In vivo biomechanical behavior of the human heel pad during the stance phase of gait

A technique is introduced for simultaneous measurements of the heel pad tissue deformation and the heel–ground contact stresses developing during the stance phase of gait. Subjects walked upon a gait platform integrating the contact pressure display optical method for plantar pressure measurements and a digital radiographic fluoroscopy system for skeletal and soft tissue motion recording. Clear images of the posterior-plantar aspect of the calcaneus and enveloping soft tissues were obtained simultaneously with the pressure distribution under the heel region throughout the stance phase of gait. The heel pad was shown to undergo a rapid compression during initial contact and heel strike, reaching a strain of 0.39±0.05 in about 150 ms. The stress–strain relation of the heel pad was shown to be highly non-linear, with a compression modulus of 105±11 kPa initially and 306±16 kPa at 30% strain. The energy dissipation during heel strike was evaluated to be 17.8±0.8%. The present technique is useful for biomechanical as well as clinical evaluation of the stress–strain and energy absorption characteristics of the heel pad in vivo, during natural gait.     

Lower limb co-contraction during walking in subjects with stroke: A systematic review

PurposeThe aim of this paper was to identify and synthesise existing evidence on lower limb muscle co-contraction (MCo) during walking in subjects with stroke.MethodsAn electronic literature search on Web of Science, PubMed and B-on was conducted. Studies from 1999 to 2012 which analysed lower limb MCo during walking in subjects with stroke, were included.ResultsEight articles met the inclusion criteria: 3 studied MCo in acute stage of stroke, 3 in the chronic stage and 2 at both stages. Seven were observational and 1 had a pretest–posttest interventional design. The methodological quality was “fair to good” to “high” quality (only 1 study). Different methodologies to assess walking and quantify MCo were used. There is some controversy in MCo results, however subjects with stroke tended towards longer MCo in both lower limbs in both the acute and chronic stages, when compared with healthy controls. A higher level of post-stroke walking ability (speed; level of independence) was correlated with longer thigh MCo in the non-affected limb. One study demonstrated significant improvements in walking ability over time without significant changes in MCo patterns.ConclusionsSubjects with stroke commonly present longer MCo during walking, probably in an attempt to improve walking ability. However, to ensure recommendations for clinical practice, further research with standardized methodologies is needed.     

Stable bipedal walking with a swing-leg protraction strategy

In bipedal locomotion, swing-leg protraction and retraction refer to the forward and backward motion, respectively, of the swing-leg before touchdown. Past studies have shown that swing-leg retraction strategy can lead to stable walking. We show that swing-leg protraction can also lead to stable walking. We use a simple 2D model of passive dynamic walking but with the addition of an actuator between the legs. We use the actuator to do full correction of the disturbance in a single step (a one-step dead-beat control). Specifically, for a given limit cycle we perturb the velocity at mid-stance. Then, we determine the foot placement strategy that allows the walker to return to the limit cycle in a single step. For a given limit cycle, we find that there is swing-leg protraction at shallow slopes and swing-leg retraction at steep slopes. As the limit cycle speed increases, the swing-leg protraction region increases. On close examination, we observe that the choice of swing-leg strategy is based on two opposing effects that determine the time from mid-stance to touchdown: the walker speed at mid-stance and the adjustment in the step length for one-step dead-beat control. When the walker speed dominates, the swing-leg retracts but when the step length dominates, the swing-leg protracts. This result suggests that swing-leg strategy for stable walking depends on the model parameters, the terrain, and the stability measure used for control. This novel finding has a clear implication in the development of controllers for robots, exoskeletons, and prosthetics and to understand stability in human gaits.     

Cross training effects of non-paralytic dorsiflexion muscle strengthening exercise on paralytic dorsiflexor muscle activity,gait ability,and balancing ability in patients with chronic stroke: A randomized,controlled, pilot trial

Objective:To investigate the effects of non-paralytic dorsiflexion muscle strengthening exercise on functional abilities in chronic hemiplegic patients after stroke.Methods:A total of 21 patients with chronic stroke underwent dorsiflexion muscle strengthening exercise (MST) 5 times a week for 6 weeks (the experimental group, MST to non-paralytic dorsiflexion muscles, n=11; the control group, MST to paralytic dorsiflexion muscles; n=10). Paralytic dorsiflexor muscle activities (DFA) and 10 m walking tests (10MWT) and timed up and go tests (TUG) were measured before and after intervention.Results:A significant increase in DFA was observed after intervention in the experimental and control groups (p<0.05) (experimental 886.6% for reference voluntary contraction (RVC), control 931.6% for RVC). TUG and 10MWT results showed significant reductions post-intervention in the experimental and control groups (experimental group -5.6 sec, control -4.8 sec; experimental group -3.1 sec, control, -3.9 sec; respectively). No significant intergroup difference was observed between changes in DFA or between changes in TUG and 10MWT results after intervention (p>.05).Conclusion:Strengthening exercise performed on non-paralytic dorsiflexion muscles had positive cross-training effects on paralytic dorsiflexor muscle activities, balance abilities, and walking abilities in patients with chronic stroke.     

The effect of prolonged level and uphill walking on the postural control of older adults

Prolonged walking could alter postural control leading to an increased risk of falls in older adults. The aim of this study was to determine the effect of level and uphill prolonged walking on the postural control of older adults. Sixteen participants (64 ± 5 years) attended 3 visits. Postural control was assessed during quiet standing and the limits of stability immediately pre, post and post 15 min rest a period of 30 min walking on level and uphill (5.25%) gradients on separate visits. Each 30 min walk was divided into 3 10 min blocks, the limits of stability were measured between each block. Postural sway elliptical area (PRE: 1.38 ± 0.22 cm², POST: 2.35 ± 0.50 cm², p = .01), medio-lateral (PRE: 1.33 ± 0.03, POST: 1.40 ± 0.03, p = .01) and anterio-posterior detrended fluctuation analysis alpha exponent (PRE: 1.43 ± 0.02, POST: 1.46 ± 0.02, p = .04) increased following walking. Medio-lateral alpha exponent decreased between post and post 15 min’ rest (POST: 1.40 ± 0.03, POST15: 1.36 ± 0.03, p = .03). Forward limits of stability decreased between the second walking interval and post 15 min’ rest (Interval 2: 28.1 ± 1.6%, POST15: 25.6 ± 1.6%, p = .01) and left limits of stability increased from pre-post 15 min’ rest (PRE: 27.7 ± 1.2%, POST15: 29.4 ± 1.1%, p = .01). The neuromuscular alterations caused by prolonged walking decreased the anti-persistence of postural sway and altered the limits of stability in older adults. However, 15 min’ rest was insufficient to return postural control to pre-exercise levels.     

Ratings of perceived exertion in individuals with varying fitness levels during walking and running

It was the purpose of this investigation to: 1) compare the ratings of perceived exertion (RPEs) in high and low fit individuals when walking and running at comparable exercise intensities and 2) to determine if ventilation (VE) provides a central signal for RPEs. Nine high fit and nine low fit male subjects completed two exercise bouts on a treadmill, one uphill walking and the other level running. Workloads for each bout were set at 90% of each subject's ventilatory threshold (VT) as determined from a graded exercise test. Oxygen consumption (Vo2), heart rate (HR), and VE were all similar between the walk and run trials for the low fit subjects (P greater than 0.05). HR were found to be significantly greater during the walk trial vs. the run trial (P less than 0.05) for the high fit subjects, whereas, VE was significantly greater during the run trial. Oxygen consumption was similar for the high fit subjects during both trials (P greater than 0.05). During the walk and run trials, central (12.1 +/- 1.6 vs. 11.4 +/- 1.5), local (14.0 +/- 1.3 vs. 13.9 +/- 1.1) and overall (12.8 +/- 1.2 vs. 12.4 +/- 1.4) RPEs were not found to be significantly different for the low fit group (P greater than 0.05). In contrast, during the walk vs. the run trial there was a significant increase in central (10.7 +/- 2.0 vs. 9.2 +/- 1.9), local (11.5 +/- 2.0 vs. 9.8 +/- 1.8) and overall (11.2 +/- 2.4 vs. 9.6 +/- 2.3) RPEs for the high fit group (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Current injection into interneurones of the terminal ganglion modifies turning behaviour of walking crickets

Ascending interneurones of the terminal ganglion of orthopterous insects are known to carry information on wind stimuli perceived by cercal receptors to thoracic and cephalic ganglia. Neurones of these anterior ganglia control evasive walking behaviour. We demonstrate that current injection into individual wind-sensitive local non-spiking interneurones and ascending giant interneurones of the terminal ganglion can influence the orientation behaviour of walking crickets. To induce a change of turning during “wind puff stimulation” by current injection into the lateral giant interneurone, its spike activity has to be modified by at least 100%. In 5 of 12 different types of non-spiking interneurones a moderate shift of the membrane potential results in a change of the mean speed of rotation and/or the frequency of turns. All preparations tested with different amounts of current injection showed a proportional change of turning frequency. Normally, the turning behaviour is evasive with respect to the wind source. During current injection this dependence is preserved, but the general orientation is readjusted. Taking into account known connections between some of these interneurones and ascending neurones the tested wind-sensitive local non-spiking interneurones of the terminal ganglion are likely to impose an offset on the mean direction of orientation controlled by cephalic and thoracic neuronal networks. Accepted: 3 September 1997     

Human energy expenditure when walking on a moving platform

The assumption that working on board ship is more strenuous than comparable work ashore was investigated in this study. Various physiological parameters (V˙O₂, V˙CO₂, V˙ _E and HR) have been measured to determine the energy expenditure of subjects walking slowly on a moving platform (ship motion simulator). Twelve subjects (eight men and four women) walked either freely on the floor or on a treadmill at a speed of 1 m · s⁻¹. Platform motion was either in a heave, pitch or roll mode. These three conditions were compared with a control condition in which the platform remained stationary. The results showed that during pitch and roll movements of the platform, the energy expenditure for the same walking task was about 30% higher than under the stationary control condition (3.6 J · kg⁻¹ · m⁻¹ vs 2.5 J · kg⁻¹ · m⁻¹, P < 0.05) for both walking on a treadmill and free walking. The heart rate data supported the higher energy expenditure results with an elevation of the heart rate (112 beats · min⁻¹ vs 103 beats · min⁻¹, P < 0.05). The heave condition did not differ significantly from the stationary control condition. Pitch and roll were not significantly different from each other. During all experimental conditions free walking resulted in a higher energy cost of walking than treadmill walking (3.5 J · kg⁻¹ · m⁻¹ vs 2.7 J · kg⁻¹ · m⁻¹, P < 0.05) at the same average speed. The results of this experiment were interpreted as indicating that the muscular effort, needed for maintaining balance when walking on a pitching or rolling platform, resulted in a significantly higher work load than similar walking on a stable or a heaving floor, independent of the mode of walking. These results explain in part the increased fatigue observed when a task is performed on a moving platform. Accepted: 3 October 1997     

Calf muscle work and segment energy changes in human treadmill walking

The relation between changes in potential and kinetic energy in a seven-segment model of the human body and the work of m. triceps surae was investigated in four subjects walking on a treadmill at speeds between 0.5 and 2.0 m/s. Segment energy levels were determined by means of tachometers attached with strings to various points on the subject's body. Muscle work was assessed by electromyogram to force processing. M. triceps surae is active during stance, first doing negative (eccentric) work and ending with a short period of positive (concentric) work at “push-off”. It turned out that in normal walking these muscles provide the major part of positive work for the initiation of swing at push-off. Only at large step lengths, when push-off starts well before contralateral heel contact, is there a minor pushing forward of the trunk. In the negative work phase, m. triceps surae seem to check the forward speed of the trunk. A related decrease of trunk kinetic energy is not present, however, but this may be obscured by the simultaneous action of m. quadriceps femoris and, in a later stage, by a transfer of energy from the decelerating contralateral (swing) leg to the trunk. Energy of the trunk segment shows a sharp decline in double stance and a more gradual increase in the first half of single stance. Evidence is given that this effect is due to quadriceps action in the knee flexion-extension movement during stance. The presented results are incorporated in a general picture of energy flows in human walking.