Knee Extensor Moment Research Articles

Ankle and knee kinetics between strike patterns at common training speeds in competitive male runners

The purpose of this study was to investigate the interaction of foot strike and common speeds on sagittal plane ankle and knee joint kinetics in competitive rear foot strike (RFS) runners when running with a RFS pattern and an imposed forefoot strike (FFS) pattern. Sixteen competitive habitual male RFS runners ran at two different speeds (i.e. 8 and 6 min mile−1) using their habitual RFS and an imposed FFS pattern. A repeated measures analysis of variance was used to assess a potential interaction between strike pattern and speed for selected ground reaction force (GRF) variables and, sagittal plane ankle and knee kinematic and kinetic variables. No foot strike and speed interaction was observed for any of the kinetic variables. Habitual RFS yielded a greater loading rate of the vertical GRF, peak ankle dorsiflexor moment, peak knee extensor moment, peak knee eccentric extensor power, peak dorsiflexion and sagittal plane knee range of motion compared to imposed FFS. Imposed FFS yielded greater maximum vertical GRF, peak ankle plantarflexor moment, peak ankle eccentric plantarflexor power and sagittal plane ankle ROM compared to habitual RFS. Consistent with previous literature, imposed FFS in habitual RFS reduces eccentric knee extensor and ankle dorsiflexor involvement but produce greater eccentric ankle plantarflexor action compared to RFS. These acute differences between strike patterns were independent of running speeds equivalent to typical easy and hard training runs in competitive male runners. Current findings along with previous literature suggest differences in lower extremity kinetics between habitual RFS and imposed FFS running are consistent among a variety of runner populations.

Acute exposure to foot orthoses affects joint stiffness characteristics in recreational male runners

Commercially available foot orthoses are advocated for the treatment of chronic running injuries, such as patellofemoral pain, yet the mechanisms behind their effects are not well understood. This study aimed to examine the limb and joint stiffness characteristics when running with and without orthotics. Twelve recreational runners ran at 4.0 m/s. Limb stiffness was obtained using a spring-mass model of running by dividing the peak vertical ground reaction force (GRF) by the amount of limb compression. Knee and ankle joint stiffness’s were calculated by dividing the peak sagittal plane joint moment by the joint angular excursion. Differences between orthotic and non-orthotic running conditions were contrasted using paired samples t-tests. The results indicate that both peak knee extensor moment (orthotic = 2.74±0.57 and no-orthotic = 3.12±0.62 Nm/kg) and knee stiffness (orthotic = 5.56±1.08 and no-orthotic = 6.47±1.40 Nm/kg rad) were significantly larger when running without orthotics. This study may give further insight into the mechanical effects of commercially available foot orthoses. The current investigation provides some evidence to suggest that orthoses may be able to improve patellofemoral pathologies in recreational runners although further investigation is required.

Impaired Quadriceps Rate of Torque Development and Knee Mechanics After Anterior Cruciate Ligament Reconstruction With Patellar Tendon Autograft

Background: Rate of torque development (RTD) measures the ability of a muscle to produce torque quickly. Decreased quadriceps RTD may impair performance of sporting tasks after surgery. Currently, little is known about variations in quadriceps RTD between anterior cruciate ligament (ACL)–reconstructed and noninjured limbs. Purpose: To determine the differences in RTD of the quadriceps, the rate and timing of knee extensor moment (KEM) development, and knee flexion excursion during running after ACL reconstruction with patellar tendon autograft. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study involved 21 patients (11 female) 6 months after ACL reconstruction with patellar tendon autograft (median [IQR]: age, 18 [16-20] years; mass, 68.18 [61.34-75] kg; height, 1.74 [1.66-1.78] m). Patients performed four 5-second maximal voluntary isometric strength trials of both limbs on an isokinetic dynamometer. RTD was calculated as the mean slope of the torque-time curve between 20% and 80% of total time to peak torque. Then, patients underwent 3-dimensional motion analysis while running on an instrumented treadmill at a self-selected running speed (mean ± SD, 2.68 ± 0.28 m/s). The rate of knee extensor moment (RKEM) was calculated as the mean slope of the moment curve between 10% and 30% of stance phase. Between-limb comparisons were determined with a paired t test for peak KEM, RKEM, knee flexion excursion during 10% to 30% of stance, and time to generate KEM. Results: In the reconstructed limb, deficits in the peak rate of quadriceps torque development compared with the noninjured limb existed both isometrically (RTD, 257.56 vs 569.11 Nm/s; P < .001) and dynamically (RKEM, 16.47 vs 22.38 Nm/kg·m·s; P < .001). The reconstructed limb also generated a KEM later in the stance phase compared with the noninjured limb (11.37% vs 9.61% stance; P < .001) and underwent less knee flexion excursion (15.5° vs 19.8°; P < .001). Conclusion: After ACL reconstruction with patellar tendon autograft, patients have lower RTD and RKEM in the reconstructed limb. Deviations in RTD and the timing of the KEM can change the way the knee is loaded and can potentially increase injury risk and future development of posttraumatic osteoarthritis. Rehabilitation should consider exercises designed to improve RTD and prepare the limb for the demands of sport performance.

Reduced oxygen cost of running is related to alignment of the resultant GRF and leg axis vector: A pilot study.

This pilot study investigated whether a 10-week running program (10wkRP), which reduced the oxygen cost of running, affected resultant ground reaction force (GRF), leg axis alignment, joint moment characteristics, and gear ratios. Ten novice, female runners completed a 10wkRP. Running kinematics and kinetics, in addition to oxygen consumption ( V ˙ O 2 ) during steady-state running, were recorded pre- and post-10wkRP. V ˙ O 2 decreased (8%) from pre-10wkRP to post-10wkRP. There was a better alignment of the resultant GRF and leg axis at peak propulsion post-10wkRP compared with pre-10wkRP (10.8 ± 4.9 vs 1.6 ± 1.2°), as the resultant GRF vector was applied 7 ± 0.6° (P = 0.008) more horizontally. There were shorter external ankle moment arms (24%) and smaller knee extensor moments (23%) at peak braking post-10wkRP. The change in V ˙ O 2 was associated with the change in alignment of the resultant GRF and leg axis (rs = 0.88, P = 0.003). As runners became more economical, they exhibited a more aligned resultant GRF vector and leg axis at peak propulsion. This appears to be a self-optimization strategy that may improve performance. Additionally, changes to external ankle moment arms indicated beneficial low gear ratios were achieved at the time of peak braking force.

The influence of variations in heel and forefoot midsole stiffness on sagittal plane kinematics and joint moments at the knee and ankle

There has been a recent surge of interest in barefoot running, with potential benefits over shod, including reduced impact force and knee loading. Knee extensor moment has been found to be lower in...

The Shank-to-Vertical-Angle as a parameter to evaluate tuning of Ankle-Foot Orthoses

The effectiveness of an Ankle-Foot Orthosis footwear combination (AFO-FC) may be partly dependent on the alignment of the ground reaction force with respect to lower limb joint rotation centers, reflected by joint angles and moments. Adjusting (i.e. tuning) the AFO-FC's properties could affect this alignment, which may be guided by monitoring the Shank-to-Vertical-Angle. This study aimed to investigate whether the Shank-to-Vertical-Angle during walking responds to variations in heel height and footplate stiffness, and if this would reflect changes in joint angles and net moments in healthy adults. Ten subjects walked on an instrumented treadmill and performed six trials while walking with bilateral rigid Ankle-Foot Orthoses. The AFO-FC heel height was increased, aiming to impose a Shank-to-Vertical-Angle of 5°, 11° and 20°, and combined with a flexible or stiff footplate. For each trial, the Shank-to-Vertical-Angle, joint flexion–extension angles and net joint moments of the right leg at midstance were averaged over 25 gait cycles. The Shank-to-Vertical-Angle significantly increased with increasing heel height (p<0.001), resulting in an increase in knee flexion angle and internal knee extensor moment (p<0.001). The stiff footplate reduced the effect of heel height on the internal knee extensor moment (p=0.030), while the internal ankle plantar flexion moment increased (p=0.035). Effects of heel height and footplate stiffness on the hip joint were limited. Our results support the potential to use the Shank-to-Vertical-Angle as a parameter to evaluate AFO-FC tuning, as it is responsive to changes in heel height and reflects concomitant changes in the lower limb angles and moments.

Knee Extensor Moment Asymmetry is Related to Modulation of GRFs During Gait Post-ACL Reconstruction

Clinically it is expected that individuals will restore normal gait mechanics by 3 months post anterior cruciate ligament reconstruction (ACLr). However, biomechanical studies at this time report that large knee extensor moment asymmetries are present in the absence of large kinematic differences. This suggests that individuals may be modulating ground reaction forces to limit knee loading. PURPOSE: To determine the relationship between knee extensor moment symmetry and ground reaction force and knee flexion angle symmetry between limbs during gait at 3 months post-ACLr. METHODS: 13 individuals (8 females, 24.2 ± 9.2 yrs) performed 3 walking trials at 3 months (87.9 ± 8.9 days) post-ACLr. 3D kinematics (250 Hz), ground reaction forces (1500Hz) and anthropometrics were used to quantify knee kinematics and kinetics (inverse dynamics) in the sagittal plane. Peak knee flexion angle (kFLEX), peak knee extensor moment (kEXT) and peak posterior (pGRF) and vertical (vGRF) ground reaction forces were identified during loading response. Between limb symmetry in kFLEX, kEXT, pGRF, and vGRF were calculated as the ratio between the involved and the uninvolved limbs. Pearson’s product-moment correlations were used to determine the relationship between knee loading deficits; significance α≤0.05. RESULTS: On average, kFLEX and kEXT ratios were 0.97 ± 0.18 (range: 0.72-1.34) and 0.77 ± 0.31 (range: 0.26-1.36) at 3 months, respectively. pGRF and kEXT ratios were correlated at 3 months (r=0.706; p=0.007). kEXT ratio was not correlated with vGRF ratio (r=0.290; p=0.337) or kFLEX ratio (r=0.440; p=0.132) at 3 months. CONCLUSIONS: Larger asymmetries in pGRF were strongly related to larger asymmetries in kEXT during gait at 3 months post-op, suggesting that smaller pGRFs are related to smaller kEXT. These data suggest that individuals post-ACLr modulate braking forces (pGRF), not vertical forces or knee flexion angle, to limit knee extensor moments during gait. Future studies should investigate how gait mechanics modulate braking force and sagittal plane knee loading and the mechanisms that underlie these movement patterns.

Characterizing Knee Loading Asymmetry In Individuals Following Anterior Cruciate Ligament Reconstruction Using Inertial Measurement Units

Clinically it is expected that gait mechanics will be restored by 3 months post ACL reconstruction (ACLr), however, biomechanical studies suggests that reduced knee extensor moments persist well after 3 months. Extensor moment asymmetries are often present in the absence of observable knee flexion deficits making them difficult to detect clinically. Inertial measurement units (IMU) are able to detect gait spatiotemporal asymmetries, but it is not known if variables measured with IMUs are related to knee moment asymmetry during gait. PURPOSE: To determine the relationship between knee extensor moment asymmetry and IMU-measured sagittal plane shank angular velocity asymmetry during gait in individuals 3 months post-ACLr. METHODS: 8 subjects (6 females, 23.9 ± 12.4 yrs) performed 4 walking trials 98.4 ± 12.7 days post-ACLr. Sagittal shank angular velocity (128Hz) was measured with tri-axial gyroscopes within IMUs attached to the anterior lower leg bilaterally. Knee extensor moments were quantified using motion analysis (kinematics, 250Hz; ground reaction force, 1500Hz). Stance phase and loading response were determined using previously established algorithms. Peak shank angular velocity (skAV) and knee extensor moment (kEXT) were identified during loading response. skAV and kEXT asymmetry were calculated as the ratio between involved and uninvolved limbs. Pearson’s product correlations were used to determine the relationship between skAV and kEXT; significance α ≤ .05. RESULTS: On average, skAV and kEXT ratios were 0.90 ± 0.11 and 0.77 ± 0.35 at 3 months, respectively. skAV and kEXT ratios were positively correlated at 3 months (r= .822;p=.012). CONCLUSIONS: skAV is part of the functional heel rocker, the mechanism associated with tibial progression during loading response phase of gait. These data suggest that individuals 3 months post-ACLr utilized different heel rocker mechanics, resulting in decreased skAV in the involved limb. skAV asymmetries are correlated with knee extensor moment asymmetry, however, there is not enough to support a causal effect at this time. The strong correlations between skAV and kEXT ratios suggest that IMUs can provide important information regarding knee loading deficits in individuals following ACLr. A larger sample size is needed to determine the clinical feasibility of IMU use for detection loading asymmetries.

Changes in Joint Contributions to the Support Impulse During an Acute Transition to Barefoot Running

INTRODUCTION: The knee is the most commonly injured joint from running participation. Relative to shod rear-foot strike (RFS) running, a forefoot strike (FFS) is associated with a shift in mechanical demand from the knee to the ankle. Accordingly, a FFS has been promoted as a method to reduce injury rates. Largely attributed to its association with a FFS among habituated populations, barefoot running has risen in popularity. However, recent investigations indicate that habitually shod runners do not innately adopt a FFS when acutely transitioning to barefoot running. Thus, it is unknown whether altered joint demands are a function of the adopted foot strike pattern or running barefoot. PURPOSE: To examine the relative contribution of the ankle, knee and hip to the support impulse in habitually shod runners during an acute bout of barefoot running. METHODS: 22 habitually shod RFS runners performed over-ground running shod and barefoot. Runners were grouped according to their barefoot foot strike pattern: RFS, mid-foot strike (MFS), and FFS. The support impulse was a measure of the cumulative ankle, knee and hip extensor moments during absorption (initial contact to peak knee flexion). The relative contributions of the ankle, knee, and hip were calculated as a percentage. RESULTS: 5 runners adopted a FFS, 9 adopted a MFS, and 8 maintained a RFS during the barefoot condition. There were no differences in support impulse magnitude (p>0.05). All barefoot runners demonstrated increased ankle contribution relative to shod (p≤0.028) while only MFS runners demonstrated reduced knee and hip contribution (p≤0.021). FFS demonstrated a trend towards decreased knee contribution (p=0.095). FFS and MFS runners had a larger ankle contribution and lesser knee contribution than RFS runners (p≤0.021). Furthermore, when shod, the FFS runners presented with greater ankle contribution than RFS runners (p≤0.007). CONCLUSIONS: Similar to previous research, there was an increase in the demands at the ankle across all foot strike patterns while only MFS runners presented with reduced demands at the knee and hip. FFS runners demonstrated a trend towards reduced knee demands suggesting that adopting a FFS or MFS when running barefoot can reduce knee injury risk. However, due to the increased demands at the ankle, it is important that all habitually shod runners gradually transition to barefoot running.

Lower Extremity Joint Kinetics Do Not Differ Between Different Athletic Upper Body Positions

Increased lower extremity injury risk has been speculated to relate with out-of-plane upper body position while performing running, cutting, and landing tasks. It remains poorly understood if athletic tasks that require different upper body positions do influence lower extremity kinetics. PURPOSE: To investigate if four different athletic upper body positions affect lower extremity joint kinetics. METHODS: Thirty healthy participants (23.4±4.3years, 1.70±0.11m, 72.8±14.9kg) volunteered for the study. Participants performed 5 landings from a 45cm box using four different upper body positions: 1) arms at chest level while holding a basketball (CH), 2) arms extended at chest level holding a basketball (FR), 3) arms extended straight up over head (UP), and 4) placing hands on hips (HIP). Forty markers were placed on the lower extremity. Trajectory and ground reaction force (GRF) data were collected at 200 and 1000Hz, respectively. Data were filtered with a 4th order Butterworth low pass filter with cutoff frequencies of 7 and 15Hz for trajectory and GRF data, respectively. Peak joint moments were attained between initial contact and minimum vertical displacement of center of mass; hip and knee flexor and extensor moments normalized to body mass and height (Nm/Kgm) were calculated. Peak vertical GRF was calculated for each arm position. Repeated measures ANOVAs and Bonferroni pairwise comparisons examined differences across conditions. RESULTS: CH position (-0.74±0.29 Nm/Kgm) presented lower knee flexor moment than UP (-0.81±0.26 Nm/Kgm) and HIP (-0.89±0.27 Nm/Kgm) positions (p0.05). CONCLUSIONS: Overall, It is noteworthy that when landing with the arms above the head and landing with the hands on the hips, the knee joint flexor moment significantly increased when compared with holding a ball at chest level. The higher knee flexor moment may increase the stress transmitted to the tibia, and result in a detrimental loading for the knee articular cartilage. When developing intervention strategies, health professionals should consider the effects of various arm positions on lower extremity kinetics to potentially minimize excessive knee joint loading.

Three-dimensional kinematic and kinetic gait deviations in individuals with chronic anterior cruciate ligament deficient knees: a systematic review

Background: Altered joint motion that occurs in people with an anterior cruciate ligament deficient (ACLD) knee has been proposed to play a role in the initiation of knee osteoarthritis (OA), although the exact mechanism behind this is poorly understood. There is evidence that frontal plane knee motion plays a crucial role in the pathogenesis of knee OA. However, limited information exists with regards to frontal and transverse plane knee kinematics and kinetics. Purpose: We aimed to identify all relevant articles and synthesize the findings of the literature on 3D gait deviations emphasising on the frontal and transverse plane in individuals with chronic ACLD knee; those who have had the injury for 6 months or longer compared to their uninjured knee or a control group. Methods: As per the PRISMA guidelines, we searched five electronic databases from inception to 14th October 2013, with key words related to ACL, biomechanics and gait, limited to human studies only. Two independent reviewers assessed study eligibility based on predetermined inclusion/exclusion criteria and methodological quality was evaluated using the STROBE statement checklist. Results: Of the 1075 identified citations, 16 studies met the inclusion criteria. The selected studies have a small sample size (range = 20–72) and a higher number of male participants compared to women (average = 69.3% men). The participants with ACLD knee had an average age of 30.4± 8.95 years and time from injury that ranged from 6 months to more than 7.5 years. Comparing the two groups (ACLD vs. healthy controls) most studies found no kinetic or kinematic differences. However, individual studies identified the following differences during the stance phase of gait with the ACLD group exhibiting: a) greater knee abduction angle at heel strike (1 out of 3 studies); b) greater tibial external rotation (2 out of 4 studies); c) greater average knee flexion angle (6 out of 11 studies); lower knee adduction moment (1 out of 3 studies) and e) greater knee extensor moment at heel strike (1 out of 7 studies) and terminal stance (1 out of 7 studies), and lower knee flexor moment at midstance (1 out of 7 studies). When comparing the two knees of the ACLD group, one study investigated the internal-external rotation kneemoment with no significant difference. Conclusion(s):There is limited and inconsistent evidence of altered knee kinematic and kinetic in the in individualswith chronicACLD;. Themost consistentfindingwas greater knee flexion during the stance phase. Implications: There is a need for more prospective studies that evaluate the gait characteristics of the chronic ACLD knee population in all planes; especially in the frontal and transverse. If consistently occurring gait deviations can be identified, it will provide insight in the initiation of knee osteoarthritis in individuals with chronic ACLD.

Muscle Co-contractions Worsen In The ACL Reconstructed Limb When Gait Is Challenged Compared To Normal Gait

PURPOSE: Greater and more symmetrical IKEM predict better functional outcomes after anterior cruciate ligament reconstruction (ACLR). Challenging walking tasks create greater internal knee extensor moments (IKEM) than normal walking after ACLR. Exploring muscle activity during normal and challenging walking could elucidate the underlying muscle responses to increased knee moments. METHODS: Three females (5-12 months post ACLR) who were cleared to return to sports participated. Subjects first completed normal walking followed by walking with a 50% body weight load while towing a sled and wearing a weighted vest. Order of the loaded conditions was randomized. Muscle activity of the medial and lateral quadriceps and hamstrings was measured bilaterally with surface electrodes (Fig 2). Walking speed was controlled. IKEM impulses and muscle activity while generating an IKEM were calculated during the stance phase of the task. Integrated electromyography (EMG) data were normalized to maximal EMG activity during a voluntary isometric contraction (MVIC). RESULTS: Descriptive statistics demonstrate that IKEM impulses and quadriceps activity increased when challenged (vest and sled) compared to normal walking. (Fig 1 and 2) EMG activity was greater in the ACLR limb across tasks, though the confidence intervals were large. (Fig 2) Though the small sample size was not powered to determine statistical significance, the greater magnitude of co-contraction activity in the ACLR limb was apparent for all females across all walking tasks. CONCLUSION: Quadriceps muscle activity increased along with IKEM impulses as expected. The asymmetrical muscle activity and large magnitude of hamstring activity was not expected. High levels of muscle co-contractions to achieve greater IKEM in the ACLR limb in these females is concerning.

Cutting mechanics: relation to performance and anterior cruciate ligament injury risk.

Quick changes of direction during running (cutting) are necessary for successful performance of many sports but are associated with noncontact anterior cruciate ligament (ACL) injuries. Currently, it is not known how biomechanics associated with fast performance of cutting tasks relate to the mechanics associated with increased risk for injury. Without this knowledge, the technique emphasized in injury prevention programs may be at odds with the demands of cutting tasks. The purposes of this study were to 1) identify whole body and/or joint mechanics that are related to completion times of 45° and 90° cuts and, from these variables, 2) determine which variables are predictors of performance (i.e., completion time) and/or ACL injury risk (i.e., peak knee adductor moment). Whole body and joint biomechanics were analyzed during the execution of two sidestep cutting maneuvers (to 45° and 90°) in 25 healthy experienced soccer players. Pearson correlation coefficients and stepwise multiple regression were used to analyze relations between variables. The variables predictive of 45° cut performance included hip extensor moment and hip sagittal plane power generation as well as medial-lateral center-of-mass to center-of-pressure separation distance. This separation distance was also predictive of peak knee adductor moment. During the 90° cut, medial-lateral ground reaction force impulse and hip frontal plane power generation were predictive of performance whereas hip internal rotation and knee extensor moment were predictive of peak knee adductor moment. These relations have important implications for ACL injury prevention programs. Although restricting frontal and transverse plane movement has been emphasized in many programs, these movement recommendations may not be appropriate for cutting tasks performed at greater angles.

The Effect of Isolated Hamstrings Fatigue on Landing and Cutting Mechanics.

The function of the hamstrings in protecting the ACL is not fully understood. The purpose of this study was to determine how landing knee mechanics were affected by hamstrings fatigue, analyzed with principal components analysis (PCA). Knee joint mechanics were collected during single-leg stride landings that were followed by lateral and vertical jumps. An isokinetic fatigue protocol was employed to reduce hamstrings strength by 75% at the cessation of the exercise protocol. On the landing test day, participants performed the stride landing maneuvers before and after the fatigue protocol. PCA was performed on the landing knee joint angle, moment, and power waveforms, and MANOVAs were conducted on the retained PCs of each waveform (P < .05). On the strength test day, hamstrings strength recovery was assessed with an identical fatigue protocol followed by strength assessment ~75 s after the cessation of exercise. Pre- and postexercise hamstrings strength on this day was assessed with a dependent t test (P < .05). The hamstrings strength remained significantly reduced by ~8% postexercise (75 s). For stride landings followed by vertical jumps, there were significantly reduced knee flexion angles, extensor moments, and energy absorption. This was indicative of a stiffer landing strategy postfatigue, which has been associated with increased ACL loading.

The use of McConnell taping to correct abnormal biomechanics and muscle activation patterns in subjects with anterior knee pain: a systematic review.

[Purpose] The aim of this review was to present the available evidence for the effect of McConnell taping on knee biomechanics in individuals with anterior knee pain. [Methods] The PubMed, Medline, Cinahl, SPORTDiscus, PEDro and ScienceDirect electronic databases were searched from inception until September 2014. Experimental research on knee biomechanical or EMG outcomes of McConnell taping compared with no tape or placebo tape were included. Two reviewers completed the searches, selected the full text articles, and assessed the risk of bias of eligible studies. Authors were contacted for missing data. [Results] Eight heterogeneous studies with a total sample of 220 were included in this review. All of the studies had a moderate to low risk of bias. Pooling of data was possible for three outcomes: average knee extensor moment, average VMO/VL ratio and average VMO-VL onset timing. None of these outcomes revealed significant differences. [Conclusion] The evidence is currently insufficient to justify routine use of the McConnell taping technique in the treatment of anterior knee pain. There is a need for more evidence on the aetiological pathways of anterior knee pain, level one evidence, and studies investigating other potential mechanisms of McConnell taping.

Knee muscle strength in multiple sclerosis: relationship with gait characteristics.

[Purpose] To investigate the relationship between isokinetic knee muscle strength and kinematic, kinetic and spatiotemporal gait parameters of patients with multiple sclerosis (MS). [Subjects and Methods] Twenty-nine MS patients (mean age 31.5±6.5) were investigated in this study. The isokinetic knee muscle strength and gait parameters of MS patients with moderate and severe disability, as determined by the expanded disability status scale (EDSS): EDSS=1–4.5 (n=22, moderate disability) and EDSS>4.5 (n=7, severe disability) were measured. [Results] Isokinetic knee muscle strength, kinematic, kinetic and spatiotemporal gait parameters differed between moderate (EDSS=1–4.5, n=22) and severe disability (EDSS>4.5, n=7). The correlation between each of gait speed, stride length, total range of knee joint movement and the four strength parameters (minimum and maximum quadriceps and hamstring muscle strengths) were significant for the MS group as a whole. Within subgroups, the correlation between minimum hamstring strength and total range of knee movement was significant only in group EDSS>4.5; minimum hamstring correlated with peak knee extensor moment in group EDSS=1–4.5, but at a reduced level of significance. [Conclusion] The present study revealed significant correlations between gait characteristics and isokinetic strength parameters of the quadriceps and hamstring muscles. Our study suggests that rehabilitation protocols for MS patients should include a critical strength training programme particularly for the hamstring and quadriceps muscles.

Age-related changes in physical functioning: correlates between objective and self-reported outcomes

ObjectivesTo quantify the variance attributable to age and estimate annual decline in physical function and self-reported health using a battery of outcome measures in healthy older females. To determine whether self-reported functional losses are similar to those measured objectively and which best represent overall physical capacity. DesignExperimental study, cross-sectional analysis. SettingHuman Performance Laboratory, University setting. ParticipantsThirty-nine community-dwelling women (mean [SD] age=71.5 [7.3] years, range 60 to 83 years) completed a battery of objective measures of function and a self-reported health status survey. Main outcome measuresObjective measures: gait speed; TUG test; sit-to-stand; concentric knee flexor and extensor moments; self-reported: the SF-36. ResultsUsing a cross-sectional approach, annual declines were estimated for: TUG time (2.1%); gait speed (1.2%); knee extensor (2.2%) and flexor moments (3.0%); and self-reported Physical Functioning (0.9 to 1.2%) (p≤0.001). Linear regression indicated that age explained moderate variance in the objective (R2=21 to 34%) and self-reported (R2=14 to 28%) outcomes. TUG time and gait speed was significantly correlated with all objective outcomes except sit-to-stand (r=0.46 to 0.83) and most of the self-reported (r=0.40 to 0.63) outcomes (p<0.01). ConclusionsAge-related functional deterioration was estimated precisely across both objective and self-reported outcomes. Greater strength losses for the knee flexors compared to the extensors indicate an unequal strength loss of antagonistic muscle pairs which has implications for the safe completion of many functional tasks including obstacle negotiation, stair locomotion, postural transitions, and ultimately knee joint stability. Furthermore, walking speed and TUG time correlated most strongly with many of the outcomes highlighting their importance as global indicators of physical capacity.

Knee joint loading in knee osteoarthritis: influence of abdominal and thigh fat.

Using three separate models that included total body mass, total lean and total fat mass, and abdominal and thigh fat as independent measures, we determined their association with knee joint loads in older overweight and obese adults with knee osteoarthritis (OA). Fat depots were quantified using computed tomography, and total lean and fat mass were determined with dual energy x-ray absorptiometry in 176 adults (age, 66.3 yr; body mass index, 33.5 kg·m) with radiographic knee OA. Knee moments and joint bone-on-bone forces were calculated using gait analysis and musculoskeletal modeling. Higher total body mass was significantly associated (P ≤ 0.0001) with greater knee compressive and shear forces, compressive and shear impulses (P < 0.0001), patellofemoral forces (P < 0.006), and knee extensor moments (P = 0.003). Regression analysis with total lean and total fat mass as independent variables revealed significant positive associations of total fat mass with knee compressive (P = 0.0001), shear (P < 0.001), and patellofemoral forces (P = 0.01) and knee extension moment (P = 0.008). Gastrocnemius and quadriceps forces were positively associated with total fat mass. Total lean mass was associated with knee compressive force (P = 0.002). A regression model that included total thigh and total abdominal fat found that both were significantly associated with knee compressive and shear forces (P ≤ 0.04). Thigh fat was associated with knee abduction (P = 0.03) and knee extension moment (P = 0.02). Thigh fat, consisting predominately of subcutaneous fat, had similar significant associations with knee joint forces as abdominal fat despite its much smaller volume and could be an important therapeutic target for people with knee OA.

Ability of sagittal kinematic variables to estimate ground reaction forces and joint kinetics in running.

Controlled laboratory study, cross-sectional design. To determine if sagittal kinematic variables can be used to estimate select running kinetics. Excessive loading during running has been implicated in a variety of injuries, yet this information is typically not assessed during a standard clinical examination. Developing a clinically feasible strategy to estimate ground reaction forces and joint kinetics may improve the ability to identify those at an increased risk of injury. Three-dimensional kinematics and ground reaction forces of 45 participants were recorded during treadmill running at self-selected speed. Kinematic variables used to estimate specific kinetic metrics included vertical excursion of the center of mass, foot inclination angle at initial contact, horizontal distance between the center of mass and heel at initial contact, knee flexion angle at initial contact, and peak knee flexion angle during stance. Linear mixed-effects models were fitted to explore the association between the kinetic and kinematic measures, including step rate and sex, with final models created using backward variable selection. Models were developed to estimate peak knee extensor moment (R(2) = 0.43), energy absorbed at the knee during loading response (R(2) = 0.58), peak patellofemoral joint reaction force (R(2) = 0.55), peak vertical ground reaction force (R(2) = 0.48), braking impulse (R(2) = 0.50), and average vertical loading rate (R(2) = 0.04). Our findings suggest that insights into important running kinetics can be obtained from a subset of sagittal plane kinematics common to a clinical running analysis. Of note, the limb posture at initial contact influenced subsequent loading patterns in stance.

Kinetic comparison of older men and women during walk-to-stair descent transition

Stair walking is one of the most challenging tasks for older adults, with women reporting higher incidence of falls. The purpose of this study was to investigate the gender differences in kinetics during stair descent transition. Twenty-eight participants (12 male and 16 female; 68.5 and 69.0 years of mean age, respectively) performed stair descent from level walking in a step-over-step manner at a self-selected speed over a custom-made three-step staircase with embedded force plates. Kinematic and force data were combined using inverse dynamics to generate kinetic data for gender comparison. The top and the first step on the staircase were chosen for analysis. Women showed a higher trail leg peak hip abductor moment (−1.0Nm/kg), lower trail leg peak knee extensor moment and eccentric power (0.74Nm/kg and 3.15W/kg), and lower peak concentric power at trail leg ankle joint (1.29W/kg) as compared to men (p<0.05; −0.82Nm/kg, 0.89Nm/kg, 3.83W/kg, and 1.78W/kg, respectively). The lead leg knee eccentric power was also lower in women (p<0.05). This decreased ability to exert knee control during stair descent transition may predispose women to a higher risk of fall.