The influence of lower extremity postures on kinematics and injuries of cyclists in vehicle side collisions

OBJECTIVE

A cyclist assumes various cyclic postures of the lower extremities while pushing the pedals in a rotary motion while pedaling. In order to protect cyclists in collisions, it is necessary to understand what influence these postures have on the global kinematics and injuries of the cyclist.

METHOD

Finite element (FE) analyses using models of a cyclist, bicycle, and car were conducted. In the simulations, the Total Human Model of Safety (THUMS) occupant model was employed as a cyclist, and the simulation was set up such that the cyclist was hit from its side by a car. Three representative postures of the lower extremities of the cyclist were examined, and the kinematics and injury risk of the cyclist were compared to those obtained by a pedestrian FE model. The risk of a lower extremity injury was assessed based on the knee shear displacement and the tibia bending moment.

RESULTS

When the knee position of the cyclist was higher than the hood leading edge, the hood leading edge contacted the leg of the cyclist, and the pelvis slid over the hood top and the wrap-around distance (WAD) of the cyclist's head was large. The knee was shear loaded by the hood leading edge, and the anterior cruciate ligament (ACL) ruptured. The tibia bending moment was less than the injury threshold. When the cyclist's knee position was lower than the hood leading edge, the hood leading edge contacted the thigh of the cyclist, and the cyclist rotated with the femur as the pivot point about the hood leading edge. In this case, the head impact location of the cyclist against the car was comparable to that of the pedestrian collision. The knee shear displacement and the tibia bending moment were less than the injury thresholds.

CONCLUSION

The knee height of the cyclist relative to the hood leading edge affected the global kinematics and the head impact location against the car. The loading mode of the lower extremities was also dependent on the initial positions of the lower extremities relative to the car structures. In the foot up and front posture, the knee was loaded in a lateral shear direction by the hood leading edge and as a result the ACL ruptured. The bicycle frame and the struck-side lower extremity interacted and could influence the loadings on lower extremities.

Theoretical and experimental study on a compliant flipper-leg during terrestrial locomotion

An amphibious robot with straight compliant flipper-legs can conquer various amphibious environments. The robot can rotate its flipper-legs and utilize their large deflection to walk on rough terrain, and it can oscillate the straight flipper-legs to propel itself underwater. This paper focuses on the dynamics of the compliant straight flipper-legs during terrestrial locomotion by modeling its deformation dynamically with large deflection theory and simulating it to investigate the parameters of locomotion such as trajectory, velocity, and propulsion. To validate the theoretical model of dynamic locomotion, a single-leg experimental platform is used to explore the flipper-legs in motion with various structural and kinematic parameters. Furthermore, a robotic platform mounting with four compliant flipper-legs is also developed and used to experiment with locomotion. The trajectories of the rotating axle of the compliant flipper-leg during locomotion were approximately coincidental in simulation and in experiments. The speed of locomotion and cost of transport during locomotion were explored and analyzed. The performance of different types of compliant flipper-legs during locomotion shows that varying the degrees of stiffness will have a significant effect on their locomotion. The dynamic model and analysis of the compliant flipper-leg for terrestrial locomotion facilitates the ability of amphibious robots to conquer complex environments.

Associations Between Measures of Balance and Lower-Extremity Muscle Strength/Power in Healthy Individuals Across the Lifespan: A Systematic Review and Meta-Analysis

BACKGROUND

It has frequently been reported that balance and lower-extremity muscle strength/power are associated with sports-related and everyday activities. Knowledge about the relationship between balance, strength, and power are important for the identification of at-risk individuals because deficits in these neuromuscular components are associated with an increased risk of sustaining injuries and falls. In addition, this knowledge is of high relevance for the development of specifically tailored health and skill-related exercise programs.

OBJECTIVES

The objectives of this systematic literature review and meta-analysis were to characterize and, if possible, quantify associations between variables of balance and lower-extremity muscle strength/power in healthy individuals across the lifespan.

DATA SOURCES

A computerized systematic literature search was performed in the electronic databases PubMed, Web of Science, and SPORTDiscus up to March 2015 to capture all relevant articles.

STUDY ELIGIBILITY CRITERIA

A systematic approach was used to evaluate the 996 articles identified for initial review. Studies were included only if they investigated healthy individuals aged ≥6 years and tested at least one measure of static steady-state balance (e.g., center of pressure [CoP] displacement during one-legged stance), dynamic steady-state balance (e.g., gait speed), proactive balance (e.g., distance in the functional-reach-test), or reactive balance (e.g., CoP displacement during perturbed one-legged stance), and one measure of maximal strength (e.g., maximum voluntary contraction), explosive force (e.g., rate of force development), or muscle power (e.g., jump height). In total, 37 studies met the inclusionary criteria for review.

STUDY APPRAISAL AND SYNTHESIS METHODS

The included studies were coded for the following criteria: age (i.e., children: 6-12 years, adolescents: 13-18 years, young adults: 19-44 years, middle-aged adults: 45-64 years, old adults: ≥65 years), sex (i.e., female, male), and test modality/outcome (i.e., test for the assessment of balance, strength, and power). Studies with athletes, patients, and/or people with diseases were excluded. Pearson's correlation coefficients were extracted, transformed (i.e., Fisher's z-transformed r z value), aggregated (i.e., weighted mean r z value), back-transformed to r values, classified according to their magnitude (i.e., small: r ≤ 0.69, medium: r ≤ 0.89, large: r ≥ 0.90), and, if possible, statistically compared. Heterogeneity between studies was assessed using I2 and Chi-squared (χ2) statistics.

RESULTS

Three studies examined associations between balance and lower-extremity muscle strength/power in children, one study in adolescents, nine studies in young adults, three studies in middle-aged adults, and 23 studies in old adults. Overall, small-sized associations were found between variables of balance and lower-extremity muscle strength/power, irrespective of the age group considered. In addition, small-sized but significantly larger correlation coefficients were found between measures of dynamic steady-state balance and maximal strength in children (r = 0.57) compared with young (r = 0.09, z = 3.30, p = 0.001) and old adults (r = 0.35, z = 2.94, p = 0.002) as well as in old compared with young adults (z = 1.95, p = 0.03).

LIMITATIONS

Even though the reported results provided further insight into the associations between measures of balance and lower-extremity muscle strength/power, they did not allow us to deduce cause and effect relations. Further, the investigated associations could be biased by other variables such as joint flexibility, muscle mass, and/or auditory/visual acuity.

CONCLUSIONS

Our systematic review and meta-analysis showed predominately small-sized correlations between measures of balance and lower-extremity muscle strength/power in children, adolescents, and young, middle-aged, and old adults. This indicates that these neuromuscular components are independent of each other and should therefore be tested and trained complementarily across the lifespan. Significantly larger but still small-sized associations were found between measures of dynamic steady-state balance and maximal strength in children compared with young and old adults as well as in old compared with young adults. These findings imply that age/maturation may have an impact on the association of selected components of balance and lower-extremity muscle strength.

[Research on Adaptive Balance Adjustment of Lower Limb Joints and Muscles in the Process of Unexpected Slip]

Aiming at the gait instability phenomenon under disturbed conditions,domestic and foreign scholars have done some research works,but the relationship between the independent balancing act with the surface electromyographic and gait parameters in the process of instability has yet rarely been involved.In this study,using the gait analysis combined with electromyographic signal analysis,we investigated balance adjustment mechanism of joints and muscles of the human lower limb under the condition of walking on the level trail and after foot heel touching the ground and unexpected sliding.Studying 10 healthy subjects with the unified shoes,we acquired and analyzed the changing rule of the lower limb joint torque,joint angle,and the surface electromyographic of the main muscle groups involved in situations of dry or oid trails.Studies showed that when accident sliding happened,the body would increase ankle dorsiflexion torque moment,knee unbend torque and straight angle,and meanwhile increase the torque of hip extension,and timely adjust muscle activation time(Followed by activation of Tibialis anterior muscle→Rectus femoris→Gastrocnemius→Femoral biceps)to adjust the center of gravity,to maintain balance of the body,and to avoid falling down.The results of the research could be used to explore new ideas and to provide a certain reference value for preventing slip damage,rehabilitation training and development of lower limb walker.

Changes in Gait with Anteriorly Added Mass: A Pregnancy Simulation Study

During pregnancy, the female body experiences structural changes, such as weight gain. As pregnancy advances, most of the additional mass is concentrated anteriorly on the lower trunk. The purpose of this study is to analyze kinematic and kinetic changes when load is added anteriorly to the trunk, simulating a physical change experienced during pregnancy. Twenty healthy females walked on a treadmill while wearing a custom made pseudo-pregnancy sac (1 kg) under 3 load conditions: sac-only condition, 10-lb condition (4.535 kg added anteriorly), and 20-lb condition (9.07 kg added anteriorly), used to simulate pregnancy in the second trimester and at full-term pregnancy, respectively. The increase in anterior mass resulted in kinematic changes at the knee, hip, pelvis, and trunk in the sagittal and frontal planes. In addition, ankle, knee, and hip joint moments normalized to baseline mass increased with increased load; however, these moments decreased when normalized to total mass. These kinematic and kinetic changes may suggest that women modify gait biomechanics to reduce the effect of added load. Furthermore, the increase in joint moments increases stress on the musculoskeletal system and may contribute to musculoskeletal pain.

Laterality and Plantar Pressure Distribution During Gait in Healthy Children: Comment on Mayolas Pi, Arrese, Aparicio, and Masià (2015)

In a recent paper, Mayolas Pi, Arrese, Aparicio, and Masià reported the absence of significant bilateral differences between legs in the average plantar pressure during walking in six- to seven-year-old children. However, the authors demonstrated bilateral differences in the distribution of plantar pressure during walking independent of foot preference in three tests: kicking a ball with precision, balancing on one foot, and jumping on one foot. From the results, Mayolas Pi et al. proposed that this asymmetric pattern of plantar pressure distribution is not caused by laterality. This paper suggests that the selected age range of participants and methods of diagnosing of laterality and data analysis could have significant effects on the results. Indeed, according to the literature, laterality in humans is a multidimensional trait with poor stabilization and conformity between different dimensions in preschool and younger school children.

Normative values of spino-pelvic sagittal alignment, balance, age, and health-related quality of life in a cohort of healthy adult subjects

PURPOSE

To elucidate the normative values of whole body sagittal alignment and balance of a healthy population in the standing position; and to clarify the relationship among the alignment, balance, health-related quality of life (HRQOL), and age.

METHODS

Healthy Japanese adult volunteers [n = 126, mean age 39.4 years (20-69), M/F = 30/96] with no history of spinal disease were enrolled in a cross-sectional cohort study. The Oswestry Disability Index (ODI) questionnaire was administered and subjects were scanned from the center of the acoustic meati (CAM) to the feet while standing on a force plate to determine the gravity line (GL), and the distance between CAM and GL (CAM-GL) was measured in the sagittal plane. Standard X-ray parameters were measured from the head to the lower extremities. ODI was compared among age groups stratified by decade. Correlations were investigated by simple linear regression analysis. Ideal lumbar lordosis was investigated using the least squares method.

RESULTS

The present study yielded normative values for whole standing sagittal alignment including head and lower extremities in a cohort of 126 healthy adult volunteers, comparable to previous reports and thus a formula for ideal lumbar lordosis was deduced: LL = 32.9 + 0.60 × PI - 0.23 × age. There was a tendency of positive correlation between McGregor slope, thoracic kyphosis, PT, and age. SVA, T1 pelvic angle, sacrofemoral angle, knee flexion angle, and ankle flexion angle, but not CAM-GL, increased with age, suggesting that the spinopelvic alignment changes with age, but standing whole body alignment is compensated for to preserve a horizontal gaze. ODI tended to increase from the 40s in the domain of pain intensity, personal care, traveling, and total score. ODI weakly, but significantly positively correlated with age and PI-LL.

CONCLUSION

Whole body standing alignment even in healthy subjects gradually deteriorates with age, but is compensated to preserve a horizontal gaze. HRQOL is also affected by aging and spinopelvic malalignment.

Timing characteristics of body segments during the maximal instep kick in experienced football players

BACKGROUND

The first aim of this study was to describe duration and relative timing of the phases of the maximal instep kick. The second aim was to describe the concurrence of maximal range of motion, maximal angular acceleration, maximal angular deceleration and maximal angular velocity of body segments with four key points.

METHODS

Twenty experienced football players performed three maximal instep kicks. The kicks were analysed using a full body, three-dimensional motion capture system. Camera recordings determined kicking leg events. The concurrence of peak kinematics of body segments with four key points was calculated.

RESULTS

Duration and timing of five phases were identified. Key point maximal hip extension (51.4±5.0%) concurred significantly with maximal range of motion (ROM) of shoulder extension. Key point maximal knee flexion (63.6±5.2%) concurred significantly with maximal angular acceleration of spine flexion and pelvis posterior tilt. Key point knee flexion 90 degrees (69.3±4.9%) concurred significantly with maximal angular velocity of shoulder flexion and spine flexion, maximal angular deceleration of hip flexion and maximal angular acceleration of knee extension. Key point ball impact (75.2±5.2%) concurred significantly with maximal ROM of hip deflexion and pelvis anterior rotation and with maximal angular deceleration of spine flexion and pelvis anterior rotation.

CONCLUSIONS

This study demonstrated that eleven peak kinematics of upper body and kicking leg segments, significantly concurred with four kicking leg positions. These results provide Key points for kicking coordination and stress the importance of dynamical coupling as a kicking mechanism.

Lower limb muscle strength is associated with poor balance in middle-aged women: linear and nonlinear analyses

This was the first study investigating both linear associations between lower limb muscle strength and balance in middle-aged women and the potential for thresholds for the associations. There was strong evidence that even in middle-aged women, poorer LMS was associated with reduced balance. However, no evidence was found for thresholds.

INTRODUCTION

Decline in balance begins in middle age, yet, the role of muscle strength in balance is rarely examined in this age group. We aimed to determine the association between lower limb muscle strength (LMS) and balance in middle-aged women and investigate whether cut-points of LMS exist that might identify women at risk of poorer balance.

METHODS

Cross-sectional analysis of 345 women aged 36-57 years was done. Associations between LMS and balance tests (timed up and go (TUG), step test (ST), functional reach test (FRT), and lateral reach test (LRT)) were assessed using linear regression. Nonlinear associations were explored using locally weighted regression smoothing (LOWESS) and potential cut-points identified using nonlinear least-squares estimation. Segmented regression was used to estimate associations above and below the identified cut-points.

RESULTS

Weaker LMS was associated with poorer performance on the TUG (β -0.008 (95 % CI: -0.010, -0.005) second/kg), ST (β 0.031 (0.011, 0.051) step/kg), FRT (β 0.071 (0.047, 0.096) cm/kg), and LRT (β 0.028 (0.011, 0.044) cm/kg), independent of confounders. Potential nonlinear associations were evident from LOWESS results; significant cut-points of LMS were identified for all balance tests (29-50 kg). However, excepting ST, cut-points did not persist after excluding potentially influential data points.

CONCLUSIONS

In middle-aged women, poorer LMS is associated with reduced balance. Therefore, improving muscle strength in middle-age may be a useful strategy to improve balance and reduce falls risk in later life. Middle-aged women with low muscle strength may be an effective target group for future randomized controlled trials.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (ANZCTR) NCT00273260.

A Method for Locomotion Mode Identification Using Muscle Synergies

Active lower limb transfemoral prostheses have enabled amputees to perform different locomotion modes such as walking, stair ascent, stair descent, ramp ascent and ramp descent. To achieve seamless mode transitions, these devices either rely on neural information from the amputee's residual limbs or sensors attached to the prosthesis to identify the intended locomotion modes or both. We present an approach for classification of locomotion modes based on the framework of muscle synergies underlying electromyography signals. Neural information at the critical instances (e.g., heel contact and toe-off) was decoded for this purpose. Non-negative matrix factorization was used to extract the muscles synergies from the muscle feature matrix. The estimation of the neural command was done using non-negative least squares. The muscle synergy approach was compared with linear discriminant analysis (LDA), support vector machine (SVM), and neural network (NN) and was tested on seven able-bodied subjects. There was no significant difference ( p > 0.05 ) in transitional and steady state classification errors during stance phase. The muscle synergy approach performed significantly better ( ) than NN and LDA during swing phase while results were similar to SVM. These results suggest that the muscle synergy approach can be used to discriminate between locomotion modes involving transitions.

Neuromechanical synergies in single-leg landing reveal changes in movement control

Our purpose was to examine changes in single-leg landing biomechanics and movement control following alterations in mechanical task demands via external load and landing height. We examined lower-extremity kinematic, kinetic, and electromyographic (EMG) adjustments, as well as changes in movement control from neuromechanical synergies using separate principal component analyses (PCA). Nineteen healthy volunteers (15M, 4F, age: 24.3±4.9y, mass: 78.5±14.7kg, height: 1.73±0.08m) were analyzed among 9 single-leg drop landing trials in each of 6 experimental conditions (3 load and 2 landing height) computed as percentages of subject bodyweight (BW, BW+12.5%, BW+25%) and height (H12.5% & H25%). Condition order was counterbalanced, including: 1.) BW·H12.5, 2.) BW+12.5·H12.5, 3.) BW+25·H12.5, 4.) BW·H25, 5.) BW+12.5·H25, 6.) BW+25·H25. Lower-extremity sagittal joint angles and moments (hip, knee, & ankle), vertical ground reaction force (GRFz), and electrical muscle activity (gluteus maximus, biceps femoris, vastus medialis, medial gastrocnemius, & tibialis anterior muscles), were analyzed in each trial. Biomechanical adjustments and neuromechanical synergies were assessed using PCA. Subjects reduced effective landing height through segmental configuration adjustments at ground contact, extending at the hip and ankle joints with greater load and landing height (p⩽0.028 and p⩽0.013, respectively), while using greater medial gastrocnemius pre-activation with greater load (p⩽0.006). Dimension reduction was observed under greater mechanical task demands, compressing and restructuring synergies among patterns of muscle activation, applied loads, and segmental configurations. These results provide insight into movement control and potential injury mechanisms in landing activities.

Effect of sloped walking on lower limb muscle forces

Lower limb joint loadings are increased during sloped walking compared to level walking and muscle forces are major contributors to lower limb joint forces. Therefore, the aim of this study was to analyze lower limb muscle forces during sloped walking at different inclinations. Eighteen healthy male participants (27.0±4.7y, 1.80±0.05m, 74.5±8.2kg) walked at a pre-set speed of 1.1m/s on a ramp at the inclinations of 0°, ±6°, ±12° and ±18°. Kinematic data were captured with a motion capture system and kinetic data were recorded with two force plates imbedded into the ramp. A musculoskeletal model was used to compute lower limb muscle forces (normalized to body weight and gait cycle duration). During downhill walking gluteus maximus, quadriceps, soleus, peroneus and tibialis anterior muscle forces increased (p≤0.002) compared to level walking, while gluteus minimus, piriformis, adductor, iliopsoas, hamstrings and gastrocnemii muscle forces decreased (p≤0.002). Uphill walking decreased gluteus minimus, iliopsoas and tibialis anterior muscle forces (p≤0.002), while all other muscle forces increased (p≤0.002, except gluteus medius). Joint-muscle-force waveforms provided information on possible muscle contributions to joint compression forces. The most important muscles were: gluteus medius for hip forces, quadriceps and gastrocnemii for tibiofemoral forces, quadriceps for patellofemoral forces and triceps surae for ankle forces. The contribution of each muscle changed with the inclination during sloped walking compared to level walking. The current study provided important information on muscle forces during sloped walking that can be useful for rehabilitation and training procedures.

Comparison of motor performance of upper and lower extremities in dual-task tests in patients with mild Alzheimer's dementia

BACKGROUND

Alzheimer's dementia (AD) is a progressive disease that threatens the self-care and quality of life of elderly people. Early diagnosis and early treatment are crucial.

AIM

To examine the difference in executive function of patients with AD by analyzing their performance in gait analysis (Vicon MX system) and a trial making test (TMT) while counting forward or backward.

METHODS

Ten elderly persons who had been diagnosed by neurological specialists with mild AD were selected as study participants. Of these patients, 2 were men and 8 were women, and the average age was 74.0 ± 8.6 years. An additional group of 10 elderly persons without AD and matched according to age and sex constituted a control group.

RESULTS

The average Mini-Mental State Examination score was 17.7 ± 4.1, and the average clinical dementia rating scale score was 0.8 ± 0.3. We found that backward counting of 3 digits during gait performance in mild AD patients elicited substantial changes in velocity, cadence, coefficient of variation of the stride length, and stride time compared with those of the control group. Regarding upper extremity performance, all TMT tasks were highly sensitive in revealing differences in reaction time between the mild AD group and the control group.

DISCUSSION

Dual-task challenges for examining gait parameters and TMT performance can reveal obvious impairment of executive motor function in patients with very mild AD.

CONCLUSION

Dual-task motor tests of the upper extremities can be used as screening tools for detecting AD at an early stage.

Simulator study of young driver's instinctive response of lower extremity to a collision

OBJECTIVE

A driver's instinctive response of the lower extremity in braking movement consists of two parts, including reaction time and braking reaction behavior. It is critical to consider these two components when conducting studies concerning driver's brake movement intention and injury analysis. The purposes of this study were to investigate the driver reaction time to an oncoming collision and muscle activation of lower extremity muscles at the collision moment. The ultimate goal is to provide data that aid in both the optimization of intervention time of an active safety system and the improvement of precise protection performance of a passive safety system.

METHOD

A simulated collision scene was constructed in a driving simulator, and 40 young volunteers (20 male and 20 female) were recruited for tests. Vehicle control parameters and electromyography characteristics of eight muscles of the lower extremity were recorded. The driver reaction time was divided into pre-motor time (PMT) and muscle activation time (MAT). Muscle activation level (ACOL) at the collision moment was calculated and analysed.

RESULTS

PMT was shortest for the tibialis anterior (TA) muscle (243∼317 ms for male and 278∼438 ms for female). Average MAT of the TA ranged from 28-55 ms. ACOL was large (5∼31% for male and 5∼23% for female) at 50 km/h, but small (<12%) at 100 km/h. ACOL of the gluteus maximus was smallest (<3%) in the 25 and 100 km/h tests. ACOL of RF of men was significantly smaller than that of women at different speeds.

CONCLUSIONS

Ankle dorsiflexion is firstly activated at the beginning of the emergency brake motion. Males showed stronger reaction ability than females, as suggested by male's shorter PMT. The detection of driver's brake intention is upwards of 55ms sooner after introducing the electromyography. Muscle activation of the lower extremity is an important factor for 50 km/h collision injury analysis. For higher speed collisions, this might not be a major factor. The activations of certain muscles may be ignored for crash injury analysis at certain speeds, such as gluteus maximus at 25 or 100 km/h. Furthermore, the activation of certain muscles should be differentiated between males and females during injury analysis.

Simulation-Based Design for Wearable Robotic Systems: An Optimization Framework for Enhancing a Standing Long Jump

GOAL

Technologies that augment human performance are the focus of intensive research and development, driven by advances in wearable robotic systems. Success has been limited by the challenge of understanding human-robot interaction. To address this challenge, we developed an optimization framework to synthesize a realistic human standing long jump and used the framework to explore how simulated wearable robotic devices might enhance jump performance.

METHODS

A planar, five-segment, seven-degree-of-freedom model with physiological torque actuators, which have variable torque capacity depending on joint position and velocity, was used to represent human musculoskeletal dynamics. An active augmentation device was modeled as a torque actuator that could apply a single pulse of up to 100 Nm of extension torque. A passive design was modeled as rotational springs about each lower limb joint. Dynamic optimization searched for physiological and device actuation patterns to maximize jump distance.

RESULTS

Optimization of the nominal case yielded a 2.27 m jump that captured salient kinematic and kinetic features of human jumps. When the active device was added to the ankle, knee, or hip, jump distance increased to between 2.49 and 2.52 m. Active augmentation of all three joints increased the jump distance to 3.10 m. The passive design increased jump distance to 3.32 m by adding torques of 135, 365, and 297 Nm to the ankle, knee, and hip, respectively.

CONCLUSION

Dynamic optimization can be used to simulate a standing long jump and investigate human-robot interaction.

SIGNIFICANCE

Simulation can aid in the design of performance-enhancing technologies.

Physiological characteristics of elite snowboarders

BACKGROUND

The aim of this study was to profile the physiological qualities of elite snowboarders and quantified the relationships with snowboarding performance.

METHODS

Ten alpine (ALP, mean±SD age: 25.6±4.4 yrs; body mass 78.1±12.1; height 178.4±9.8 cm; sum of 7 skinfolds 74.8±19.4 mm; body fat 13.8±3.7%) and ten snowboard cross (SBX, mean±SD age: 23.5±4.3 yrs; body mass 77.2±9.2; height 181.0±4.9 cm; sum of 7 skinfolds 70.1±21.1 mm; body fat 11.9±3.5%) elite male athletes undertook aerobic power (cycle ergometer maximum oxygen uptake), muscular isometric strength (maximal isometric voluntary contraction, MVC), and muscle-power (vertical jumps), as well as ALP (parallel giant slalom [PGS] and parallel slalom [PSL]) and SBX simulated competitions. Associations between measurements were assessed by correlation analysis.

RESULTS

Absolute (ALP 383.1±38.0 W, P<0.01; SBX 339.7±41.3 W, P<0.05) and relative (ALP, 4.6±0.5 W·kg-1, P<0.01; SBX 4.5±0.3 W·kg-1, P<0.05) power output, power at the first (ALP 196.0±53.7 W, P<0.01; SBX 192.8±24.3, P<0.01) and second (ALP 285.4±60.6 W, P<0.01; SBX 280.4±20.3 W, P<0.01) ventilatory threshold, MVC (ALP 731.9±181.9 N·m-1, P<0.001; SBX 680.1±76.8 N·m-1, P<0.001) and leg stiffness (ALP 31.4±4.8 N·m-1·kg-1, P<0.01; SBX 25.4±3.0 N·m-1·kg-1, P<0.01) were highly correlated with PGS (r=-0.88 to -0.97), PSL (r=-0.84 to -0.94), and SBX (r=-0.89 to -0.93) performance times.

CONCLUSIONS

To meet the demands of snowboarding competition, elite snowboarders require highly developed muscular strength and power. This study provides criteria for the selection of appropriate physiological variables for the longitudinal monitoring of relevant parameters in snowboarding.

Lower extremity muscular strength, sedentary behavior, and mortality

To examine whether lower extremity strength (LES) is predictive of all-cause mortality, independent of physical activity and among those with vary levels of sedentary behavior. Data from the 1999-2002 National Health and Nutrition Examination Survey was used (N = 2768; 50-85 years). Peak isokinetic knee extensor strength was objectively measured, sedentary behavior and physical activity were self-reported, and mortality was assessed via the National Death Index, with follow-up through 2011. Participants were followed for up to 12.6 years with the weighted average follow-up period lasting 9.9 years (standard error, 1.13). In the sample, 321,996 person-months occurred with a mortality rate of 2.1 deaths per 1000 person-months. After adjustments (including physical activity), for every 15 N increase in LES, participants had a 7 % reduced risk of all-cause mortality (HR = 0.93; 95 % CI 0.91-0.95; P < 0.001). When adding a three-level sedentary behavior variable (< 2, 2-4, 5+ h/day) as a covariate in this model, results were unchanged (HR = 0.93; 95 % CI 0.92-0.96; P < 0.001). Similarly, when sedentary behavior was included as a continuous covariate in the model, results regarding the relationship between LES and mortality were unchanged (HR = 0.94; 95 % CI 0.91-0.96; P < 0.001). There was no evidence of statistical interaction between LES and sedentary behavior on all-cause mortality (HRinteraction = 1.01; 95 % CI 0.92-1.10; P = 0.88). LES was inversely associated with all-cause mortality, and this association was unchanged when considering the participant's sedentary behavior.

Six weeks' aerobic retraining after two weeks' immobilization restores leg lean mass and aerobic capacity but does not fully rehabilitate leg strength in young and older men

OBJECTIVE

To determine the effect of aerobic retraining as rehabilitation after short-term leg immobilization on leg strength, leg work capacity, leg lean mass, leg muscle fibre type composition and leg capillary supply, in young and older men.Subjects and design: Seventeen young (23 ± 1 years) and 15 older (68 ± 1 [standard error of the mean; SEM] years) men had one leg immobilized for 2 weeks, followed by 6 weeks' bicycle endurance retraining.

METHODS

Maximal voluntary contraction, leg work capacity (Wmax), and leg lean mass by dual energy X-ray absorptiometry were measured at inclusion, after immobilization and after 3 and 6 weeks' retraining. Muscle biopsies were evaluated for fibre type, fibre area, and capillarization.

RESULTS

Immobilization decreased maximal voluntary contraction (-28 ± 6% and -23 ± 3%); Wmax (-13 ± 5% and -9 ± 4%) and leg lean mass (only in young, -485 ± 105g) in young and older men, respectively. Six weeks' retraining increased maximal voluntary contraction (34 ± 8% and 17 ± 6%), Wmax (33 ± 5% and 20 ± 5%) and leg lean mass (only in young 669 ± 69 g) in young and older men, respectively, compared with the immobilized value.

CONCLUSION

Short-term leg immobilization had marked effects on leg strength, and work capacity and 6 weeks' retraining was sufficient to increase, but not completely rehabilitate, muscle strength, and to rehabilitate aerobic work capacity and leg lean mass (in the young men).

Applications of markerless motion capture in gait recognition

This thesis is based on four manuscripts where two of them were accepted and two were submitted to peer-reviewed journals. The experimental work behind the thesis was conducted at the Institute of Neuroscience and Pharmacology, University of Copenhagen. The purpose of the studies was to explore the variability of human gait and to conduct new methods for precise estimation of the kinematic parameters applied in forensic gait analysis. The gait studies were conducted in a custom built gait laboratory designed to obtain optimal conditions for markerless motion analysis. The set-up consisted of eight synchronised cameras located in the corners of the laboratory, which were connected to a single computer. The captured images were processed with stereovision-based algorithms to provide accurate 3D reconstructions of the participants. The 3D reconstructions of the participants were obtained during normal walking and the kinematics were extracted with manual and automatic methods. The kinematic results from the automatic approach were compared to marker-based motion capture to validate the precision. The results showed that the proposed markerless motion capture method had a precision comparable to marker-based methods in the frontal plane and the sagittal plane. Similar markerless motion capture methods could therefore provide the basis for reliable gait recognition based on kinematic parameters. The manual annotations were compared to the actual anthropometric measurements obtained from MRI scans and the intra- and inter-observer variability was also quantified to observe the associated effect on recognition. The results showed not only that the kinematics in the lower extremities were important but also that the kinematics in the shoulders had a high discriminatory power. Likewise, the shank length was also highly discriminatory, which has not been previously reported. However, it is important that the same expert performs all annotations, as the inter-observer variability was high compared to the variability between the participants. The MRI scans were also applied to estimate the errors of existing marker-based regression equations to predict the joint centres. The errors in the HJC and the AJC were surprisingly high, which may affect the computations of the joint kinetics and thus the understanding of gait dynamics. On the other hand, the effect on the kinematics would be limited and thus the existing regression equations provide a reliable basis to validate markerless motion capture methods as long as the limitations regarding STA and the placement of the markers are considered in the data interpretation. New regression equations corrected the estimated bias and they also accounted for the significant sex differences in pelvis.

Learning new gait patterns: Exploratory muscle activity during motor learning is not predicted by motor modules

The motor module hypothesis in motor control proposes that the nervous system can simplify the problem of controlling a large number of muscles in human movement by grouping muscles into a smaller number of modules. Here, we tested one prediction of the modular organization hypothesis by examining whether there is preferential exploration along these motor modules during the learning of a new gait pattern. Healthy college-aged participants learned a new gait pattern which required increased hip and knee flexion during the swing phase while walking in a lower-extremity robot (Lokomat). The new gait pattern was displayed as a foot trajectory in the sagittal plane and participants attempted to match their foot trajectory to this template. We recorded EMG from 8 lower-extremity muscles and we extracted motor modules during both baseline walking and target-tracking using non-negative matrix factorization (NMF). Results showed increased trajectory variability in the first block of learning, indicating that participants were engaged in exploratory behavior. Critically, when we examined the muscle activity during this exploratory phase, we found that the composition of motor modules changed significantly within the first few strides of attempting the new gait pattern. The lack of persistence of the motor modules under even short time scales suggests that motor modules extracted during locomotion may be more indicative of correlated muscle activity induced by the task constraints of walking, rather than reflecting a modular control strategy.

Effect of structured physical activity on prevention of serious fall injuries in adults aged 70-89: randomized clinical trial (LIFE Study)

OBJECTIVE

To test whether a long term, structured physical activity program compared with a health education program reduces the risk of serious fall injuries among sedentary older people with functional limitations.

DESIGN

Multicenter, single blinded randomized trial (Lifestyle Interventions and Independence for Elders (LIFE) study).

SETTING

Eight centers across the United States, February 2010 to December 2011.

PARTICIPANTS

1635 sedentary adults aged 70-89 years with functional limitations, defined as a short physical performance battery score ≤ 9, but who were able to walk 400 m.

INTERVENTIONS

A permuted block algorithm stratified by field center and sex was used to allocate interventions. Participants were randomized to a structured, moderate intensity physical activity program (n=818) conducted in a center (twice a week) and at home (3-4 times a week) that included aerobic, strength, flexibility, and balance training activities, or to a health education program (n=817) consisting of workshops on topics relevant to older people and upper extremity stretching exercises.

MAIN OUTCOME MEASURES

Serious fall injuries, defined as a fall that resulted in a clinical, non-vertebral fracture or that led to a hospital admission for another serious injury, was a prespecified secondary outcome in the LIFE Study. Outcomes were assessed every six months for up to 42 months by staff masked to intervention assignment. All participants were included in the analysis.

RESULTS

Over a median follow-up of 2.6 years, a serious fall injury was experienced by 75 (9.2%) participants in the physical activity group and 84 (10.3%) in the health education group (hazard ratio 0.90, 95% confidence interval 0.66 to 1.23; P=0.52). These results were consistent across several subgroups, including sex. However, in analyses that were not prespecified, sex specific differences were observed for rates of all serious fall injuries (rate ratio 0.54, 95% confidence interval 0.31 to 0.95 in men; 1.07, 0.75 to 1.53 in women; P=0.043 for interaction), fall related fractures (0.47, 0.25 to 0.86 in men; 1.12, 0.77 to 1.64 in women; P=0.017 for interaction), and fall related hospital admissions (0.41, 0.19 to 0.89 in men; 1.10, 0.65 to 1.88 in women; P=0.039 for interaction).

CONCLUSIONS

In this trial, which was underpowered to detect small, but possibly important reductions in serious fall injuries, a structured physical activity program compared with a health education program did not reduce the risk of serious fall injuries among sedentary older people with functional limitations. These null results were accompanied by suggestive evidence that the physical activity program may reduce the rate of fall related fractures and hospital admissions in men.Trial registration ClinicalsTrials.gov NCT01072500.

Influence of Whole-Body Vibration Training Without Visual Feedback on Balance and Lower-Extremity Muscle Strength of the Elderly: A Randomized Controlled Trial

The purpose of this study was to investigate the influence of whole-body vibration (WBV) training without visual feedback on balance and lower-extremity muscle strength in the elderly.Elderly subjects who did not exercise regularly participated in this study. Subjects were randomly divided into a WBV with eyes open group, a visual feedback-deprived plus WBV (VFDWBV) group, and a control group (0 Hz, eyes open). WBV training was provided over a 3-month period, 3 times per week for 5 min each session. Balance performance was measured with the limits of stability test, and muscle strength was measured with an isokinetic dynamometer.A total of 45 elderly subjects with an average age of 69.22  ±  3.97 years, divided into a WBV group (n = 14), a VFDWBV group (n = 17), and a control group (n = 14), completed the trial. Statistically significant differences were found in the balance performance of the 3 groups at different time points (time × group interaction: F = 13.213, P < 0.001), and the VFDWBV group had more improvement in balance than the WBV and control groups. The strength of the knee extensor and flexor muscles had time × group interactions: F = 29.604, P < 0.001 and F = 4.684, P = 0.015, respectively; the VFDWBV group had more improvement on lower-extremity muscle strength than the WBV and control groups. The 6-month follow-up showed that the rates of hospital visits for medical services due to falls were 0% in the WBV group (0/14), 0% in the VFDWBV group (0/17), and 28.57% in the control group (4/14).Results showed that WBV training at 20  Hz without visual feedback can significantly improve the balance performance and lower-extremity muscle strength of the elderly.

Determining the Importance of Meeting Muscle-Strengthening Activity Guidelines: Is the Behavior or the Outcome of the Behavior (Strength) a More Important Determinant of All-Cause Mortality?

OBJECTIVE

To determine whether the behavioral participation in muscle-strengthening activity (MSA) or the strength outcome produces the largest reduction in all-cause mortality risk.

PATIENTS AND METHODS

The 1999-2002 National Health and Nutritional Examination Survey was used, with follow-up of up to 12.6 years (mean, 9.9 years) (N=2773 adults aged ≥50 years). Participants were placed into 4 groups based on 2 dichotomously categorized variables: lower-extremity strength (LES) of the knee extensors (top quartile) and adherence to MSA guidelines (≥2 MSA sessions per week). Approximately 21% of the population died during follow-up.

RESULTS

Compared with individuals not meeting MSA guidelines and not in top quartile for LES, the adjusted hazard ratios (HRs) and 95% CIs were as follows: (1) meets MSA guidelines but not in top quartile for LES (HR=0.96; 95% CI, 0.63-1.45; P=.84), (2) in top quartile for LES but does not meet MSA guidelines (HR=0.54; 95% CI, 0.42-0.71; P<.001), and (3) in top quartile for LES and meets MSA guidelines (HR=0.28; 95% CI, 0.12-0.66; P=.005). Further analyses revealed that individuals in the top quartile for LES who also met MSA and moderate to vigorous physical activity guidelines were at even further reduced risk for premature all-cause mortality (HR=0.23; 95% CI, 0.08-0.61; P=.005).

CONCLUSION

These results demonstrate that muscle strength seems to be more important than the behavioral participation in MSA for reducing the risk of premature all-cause mortality.

Biomechanical walking mechanisms underlying the metabolic reduction caused by an autonomous exoskeleton

BACKGROUND

Ankle exoskeletons can now reduce the metabolic cost of walking in humans without leg disability, but the biomechanical mechanisms that underlie this augmentation are not fully understood. In this study, we analyze the energetics and lower limb mechanics of human study participants walking with and without an active autonomous ankle exoskeleton previously shown to reduce the metabolic cost of walking.

METHODS

We measured the metabolic, kinetic and kinematic effects of wearing a battery powered bilateral ankle exoskeleton. Six participants walked on a level treadmill at 1.4 m/s under three conditions: exoskeleton not worn, exoskeleton worn in a powered-on state, and exoskeleton worn in a powered-off state. Metabolic rates were measured with a portable pulmonary gas exchange unit, body marker positions with a motion capture system, and ground reaction forces with a force-plate instrumented treadmill. Inverse dynamics were then used to estimate ankle, knee and hip torques and mechanical powers.

RESULTS

The active ankle exoskeleton provided a mean positive power of 0.105 ± 0.008 W/kg per leg during the push-off region of stance phase. The net metabolic cost of walking with the active exoskeleton (3.28 ± 0.10 W/kg) was an 11 ± 4 % (p = 0.019) reduction compared to the cost of walking without the exoskeleton (3.71 ± 0.14 W/kg). Wearing the ankle exoskeleton significantly reduced the mean positive power of the ankle joint by 0.033 ± 0.006 W/kg (p = 0.007), the knee joint by 0.042 ± 0.015 W/kg (p = 0.020), and the hip joint by 0.034 ± 0.009 W/kg (p = 0.006).

CONCLUSIONS

This study shows that the ankle exoskeleton does not exclusively reduce positive mechanical power at the ankle joint, but also mitigates positive power at the knee and hip. Furthermore, the active ankle exoskeleton did not simply replace biological ankle function in walking, but rather augmented the total (biological + exoskeletal) ankle moment and power. This study underscores the need for comprehensive models of human-exoskeleton interaction and global optimization methods for the discovery of new control strategies that optimize the physiological impact of leg exoskeletons.

[Cross-cultural adaptation and Argentine validation of the Lower Extremity Functional Scale Questionnaire]

The Lower Extremity Functional Scale (LEFS) is a self-report questionnaire created to evaluate a patient's functional status in a wide spectrum of lower extremity musculoskeletal conditions. Thus far, there is no valid version in Argentina. The aims of this study were to translate the LEFS, cross-culturally adapt it for use in the Argentine population, and validate it in our country by determining its psychometric properties in patients over the age of 18 with lower extremity musculoskeletal conditions, comparing it with the SF-36 and the following functional tests: step test and timed up and go. One hundred and thirty three patients were included between July 2010 and January 2012. The test-retest reliability was high, with an ICC of 0.91 (95% CI 0.85 - 0.94). The correlation of the LEFS with the physical functioning subscale and the physical component summary score of the SF-36 was high (p < 0.001) and showed moderate response with the timed up and go and step test at the baseline (p < 0.001). This version of the LEFS is a valid, reliable tool used in Argentina to measure functional status in patients with lower extremity musculoskeletal conditions that we recommend for future clinical research projects and daily clinical use.