Influence of anterior load carriage on lumbar muscle activation while walking in stable and unstable shoes

Load carriage can be harmful for workers, and alternative interventions to reduce back pain while walking and carrying loads are necessary. Unstable shoes have been used to improve balance and reduce back pain, but it is unknown whether walking wearing unstable shoes while carrying loads anteriorly causes excessive trunk extensors muscle activation. The aim of this study was to investigate the effects of different shoe types and anterior load carriage on gait kinematics and lumbar electromyographic (EMG) activity. Fourteen adults that predominantly walk or stand during the work day were asked to walk with and without carrying 10% of body mass anteriorly while wearing regular walking shoes (REG) and unstable shoes (MBT). The effects of shoe type, load carriage, and shoe × load interactions on the longissimus thoracis (LT) and iliocostalis lumborum (IC) EMG, stride duration, and stride frequency were assessed. MBT shoes induced a significant increase in LT (44.4 ± 35%) and IC EMG (33.0 ± 32%, p < .005), while load carriage increased LT (58.5 ± 41%) and IC EMG (55.1 ± 32%, p < .001). No significant shoe × load interaction was found (p>.05). However, walking wearing MBT shoes while carrying loads induced a 46 ± 40% higher EMG activity compared to walking wearing MBT shoes without load carriage. No effects of shoes or load carriage were found on stride duration and stride frequency. It was concluded that walking wearing MBT shoes and carrying 10% of total body mass induced greater activation of trunk extensors muscle compared to these factors in isolation, such a combination may not influence gait patterns.     

Effects of Backpack Carriage on Dual-Task Performance in Children During Standing and Walking

Primary school children perform parts of their everyday activities while carrying school supplies and being involved in attention-demanding situations. Twenty-eight children (8–10 years old) performed a 1-legged stance and a 10 m walking test under single- and dual-task situations in unloaded (i.e., no backpack) and loaded conditions (i.e., backpack with 20% of body mass). Results showed that load carriage did not significantly influence children's standing and walking performance (all p > .05), while divided attention affected all proxies of walking (all p < .001). Last, no significant load by attention interactions was detected. The single application of attentional but not load demand negatively affects children's walking performance. A combined application of both did not further deteriorate their gait behavior.     

Inclined Weight-Loaded Walking at Different Speeds: Pelvis-Shoulder Coordination,Trunk Movements and Cost of Transport

Although studied at level surface, the trunk kinematics and pelvis-shoulder coordination of incline walking are unknown. The aim of this study was to evaluate the speed effects on pelvis-shoulder coordination and trunk movement and the cost of transport (C) during unloaded and loaded (25% of body mass) 15% incline walking. We collected 3-dimensional kinematic and oxygen consumption data from 10 physically active young men. The movements were analyzed in the sagittal plane (inclination and range of trunk motion) and the transverse plane (range of shoulder and pelvic girdle motion and phase difference). The rotational amplitude of the shoulder girdle decreased with load at all speeds, and it was lower at the highest speeds. The rotational amplitude of the pelvic girdle did not change with the different speeds. The phase difference was greater at optimal speed (3 km.hr^?1, at the lowest C) in the loaded and the unloaded conditions. The trunk inclination was greater with load and increased with speed, whereas the range of trunk motion was lower in the loaded condition and decreased with increasing speed. In conclusion, the load decreased the range of girdles and trunk motion, and the pelvis-shoulder coordination seemed to be critical for the incline walking performance.     

Optimization characteristics of walking with and without a load on the trunk of the body

Previous work showed that subjects naturally adopt a walking speed which optimizes energy cost of locomotion and stability of stride; however, no studies have examined whether these criteria are affected by carrying an external load. The purpose of this study was to compare optimization characteristics during loaded or unloaded walking. Energy cost and stride characteristics were measured for 10 subjects with and without a load on the trunk of the body of 10% of the body weight during 4 sessions. The first 2 sessions represent free walking at 2.5, 3, 3.5, 4, 4.5, and 5 km x hr.(-1). The last sessions represent free vs forced walking at constant speed (preferred frequency and +/- 10 PF and +/-20% of preferred frequency). Results show an effect of load on energy cost of walking but no effect on the optimal speed for stability. Furthermore, when carrying a load the subject does not adopt systematically the speed that minimizes physiological cost. Our findings suggest the necessity to consider this effect to prevent gait disturbance and maintain the health benefits of walking.     

How does normal variability in trunk flexion affect lower limb muscle activity during walking?

A large proportion of the mass of the body is contained within the trunk segment. Therefore, small changes in the inclination of this segment have the potential to influence the direction of the ground reaction force and alter lower limb joint moments and muscle activation patterns during walking. The aim of this study was to investigate if variability in sagittal trunk inclination in healthy participants is associated with differences in lower limb biomechanics. Gait analysis data was collected on 41 healthy participants during walking. Two groups were defined based on habitual trunk flexion angle during normal walking, a forward lean group (n = 18) and a backward lean group (n = 17). Lower limb moments, muscle activation patterns and co-contraction levels were compared between the two groups using independent t-tests. The forward lean group walked with 5° more trunk flexion than the backward lean group. This difference was associated with a larger peak hip moment (effect size = 0.7) and higher activation of the lateral gastrocnemius (effect size =0.6) and the biceps femoris (effect size =0.7) muscles. The forward lean group also exhibited greater co-contraction in late stance (effect size =0.7). This is the first study to demonstrate that small differences in trunk flexion are associated with pronounced alterations in the activation of the lateral knee flexor muscles. This is important because people with knee osteoarthritis have been observed to walk with increased trunk flexion. It is possible that increased sagittal trunk inclination may be associated with elevated joint loads in people with knee osteoarthritis.     

Walking reveals trunk orientation bias for visual attention

Our trunks influence where we perform actions in space. Thus, trunk direction may define a region of spacethat is accorded special treatment by the attention system. We investigated conditions under which a trunk orientation bias for attention might be relevant for healthy adults. Three experiments compared visual detection performance for participants standing and walking on a treadmill. Together, the experiments disambiguate the relative contributions of motor activity, motor load, and cognitive load on trunk orientation biases. In Experiment 1, trunk orientation biases (i.e., faster target detection for targets in front of the body midline) were observed in both forward and sideways walking conditions, but not in standing conditions. In Experiment 2, we ruled out the notion that the trunk orientation bias arose from increased motor activity; in fact, the bias was greatest when participants walked at an unusually slow pace. In Experiment 3, we directly compared motor load with cognitive load in a dual-task paradigm; cognitive load influenced overall performance speed, but only motor load produced trunk orientationbias. These results suggest that a trunk orientation bias emerges during walking and motor load conditions.     

Effect of stride length on overarm throwing delivery: Part II: An angular momentum response

This is the second component of a two-part series investigating 3D momentum profiles specific to overhand throwing, where altering stride reportedly influences throwing mechanics resulting in significantly different physiologic outcomes and linear momentum profiles. Using a randomized cross-over design, nineteen pitchers (15 collegiate and 4 high school) were assigned to pitch two simulated 80-pitch games at ±25% of their desired stride length. An 8-camera motion capture system (240 Hz) integrated with two force plates (960 Hz) and radar gun tracked each overhand throw. Segmental angular momentums were summed yielding throwing arm and total body momentums, from which compensation ratio’s (relative contribution between the two) were derived. Pairwise comparisons at hallmark events and phases identified significantly different angular momentum profiles, in particular total body, throwing arm, and momentum compensation ratios (P ⩽ 0.05) as a result of manipulating stride length. Sagittal, frontal, and transverse angular momentums were affected by stride length changes. Transverse magnitudes showed greatest effects for total body, throwing arm, and momentum compensation ratios. Since the trunk is the main contributor to linear and angular momentum, longer strides appear to better regulate transverse trunk momentum in double support, whereas shorter strides show increased momentum prior to throwing arm acceleration.     

Residual attentional capacity amongst young and elderly during dual and triple task walking

Walking is considered an automatic function which demands little attentional resources. Thus a residual attentional capacity is available for a concurrent task (dual task). Minor age-related deficits in postural control may minimize the residual attentional capacity, however this may not be detected by a simple examination of the individuals gait performance. This study investigated the use of challenging dual task combinations to detect age related changes in gait performance. Eleven community-dwelling elderly (mean age 76 years) and 13 young subjects (mean age 26 years) participated in the study. The participants walked along a figure-of-eight track at a self-selected speed. The effect of introducing a concurrent cognitive task and a concurrent functional motor task was evaluated. Stride-to-stride variability was measured by heel contacts and by trunk accelerometry. In response to the cognitive task the elderly increased their temporal stride-to-stride variability by 39% in the walking task and by 57% in the combined motor task. These increases were significantly larger than observed for the young. Equivalent decreases in trunk acceleration autocorrelation coefficients and gait speed were found. A combination of sufficiently challenging motor tasks and concurrent cognitive tasks can reveal signs of limited residual attentional capacity during walking amongst the elderly.     

Local dynamic stability of trunk movements during the repetitive lifting of loads

The local dynamic stability of trunk movements was assessed during repetitive lifting using nonlinear Lyapunov analyses. The goal was to assess how varying the load-in-hands affects the neuromuscular control of lumbar spinal stability. Thirty healthy participants (15M, 15F) performed repetitive lifting at 10 cycles per minute for three minutes under two load conditions: zero load and 10% of each participant's maximum back strength. Short- and long-term maximum finite-time Lyapunov exponents (λ(max-s) and λ(max-l)), describing responses to infinitesimally small perturbations, were calculated from the measured trunk kinematics to estimate the local dynamic stability of the system. Kinematic variability was also assessed using mean standard deviations (MeanSD) across cycles. The results of a mixed-design repeated-measures ANOVA showed that increasing the load lifted significantly reduced λ(max-s) (μ(0%-LOAD)=0.379, μ(10%-LOAD)=0.335, p<.001), but not λ(max-l) (μ(0%-LOAD)=0.46E-03, μ(10%-LOAD)=2.41E-03, p=.055) or MeanSD (μ(0%-LOAD)=2.57, μ(10%-LOAD)=2.89, p=.164). There were no between-subject effects of sex, or significant interactions (α<.05). The present findings indicated improved dynamic spinal stability when lifting the heavier load; meaning that as muscular and moment demands increased, so too did participants' abilities to respond to local perturbations. These results support the notion of greater spinal instability during movement with low loads due to decreased muscular demand and trunk stiffness, and should aid in understanding how lifting various loads contributes to occupational low back pain.     

Effects of surface texture and grip force on the discrimination of hand-held loads

In this paper, we report the results from two experiments in which subjects were required to discriminate horizontal load forces applied to a manipulandum held with a precision grip. The roughness (and hence friction) of the grip surfaces and required grip force were manipulated. In the first experiment, subjects were instructed to judge the load while maintaining hand position and not letting the manipulandum slip. It was found that performance was influenced by surface texture; a given load was judged to be greater when the surface texture was smooth than when it was rough. This result is consistent with a previous study based on lifting objects and indicates that the effect of surface texture applies to loads in general and not just to gravitational loads (i.e., weight). To test whether the load acting on a smooth object is judged to be greater because the grip force required to prevent it from slipping is larger, a second experiment was carried out. Subjects used a visual feedback display to maintain the same grip force for smooth and rough manipulandum surfaces. In this case, there was no effect of surface texture on load perception. These results provide evidence that perceived load depends on the grip force used to resist the load. The implications of these results in terms of central and peripheral factors underlying load discrimination are considered.     

Effects of passive interpersonal light touch during walking on postural control responses: An exploratory study

The effects of passive interpersonal light touch (PILT) on postural stability can be observed through improved postural coordination through haptic feedback from the contact provider to the contact receiver while walking. It is unclear, however, whether PILT affects the contact receiver's detailed physical responses, such as muscle activity, body sway, and joint movements. In this study, surface electromyography and an inertial measurement unit were used simultaneously to explore changes in walking speed and control responses induced by PILT. We evaluated fourteen healthy participants for their walking speed and physical responses under two walking conditions: no-touch (NT) and PILT. As a physical response during walking, we measured muscle activity (rectus femoris, semitendinosus, tibialis anterior, and soleus muscles), body sway (pelvis and neck), and joint angles (direction of hip, knee, and ankle joint movements). In PILT condition, fingertip contact force was measured while the contact provider touched the third level of the recipient's lumbar spine. In comparison with the NT condition, PILT condition increased walking speed and decreased body sway on neck position. There were significant correlations between walking speed and neck sway regarding NT and PILT change values. Passive haptic information to the contact receiver may assist in the smooth shift of the center of gravity position during gait through interpersonal postural coordination. These findings suggest that PILT may provide an efficient and stable gait.     

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.     

How trunk turns affect locomotion when you are not looking where you go

How well do we maintain heading direction during walking while we look at objects beside our path by rotating our eyes, head, or trunk? Common experience indicates that it may be fairly hazardous not to look where you are going. In the present study, 12 young adults walked on a treadmill while they followed a moving dot along a horizontal line with their gaze by rotating primarily either their eyes, head, or trunk for amplitudes of up to 25 degrees . During walking the movement of the center of pressure (COP) was monitored using force transducers under a treadmill. Under normal light conditions, the participants showed little lateral deviation of the COP from the heading direction when they performed the eye or head movement task during walking, even when optic flow information was limited. In contrast, trunk rotations led to a doubling of the COP deviation in the mediolateral direction. Some of this deviation was attributed to foot rotation. Participants tended to point their feet in the gaze direction when making trunk turns. The tendency of the feet to be aligned with the trunk is likely to be due to a preference to have feet and body in the same orientation. Such alignment is weaker for the feet with respect to head position and it is absent with respect to eye position. It is argued that feet and trunk orientation are normally tightly coupled during gait and that it requires special abilities to move both segments independently when walking.     

Comparison of kinematic and kinetic methods for computing the vertical motion of the body center of mass during walking

The vertical excursion of the body center of mass (BCOM) was calculated using three different techniques commonly used by motion analysis laboratories. The sacral marker method involved estimating vertical BCOM motion by tracking the position of a reflective marker that was placed on the sacrum of subjects as they walked. The body segmental analysis technique determined the vertical motion of the BCOM from a weighted average of the vertical positions of the centers of mass of individual body segments for each frame of kinematic data acquired during the data trial. Anthropomorphic data from standard tables were used to determine the mass fractions and the locations of the centers of mass of each body segment. The third technique involved calculating BCOM vertical motion through double integration of force platform data. Data was acquired from 10 able-bodied, adult research subjects--5 males and 5 females--walking at speeds of 0.8, 1.2, 1.6, and 2.0 m/s. A repeated measures ANOVA indicated that at the slowest walking speed the vertical excursions calculated by all three techniques were similar, but at faster speeds the sacral marker significantly (p < 0.001) overestimated the vertical excursion of the BCOM compared with the other two methods. The body segmental analysis and force platform techniques were in agreement at all walking speeds. Discrepancies between the sacral marker method and the other two techniques were explained using a simple model; the reciprocal configuration of the legs during double support phase significantly raises the position of the BCOM within the trunk at longer step lengths, corresponding to faster walking speeds. The sacral marker method may provide a reasonable approximation of vertical BCOM motion at slow and freely selected speeds of able-bodied walking. However, the body segmental analysis or force platform techniques will probably yield better estimates at faster walking speeds or in persons with gait pathologies.     

Age-related changes in grip force and dynamics of hand movement

The authors investigated whether older adults (n = 16; mean age = 65 years) increased grip force to compensate for load force fluctuations during up and down movements more than young adults did (n = 16; mean age = 24 years) and whether older and young adults exhibited similar adaptation of grip force to alterations in friction associated with changes in object surface texture. As previously reported, older adults used a higher level of grip force than young adults during static holding. Increased grip force was observed in the older group during movement. The increase was appropriate to the lower coefficient of friction estimated for the older group. In both groups, grip force was greater with a smooth than with a rough surface (the latter having the higher coefficient of friction) during static holding and during movement. Moreover, grip force modulation was equally well synchronized with load force fluctuation during movement in the two groups. The authors concluded that changes in organization of grip force with age are well adapted to change in hand-object interface properties. Elevated grip force in older adults does not necessarily signify a fundamental change in synchronizing grip force modulation with load force fluctuation.     

Effects of back loading on the biomechanics of sit-to-stand motion in healthy children

The goal of the present study was to determine the thus far unstudied effects of back loading on the kinematics and kinetics of sit-to-stand (STS) motion in healthy children. Fifteen children (8 boys, 7 girls, mean age 9.6 years, SD 1.2 years) were tested with no back load and with a back load of 10% and 20% of body weight, respectively. A motion analysis system was used with six infrared cameras and two force plates. Total STS duration did not change; however, differential effects were shown for the durations of its phases. Back loading increased ankle dorsiflexion yielding a greater maximal dorsiflexion angle. Effects on the knee angle were limited except for a significant decrease in final knee flexion. Initial and maximal hip flexion increased but final hip angle did not change. Initial backward pelvic tilt decreased and a shift to forward pelvic tilt occurred at an earlier stage of STS motion. Back loading affected trunk motion: maximal and final forward shoulder tilt increased. Maximal ankle and knee moments and powers increased; however, hip joint kinetics was not affected significantly. Therefore, while maintaining the general pattern of STS motion, participants showed selectively significant adjustments to back loading during its different phases. The main kinematic adjustments were increased trunk flexion and greater ankle dorsiflexion, while the major kinetic adjustment was increased knee extension moment. Increased back loading yielded more pronounced effects, primarily in the ankle. In sum, back loading substantially affected the biomechanics of STS motion even for the lower load level studied. This finding may be of clinical relevance for musculoskeletal disorders, but this needs to be examined.     

Gradual increase of perturbation load induces a longer retention of locomotor adaptation in children with cerebral palsy

The goal of this study is to determine whether the size and the variability of error have an impact on the retention of locomotor adaptation in children with cerebral palsy (CP). Eleven children with CP, aged 7–16 years old, were recruited to participate in this study. Three types of force perturbations (i.e., abrupt, gradual and noisy loads) were applied to the right leg above the ankle starting from late stance to mid-swing in three test sessions while the subject walked on a treadmill. Spatial-temporal gait parameters were recorded using a custom designed 3D position sensor during treadmill walking. We observed that children with CP adapted to the resistance force perturbation and showed an aftereffect consisting of increased step length after load release. Further, we observed a longer retention of the aftereffect for the condition with a gradual load than that with an abrupt load. Results from this study suggested that the size of error might have an impact on the retention of motor adaptation in children with CP with a longer retention of motor adaptation for the condition with a small size of error than that with a large error. In addition, enhanced variability of error seems facilitate motor learning during treadmill training. Results from this study may be used for the development of force perturbation based training paradigms for improving walking function in children with CP.     

Kinetic potential influences visual and remote haptic perception of affordances for standing on an inclined surface

The ability of a perceiver–actor to perform a particular behaviour depends on their ability to generate and control the muscular forces required to perform that behaviour. If an intended behaviour is to be successful, perception must be relative to this ability. We investigated whether perceiver–actors were sensitive to how changes in their mass distribution influenced their ability to stand on an inclined surface. Participants reported whether they would be able to stand on an inclined surface while wearing a weighted backpack on their back, while wearing a weighted backpack on their front, and while not wearing a weighted backpack. In addition, participants performed this task by either viewing the surface or exploring it with a hand-held rod (while blindfolded). The results showed that perception of affordances for standing on the inclined surface depended on how the backpack influenced the ability of the participant to stand on the surface. Specifically, perceptual boundaries occurred at steeper inclinations when participants wore the backpack on their front than when they wore it on their back. Moreover, this pattern occurred regardless of the perceptual modality by which the participants explored the inclined surface.     

Local Dynamic Stability of the Locomotion of Lower Extremity Joints and Trunk During Backward Upslope Walking

Backward slope walking was considered as a practical rehabilitation and training skill. However, its gait stability has been hardly studied, resulting in its limited application as a rehabilitation tool. In this study, the effect of walking direction and slope grade were investigated on the local dynamic stability of the motion of lower extremity joints and trunk segment during backward and forward upslope walking (BUW/FUW). The local divergence exponents (λ_S) of 16 adults were calculated during their BUW and FUW at grades of 0%, 5%, 10%, and 15%. Mean standard deviation over strides (MeanSD) was analyzed as their gait variability. Backward walking showed larger λ_S for the abduction-adduction and rotational angles of knee and ankle on inclined surface than forward walking, while λ_S for hip flexion-extension angle at steeper grades was opposite. No grade effect for any joint existed during BUW, while λ_S increased with the increasing grade during FUW. As to the trunk, walking direction did little impact on λ_S. Still, significant larger λ_S for its medial-lateral and vertical motion were found at the steeper grades during both FUW and BUW. Results indicate that during BUW, the backward direction may influence the stability of joint motions, while the trunk stability was challenged by the increasing grades. Therefore, BUW may be a training tool for the stability of both upper and lower body motion during gait.     

Age-Related Changes in Grip Force and Dynamics of Hand Movement

The authors investigated whether older adults (n = 16; mean age = 65 years) increased grip force to compensate for load force fluctuations during up and down movements more than young adults did (n = 16; mean age = 24 years) and whether older and young adults exhibited similar adaptation of grip force to alterations in friction associated with changes in object surface texture. As previously reported, older adults used a higher level of grip force than young adults during static holding. Increased grip force was observed in the older group during movement. The increase was appropriate to the lower coefficient of friction estimated for the older group. In both groups, grip force was greater with a smooth than with a rough surface (the latter having the higher coefficient of friction) during static holding and during movement. Moreover, grip force modulation was equally well synchronized with load force fluctuation during movement in the two groups. The authors concluded that changes in organization of grip force with age are well adapted to change in hand-object interface properties. Elevated grip force in older adults does not necessarily signify a fundamental change in synchronizing grip force modulation with load force fluctuation.