Effects of muscular and mental fatigue on spatiotemporal gait parameters in dual task walking in young, non-frail and frail older adults.

BACKGROUND: Dual-task (DT) walking is of great interest in clinical evaluation to evaluate frailty or cognitive declines in older adults. Frail older adults are known to adopt different walking strategy to overcome fatigue. However, no studies evaluated the effect of muscular or mental fatigue on dual-task walking strategy and the difference between frail and non-frail older adults. AIMS: Evaluate the effect of mental and muscular fatigue on spatio-temporal parameters in dual-task walking in young, non-frail and frail older adults. METHODS: 59 participants divided into 20 young (Y) (24.9 ± 3 years old), 20 non-frail (NF) (75.8 ± 4.9 years old) and 19 frail older adults (F) (81 ± 4.7 years old) performed single-task (ST) walking, single-task cognitive (serial subtraction of 3), and dual-task (subtraction + walking) for 1 min at their fast pace. Gait speed, step length, step length variability, stance and swing phase time, single and double support time, cadence, gait speed variability were recorded in single- and dual-task walking. The dual-task effect (DTE) was calculated as ((DT - ST)/ST) × 100). Generalized linear mixed models (GLMM) were used to compare the effects of mental and muscular fatigue on gait and cognitive variables between the groups. RESULTS: The DTE walking parameters were worse in F compared to NF or Y but no significant effect of fatigue were highlighted except for swing time and single support time DTEs. CONCLUSIONS: The results were mitigated but a clear difference in dual-task spatio-temporal parameters was found between F and NF which brings hope into the capacity of DT to better reveal frailty.

Validation of 3D Knee Kinematics during Gait on Treadmill with an Instrumented Knee Brace.

To test a novel instrumented knee brace intended for use as a rehabilitation system, based on inertial measurement units (IMU) to monitor home-based exercises, the device was compared to the gold standard of motion analysis. The purpose was to validate a new calibration method through functional tasks and assessed the value of adding magnetometers for motion analysis. Thirteen healthy young adults performed a 60-second gait test at a comfortable walking speed on a treadmill. Knee kinematics were captured simultaneously, using the instrumented knee brace and an optoelectronic camera system (OCS). The intraclass correlation coefficient (ICC) showed excellent reliability for the three axes of rotation with and without magnetometers, with values ranging between 0.900 and 0.972. Pearson's r coefficient showed good to excellent correlation for the three axes, with the root mean square error (RMSE) under 3° with the IMUs and slightly higher with the magnetometers. The instrumented knee brace obtained certain clinical parameters, as did the OCS. The instrumented knee brace seems to be a valid tool to assess ambulatory knee kinematics, with an RMSE of <3°, which is sufficient for clinical interpretations. Indeed, this portable system can obtain certain clinical parameters just as well as the gold standard of motion analysis. However, the addition of magnetometers showed no significant advantage in terms of enhancing accuracy.

Effects of age, sex, frailty and falls on cognitive and motor performance during dual-task walking in older adults.

BACKGROUND: Dual-task (DT) walking is of great interest in clinical evaluation to evaluate the risk of falling or cognitive declines in older adults. However, it appears necessary to investigate deeply the confounding factors to better understand their impact on dual-task performance. OBJECTIVE: To evaluate the effect of age, sex, falls and frailty on cognitive and motor parameters in dual-task walking. SUBJECTS: 66 older participants (mean age = 75.5 ± 6.3; mean height = 165.8 ± 8.4 cm; mean weight = 68.4 ± 14 kgs) were split into groups based on their age, sex, fall and frailty status. METHODS: Participants performed single-task walking, single-task cognitive (serial subtraction of 3), and dual-task walking (subtraction + walking) for 1 min at their fast pace. Gait speed, step length, step length variability, stance and swing phase time, single and double support, cadence, step time variability and gait speed variability were recorded in single- and dual-task walking and used to calculate the dual-task effect (DTE) as ((DT - ST) / ST) ∗ 100). The cognitive score (DTEcog) was calculated as the number of correct responses minus errors. Generalized linear mixed models (GLMM) were used to compare the effects of falls, frailty, age and sex on gait and cognitive variables. RESULTS: The interaction frailty*sex and frailty*age were the major effect on the DTEs. Specifically, the DTE was higher in women than men and in the frail group compared to non-frail. CONCLUSIONS: The present findings provide a better understanding on the confounding factors explaining the behavior in DT that could be used to develop more effective dual-task clinical programs for community-living older adults.

Concentric or eccentric physical activity for patients with symptomatic osteoarthritis of the knee: a randomized prospective study.

Background: Knee osteoarthritis-related pain limits physical function and leads to functional disability. Physical activity is one of the central recommendations for the management of knee osteoarthritis. Although concentric muscle activities are often preferred to eccentric ones, the corresponding rationale remains controversial. Objective: To explore the effect of a 6-week exercise program on function, pain, and performance in patients with symptomatic knee osteoarthritis. Methods: Patients with symptomatic knee osteoarthritis were included in the prospective EX-ART project (Walking performance in osteoARThritic subjects: effect of an ECCentric muscle strengthening program) and randomized in a 6-week rehabilitation program including either eccentric or concentric activities. Metrics of interest chosen as end points measured before and after the rehabilitation were WOMAC score, pain, and muscular performance (quadriceps power PMAX and contraction strength MMAX). MRI was also used to assess muscle volume and fat infiltration changes. Results: 30 patients were included in each group; mean age was 74 (±7.6); 69% were women. At week 6, both groups showed a significant improvement in the WOMAC without difference between the two groups (p = 0.7). No difference between the two groups was identified for the pain reduction (p = 0.7). A significant improvement in the change in PMAX and MMAX at high velocity (p = 0.001 and p = 0.002) was observed in the eccentric group only. A vastus medialis hypertrophy was quantified in the eccentric group only (p = 0.002), whereas fat infiltration in the quadriceps muscles was unchanged. Conclusion: Physical activity, whether eccentric or concentric, has a benefit on function and pain in patients with symptomatic knee osteoarthritis. A few differences have been identified between the two types of rehabilitation. More particularly, a gain in muscle performance and vastus medialis volume was found with eccentric rehabilitation only. Registration: www.ClinicalTrials.gov, registration number NCT03167502.

Impact of a Wearable Activity Tracker on Disease Flares in Spondyloarthritis: A Randomized Controlled Trial.

OBJECTIVE: To evaluate the impact of a wearable activity tracker used to encourage physical activity, on disease flares in patients with spondyloarthritis (SpA). METHODS: This randomized controlled trial involved randomizing 108 patients with SpA into tracker and nontracker groups. The participants were then subjected to assessments of disease activity, performance (6-minute walk test), and quality of life (QOL; 36-item Short Form Health Survey) at the 12th, 24th, and 36th week. The primary outcome was the change in the frequency of flare episodes (categorized as no flare, flare in ≤ 3 days, and flare in > 3 days) between baseline and 12 weeks. RESULTS: The results of the study showed that at the 12th week, the mean change (∆) of the number of flares improved in both groups: -0.32 (95% CI -0.66 to 0.02) and -0.38 (95% CI -0.68 to -0.09) in the tracker and nontracker group, respectively. However, the between-group differences were insignificant (P = 0.87). Performance scores improved in both groups at the 12th, 24th, and 36th week (all P < 0.01). The different dimensions of QOL also improved at the 12th week (P < 0.01). Conversely, moderate flares (P < 0.01) and performance (P < 0.01) improved over time; however, the influence over time of a wearable activity tracker was not significant (P = 0.29 and P = 0.66, respectively). CONCLUSION: The use of a wearable activity tracker did not affect the number of flares, performance, or QOL of patients with SpA. Nevertheless, this study confirmed the benefits of physical activity on flares, disease activity, QOL, and physical performance in patients with SpA. (Move Your Spondyl "Better Live Its Rheumatism With the Physical Activity"; ClinicalTrials.gov: NCT03458026).

The effect of different dual tasks conditions on gait kinematics and spatio-temporal walking parameters in older adults.

BACKGROUND: Dual-task (DT) walking has increasingly been investigated over the last decade because of its valuable role as a clinical marker of both cognitive impairment and fall risk in older adults based on cognitive and motor performance (DTEcog, DTEmotor). However, there is still a lack of information on what type of dual task to choose and which is the most adapted to the population of interest. RESEARCH QUESTION: To evaluate the effect of different dual-tasks (DT3, DT7, FLU, STROOP) on the spatiotemporal and kinematic parameters of hip, knee, and ankle joints. METHODS: Thirty-eight older adults were recruited (9 men, 29 women, mean age = 77.5 +/- 6.5 years, mean height = 163.6 +/- 8.6 cm, mean weight = 67.5 +/- 15.3 kg). They performed a single and dual-task walk with the 4 types of tasks during 1 min, equipped with an inertial system. Dual-task effect (DTE) on spatiotemporal and kinematic variables as well as cognitive score and speed were calculated. RESULTS: An alteration in most of the spatiotemporal parameters was observed in each DT condition (p < 0.05), especially in arithmetic tasks (DT3, DT7), while no DT effect was noticed on kinematic parameters (RMSE<3°) except on hip and knee angular velocities (RMSE>15°). Arithmetic tasks seemed to alter more spatiotemporal and kinematic parameters than the verbal fluency or STROOP test. However, DT7 appeared to be too difficult for the population of interest. SIGNIFICANCE: Arithmetic tasks seemed to be very pertinent as a clinical dual-task protocol for older adults. The use of an inertial system to retrieve kinematic variables is an improvement in these dual-task protocols.

How fiber dynamics of plantarflexor and dorsiflexor muscles based on EMG-driven approach can explain the metabolic cost at different gait speeds.

PURPOSE: The aim of this study was to investigate the fiber dynamics of plantarflexor and dorsiflexor muscles and their association with the net metabolic rate (NCw). METHODS: Metabolic, kinematic, kinetic, and electromyography measurements were made on seven young subjects while they walked on a force-plate instrumented treadmill at 1.00, 1.20, 1.40, 1.60, and 1.8 m/s for 1:30 min. The net metabolic rate was computed, and a one degree-of freedom EMG-driven approach was used to extract the force generation ability (Fability), and active force-length (fAL) and force-velocity (fV) multiplier of each muscle. A one-way (speeds) repeated measures ANOVA was performed for each muscle and a multiple linear regression model was used to explain NCw. RESULTS: Fability was significantly affected by gait speed for the GasMed and the SOL muscles. The decrease of Fability for the SOL and the GasMed was accompanied by a decrease in the force-velocity multiplier. The peak muscle force for the SOL increased for the lowest speed compared to the higher speed, and for the TibAnt increased at high speed compared to low speed. In addition, Fability fAL, and fV of the SOL predicted over 58% of NCw and FMax of the TibAnt accounts for 39.9% of the variance in NCw. CONCLUSION: The increase of NCw with gait speed over the preferred walking speed can be partially explained by the decreasing capacity of the SOL muscle to produce muscle force and more specifically by the force-velocity relationship and an increase in muscle force for the TibAnt.

Metabolic cost and co-contraction during walking at different speeds in young and old adults.

BACKGROUND: The net metabolic cost of walking (NCw) and the co-activation of leg muscles are both higher in old adults (OG) than in young adults (YG). Nevertheless, the relation between the two remains unresolved, mainly due to the controversial co-activation measurement method used in previous studies. RESEARCH QUESTION: To compare ankle and knee co-contraction (CCI), calculated using an EMG-driven method, between the groups and to examine their relationship with NCw. METHODS: Nine young (YG = 25.2 +/- 3.3 years old) and nine older (OG = 68.7 +/5.9 years old) adults walked on a treadmill at five speeds (YG: 1; 1.2; 1.4; 1.6; 1.8 m/s; OG: 0.6; 0.8; 1; 1.2; 1.4 m/s) while electromyography (sEMG) and oxygen consumption were measured. CCI were calculated around the ankle and knee for different parts of the gait cycle (entire gait cycle 0-100 %, stance phase 0-60 %, swing phase 60-100 %). RESULTS: NCw was significantly higher (25 %, averaged over the walking speeds) in OG as were Knee_CCI, Knee_CCI_swing and Knee_CCI_stance. Multiple regression models in YG, OG and YG + OG highlighted Ankle_CCI as the main contributor in NCw (ß = 0.08-0.188, p < 0.05) with a positive relation between the two variables. SIGNIFICANCE: The present findings provide a better understanding of the association between muscle co-contraction and metabolic cost in older adults. It may help scientists and clinicians to further develop strategies aimed at neuromuscular rehabilitation as a means of improving mobility and independence among older adults.

6MWT on a new self-paced treadmill system compared with overground.

The 6-min walk test (6MWT) is a useful tool for clinicians and researchers to estimate gait performance and fatigue affecting functional mobility. A modified 6MWT administered on a treadmill (TM) can be an efficient, space-saving alternative to perform the 6MWT. The aim of this study was to investigate if a 6MWT on a self-paced (SP) TM produced similar results compared to an overground (OG) 6MWT among healthy participants with the hypothesis that users would demonstrate similar gait parameters. The second aim was to assess the reliability of SP TM sessions with the hypothesis that gait parameters would be reliable. Twelve healthy young adults performed one OG 6MWT and two SP TM 6MWTs, with the TM tests performed on two different testing days. The OG 6MWTs were conducted along a 20 m corridor with a portable optometric system. The SP TM 6MWTs were performed using a dual-belt instrumented TM with speed controlled by feedback from a LIDAR sensor. In the OG condition, participants walked 664.8 m ± 48.9 m when the standard method was used to calculate distance and 721.3 m ± 56.2 m with an average-speed-based estimation of distance, which corrects for U-turns. For the SP TM 6MWT, they covered 729.4 m ± 45.8 m in the first session and 727.4 m ± 56.0 m in the second session. Gait parameters showed good to excellent within- and between-day reliability on the adaptive TM. Gait parameters were similar between modalities. A significant difference in the 6MWT distance was found between modalities. This is attributable to the U-turns, because a comparison between TM 6MWT distance and the average-speed-based estimation of the distance for the OG modality showed no significant difference. However, this system produced similar spatiotemporal gait parameters among participants compared to OG.

Validity of a simple sit-to-stand method for assessing force-velocity profile in older adults.

BACKGROUND: Lower limb muscle strength is an important determinant of physical function in older adults. However, its measure in clinical settings is limited because of the requirement for large-scale and costly equipment. A new simple protocol based on sit-to-stand test (STS) is developed to measure force velocity (F-v) and power velocity (P-v) profile in the community-dwelling older adults. OBJECTIVE: The objective of this study was to assess the validity of this new methodology for measuring F-v and P-v profile compared to the gold standard isokinetic BIODEX. PARTICIPANTS: 46 older people aged 65-85 years (M = 73.7; SD = 7.7). METHODS: F-v and P-v profiles were assessed in participants on their dominant leg. The concurrent validity of STS was tested using Spearman's rank correlation coefficient and Passing Bablok: maximal power output Pmax, optimal velocity and force Vopt and Fopt, maximal force at null velocity F0, maximal unloaded velocity V0 and coefficient of F-v (SFV) and P-v equation (a_poly, b_poly). RESULTS: No proportional difference for F0 and b_poly and a low significant correlation for Pmax (r = 0.314), Sfv (r = 0.229), a_poly (r = 0.335) and b_poly (r = 0.226) whereas the other parameters were non correlated significantly. CONCLUSION: STS method is moderately reliable on force and power parameters whereas further improvements are needing for velocity parameters. However, its feasibility, portability and lower cost compared to other methods makes it very affordable in clinical context and will allow easy investigation of aging population.

Effects of age, gender, frailty and falls on spatiotemporal gait parameters: a retrospective cohort study.

BACKGROUND: Many studies have explored spatial and temporal gait parameters in the elderly, and showed that frailty status, fall history, age, and gender may individually strongly influence these parameters. However, it appears necessary to investigate the confounding factors more deeply in order to better know the specific role of each of these factors impacting the evolution of gait with the increase of age. AIM: The aim of the present study was to determine the influence of frailty status, fall history, age and gender on spatiotemporal gait parameters. We hypothesized that frailty was the factor that most influence gait parameters. DESIGN: The present is a monocentric retrospective study. SETTING: This is a monocentric retrospective study performed at Nice University Hospital Center on older out-patients. POPULATION: Older adults were included in the study. This study explored for the first time how frailty status, age, gender and history of falls impact the multiple spatiotemporal parameters of gait using linear mixed models (LMM). RESULTS: 479 older adults (360 women and 119 men; 213 non-frail, 228 prefrail and 38 frail; aged from 65 to 94 years; 403 non-fallers and 73 fallers). Frailty status explained fully: 1) the gait speed; 2) the cadence; 3) the initial double contact (DS1); 4) the percentage of the single support phase; 5) the final double contact (DS2); and VI) the percentage of the swing phase of the gait cycle. CONCLUSIONS: The results of this study allowed a deeper understanding of the confounding factors since LMM highlighted the importance of frailty status for explaining all the spatiotemporal gait parameters. CLINICAL REHABILITATION IMPACT: These results showed that clinical intervention should focus on reducing frailty status to improve gait. It is also interesting to note that a history of falls explains none of the spatiotemporal gait parameters which suggests that it may be possible to improve gait in all frail subjects irrespective of their history of falls.

Impact of Hip Flexion Angle on Unilateral and Bilateral Nordic Hamstring Exercise Torque and High-Density Electromyography Activity.

BACKGROUND: In the bilateral Nordic hamstring exercise (NHE), hamstrings operate at relatively short lengths, which may limit the efficacy of the NHE in hamstring injury prevention. OBJECTIVES: To examine knee flexion torque and biceps femoris long head (BFLH) and semitendinosus (ST) high-density electromyography (EMG) activity during the unilateral and bilateral NHE, performed with either neutral (NHE0) or 90°-flexed (NHE90) hips. METHODS: In this laboratory study, exercises were performed on a novel device at the eccentric 1-repetition maximum load defined for 90° to 15° of knee range of motion. Torque and EMG signals normalized to maximal voluntary isometric activity were compared in different phases of the exercises with statistical parametric mapping. RESULTS: The EMG levels were lower in NHE90 than in NHE0, mainly in the second half of the movement. Knee flexor eccentric torque was higher in NHE90 than in NHE0 from the beginning to 87% of the bilateral movement, and over the entire unilateral movement. In NHE0, ST activity compared to BFLH activity was higher during the initial movement phase and lower when the movement was close to knee extension. Torque and EMG activity were generally similar in the bilateral and unilateral modes. CONCLUSION: If performed with neutral hips, the NHE selectively activates the BFLH near full knee extension. Performing the NHE with hips flexed to 90° is preferable when higher passive torque and ST selectivity are targeted at a longer muscle length. Performing these exercises unilaterally could help train each limb separately, with similar torque and EMG output to those of the bilateral conditions. J Orthop Sports Phys Ther 2019;49(8):584-592. Epub 26 Mar 2019. doi:10.2519/jospt.2019.8801.

Greater magnitude tibiofemoral contact forces are associated with reduced prevalence of osteochondral pathologies 2-3 years following anterior cruciate ligament reconstruction.

PURPOSE: External loading of osteoarthritic and healthy knees correlates with current and future osteochondral tissue state. These relationships have not been examined following anterior cruciate ligament reconstruction. We hypothesised greater magnitude tibiofemoral contact forces were related to increased prevalence of osteochondral pathologies, and these relationships were exacerbated by concomitant meniscal injury. METHODS: This was a cross-sectional study of 100 individuals (29.7 ± 6.5 years, 78.1 ± 14.4 kg) examined 2-3 years following hamstring tendon anterior cruciate ligament reconstruction. Thirty-eight participants had concurrent meniscal pathology (30.6 ± 6.6 years, 83.3 ± 14.3 kg), which included treated and untreated meniscal injury, and 62 participants (29.8 ± 6.4 years, 74.9 ± 13.3 kg) were free of meniscal pathology. Magnetic resonance imaging of reconstructed knees was used to assess prevalence of tibiofemoral osteochondral pathologies (i.e., cartilage defects and bone marrow lesions). A calibrated electromyogram-driven neuromusculoskeletal model was used to predict medial and lateral tibiofemoral compartment contact forces from gait analysis data. Relationships between contact forces and osteochondral pathology prevalence were assessed using logistic regression models. RESULTS: In patients with reconstructed knees free from meniscal pathology, greater medial contact forces were related to reduced prevalence of medial cartilage defects (odds ratio (OR) = 0.7, Wald χ2(2) = 7.9, 95% confidence interval (CI) = 0.50-95, p = 0.02) and medial bone marrow lesions (OR = 0.8, Wald χ2(2) = 4.2, 95% CI = 0.7-0.99, p = 0.04). No significant relationships were found in lateral compartments. In reconstructed knees with concurrent meniscal pathology, no relationships were found between contact forces and osteochondral pathologies. CONCLUSIONS: In patients with reconstructed knees free from meniscal pathology, increased contact forces were associated with fewer cartilage defects and bone marrow lesions in medial, but not, lateral tibiofemoral compartments. No significant relationships were found between contact forces and osteochondral pathologies in reconstructed knees with meniscal pathology for any tibiofemoral compartment. Future studies should focus on determining longitudinal effects of contact forces and changes in osteochondral pathologies. LEVEL OF EVIDENCE: IV.

Muscle force strategies for poststroke hemiparetic patients during gait.

BACKGROUND AND OBJECTIVE: Individuals who survive a stroke often display considerable gait impairments that occur in part due to inadequate muscle force production. This study aimed to investigate lower limb muscle forces in poststroke patients during walking. METHODS: Kinematics, kinetics, and electromyographic (EMG) measurements were performed on nine poststroke and healthy individuals walking at natural speed in a cross-sectional study. Recorded parameters were used in an EMG-driven model to estimate the forces exerted by the muscles around the knee and ankle joints during the stance (braking and propulsion) and swing phases. RESULTS: For hemiparetic patients, in comparison to healthy controls, the paretic side exhibited (i) lower forces generated by plantar-flexors and quadriceps respectively during the braking and propulsion phases, but (ii) higher knee-flexors forces during the propulsion phase. Regarding the non-paretic side, it displayed (i) higher forces generated by knee-flexors and quadriceps (only for the propulsion phase) forces during the stance phase, and (iii) higher plantar-flexors forces during the swing phase, in comparison to controls. CONCLUSION: Reduced forces exerted by the plantar-flexors and the knee-extensors along with increased force generated by the knee-flexors on the paretic side give possible explanation for hemiparetic gait abnormalities. Increased muscle forces exerted by the non-paretic side might be a compensatory strategy to better support body weight and properly adjust the center of mass forward.

Co-contraction around the knee and the ankle joints during post-stroke gait.

BACKGROUND: Impairments resulting from hemiparetic stroke lead to persistent difficulties with walking. Abnormal co-contraction patterns of lower limb muscles might be a compensatory mechanism to deal with its resulting gait impairments. AIM: The aim of this study was to assess muscle co-contraction obtained from muscle moments in chronic hemiparetic patients presenting a stiff-knee gait (SKG) during walking. DESIGN: Cross-sectional study. SETTING: Clinical movement analysis laboratory in a health center and a community hospital. POPULATION: Twelve hemiparetic patients 6 months' post-stroke (mean±SD age 49.3±12.5) walking with a SKG and twelve healthy adults (mean±SD age 23.5±7.7). METHODS: Hemiparetic patients walked at their natural gait speed while healthy adults walked at their natural and slow gait speed. Spatiotemporal, kinetic and kinematic gait parameters were determined for both lower limbs. Co-Contraction Index at the knee and the ankle was calculated from muscle moments estimated using an EMG-driven model during the first (DS1) and second (DS2) double support and the single support (SS) phases and the swing phase (SW). RESULTS: The results revealed that chronic stroke patients have reduced ankle co-contraction and increased knee co-contraction during DS1 phase, increased ankle co-contraction during DS2 phase and increased knee co-contraction during SW phase on the paretic side. On the non-paretic side, muscle co-contraction was higher at the knee during SS phase. CONCLUSIONS: Increased co-contraction during walking in both the paretic and the non-paretic side, in patients with hemiparesis exhibiting a SKG, might be an adaptive strategy to increase walking stability, as it may be related to spasticity, but also could result in a high metabolic cost. CLINICAL REHABILITATION IMPACT: The information obtained in this study may be used to support rehabilitation programs focusing on the selectivity of movement control such as strength or power training.

Relationships Between Tibiofemoral Contact Forces and Cartilage Morphology at 2 to 3 Years After Single-Bundle Hamstring Anterior Cruciate Ligament Reconstruction and in Healthy Knees.

BACKGROUND: Prevention of knee osteoarthritis (OA) following anterior cruciate ligament (ACL) rupture and reconstruction is vital. Risk of postreconstruction knee OA is markedly increased by concurrent meniscal injury. It is unclear whether reconstruction results in normal relationships between tibiofemoral contact forces and cartilage morphology and whether meniscal injury modulates these relationships. HYPOTHESES: Since patients with isolated reconstructions (ie, without meniscal injury) are at lower risk for knee OA, we predicted that relationships between tibiofemoral contact forces and cartilage morphology would be similar to those of normal, healthy knees 2 to 3 years postreconstruction. In knees with meniscal injuries, these relationships would be similar to those reported in patients with knee OA, reflecting early degenerative changes. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Three groups were examined: (1) 62 patients who received single-bundle hamstring reconstruction with an intact, uninjured meniscus (mean age, 29.8 ± 6.4 years; mean weight, 74.9 ± 13.3 kg); (2) 38 patients with similar reconstruction with additional meniscal injury (ie, tear, repair) or partial resection (mean age, 30.6 ± 6.6 years; mean weight, 83.3 ± 14.3 kg); and (3) 30 ligament-normal, healthy individuals (mean age, 28.3 ± 5.2 years; mean weight, 74.9 ± 14.9 kg) serving as controls. All patients underwent magnetic resonance imaging to measure the medial and lateral tibial articular cartilage morphology (volumes and thicknesses). An electromyography-driven neuromusculoskeletal model determined medial and lateral tibiofemoral contact forces during walking. General linear models were used to assess relationships between tibiofemoral contact forces and cartilage morphology. RESULTS: In control knees, cartilage was thicker compared with that of isolated and meniscal-injured ACL-reconstructed knees, while greater contact forces were related to both greater tibial cartilage volumes (medial: R2 = 0.43, ß = 0.62, P = .000; lateral: R2 = 0.19, ß = 0.46, P = .03) and medial thicknesses (R2 = 0.24, ß = 0.48, P = .01). In the overall group of ACL-reconstructed knees, greater contact forces were related to greater lateral cartilage volumes (R2 = 0.08, ß = 0.28, P = .01). In ACL-reconstructed knees with lateral meniscal injury, greater lateral contact forces were related to greater lateral cartilage volumes (R2 = 0.41, ß = 0.64, P = .001) and thicknesses (R2 = 0.20, ß = 0.46, P = .04). CONCLUSION: At 2 to 3 years postsurgery, ACL-reconstructed knees had thinner cartilage compared with healthy knees, and there were no positive relationships between medial contact forces and cartilage morphology. In lateral meniscal-injured reconstructed knees, greater contact forces were related to greater lateral cartilage volumes and thicknesses, although it was unclear whether this was an adaptive response or associated with degeneration. Future clinical studies may seek to establish whether cartilage morphology can be modified through rehabilitation programs targeting contact forces directly in addition to the current rehabilitation foci of restoring passive and dynamic knee range of motion, knee strength, and functional performance.

Tibiofemoral contact forces during walking, running and sidestepping.

We explored the tibiofemoral contact forces and the relative contributions of muscles and external loads to those contact forces during various gait tasks. Second, we assessed the relationships between external gait measures and contact forces. A calibrated electromyography-driven neuromusculoskeletal model estimated the tibiofemoral contact forces during walking (1.44±0.22ms(-1)), running (4.38±0.42ms(-1)) and sidestepping (3.58±0.50ms(-1)) in healthy adults (n=60, 27.3±5.4years, 1.75±0.11m, and 69.8±14.0kg). Contact forces increased from walking (∼1-2.8 BW) to running (∼3-8 BW), sidestepping had largest maximum total (8.47±1.57 BW) and lateral contact forces (4.3±1.05 BW), while running had largest maximum medial contact forces (5.1±0.95 BW). Relative muscle contributions increased across gait tasks (up to 80-90% of medial contact forces), and peaked during running for lateral contact forces (∼90%). Knee adduction moment (KAM) had weak relationships with tibiofemoral contact forces (all R(2)<0.36) and the relationships were gait task-specific. Step-wise regression of multiple external gait measures strengthened relationships (0.20

Tibiofemoral Contact Forces in the Anterior Cruciate Ligament-Reconstructed Knee.

PURPOSE: To investigate differences in anterior cruciate ligament-reconstructed (ACLR) and healthy individuals in terms of the magnitude of the tibiofemoral contact forces, as well as the relative muscle and external load contributions to those contact forces, during walking, running, and sidestepping gait tasks. METHODS: A computational EMG-driven neuromusculoskeletal model was used to estimate the muscle and tibiofemoral contact forces in those with single-bundle combined semitendinosus and gracilis tendon autograft ACLR (n = 104, 29.7 ± 6.5 yr, 78.1 ± 14.4 kg) and healthy controls (n = 60, 27.5 ± 5.4 yr, 67.8 ± 14.0 kg) during walking (1.4 ± 0.2 m·s), running (4.5 ± 0.5 m·s) and sidestepping (3.7 ± 0.6 m·s). Within the computational model, the semitendinosus of ACLR participants was adjusted to account for literature reported strength deficits and morphological changes subsequent to autograft harvesting. RESULTS: ACLR had smaller maximum total and medial tibiofemoral contact forces (~80% of control values, scaled to bodyweight) during the different gait tasks. Compared with controls, ACLR were found to have a smaller maximum knee flexion moment, which explained the smaller tibiofemoral contact forces. Similarly, compared with controls, ACLR had both a smaller maximum knee flexion angle and knee flexion excursion during running and sidestepping, which may have concentrated the articular contact forces to smaller areas within the tibiofemoral joint. Mean relative muscle and external load contributions to the tibiofemoral contact forces were not significantly different between ACLR and controls. CONCLUSIONS: ACLR had lower bodyweight-scaled tibiofemoral contact forces during walking, running, and sidestepping, likely due to lower knee flexion moments and straighter knee during the different gait tasks. The relative contributions of muscles and external loads to the contact forces were equivalent between groups.

Ultrasound-based subject-specific parameters improve fascicle behaviour estimation in Hill-type muscle model.

The estimation of muscle fascicle behaviour is decisive in a Hill-type model as they are related to muscle force by the force-length-velocity relationship and the tendon force-strain relationship. This study was aimed at investigating the influence of subject-specific tendon force-strain relationship and initial fascicle geometry (IFG) on the estimation of muscle forces and fascicle behaviour during isometric contractions. Ultrasonography was used to estimate the in vivo muscle fascicle behaviour and compare the muscle fascicle length and pennation angle estimated from the Hill-type model. The calibration-prediction process of the electromyography-driven model was performed using generic or subject-specific tendon definition with or without IFG as constraint. The combination of subject-specific tendon definition and IFG led to muscle fascicle behaviour closer to ultrasound data and significant lower forces of the ankle dorsiflexor and plantarflexor muscles compared to the other conditions. Thus, subject-specific ultrasound measurements improve the accuracy of Hill-type models on muscle fascicle behaviour.

Subject-specific knee joint geometry improves predictions of medial tibiofemoral contact forces.

Estimating tibiofemoral joint contact forces is important for understanding the initiation and progression of knee osteoarthritis. However, tibiofemoral contact force predictions are influenced by many factors including muscle forces and anatomical representations of the knee joint. This study aimed to investigate the influence of subject-specific geometry and knee joint kinematics on the prediction of tibiofemoral contact forces using a calibrated EMG-driven neuromusculoskeletal model of the knee. One participant fitted with an instrumented total knee replacement walked at a self-selected speed while medial and lateral tibiofemoral contact forces, ground reaction forces, whole-body kinematics, and lower-limb muscle activity were simultaneously measured. The combination of generic and subject-specific knee joint geometry and kinematics resulted in four different OpenSim models used to estimate muscle-tendon lengths and moment arms. The subject-specific geometric model was created from CT scans and the subject-specific knee joint kinematics representing the translation of the tibia relative to the femur was obtained from fluoroscopy. The EMG-driven model was calibrated using one walking trial, but with three different cost functions that tracked the knee flexion/extension moments with and without constraint over the estimated joint contact forces. The calibrated models then predicted the medial and lateral tibiofemoral contact forces for five other different walking trials. The use of subject-specific models with minimization of the peak tibiofemoral contact forces improved the accuracy of medial contact forces by 47% and lateral contact forces by 7%, respectively compared with the use of generic musculoskeletal model.