic data of the right lower limb were captured during the experimental running protocol using eight infrared cameras with a sampling frequency of 150 Hz. Running kinematics were calculated using a lower body model and inverse kinematics approach. The generic model contained three, one, and two degrees of freedom at the hip, knee, and ankle joints, respectively. Oxygen uptake was measured throughout the experimental protocol. Maximum hip extension and flexion during the stance phase increased due to higher speed (p < 0.01 and p < 0.01, respectively). Knee extension at the touchdown and maximal knee flexion in the stance phase both increased on steeper downhill slopes (both p < 0.05). Ground contact time (GCT) decreased as the speed increased (p < 0.01) but was unaffected by slope (p = 0.73). Runners modified their hip movement pattern in the sagittal plane in response to changes in speed, whereas they altered their knee movement pattern during the touchdown and stance phases in response to changes in slope. While energy cost of running was unaffected by speed alone (p = 0.379), a shift in energy cost was observed for different speeds as the downhill gradient increased (p < 0.001). Energy cost was lower at V80 than 12 km·h−1 on a −5° slope but worse on a −10° slope. This indicates that higher speeds are more efficient on moderate downhill slopes (−5°), while lower speeds are more efficient on steeper downhill slopes (−10°).

Download Full-text

Lower limb symmetry index (LLSI) pre- and post-reconstruction of the ACL: a controlled study

Manual Therapy Posturology & Rehabilitation Journal ◽

10.17784/mtprehabjournal.2018.16.597 ◽

2020 ◽

pp. 1-6

Author(s):

Luma Soares Lustosa ◽

Nyck Douglas Claro Pereira ◽

José Jamacy de Almeida Ferreira ◽

Palloma Rodrigues de Andrade ◽

Heleodório Honorato dos Santos

Keyword(s):

Lower Limb ◽

Knee Extension ◽

Lower Limbs ◽

Controlled Study ◽

Knee Extensors ◽

Emg Activity ◽

Symmetry Index ◽

Limb Symmetry Index ◽

Treatment Comparison ◽

Hip Abduction

Background: The anterior cruciate ligament (ACL) lesion causes a deficit in joint stability and mobility, trophism and muscular strength, generating asymmetries between the lower limbs. Objective: To verify the effect of a physiotherapeutic protocol on the Lower Limb Symmetry Index (LLSI) and the correlation between strength and EMGs, pre and post reconstruction of the ACL. Methods: Twenty subjects (10 ACLrg + 10 CONTg) were evaluated regarding isometric force and electrical activity of knee extensors, knee flexors and hip abductors. Results: A significant increase (P<0.01) in knee extension and flexion strength and hip abduction strength were observed both for the affected limb and non-affected limb. Regarding the LLSI, a significant increase was observed for knee extension and hip abduction movements in the pre- and post-treatment comparison, and between ACLrg X CONTg (P<0.01) for the knee extension movement in the pre-reconstruction phase of the ACL. A very strong correlation (r=0.945; P<0.01) was also observed between the LLSI strength X EMGs during knee extension, pre- and post-reconstruction surgery. Conclusions: Six months after reconstruction of the ACL, there was an increase in strength and EMG activity of the knee flexor, knee extensor and hip abductor muscles, leveling the LLSI between ACLrg and the CONTg, however, with a significant correlation between the two variables (strength X EMGs) for only one of the three movements (knee extension).

Download Full-text

Altered neuromechanical strategies of the paretic hip and knee joints during a step-up task

10.1101/2020.12.02.407122 ◽

2020 ◽

Author(s):

Vatsala Goyal ◽

Andrew Dragunas ◽

Robert L. Askew ◽

Theresa Sukal-Moulton ◽

Roberto López-Rosado

Keyword(s):

Lower Limb ◽

Fixed Effects ◽

Sagittal Plane ◽

Knee Extension ◽

Mixed Effects ◽

Chronic Stroke ◽

Knee Joints ◽

Uneven Terrain ◽

Hip Abduction ◽

Hemiparetic Stroke

AbstractBackgroundStroke often leads to chronic, neural-derived motor impairments in the paretic lower limb, such as weakness, abnormal extensor torque coupling, and reduced ranges of motion. These impairments can constrain lower extremity movement and negatively impact the ability to navigate uneven terrain. Quantification of biomechanical strategies used by individuals with chronic stroke to step up would offer insight into the neural consequences of a stroke.Research QuestionWhat are the altered kinetic and kinematic strategies of the leading paretic hip and knee joints while swinging and pulling-up onto a step?MethodsA total of 10 participants were included in this mixed design study: 5 adults with hemiparetic stroke and 5 age-matched adults without stroke. Participants were instructed to step up onto a 4-inch platform, where joint kinetic and kinematics of the hip in the frontal plane and the hip and knee in the sagittal plane were quantified. A mixed effects linear regression model with two fixed effects of group (stroke and control) and lower limb (LL: dominant/non-paretic and non-dominant/paretic) was used to compare peak joint torques and angles. Another mixed effects model with two fixed effects of peak hip and knee extension torque was used to investigate whether these main effects could predict peak hip abduction torque.ResultsAltered biomechanical strategies of the paretic limb for step ascent included reduced sagittal plane flexion angles during swing, reduced hip abduction and knee extension torque combined with increased hip extension torque during pull-up stance, and abnormal torque coupling between the hip adductors and sagittal plane extensors.SignificanceThese differences can be linked to the neural consequences of a hemiparetic stroke, including corticospinal damage and upregulation of bulbospinal pathways as compensation. Overall, our findings can inform interventions for individuals with chronic stroke in navigating uneven terrain to maximize daily community activity.

Download Full-text

Analysis of The Global Posture of College Students With Chronic Neck Pain

10.21203/rs.3.rs-1089151/v1 ◽

2021 ◽

Author(s):

Jiugen Zhong ◽

Wenhao Wang ◽

Ligen Yu ◽

Xiaohui Hou

Keyword(s):

Risk Factors ◽

College Students ◽

Neck Pain ◽

Lower Limb ◽

Knee Flexion ◽

Sagittal Plane ◽

Chronic Neck Pain ◽

Control Group ◽

Limb Alignment ◽

Lower Limb Alignment

Abstract Background: Chronic neck pain (CNP) is common, but methods that focus on the cervical spine have not met the patients' medical expectations.Objective: To investigate the global postural difference between students with CNP and healthy people.Design: Cross-sectional study.Methods: Twenty-seven healthy college students without neck pain and 31 students with CNP were recruited and allocated into a control group and a CNP group. Differences in standing postural indicators between the two groups were compared.Results: Compared to the control group, the leg length discrepancy and the right rearfoot angle were larger and the anterior lower limb alignment angle was smaller. In the sagittal plane, the left sagittal lower limb alignment and right cervical alignment angles were larger, while the left and right sagittal body alignment angles in the CNP group were smaller. The odds ratio calculation for the trunk forward lean, right foot valgus, and knee flexion on both sides indicated that these are risk factors for CNP, while knee varus is not a risk factor for CNP. The remaining abnormal postures were shown not to be associated with CNP.Limitation: This study did not conduct in-depth research on the physiological state of the muscles, joints, and other structures, and we did not apply these theories to practice.Conclusions: Abnormal posture in students with CNP is mainly concentrated in the sagittal plane. Trunk forward lean, foot valgus, and knee flexion on both sides are risk factors for CNP.

Download Full-text

Does Chronic Ankle Instability Influence Knee Biomechanics of Females during Inverted Surface Landings?

International Journal of Sports Medicine ◽

10.1055/s-0044-102130 ◽

2018 ◽

Vol 39 (13) ◽

pp. 1009-1017 ◽

Cited By ~ 2

Author(s):

Yumeng Li ◽

Jupil Ko ◽

Marika Walker ◽

Cathleen Brown ◽

Julianne Schmidt ◽

...

Keyword(s):

Internal Rotation ◽

Knee Flexion ◽

Sagittal Plane ◽

Ankle Instability ◽

Knee Extension ◽

Chronic Ankle Instability ◽

Initial Contact ◽

Knee Biomechanics ◽

Peak Knee ◽

Eccentric Work

AbstractThe primary purpose of the study was to determine whether atypical knee biomechanics are exhibited during landing on an inverted surface. A seven-camera motion analysis system and two force plates were used to collect lower extremity biomechanics from two groups of female participants: 21 subjects with chronic ankle instability (CAI) and 21 with pair-matched controls. Subjects performed ten landings onto inverted and flat platforms on the CAI/matched and non-test limbs, respectively. Knee and ankle joint angles, joint angular displacements, joint moments and eccentric work were calculated during the landing phase and/or at the initial contact. Paired t-tests were used to compare between-group differences (p<0.05). We observed that CAI group displayed a significantly increased knee flexion angle, knee flexion displacement, peak knee extension moment and internal rotation moment, and eccentric work in the sagittal plane, possibly due to altered ankle biomechanics. Participants with CAI employed some compensatory strategy to improve their ankle and postural stability during landing onto the tilted surface. The increased knee extension and internal rotation moments of CAI participants could potentially result in a greater ACL loading. In future studies, it may be worthwhile to measure or estimate the ACL loading to confirm whether CAI could relate to the mechanism of ACL injury.

Download Full-text