Extensor Moment Research Articles

Effects of barbell load on kinematics, kinetics, and myoelectric activity in back squats

ABSTRACT Shortly after beginning the upward phase of a free-weight barbell back squat there is often a deacceleration phase (sticking region) that may lead to repetition failure. The cause for this region is not well understood. Therefore, this study investigated the effects of 90%, 100%, and 102% of 1-RM barbell loads on kinematics, kinetics, and myoelectric activity in back squats. Twelve resistance-trained healthy males (body mass: 83.5 ± 7.8 kg, age: 27.3 ± 3.8 years, height: 180.3 ± 6.7 cm) participated in the study and lifted 134 ± 17 kg at 90% and 149 ± 19 kg at 100%, while they failed at 153 ± 19 kg with 102% load. The main findings were that barbell displacement and barbell velocity in the sticking region decreased with increasing loads. Moreover, the external hip extensor moment increased with heavier loads, whereas the knee extension and ankle plantarflexion moments were similar during the concentric phase. Also, reduced hip and knee extension together with lower myoelectric activity for all hip extensors and vastus lateralis were found for the 102% load compared to the others. Our finding suggests that the increased external hip extensor moment together with lower hip extensor myoelectric activity due to a reduced hip extension and thereby are responsible for lifting failure among resistance-trained males.

Experimental Verification of Kinematics and Kinetics in a Biomimetic Bipedal Robot

Abstract This article presents experimental test results for joints used in a biomimetic bipedal robot. In this work, magnetic resonance imaging (MRI) and computed tomography (CT) scans are utilized to inform the design of joints of similar size and function to the biological counterparts. Three lower body joints, to be actuated by artificial muscles, were designed and constructed. Then the range of motion and passive stiffness were tested. The knee joint consists of a four-bar mechanism that provides increased extensor moment arm as the joint becomes more flexed, a “screw home” locking mechanism analog, and large contact surfaces for force distribution. The hip, ankle, and foot are hybrid hard-soft joints, consisting of a ball and socket held together with an outer, inflatable sleeve made from a braided pneumatic actuator (BPA) material. These joints provide a novel way for real-time stiffness adjustments and energy storage during the gait cycle. Results show that the physical knee prototype matches the previous simulation of joint movement (Steele, A., Hunt, A., and Etoundi, A., 2018, “Biomimetic Knee Design to Improve Joint Torque and Life for Bipedal Robotics,” Bristol, UK.). A linear relationship exists between the increase in angle and the force required to bend the hybrid joints. First, this article documents a process that others may use to develop their own joints. Second, the range of motion and passive forces in the hybrid hard-soft joints is characterized, which will enable improved control of the joints and inform other researchers to whether a hybrid joint design is appropriate for their applications. This process has several applications in prosthetic designs and robotics.

The effects of foot orthosis and low-dye tape on lower limb joint angles and moments during running in individuals with pes planus

BackgroundPes Planus or Flat feet is one of the most common lower limb abnormalities. When runners with this abnormality participate in recreational running, interventional therapies could help in pain alleviation and enhance performance. To determine the most effective treatment, however, a biomechanical examination of the effects of each treatment modality is required. Research questionThe aim of the present study was to investigate the effects of Foot Orthoses (FOs) and Low-Dye Tape (LDT) on lower limb joint angles and moments during running in individuals with pes planus. Methodskinematic and kinetic data of 20 young people with pes planus were measured during running in three conditions: (1) SHOD (2) with shoes and FOs (3) with shoes and LDT. One-way repeated measure ANOVA was used to investigate the impacts of the FOs and LDT on the lower limb joint angles and moments throughout the stance phase of the running cycle. ResultsThe results showed that FOs reduced ankle eversion compared to SHOD and LDT (P < 0.001) and decreased the dorsiflexion angle (P = 0.005) and the plantarflexor moment compared to the SHOD (P < 0.001). FOs increased knee adduction angle (P = 0.021) and knee external rotator moment (P < 0.001) compared to both conditions and increased knee extensor and abductor moments compared to SHOD (P < 0.001). At the hip joint, FOs only increased hip external rotation compared with the LDT condition (P = 0.031); and LDT increased hip extensor moment compared to SHOD and FOs (P = 0.037) and also increased hip adduction angle compared to SHOD (P = 0.037). SignificanceFOs with a medial wedge appears to increase the external knee adduction moment and knee adduction angles, which are risk factors for the development and progression of knee osteoarthritis. Further, usage of FOs seems to reduce the ankle joint role in propulsion as it impacts the ankle sagittal angles and moments.

GMFCS Level-Specific Differences in Kinematics and Joint Moments of the Involved Side in Unilateral Cerebral Palsy.

A variety of gait pathologies is seen in cerebral palsy. Movement patterns between different levels of functional impairment may differ. The objective of this work was the evaluation of Gross Motor Function Classification System (GMFCS) level-specific movement disorders. A total of 89 individuals with unilateral cerebral palsy and no history of prior treatment were included and classified according to their functional impairment. GMFCS level-specific differences, kinematics and joint moments, exclusively of the involved side, were analyzed for all planes for all lower limb joints, including pelvic and trunk movements. GMFCS level I and level II individuals most relevantly showed equinus/reduced dorsiflexion moments, knee flexion/reduced knee extension moments, reduced hip extension moments with pronounced flexion, internal hip rotation and reduced hip abduction. Anterior pelvic tilt, obliquity and retraction were found. Individuals with GMFCS level II were characterized by an additional pronounced reduction in all extensor moments, pronounced rotational malalignment and reduced hip abduction. The most striking characteristics of GMFCS level II were excessive anterior pelvic/trunk tilt and excessive trunk obliquity. Pronounced reduction in extensor moments and excessive trunk lean are distinguishing features of GMFCS level II. These patients would benefit particularly from surgical treatment restoring pelvic symmetry and improving hip abductor leverage. Future studies exploring GMFCS level-specific compensation of the sound limb and GMFCS level-specific malalignment are of interest.

Hip medial rotator action of gluteus medius in Japanese macaque (Macaca fuscata) and implications to adaptive significance for quadrupedal walking in primates.

The gluteus medius (GM) muscle in quadrupedal primates has long been thought to mainly act as a hip extensor. However, previous reports argue that it may be a prime hip medial rotator and functions to rotate the pelvis in the horizontal plane, suggesting the functional differentiation between the GM and other hip extensors as hamstrings. In this study, we aim to quantify the muscle actions of the GM and hamstrings using muscle moment arm lengths and discuss the functional differentiation among hip extensors. Muscle attachment sites of eight specimens of Japanese macaque (Macaca fuscata) were digitized, and musculoskeletal models were constructed. Flexor-extensor, abductor-adductor, and medial-lateral rotator moment arms were calculated as the models were moved following the experimentally acquired kinematic data during walking on a pole substrate. Using electromyography, we also recorded the pattern of muscle activation. The GM showed a larger medial rotator moment arm length than the extensor moment arm length when it was activated, suggesting this muscle acts mainly as a hip medial rotator rather than as a hip extensor. The medial rotator action of the GM in the early support phase may rotate the pelvis in the horizontal plane and function to help contralateral forelimb reaching as a previous study suggested and facilitate contralateral hindlimb swinging to place the foot near the ipsilateral forelimb's hand.

Identification of Sex Differences within Lunge Decelerations via Lower Extremity Support Moments; Implications for ACL Injury Disparity, Prevention, and Rehabilitation

Loading characteristics and lower extremity injury mechanisms, such as the non-contact mechanism of cruciate ligament injury, differ between sexes. The Limb Support Moment (LSM) quantifies hip, knee, and ankle moment contribution to the net moment required to prevent limb collapse during deceleration tasks. In total, 10 males and 10 females performed single limb deceleration landings within three knee flexion ranges: 0–25°, 25–50°, and 50–75°. Lower extremity joint moments and LSMs were calculated for all planes at initial contact (IC) through 50 ms. A two-way multivariate ANOVA compared LSMs and joint moments between sexes for all planes. Female LSMs were significantly greater at IC in the sagittal and transverse planes due to the generation of hip and ankle extensor moments and larger hip, knee, and ankle internal rotation moments. Males demonstrated significantly greater LSMs in the frontal plane due to the generation of hip abductor moments. Results suggest that females have a more rigid lower limb than males at landing, with less shock absorption capacity and greater potential for frontal plane collapse due to an unsupportive hip adductor moment. Quantifying the contribution of joint moments to limb support via LSMs suggests that there are landing characteristic sex differences, which may provide insight into injury disparity while guiding injury prevention/rehabilitation methodology.

Biomechanical Markers of Forward Hop-Landing After ACL-Reconstruction: A Pattern Recognition Approach

Biomechanical changes after anterior cruciate ligament reconstruction (ACLR) may be detrimental to long-term knee-joint health. We used pattern recognition to characterise biomechanical differences during the landing phase of a single-leg forward hop after ACLR. Experimental data from 66 individuals 12-24 months post-ACLR (28.2 ± 6.3 years) and 32 controls (25.2 ± 4.8 years old) were input into a musculoskeletal modelling pipeline to calculate joint angles, joint moments and muscle forces. These waveforms were transformed into principal components (features), and input into a pattern recognition pipeline, which found 10 main distinguishing features (and 8 associated features) between ACLR and control landing biomechanics at significance alpha =0.05. Our process identified known biomechanical characteristics post-ACLR: smaller knee flexion angle; less knee extensor moment; lower vasti, rectus femoris and hamstrings forces. Importantly, we found more novel and less well-understood adaptations: smaller ankle plantar flexor moment; lower soleus forces; and altered patterns of knee rotation angle, hip rotator moment and knee abduction moment. Crucially, we identified, with high certainty, subtle aberrations indicating landing instability in the ACLR group for: knee flexion and internal rotation angles and moments; hip rotation angles and moments; and lumbar rotator and bending moments. Our findings may benefit rehabilitation and assessment for return-to-sport 12–24 months post-ACLR.

Gait Biomechanics and Balance Associate with Talar and Subtalar T1ρ Relaxation Times in Those with Chronic Ankle Instability.

This study aimed to determine associations between T1ρ relaxation times of talar and subtalar articular cartilage and commonly altered gait biomechanics and postural control outcomes in those with chronic ankle instability (CAI). Fifteen individuals with CAI (21.13 ± 1.81 yr) completed a T1ρ magnetic resonance imaging as well as a postural control and an overground gait assessment. Talocrural and subtalar cartilage was segmented manually to calculate T1ρ relaxation times. Greater T1ρ relaxation times were interpreted as decreased proteoglycan content. Pearson product-moment bivariate correlations examined the relationships between T1ρ relaxation times and the gait biomechanics and postural control outcomes. Across multiple variables, worse postural control demonstrated moderate to strong associations (range, 0.433-0.642 and -0.713) with greater talar T1ρ relaxation times. At the subtalar joint, greater T1ρ relaxation times were associated with lower peak vertical ground reaction forces, lower average vertical ground reaction force loading rates, and lower peak loading rates (range, -0.438 to -0.622). At the talar dome, greater talar T1ρ relaxation times were associated with increased knee extensor moments (r = 0.457), as well as greater knee flexion (r = 0.482) and knee adduction (r = 0.407) at initial contact. Larger step spatiotemporal gait parameters also associated with greater talar and subtalar T1ρ relaxation times (range, 0.434-0.697). In individuals with CAI, worse postural control and altered kinematic, kinetic, and spatiotemporal outcomes demonstrate moderate to strong associations with greater talar T1ρ and/or subtalar relaxation times (i.e., less proteoglycan content). Associations between modifiable neuromechanical variables and greater T1ρ relaxation times may represent potential therapeutic interventions to mitigate ankle joint degeneration in those with CAI.

A test of the effort equalization hypothesis in children with cerebral palsy who have an asymmetric gait.

Healthy people can walk nearly effortlessly thanks to their instinctively adaptive gait patterns that tend to minimize metabolic energy consumption. However, the economy of gait is severely impaired in many neurological disorders such as stroke or cerebral palsy (CP). Moreover, self-selected asymmetry of impaired gait does not seem to unequivocally coincide with the minimal energy cost, suggesting the presence of other adaptive origins. Here, we used hemiparetic CP gait as a model to test the hypothesis that pathological asymmetric gait patterns are chosen to equalize the relative muscle efforts between the affected and unaffected limbs. We determined the relative muscle efforts for the ankle and knee extensors by relating extensor joint moments during gait to maximum moments obtained from all-out hopping reference test. During asymmetric CP gait, the unaffected limb generated greater ankle (1.36±0.15 vs 1.17±0.16 Nm/kg, p = 0.002) and knee (0.74±0.33 vs 0.44±0.19 Nm/kg, p = 0.007) extensor moments compared with the affected limb. Similarly, the maximum moment generation capacity was greater in the unaffected limb versus the affected limb (ankle extensors: 1.81±0.39 Nm/kg vs 1.51±0.34 Nm/kg, p = 0.033; knee extensors: 1.83±0.37 Nm/kg vs 1.34±0.38 Nm/kg, p = 0.021) in our force reference test. As a consequence, no differences were found in the relative efforts between unaffected and affected limb ankle extensors (77±12% vs 80±16%, p = 0.69) and knee extensors (41±17% vs 38±23%, p = 0.54). In conclusion, asymmetric CP gait resulted in similar relative muscle efforts between affected and unaffected limbs. The tendency for effort equalization may thus be an important driver of self-selected gait asymmetry patterns, and consequently advantageous for preventing fatigue of the weaker affected side musculature.

Stride Length Impacts on Sagittal Knee Biomechanics in Flat Ground Baseball Pitching

Coordinated lower extremity biomechanics are altered in response to changes in stride length, influencing the kinetic chain that potentially induces compensatory throwing mechanics throughout the baseball pitching cycle. The respective sagittal knee dynamic profiles, for both the stride (lead) and drive (trail) leg, were analyzed during flat ground baseball pitching to determine whether the stride length variation elicits compensatory drive and stride leg knee joint kinematics, kinetics, and joint powers. Using a randomized cross-over design, a cohort of 19 healthy skilled competitive pitchers from collegiate and high school travel programs from across Western New York were assigned to throw 2 simulated 80 pitch games at ±25% of their desired stride length. An integrated motion capture system with two force plates and a radar gun tracked each throw. Pairwise comparisons at hallmark events and phases identified significantly different sagittal knee dynamics for both the drive and stride leg between the stride length conditions. During the acceleration phase, the drive knee moments between the stride length conditions demonstrated differences in power generation and absorption. Longer strides allowed for greater knee propulsion dynamics, exemplified by eccentric drive knee extensor moments with a concomitant power absorption that slowed the rate of drive knee flexion (p ≤ 0.001). Conversely, shorter strides generated power through concentric knee flexor moments that increased the rate of drive knee flexion (p ≤ 0.001). Stride knee extensor moments and power generation during the acceleration phase were also significantly higher with shorter strides (p ≤ 0.05). Adapted knee joint dynamics may offer insights into stride length optimization, training, and injury prevention strategies.

Training History-Dependent Functional Role of EMG Model-Predicted Antagonist Moments in Knee Extensor Moment Generation in Healthy Young Adults

Resistance training (RT) improves the skeletal muscle’s ability to generate maximal voluntary force and is accompanied by changes in the activation of the antagonist muscle which is not targeted primarily by RT. However, the nature and role of neural adaptation to RT in the antagonist muscle is paradoxical and not well understood. We compared moments, agonist muscle activation, antagonist activation, agonist-antagonist coactivation, and electromyographic (EMG) model-predicted moments generated by antagonist hamstring muscle coactivation during isokinetic knee extension in leg strength-trained (n = 10) and untrained (n = 11) healthy, younger adults. Trained vs. untrained adults were up to 58% stronger. During knee extension, hamstring activation was 1.6-fold greater in trained vs. untrained adults (p = 0.022). This hamstring activation produced 2.6-fold greater model-predicted antagonist moments during knee extension in the trained (42.7 ± 19.55 Nm) vs. untrained group (16.4 ± 12.18 Nm; p = 0.004), which counteracted (reduced) quadriceps knee extensor moments ~43 Nm (0.54 Nm·kg−1) and by ~16 Nm (0.25 Nm·kg−1) in trained vs. untrained. Antagonist hamstring coactivation correlated with decreases and increases, respectively, in quadriceps moments in trained and untrained. The EMG model-predicted antagonist moments revealed training history-dependent functional roles in knee extensor moment generation.

A Lower-Back Exoskeleton With a Four-Bar Linkage Structure for Providing Extensor Moment and Lumbar Traction Force

Lower back pain and related injuries are prevalent and serious problems in various industries, and high compression force to the lumbosacral (L5/S1) region has been known as one of the key factors. Previous research on passive lower back exoskeletons focused on reducing lumbar muscle activation by providing an extensor moment. Additionally, lumbar traction forces can reduce the compression force, and is a common treatment method for lower back pain in clinics. In this paper, we propose a novel passive lower back exoskeleton that provides both extensor moment and lumbar traction force. The working principle of the exoskeleton, extending the coil springs during lumbar flexion, and its design criteria regarding the amount of each force element were provided. The kinematic model explained its operation, and the dynamic simulation estimated its performance and validated its satisfaction with the design criteria. The biomechanical model provided a brief insight into the expected exoskeleton's effect on the reduced lower back compression force. Ten subjects performed static holding and dynamic lifting tasks, and the generated force elements in two directions, parallel and perpendicular to the trunk, were evaluated using a force sensor and electromyography sensors, respectively. The experiment demonstrated a pulling force opposite to the direction of intradiscal pressure and reduced erector spinae activation. This implies the effect of wearing the exoskeleton to decrease the intervertebral pressure during static back bending or heavy lifting tasks.

Association between quadriceps function, joint kinetics, and spatiotemporal gait parameters in young adults with and without obesity

BackgroundIndividuals with obesity have impaired gait and muscle function that may contribute to reduced mobility and increased fall risk. Research questions(1) what is the difference in spatiotemporal gait parameters and joint kinetics between individuals with and without obesity; (2) what is the association between spatiotemporal gait parameters, joint kinetics, and quadriceps function? MethodsForty-eight young adults with obesity (BMI = 33.0 ± 4.1 kg/m2) and 48 without obesity (BMI = 21.6 ± 1.7 kg/m2) completed assessments of quadriceps function (peak torque and early/late rate of torque development (RTD)) and walking biomechanics at self-selected speed. Spatiotemporal gait parameters (stance time, double support time, double support to stance ratio, step width, step length, cadence, and gait stability ratio (GSR)) and joint kinetics (total support moment, and relative contribution from extensor moments) were compared using one-way MANOVAs. Partial correlation examined the association between the total support moment and quadriceps function, and spatiotemporal gait parameters controlling for sex and speed. ResultsIndividuals with obesity walked with longer stance (p = 0.01), longer double-limb support (p < 0.001), wider steps (p < 0.001), lower cadence (p = 0.03), and a greater absolute (p < 0.001) but lesser normalized total support moment (p = 0.03) compared with adults without obesity. In those with obesity, greater PT was associated with less double limb support (p = 0.011) and smaller double support to stance ratio (p = 0.006); greater early RTD was associated with less double limb support (r = −0.455, p = 0.0021), less stance time (r = −0.384, p = 0.008), and a smaller double support to stance ratio (r = −0.371, p = 0.011). In those without obesity, a larger total support moment was associated with longer step length (r = 0.512, p < 0.001), lesser cadence (r = −0.497, p < 0.001), and smaller GSR (−0.460, p = 0.001). SignificanceIndividuals with obesity walk with altered spatiotemporal gait parameters and joint kinetics that may compromise stability. Extended periods of support may be a strategy used by individuals with obesity to increase stability during gait and accomodate insufficient quadriceps function.

Relationship between vastus medialis Hoffmann reflex excitability and knee extension biomechanics during different tasks in women with patellofemoral pain

BackgroundImpaired knee extension biomechanics and spinal excitability have been reported in women with patellofemoral pain, but their relationship has not been explored. A significant relationship between them could indicate the need for investigating the potential benefits of disinhibitory interventions for women with patellofemoral pain. Thus, this study aimed to investigate the relationship between vastus medialis Hoffmann reflex and (1) maximal isometric, concentric and eccentric knee extensor strength and rate of torque development; (2) knee extensor torque steadiness; and (3) knee extensor moment during functional tasks; in women with patellofemoral pain. MethodsSpinal excitability of twenty-four participants was assessed by the amplitude of maximal vastus medialis Hoffmann reflex. Knee extensor strength, rate of torque development and torque steadiness were assessed using an isokinetic dynamometer. Knee extensor moment during step-down and stair descent tasks were obtained using a three-dimensional motion analysis system. FindingsA moderate negative relationship was found between vastus medialis Hoffmann reflex and knee extensor torque steadiness (r = −0.35; p = 0.05); whereas a moderate positive relationship was found with maximal isometric knee extensor strength (r = 0.37; p = 0.044). No significant relationships were found between vastus medialis Hoffmann reflex and the other variables. InterpretationOur findings provide insight on the relationship between spinal excitability and neuromuscular control of maximal and submaximal isometric torque production in women with patellofemoral pain. Conversely, spinal excitability does not seem to be related with dynamic torques and moments of the knee extensors in women with patellofemoral pain.

Regulation of Forward Angular Impulse in Tasks With Backward Translation.

Studying how elite athletes satisfy multiple mechanical objectives when initiating well-practiced, goal-directed tasks provides insights into the control and dynamics of whole-body movements. This study investigated the coordination of multiple body segments and the reaction force (RF) generated during foot contact when regulating forward angular impulse in backward translating tasks. Six highly skilled divers performed inward somersaults (upward and backward jump with forward rotation) and inward timers (upward and backward jump without rotation) from a stationary platform. Sagittal plane kinematics and RFs were recorded simultaneously during the takeoff phase. Regulation of the forward angular impulse was achieved by redirecting the RF about the total body center of mass. Significantly more backward-directed RF was observed during the first and second peak horizontal RF of the inward somersaults than the inward timers. Modulation of the horizontal RF altered the RF direction about the center of mass and the lower-extremity segments. Backward leg and forward trunk orientation and a set of relatively large knee extensor and small hip flexor net joint moments were required for forward angular impulse generation. Understanding how the forward angular impulse is regulated in trained individuals provides insights for clinicians to consider when exploring interventions related to fall prevention.

Altered lower extremity biomechanics following anterior cruciate ligament reconstruction during single-leg and double-leg stop-jump tasks: A bilateral total support moment analysis

BackgroundInjury to the anterior cruciate ligament (ACL) can lead to long-lasting biomechanical alterations that put individuals at risk of a second ACL injury. Examining the total support moment may reveal between- and within-limb compensatory strategies. MethodsTwenty-six participants who were cleared to return to sport following ACL reconstruction were recruited. Each participant completed the single-leg and double-leg stop jump tasks. These tasks were analyzed using force plates and a 3D motion analysis system. The total support moment was calculated by summing the internal moments of the hip, knee and ankle at peak vertical ground reaction force. FindingsInternal knee extensor moment was lower in the involved limb compared to the uninvolved for both tasks (17.6%, P = 0.022; 18.4%, P = 0.008). No significant between-limb differences were found for the total support moment. The involved limb exhibited an 18.2% decrease in knee joint contribution (P = 0.01) and a 21.6% increase in ankle joint contribution (P = 0.016) to the total support moment compared to the uninvolved limb in the single-leg stop jump task. InterpretationCompensation for the involved knee is likely due to altered biomechanics that redistributes load to the uninvolved knee or to adjacent joints of the same limb. A partial shift in joint contribution from the knee to the ankle during the single-leg stop jump task demonstrates a tendency to decrease load to the knee. Further studies are needed to investigate how these adaptations impact the prevalence of subsequent injury and poor joint health.

The influence of hip extensor and lumbar spine extensor strength on lumbar spine loading during a squat lift

Weakness of the hip extensors and lumbar spine extensors has been proposed to contribute to greater demands on the lumbar spine during lifting. The purpose of the current study was to examine the associations among strength of the hip and lumbar spine extensors, lumbar spine extensor moments and lumbar paraspinal muscle activation during a squat lift task. Twenty-seven healthy females participated. Strength of the hip and lumbar spine extensors was measured using a dynamometer. Lumbar spine moments and lumbar paraspinal muscle activity were quantified during the concentric phase of the squat lifting task. There was a significant positive association between lumbar extensor strength and average lumbar extensor moment during lifting (r = 0.498, p = 0.008). Similarly, hip extensor strength was positively associated with the average lumbar extension moment (r = 0.382, p = 0.049). Hip extensor strength was negatively associated with activation of the lumbar paraspinal muscles during lifting (ρ = −0.382, p = 0.049). Stronger individuals are more likely to use their hip extensors and lumbar spine extensors to perform a squat lift task. In contrast, those with lower strength employ subtle biomechanical changes to reduce lumbar spine demand.

Bi-unicondylar arthroplasty : a biomechanics and clinical outcomes study.

AimsBi-unicondylar arthroplasty (Bi-UKA) is a bone and anterior cruciate ligament (ACL)-preserving alternative to total knee arthroplasty (TKA) when the patellofemoral joint is preserved. The aim of this study is to investigate the clinical outcomes and biomechanics of Bi-UKA.MethodsBi-UKA subjects (n = 22) were measured on an instrumented treadmill, using standard gait metrics, at top walking speeds. Age-, sex-, and BMI-matched healthy (n = 24) and primary TKA (n = 22) subjects formed control groups. TKA subjects with preoperative patellofemoral or tricompartmental arthritis or ACL dysfunction were excluded. The Oxford Knee Score (OKS) and EuroQol five-dimension questionnaire (EQ-5D) were compared. Bi-UKA, then TKA, were performed on eight fresh frozen cadaveric knees, to investigate knee extensor efficiency under controlled laboratory conditions, using a repeated measures study design.ResultsBi-UKA walked 20% faster than TKA (Bi-UKA mean top walking speed 6.7 km/h (SD 0.9),TKA 5.6 km/h (SD 0.7), p < 0.001), exhibiting nearer-normal vertical ground reaction forces in maximum weight acceptance and mid-stance, with longer step and stride lengths compared to TKA (p < 0.048). Bi-UKA subjects reported higher OKS (p = 0.004) and EQ-5D (p < 0.001). In vitro, Bi-UKA generated the same extensor moment as native knees at low flexion angles, while reduced extensor moment was measured following TKA (p < 0.003). Conversely, at higher flexion angles, the extensor moment of TKA was normal. Over the full range, the extensor mechanism was more efficient following Bi-UKA than TKA (p < 0.028).ConclusionBi-UKA had more normal gait characteristics and improved patient-reported outcomes, compared to matched TKA subjects. This can, in part, be explained by differences in extensor efficiency.Cite this article: Bone Joint Res 2021;10(11):723–733.

Effect of Assistance Timing in Knee Extensor Muscle Activation During Sit-to-Stand Using a Bilateral Robotic Knee Exoskeleton.

The population of older adults experiences a significant degradation in musculoskeletal structure, which hinders daily physical activities. Standing up from a seated position is difficult for mobility-challenged individuals since a significant amount of knee extensor moment is required to lift the body's center of mass. One solution to reduce the required muscle work during sit-to-stand is to utilize a powered exoskeleton system that can provide relevant knee extension assistance. However, the optimal exoskeleton assistance strategy for maximal biomechanical benefit is unknown for sit-to-stand tasks. To answer this, we explored the effect of assistance timing using a bilateral robotic exoskeleton on the user's knee extensor muscle activation. Assistance was provided at both knee joints from 0% to 65% of the sit-to-stand movement, with a maximum torque occurring at four different timings (10%, 25%, 40%, and 55%). Our experiment with five able-bodied subjects showed that the maximal benefit in knee extensor activation, 19.3% reduction, occurred when the assistance timing was delayed relative to the user's biological joint moment. Among four assistance conditions, two conditions with each peak occurring at 25% and 40% significantly reduced the muscle activation relative to the no assistance condition (p < 0.05). Additionally, our study results showed a U-shaped trend (R2= 0.93) in the user's muscle activation where the global optimum occurred between 25% and 40% peak timing conditions, indicating that there is an optimal level of assistance timing in maximizing the exoskeleton benefit.

Knee Extensor Morphology and Sprint Performance in Preadolescent Sprinters

ABSTRACT Purpose: We previously reported that the cross-sectional area of the quadriceps femoris is correlated with the sprint performance of preadolescent sprinters. This finding suggests a close relationship between knee extensor torque-enhancing morphology and sprint performance in this young population. To further clarify this issue, in this study, we examined the relationships of the quadriceps femoris muscle volume (MV) and knee extensor moment arm (MA) with sprint performance in preadolescent sprinters. Methods: The quadriceps femoris MV and knee extensor MA in 15 sprint-trained preadolescent boys were measured using magnetic resonance imaging. Sprint performance was evaluated using a personal best 100-m sprint time and the higher 50-m sprint velocity of two 50-m sprint tests. Results: The quadriceps femoris MV and knee extensor MA were significantly correlated with personal best 100-m sprint time (r = −0.810 and −0.752, P ≤ 0.001 for both) and 50-m sprint velocity (r = 0.814 and 0.702, P < .01 for both). Furthermore, the relative quadriceps femoris MV normalized to body mass was significantly correlated with both the personal best 100-m sprint time (r = −0.620, P = .014) and 50-m sprint velocity (r = 0.686, P = .005). In contrast, no significant correlations were observed between the relative knee extensor MA normalized to body height and both sprint performance parameters. Conclusions: These findings suggest that the quadriceps femoris size, rather than the knee extensor MA dimension, is a more important morphological factor for achieving superior sprint performance in preadolescent sprinters.