Kinematic and ground reaction force accommodation during weighted walking

Weighted walking is a functional activity common in daily life and can influence risks for musculoskeletal loading, injury and falling. Much information exists about weighted walking during military, occupational and recreational tasks, but less is known about strategies used to accommodate to weight carriage typical in daily life. The purposes of the study were to examine the effects of weight carriage on kinematics and peak ground reaction force (GRF) during walking, and explore relationships between these variables. Twenty subjects walked on a treadmill while carrying 0, 44.5 and 89 N weights in front of the body. Peak GRF, sagittal plane joint/segment angular kinematics, stride length and center of mass (COM) vertical displacement were measured. Changes in peak GRF and displacement variables between weight conditions represented accommodation. Effects of weight carriage were tested using analysis of variance. Relationships between peak GRF and kinematic accommodation variables were examined using correlation and regression. Subjects were classified into sub-groups based on peak GRF responses and the correlation analysis was repeated. Weight carriage increased peak GRF by an amount greater than the weight carried, decreased stride length, increased vertical COM displacement, and resulted in a more extended and upright posture, with less hip and trunk displacement during weight acceptance. A GRF increase was associated with decreases in hip extension (|r| = .53, p = .020) and thigh anterior rotation (|r| = .57, p = .009) displacements, and an increase in foot anterior rotation displacement (|r| = .58, p = .008). Sub-group analysis revealed that greater GRF increases were associated with changes at multiple sites, while lesser GRF increases were associated with changes in foot and trunk displacement. Weight carriage affected walking kinematics and revealed different accommodation strategies that could have implications for loading and stability.     

Frontal plane multi-segment foot kinematics in high- and low-arched females during dynamic loading tasks

The functions of the medial longitudinal arch have been the focus of much research in recent years. Several studies have shown kinematic differences between high- and low-arched runners. No literature currently compares the inter-segmental foot motion of high- and low-arched recreational athletes. The purpose of this study was to examine inter-segmental foot motion in the frontal plane during dynamic loading activities in high- and low-arched female athletes. Inter-segmental foot motions were examined in 10 high- and 10 low-arched female recreational athletes. Subjects performed five barefooted trials in each of the following randomized movements: walking, running, downward stepping and landing. Three-dimensional kinematic data were recorded. High-arched athletes had smaller peak ankle eversion angles in walking, running and downward stepping than low-arched athletes. At the rear-midfoot joint high-arched athletes reached peak eversion later in walking and downward stepping than the low-arched athletes. The high-arched athletes had smaller peak mid-forefoot eversion angles in walking, running and downward stepping than the low-arched athletes. The current findings show that differences in foot kinematics between the high- and low-arched athletes were in position and not range of motion within the foot.     

The Critical Point to Step into a Hole is Similar in Young and Older Adults

Abstract

The avoidance of a hole in the pathway while walking has been systematically investigated; however, depending on the dimensions of the hole, the option to avoid it is infeasible, and it is necessary to use the so-called accommodation strategy to step into the hole. We investigated the critical point between the avoidance and accommodation strategies when dealing with a hole in the ground during locomotion of young and older adults. Young and older adults performed two tasks: verbal estimation and walking. We used holes of different lengths and constant depth (12?cm). In the verbal estimation task, participants stood and looked at each hole and verbally respond if they would step into or avoid it. In the walking task, they walked and chose to either step or avoid the hole. Both age groups preferred to step into the hole when it was larger than 1.3 times their foot length in both tasks. The perception of affordances of young and older adults to step into a hole was similar, and it was unaffected by the investigated tasks. Thus, our participants preferred to have a safety margin that was large enough to guarantee that the whole foot would accommodate within the hole.     

Roll-over characteristics of human walking on inclined surfaces

Roll-over characteristics of able-bodied human subjects walking on ramped surfaces were examined in this study. Ten subjects walked at their normal self-selected speed on a level surface, a 5-deg ramp, and a 10-deg ramped surface. Ramps were designed such that ground reaction forces and center of pressure of the ground reaction forces could be measured on their surfaces. This set-up facilitated calculation of the effective rockers that the ankle-foot (AF) and knee-ankle-foot (KAF) systems conformed to during single-limb stance (contralateral toe off to contralateral heel contact). Since our original "roll-over shapes" were characterized between heel contact and opposite heel contact, we label the shapes found during single-limb stance as "truncated roll-over shapes". We hypothesized that the ankle-foot system would adapt to the various surfaces, creating a roll-over shape that would change in orientation with different levels of inclination. The truncated AF roll-over shapes supported this hypothesis for uphill walking but did not support the hypothesis for downhill walking. However, truncated roll-over shapes of the KAF system did adjust their orientation to match both the positive and negative levels of surface inclination. In general, the ankle appears to be the main adapting joint when walking up inclined surfaces while the knee becomes important for the overall adaptation in downhill walking. Knowledge of physiological lower-limb roll-over characteristics on ramped surfaces may help in the development of biomimetic prostheses and orthoses that will automatically adapt to changes in walking surface inclination.     

Synergistic interaction between ankle and knee during hopping revealed through induced acceleration analysis

The forces produced by the muscles can deliver energy to a target segment they are not attached to, by transferring this energy throughout the other segments in the chain. This is a synergistic way of functioning, which allows muscles to accelerate or decelerate segments in order to reach the target one. The purpose of this study was to characterize the contribution of each lower extremity joint to the vertical acceleration of the body’s center of mass during a hopping exercise. To accomplish this, an induced acceleration analysis was performed using a model with eight segments. The results indicate that the strategies produced during a hopping exercise rely on the synergy between the knee and ankle joints, with most of the vertical acceleration being produced by the knee extensors, while the ankle plantar flexors act as stabilizers of the foot. This synergy between the ankle and the knee is perhaps a mechanism that allows the transfer of power from the knee muscles to the ground, and we believe that in this particular task the net action of the foot and ankle moments is to produce a stable foot with little overall acceleration.     

Weighted vest effects on impact forces and joint work during vertical jump landings in men and women

Weighted vest (WV) use during vertical jump landings (VJL) does not appear to alter peak vertical ground reaction forces (GRF) or peak joint torques. However, WV effects on joint work and sex differences during VJL are not well understood. This study assessed WV effects on vertical GRF and sagittal joint work during VJL in men and women. Twelve men and 12 women performed VJL wearing a WV with zero added mass (unloaded) and with 10% body mass (loaded) while GRF and kinematic data were obtained. Mixed-model analyses of variance (α = 0.05) and effect sizes (ES) were used to assess differences between sexes and/or load conditions. Regardless of sex, greater landing height (p < 0.001; ES = 0.37) and peak vertical GRF (p = 0.001; ES 0.51) occurred when unloaded, while greater landing time (p = 0.001; ES = 0.46) and negative lower extremity work (p < 0.001; ES = 0.41) occurred when loaded through greater negative work about the hip (p = 0.001; ES = 0.27) and ankle (p = 0.020; ES = 0.27). No differences in hip (p = 0.753; ES = 0.03), knee (p = 0.588; ES = 0.07), or ankle (p = 0.580; ES = 0.09) joint displacement were detected between loaded and unloaded conditions. Men exhibited greater landing heights (p < 0.001; ES = 2.49) and greater peak vertical GRF than women (p = 0.007; ES = 1.18), though women exhibited greater negative lower extremity work (p < 0.001; ES = 1.98) than men through greater negative knee (p < 0.001; ES = 1.98) and ankle (p = 0.032; ES = 0.94) work. No sex differences were detected for joint angular displacement about the hip (p = 0.475; ES = 0.30), knee (p = 0.666; ES = 0.18), or ankle (p = 0.084; ES = 0.71). These data revealed a unique load accommodation strategy during VJL with a WV characterized by greater lower extremity joint work performed via increased joint torque despite lesser landing height and peak vertical GRF. Women appear to perform greater lower extremity joint work than men during VJL despite lesser landing height and peak vertical GRF. Current and prospective WV users should be aware of their load accommodation strategy during VJL with an external load. Women may consider developing more refined load accommodation strategies for VJL regardless of whether external loading is applied to avoid performing excessive amounts of lower extremity work.     

Side by side treadmill walking reduces gait asymmetry induced by unilateral ankle weight

Asymmetric gait is a hallmark of many neurological and musculoskeletal conditions. This behavior is often the result of a decrease in the stability of interlimb coordination, and synchronization to external signals such as auditory cuing or another walking individual may be helpful for altering abnormal movement patterns. The purpose of this study was to investigate the interaction between interlimb coordination and unintentional, interpersonal synchronization of gait in healthy individuals in response to unilateral ankle loading. Fifty participants completed four trials while walking on a motorized treadmill: (1) by themselves, (2) with a partner on an adjacent treadmill, (3) by themselves with additional weight applied unilaterally to their right ankle, and (4) with both a partner and unilateral weight. As expected, the addition of unilateral weight increased asymmetry according to several spatiotemporal measures of gait, but the presence of a partner on an adjacent treadmill significantly reduced this effect. Further, the amount of unintentional, interpersonal synchronization among pairings was relatively unaffected by the addition of ankle weight to one of the partners. All pairings realized a beneficial effect on asymmetrical gait but this effect was greater for pairings that consistently synchronized unintentionally. These results suggest that side by side walking might be an effective approach for influencing bilateral coordination of gait and may hold insight for understanding gait asymmetry and interlimb movement variability.     

Comparison of gait patterns between young and elderly women: an examination of coordination

This study investigated intralimb coordination during walking in young and elderly women using the theoretical model of dynamical systems. 20 women, 10 Young (M age=24.6 yr., SD= 3.2 yr.) and 10 Elderly (M age=73.7 yr., SD=4.9 yr.), were videotaped during free speed gait and gait perturbed by an ankle weight. Two parameters, one describing the phasing relationship between segments (mean absolute relative phase) and the other the variability of this relationship (deviation in phase), were calculated from the kinematics. Two-way analysis of variance (age and weight) with repeated measures on weight indicated that during the braking period the weight increased the mean absolute relative phase between the shank and the thigh and decreased it between the foot and the shank. The Elderly women had significant smaller values for the mean absolute relative phase between the shank and the thigh during the braking period. For the same period, deviation in phase increased for the segmental 'relationship between the shank and the thigh. The findings suggest that changes in intralimb coordination take place with asymmetrical weighting and the aging process. These changes are most clearly present during the braking period.     

Effect of localized muscle fatigue on vertical ground reaction forces and ankle joint motion during running

The purpose of this study was to examine the changes in the vertical ground reaction force (VGRF) and ankle joint motion during the first 50% of the stance phase of running following fatiguing exercise of either the dorsiflexors or the invertors of the foot. VGRFs, sagittal and rearfoot kinematic data were collected from 11 female recreational runners running at 2.9 m/second on a treadmill prior to and following localized muscle fatigue of either the invertors or dorsiflexors of the right foot. Loading rate of the impact peak force significantly increased following fatiguing exercise of the dorsiflexors, while the peak magnitudes of the impact and push-off forces remained unchanged. There were significant decreases in dorsiflexion at heel contact, but no significant difference in any rearfoot motion parameters tested following dorsiflexor fatigue. Following fatiguing exercise of the invertors, impact peak magnitude, push-off peak magnitude and the rate of decline of the impact peak force significantly decreased; there was no change in the loading rate of the impact peak force. Invertor fatigue also resulted in a less inverted foot position at heel contact, but there were no significant differences in any other kinematic parameters tested. The results demonstrate that localized muscle fatigue of either the invertors or dorsiflexors can have a significant effect on the loading rates, peak magnitudes and ankle joint motion seen during running. These changes, due to localized muscle fatigue, may play a role in many common lower extremity running injuries.     

SOCIAL COGNITION,EMPATHIC MOTIVATION,AND ADULTS' COMFORTING STRATEGIES

Previous research has found that social-cognitive abilities are important determinants of the competence to comfort affectively distressed others in a sensitive manner. However, being competent to comfort others sensitively does not necessarily imply that this competence will be exercised; presumably, persons must also be motivated to utilize their competencies if they are to produce highly sensitive comforting strategies. This study examined the collective contributions of a social-cognitive variable (interpersonal construct abstractness) and a motivational variable (emotional empathy) to the production of sensitive comforting strategies. Subjects were 70 college students. It was hypothesized that construct abstractness and emotional empathy would both be positively related to sensitivity of comforting strategies and that these two variables would make a significant independent contribution to the prediction of comforting strategies. Correlational and multiple regression analyses confirmed these hypotheses: construct abstractness explained a large portion of the variance in sensitivity of comforting strategies, while emotional empathy explained a smaller, but significant, portion of the variance in comforting-strategy sensitivity.     

Changes in intersegmental dynamics over time due to increased leg inertia

The purpose of this study was to investigate the effects of asymmetrical loading on the intersegmental dynamics of the swing phase. Participants were asked to walk on a treadmill for 20 min under three loading conditions: (a) unloaded baseline, (b) 2 kg attached to the dominant limb’s ankle, and (c) post-load, following load removal. Sagittal plane motion data of both legs were collected and an intersegmental dynamics analysis of each swing phase was performed. Comparisons of steady-state responses across load conditions showed that absolute angular impulses of the loaded limb’s hip and knee increased significantly after load addition, and returned to baseline following load removal. Unloaded leg steady-state responses were not different across load conditions. However, after a change in leg inertia both legs experienced a period of adaptation that lasted approximately 40 strides before a steady state walking pattern was achieved. These findings suggest that the central nervous system refined the joint moments over time to account for the altered limb inertia and to maintain the underlying kinematic walking pattern. Maintaining a similar kinematic walking pattern resulted in altered moment profiles of the loaded leg, but similar moment profiles of the unloaded leg compared with the unloaded baseline condition.     

Linking childhood personality with adaptation: evidence for continuity and change across time into late adolescence

Four personality traits--Mastery Motivation, Academic Conscientiousness, Surgent Engagement, and Agreeableness--were measured in a community sample of 205 children (ages 8-12), who were followed up 10 years later. Childhood personality was examined in relation to concurrent and longitudinal adaptation in 3 domains--academic achievement, rule-abiding versus antisocial conduct, and peer social competence. The childhood personality traits evidenced robust, conceptually coherent relationships with adaptation, both concurrently and across time. Childhood personality added to the prediction of later adaptation, beyond childhood IQ and earlier adaptation in the same domain. Few sex differences were obtained in the relationships between childhood personality and adaptation. The present results document both continuity and discontinuity in the links between childhood personality and adaptation across childhood into late adolescence.     

In-shoe multi-segment foot kinematics of children during the propulsive phase of walking and running

Certain styles of children’s shoes reduce 1st metatarsophalangeal joint (MTPJ) and midfoot motion during propulsion of walking. However, no studies have investigated if the splinting effect of shoes on children’s 1st MTPJ and midfoot motion occurs during running. This study investigated the effect of sports shoes on multi-segment foot kinematics of children during propulsion of walking and running. Twenty children walked and ran at a self-selected velocity while barefoot and shod in a random order. Reflective markers were used to quantify sagittal plane motion of the 1st MTPJ and three-dimensional motion of the midfoot and ankle. Gait velocity increased during shod walking and running and was considered a covariate in the statistical analysis. Shoes reduced 1st MTPJ motion during propulsion of walking from 36.0° to 10.7° and during running from 31.5° to 12.6°. Midfoot sagittal plane motion during propulsion reduced from 22.5° to 6.2° during walking and from 27.4° to 9.6° during running. Sagittal plane ankle motion during propulsion increased during shod running from 26.7° to 34.1°. During propulsion of walking and running, children’s sports shoes have a splinting effect on 1st MTPJ and midfoot motion which is partially compensated by an increase in ankle plantarflexion during running.     

Investigation of factors impacting mobility and gait in Parkinson disease

Mobility and gait limitations are major issues for people with Parkinson disease (PD). Identification of factors that contribute to these impairments may inform treatment and intervention strategies. In this study we investigated factors that predict mobility and gait impairment in PD. Participants with mild to moderate PD and without dementia (n = 114) were tested in one session ‘off’ medication. Mobility measures included the 6-Minute Walk test and Timed-Up-and-Go. Gait velocity was collected in four conditions: forward preferred speed, forward dual task, forward fast as possible and backward walking. The predictors analyzed were age, gender, disease severity, balance, balance confidence, fall history, self-reported physical activity, and executive function. Multiple regression models were used to assess the relationships between predictors and outcomes. The predictors, in different combinations for each outcome measure, explained 55.7% to 66.9% of variability for mobility and 39.5% to 52.8% for gait velocity. Balance was the most relevant factor (explaining up to 54.1% of variance in mobility and up to 45.6% in gait velocity). Balance confidence contributed to a lesser extent (2.0% to 8.2% of variance) in all models. Age explained a small percentage of variance in mobility and gait velocity (up to 2.9%). Executive function explained 3.0% of variance during forward walking only. The strong predictive relationships between balance deficits and mobility and gait impairment suggest targeting balance deficits may be particularly important for improving mobility and gait in people with PD, regardless of an individual’s age, disease severity, fall history, or other demographic features.     

Effects of toe length,foot arch length and toe joint axis on walking biomechanics

Toe joint articulation has been shown to affect gait mechanics, as evidenced by walking simulations, biped robots, and foot prostheses. However, it is not known how parameters such as toe length, foot arch length (i.e., heel-to-toe-joint length) or toe joint axis angle affect human walking. We utilized a previously developed adjustable ankle-toe prosthesis to systematically examine these three foot parameters. We tested ten able-bodied persons walking on a force instrumented-treadmill while wearing a pair of adjustable prostheses attached bilaterally below simulator boots (which fixated their biological ankles). We collected motion and ground reaction force data to compute lower-limb kinematics and kinetics as well as COM power and work. We observed that increasing the foot arch length by 60 mm (35%) increased COM Push-off work by ~5 J, due to increased energy storage and return by the ankle spring. Increasing the toe length by 40 mm (80%) and changing the toe joint axis by ±9° from a neutral angle resulted in negligible effects on COM mechanics and lower limb kinetics. This study provides further insights regarding toe joint function; knowledge which may benefit the design/integration of toe joints into prostheses, exoskeletons and legged robots.     

Visual and proprioceptive adaptation to altered oculomotor adjustments

Adaptation to spectacles that alter in equivalent amounts the accommodation and the convergence with which objects are viewed was produced under two conditions. In one, S alternately pushed away or pulled toward him a screen that exhibited only a single vertical contour while wearing glaaaes that caused decreases in accommodation and convergence equivalent to 1.5 lens diopters. Here kinesthesis for these arm movements provided the only veridical distance cues, A small, but highly significant, adaptation effect was obtained with a teat in which S, before and after the adaptation period, pointed to the location of a test line in the distance dimension. Corresponding tests consisting in size and in depth estimates did not show an adaptation effect. In the other condition of adaptation, S moved objects by hand toward and away from himself while wearing spectacles that increased accommodation and convergence by the equivalent of 1.5 lens diopters. In addition to the altered oculomotor cues, some veridical visual cues for distance such as are caused by perspective were present. This condition yielded changes in size and depth estimates indicative of an adaptation in visual distance perception and a larger effect of adaptation measured by the pointing test. We concluded that the excess of the adaptation effect measured by pointing over that measured by size estimation represents an adaptation in proprioception, as did the pointing effect produced by our first adaptation condition.     

Soft tissue contributions to impact forces simulated using a four-segment wobbling mass model of forefoot-heel landings

The purpose of this investigation was to develop and evaluate a wobbling mass model of a female performing a drop landing and to examine the influence of soft tissue properties on the impact loads experienced. A planar model comprising a foot, shank, thigh and upper body segment was developed. Spring-damper systems coupled the foot to the ground and the wobbling masses to the rigid masses. Unlike traditional wobbling mass models of landing, the model included a foot segment, which allowed replication of forefoot-heel landing techniques and also used subject and movement-specific properties to simulate the landings. Kinematics and force data collected for three drop landings (height 0.46 m) performed by a female were separately used to drive and evaluate the model. The wobbling mass model successfully reproduced the measured force profiles to 9% (RMS differences) of the measured range and replicated the measured peak vertical ground reaction forces to 6%. The accuracies of the wobbling mass model and a corresponding rigid mass model were compared. The inclusion of soft tissue properties in the model contributed up to an 8.6 bodyweights reduction in peak impact loading and produced a 52% more accurate replication of the measured force profiles. The prominent role soft tissues have in load attenuation and the benefits of modelling soft tissue in simulations of landings were therefore highlighted. The success of the wobbling mass model in replicating the kinetics of actual landing performances suggests the model may be used in the future to gain a realistic insight into load attenuation strategies used by females.     

A novel approach to mechanical foot stimulation during human locomotion under body weight support

Input from the foot plays an essential part in perceiving support surfaces and determining kinematic events in human walking. To simulate adequate tactile pressure inputs under body weight support (BWS) conditions that represent an effective form of locomotion training, we here developed a new method of phasic mechanical foot stimulation using light-weight pneumatic insoles placed inside the shoes (under the heel and metatarsus). To test the system, we asked healthy participants to walk on a treadmill with different levels of BWS. The pressure under the stimulated areas of the feet and subjective sensations were higher at high levels of BWS and when applied to the ball and toes rather than heels. Foot stimulation did not disturb significantly the normal motor pattern, and in all participants we evoked a reliable step-synchronized triggering of stimuli for each leg separately. This approach has been performed in a general framework looking for “afferent templates” of human locomotion that could be used for functional sensory stimulation. The proposed technique can be used to imitate or partially restore surrogate contact forces under body weight support conditions.     

Combining wearable sensor signals,machine learning and biomechanics to estimate tibial bone force and damage during running

There are tremendous opportunities to advance science, clinical care, sports performance, and societal health if we are able to develop tools for monitoring musculoskeletal loading (e.g., forces on bones or muscles) outside the lab. While wearable sensors enable non-invasive monitoring of human movement in applied situations, current commercial wearables do not estimate tissue-level loading on structures inside the body. Here we explore the feasibility of using wearable sensors to estimate tibial bone force during running. First, we used lab-based data and musculoskeletal modeling to estimate tibial force for ten participants running across a range of speeds and slopes. Next, we converted lab-based data to signals feasibly measured with wearables (inertial measurement units on the foot and shank, and pressure-sensing insoles) and used these data to develop two multi-sensor algorithms for estimating peak tibial force: one physics-based and one machine learning. Additionally, to reflect current running wearables that utilize running impact metrics to infer musculoskeletal loading or injury risk, we estimated tibial force using a commonly measured impact metric, the ground reaction force vertical average loading rate (VALR). Using VALR to estimate peak tibial force resulted in a mean absolute percent error of 9.9%, which was no more accurate than a theoretical step counter that assumed the same peak force for every running stride. Our physics-based algorithm reduced error to 5.2%, and our machine learning algorithm reduced error to 2.6%. Further, to gain insights into how force estimation accuracy relates to overuse injury risk, we computed bone damage expected due to a given loading cycle. We found that modest errors in tibial force translated into large errors in bone damage estimates. For example, a 9.9% error in tibial force using VALR translated into 104% error in estimated bone damage. Encouragingly, the physics-based and machine learning algorithms reduced damage errors to 41% and 18%, respectively. This study highlights the exciting potential to combine wearables, musculoskeletal biomechanics and machine learning to develop more accurate tools for monitoring musculoskeletal loading in applied situations.     

Coping and defence mechanisms: What are we assessing?

The present research study addresses the disparity between theoretical considerations and empirical evidence regarding the relationships between coping strategies and defence mechanisms. Self‐reported measures of coping and defences were administered to a Romanian adult sample (N = 542; 74.53% female, mean age = 31.28). Using structural equation modelling, models that assumed independence between coping and defences were compared with models that assumed the existence of relationships between the two concepts. Findings identified strong relationships between coping and defences, indicating large common variance between the two concepts. Furthermore, results suggested that coping and defences can be classified into two independent types of adaptation processes. Results of this research study suggested that coping and defences are facets of common adaptation processes.