Influence of higher-grade walking on metabolic demands in young untrained Japanese women

The primary purpose of this study was to document the physiological responses of level walking and running (LW/R) at various speeds, and grade walking (GW) at various grades on a treadmill. Twenty-four young untrained Japanese women performed 2 tests on the specially designed treadmill for a higher grade exercise. The first test was the LW/R with increase of speeds, 33.3, 66.7, 91.7, and 116.7 m.min(-1). The first 3 progressions were for walking and the last progression was for running. The second test was the GW with increase of grades 0, 10, 20, and 30% with the velocity of 33.3 m.min(-1) in all progressions. The different combinations of speeds and grade for the progressions used in this study were selected based on the results of preliminary pilot studies, so that the percent heart rate maximim (%HRmax) was reached at the minimum intensities recommended to allow improving cardiorespiratory fitness by the American College of Sports Medicine (ACSM). Significant (p 相似文献   

The influence of body weight support on ankle mechanics during treadmill walking

The use of body weight support (BWS) systems during locomotor retraining has become routine in clinical settings. BWS alters load receptor feedback, however, and may alter the biomechanical role of the ankle plantarflexors, influencing gait. The purpose of this study was to characterize the biomechanical adaptations that occur as a result of a change in limb load (controlled indirectly through BWS) and gait speed during treadmill locomotion. Fifteen unimpaired participants underwent gait analysis with surface electromyography while walking on an instrumented dual-belt treadmill at seven different speeds (ranging from 0.4 to 1.6 m/s) and three BWS conditions (ranging from 0% to 40% BWS). While walking, spatiotemporal measures, anterior/posterior ground reaction forces, and ankle kinetics and muscle activity were measured and compared between conditions. At slower gait speeds, propulsive forces and ankle kinetics were unaffected by changing BWS; however, at gait speeds ≥approximately 0.8 m/s, an increase in BWS yielded reduced propulsive forces and diminished ankle plantarflexor moments and powers. Muscle activity remained unaltered by changing BWS across all gait speeds. The use of BWS could provide the advantage of faster walking speeds with the same push-off forces as required of a slower speed. While the use of BWS at slower speeds does not appear to detrimentally affect gait, it may be important to reduce BWS as participants progress with training, to encourage maximal push-off forces. The reduction in plantarflexor kinetics at higher speeds suggests that the use of BWS in higher functioning individuals may impair the ability to relearn walking.     

The metabolic and mechanical costs of step time asymmetry in walking

Animals use both pendular and elastic mechanisms to minimize energy expenditure during terrestrial locomotion. Elastic gaits can be either bilaterally symmetric (e.g. run and trot) or asymmetric (e.g. skip, canter and gallop), yet only symmetric pendular gaits (e.g. walk) are observed in nature. Does minimizing metabolic and mechanical power constrain pendular gaits to temporal symmetry? We measured rates of metabolic energy expenditure and calculated mechanical power production while healthy humans walked symmetrically and asymmetrically at a range of step and stride times. We found that walking with a 42 per cent step time asymmetry required 80 per cent (2.5 W kg⁻¹) more metabolic power than preferred symmetric gait. Positive mechanical power production increased by 64 per cent (approx. 0.24 W kg⁻¹), paralleling the increases we observed in metabolic power. We found that when walking asymmetrically, subjects absorbed more power during double support than during symmetric walking and compensated by increasing power production during single support. Overall, we identify inherent metabolic and mechanical costs to gait asymmetry and find that symmetry is optimal in healthy human walking.     

Dynamics and stability of muscle activations during walking in healthy young and older adults

To facilitate stable walking, humans must generate appropriate motor patterns and effective corrective responses to perturbations. Yet most EMG analyses do not address the continuous nature of muscle activation dynamics over multiple strides. We compared muscle activation dynamics in young and older adults by defining a multivariate state space for muscle activity. Eighteen healthy older and 17 younger adults walked on a treadmill for 2 trials of 5 min each at each of 5 controlled speeds (80–120% of preferred). EMG linear envelopes of v. lateralis, b. femoris, gastrocnemius, and t. anterior of the left leg were obtained. Interstride variability, local dynamic stability (divergence exponents), and orbital stability (maximum Floquet multipliers; FM) were calculated. Both age groups exhibited similar preferred walking speeds (p=0.86). Amplitudes and variability of individual EMG linear envelopes increased with speed (p<0.01) in all muscles but gastrocnemius. Older adults also exhibited greater variability in b. femoris and t. anterior (p<0.004). When comparing continuous multivariate EMG dynamics, older adults demonstrated greater local and orbital instability of their EMG patterns (p<0.01). We also compared how muscle activation dynamics were manifested in kinematics. Local divergence exponents were strongly correlated between kinematics and EMG, independent of age and walking speed, while variability and max FM were not. These changes in EMG dynamics may be related to increased neuromotor noise associated with aging and may indicate subtle deterioration of gait function that could lead to future functional declines.     

The human ankle during walking: implications for design of biomimetic ankle prostheses

The non-disabled human ankle joint was examined during walking in an attempt to determine overall system characteristics for use in the design of ankle prostheses. The hypothesis of the study was that the quasi-stiffness of the ankle changes when walking at different walking speeds. The hypothesis was examined using sagittal plane ankle moment versus ankle angle curves from 24 able-bodied subjects walking over a range of speeds. The slopes of the moment versus ankle angle curves (quasi-stiffness) during loading appeared to change as speed was increased and the relationship between the moment and angle during loading became increasingly non-linear. The loading and unloading portions of the moment versus angle curves showed clockwise loops (hysteresis) at self-selected slow speeds that reduced essentially to zero as the speed increased to self-selected normal speeds. Above self-selected normal speeds, the loops started to traverse a counter-clockwise path that increased in area as the speed was increased. These characteristics imply that the human ankle joint could be effectively replaced with a rotational spring and damper for slow to normal walking speeds. However, to mimic the characteristics of the human ankle during walking at fast speeds, an augmented system would be necessary. This notion is supported by the sign of the ankle power at the time of opposite heel contact, which was negative for slow speeds, was near zero at normal speeds, and was positive for fast walking speeds.     

The effects of walking speed on obstacle crossing in healthy young and healthy older adults

The effects of walking speed and age on the peak external moments generated about the joints of the trailing limb during stance just prior to stepping over an obstacle and on the kinematics of the trailing limb when crossing the obstacle were investigated in 10 healthy young adults (YA) and 10 healthy older adults (OA). The peak hip and knee adduction moments in OA were 21-43% greater than those in YA (p相似文献   

Estimation of passive ankle joint moment during standing and walking

This study estimated the passive ankle joint moment during standing and walking initiation and its contribution to total ankle joint moment during that time. The decrement of passive joint moment due to muscle fascicle shortening upon contraction was taken into account. Muscle fascicle length in the medial gastrocnemius, which was assumed to represent muscle fascicle length in plantarflexors, was measured using ultrasonography during standing, walking initiation, and cyclical slow passive ankle joint motion. Total ankle joint moment during standing and walking initiation was calculated from ground reaction forces and joint kinematics. Passive ankle joint moment during the cyclical ankle joint motion was measured via a dynamometer. Passive ankle joint moment during standing and at the time (Tp) when the MG muscle-tendon complex length was longest in the stance phase during walking initiation were 2.3 and 5.4 Nm, respectively. The muscle fascicle shortened by 2.9 mm during standing compared with the length at rest, which decreased the contribution of passive joint moment from 19.9% to 17.4%. The muscle fascicle shortened by 4.3 mm at Tp compared with the length at rest, which decreased the contribution of passive joint moment from 8.0% to 5.8%. These findings suggest that (a) passive ankle joint moment plays an important role during standing and walking initiation even in view of the decrement of passive joint moment due to muscle fascicle shortening upon muscle contraction, and (b) muscle fascicle shortening upon muscle contraction must be taken into account when estimating passive joint moment during movements.     

Effect of walking speed on inter-joint coordination differs between young and elderly adults

Investigating inter-joint coordination at different walking speeds in young and elderly adults could provide insights to age-related changes in neuromuscular control of gait. We examined effects of walking speed and age on the pattern and variability of inter-joint coordination. Gait analyses of 10 young and 10 elderly adults were performed with different self-selected speeds, including a preferred, faster, and slower speed. Continuous relative phase (CRP), derived from phase planes of two adjacent joints, was used to assess the inter-joint coordination. CRP patterns were examined with cross-correlation measures and root-mean-square (RMS) differences when comparing ensemble mean curves of the faster or slower speed to preferred speed walking. Variability of coordination for each participant was assessed with the average value of all standard deviations calculated for each data point over a gait cycle from all CRP curves, namely the deviation phase (DP). For hip-knee CRP pattern, RMS differences were significantly greater between the slower and preferred walking speeds than between the faster and preferred walking speeds in young adults, but this was not found in elderly adults. Significant group differences in RMS differences and cross-correlation measures were detected in hip-knee CRP patterns between the slower and preferred walking speeds. No significant walking speed or age effects were detected for the knee-ankle CRP. Significant walking speed effects were also detected in hip-knee DP values. However, no significant group differences were detected for all three speeds. These findings suggested that young and elder adults compromise changes of walking speed with different neuromuscular control strategies.     

Contractile and elastic ankle joint muscular properties in young and older adults

The purpose of this study was to investigate age-related differences in contractile and elastic properties of both dorsi- (DF) and plantarflexor (PF) muscles controlling the ankle joint in young and older adults. Experimental data were collected while twelve young and twelve older male and female participants performed maximal effort isometric and isovelocity contractions on a dynamometer. Equations were fit to the data to give torque-angle (Tθ) and torque-angular velocity (Tω) relations. Muscle series-elasticity was measured during ramped dynamometer contractions using ultrasonography to measure aponeurosis extension as a function of torque; second order polynomials were used to characterize the torque-extension (TΔL) relation. The results showed no age differences in DF maximal torque and none for female PF; however, older males had smaller maximal PF torques compared to young males. In both muscle groups and genders, older adults had decreased concentric force capabilities. Both DF and PF TΔL relations were more nonlinear in the older adults. Older PF, but not DF muscles, were stiffer compared to young. A simple antagonism model suggested age-related differences in Tθ and Tω relations would be magnified if antagonistic torque contributions were included. This assessment of static, dynamic, and elastic joint properties affords a comprehensive view of age-related modifications in muscle function. Although many clinical studies use maximal isometric strength as a marker of functional ability, the results demonstrate that there are also significant age-related modifications in ankle muscle dynamic and elastic properties.     

The effects of gait strategy on metabolic rate and indicators of stability during downhill walking

When walking at a given speed, humans often appear to prefer gait patterns that minimize metabolic rate, thereby maximizing metabolic economy. However, recent experiments have demonstrated that humans do not maximize economy when walking downhill. The purpose of this study was to investigate whether this non-metabolically optimal behavior is the result of a trade-off between metabolic economy and gait stability. We hypothesized that humans have the ability to modulate their gait strategy to increase either metabolic economy or stability, but that increase in one measure will be accompanied by decrease in the other. Subjects walked downhill using gait strategies ranging from risky to conservative, which were either prescribed by verbal instructions or induced by the threat of perturbations. We quantified spatiotemporal gait characteristics, metabolic rate and several indicators of stability previously associated with fall risk: stride period variability; step width variability; Lyapunov exponents; Floquet multipliers; and stride period fractal index. When subjects walked using conservative gait strategies, stride periods and lengths decreased, metabolic rate increased, and anteroposterior maximum Lyapunov exponents increased, which has previously been interpreted as an indicator of decreased stability. These results do not provide clear support for the proposed trade-off between economy and stability, particularly when stability is approximated using complex metrics. However, several gait pattern changes previously linked to increased fall risk were observed when our healthy subjects walked with a conservative strategy, suggesting that these changes may be a response to, rather than a cause of, increased fall risk.     

The neuromuscular demands of toe walking: a forward dynamics simulation analysis

Toe walking is a gait deviation with multiple etiologies and often associated with premature and prolonged ankle plantar flexor electromyographic activity. The goal of this study was to use a detailed musculoskeletal model and forward dynamical simulations that emulate able-bodied toe and heel-toe walking to understand why, despite an increase in muscle activity in the ankle plantar flexors during toe walking, the internal ankle joint moment decreases relative to heel-toe walking. The simulations were analyzed to assess the force generating capacity of the plantar flexors by examining each muscle's contractile state (i.e., the muscle fiber length, velocity and activation). Consistent with experimental measurements, the simulation data showed that despite a 122% increase in soleus muscle activity and a 76% increase in gastrocnemius activity, the peak internal ankle moment in late stance decreased. The decrease was attributed to non-optimal contractile conditions for the plantar flexors (primarily the force-length relationship) that reduced their ability to generate force. As a result, greater muscle activity is needed during toe walking to produce a given muscle force level. In addition, toe walking requires greater sustained plantar flexor force and moment generation during stance. Thus, even though toe walking requires lower peak plantar flexor forces that might suggest a compensatory advantage for those with plantar flexor weakness, greater neuromuscular demand is placed on those muscles. Therefore, medical decisions concerning whether to reduce equinus should consider not only the impact on the ankle moment, but also the expected change to the plantar flexor's force generating capacity.     

Contractile and non-contractile tissue volume and distribution in ankle muscles of young and older adults

Magnetic resonance imaging (MRI) enables accurate in vivo quantification of human muscle volumes, which can be used to estimate subject-specific muscle force capabilities. An important consideration is the amount of contractile and non-contractile tissue in the muscle compartment, which will influence force capability. We quantified age-related differences in the proportion and distribution of contractile and non-contractile tissue in the dorsiflexor and plantar flexor (soleus, and medial and lateral heads of gastrocnemius) muscles, and examined how well these volumes can be estimated from single MRI cross-sections. Axial MRIs of the left leg for 12 young (mean age 27 years) and 12 older (72 years) healthy, active adults were used to compute muscle volumes. Contractile tissue distribution along the leg was characterized by mathematical functions to allow volume prediction from single-slice cross-sectional area (CSA) measurements. Compared to young, older adults had less contractile volume and a greater proportion of non-contractile tissue. In both age groups the proportion of non-contractile tissue increased distally, with the smallest proportion near the maximum compartment CSA. A single CSA measurement predicted contractile volume with 8-11% error, with older adults in the higher end of this range. Using multiple slices improved volume estimates by roughly 50%, with average errors of about 3-4%. These results demonstrate significant age-related differences in non-contractile tissue for the dorsi- and plantar-flexor muscles. Although estimates of contractile volume can be obtained from single CSA measurements, multiple slices are needed for increased accuracy due to inter-individual variations in muscle volume and composition.     

The influence of mechanical injury on the metabolic activity of transplanted cerebral cortex.

The authors studied the metabolic activity of rat embryonic cerebral cortex grafts (ED 15-16) implanted into rat brains immediately (TR0) and 14 days (TR14) after cavity formation. Over a period of two months, the ATP, lactate and glucose concentration in TR0 transplants remained at the same level as observed in the intact cortex, whereas in TR14 transplants the ATP and glucose concentration fell significantly and the lactate concentration rose. The DNA concentration rose in both types of transplants, but the increase was more pronounced in TR0 grafts. Choline acetyltransferase activity (a neuron marker) fell significantly in both cases, but the decrease was greater in TR14 transplants. The results indicate that grafts implanted into the brain immediately after cavities had been formed have better metabolic activity and are capable of longer survival than grafts implanted 14 days after cavitation.     

Effect of unilateral load carriage on postures and gait symmetry in ground reaction force during walking

Unilateral load carriage is more hazardous to the musculoskeletal system than bilateral load. The purpose of this study was to examine the effect of such asymmetric carriage on postures and gait symmetry in ground reaction force (GRF) during walking. Kinematics and GRF of 19 adults were recorded while they walked under five load conditions: no load, dumbbell (10 and 20% body weight) held in right and left hand, respectively. After loading, the trunk bent towards the loaded or unloaded side in right- and left-hand trials and under different load weight conditions. The amplitude of trunk bend increased with load, accompanied by decreased stride width, progressively inclined legs towards unloaded side and higher level of asymmetry in medial/lateral GRF (GRFm/l) and free vertical moment GRF (GRFm). The findings indicate the postural adjustment is likely related to the characteristics of load and the task experience and handedness of subject and the unilateral load increases the gait asymmetry in GRFm/l and GRFm.     

Maximal mechanical power output and capacity of cyclists and young adults

The maximal average power output (Wmax) has been examined in 10 male students, 22 pursuit and 12 sprint cyclists. In 24 of these subjects (8 students, 10 pursuit and 6 sprint cyclists), estimates of the maximal capacity (Wcap) of the short-term anaerobic energy yielding processes were made. The results show that the sprinters had a higher absolute Wmax (1241 +/- 266 W) and Wcap (16.7 +/- 4.9 kJ) than either the students (1019 +/- 183 W, 14.7 +/- 2.8 kJ) or the pursuit cyclists (962 +/- 206 W, 14.0 +/- 2.9 kJ). However, the differences were removed when the values were standardised for muscle size. In the sprinters the Wmax was attained at an optimal pedal frequency Vopt of 132 +/- 3 min-1 and the estimated maximal velocity of pedalling (V0) was 262 +/- 8 min-1. The comparable figures in the students and pursuit cyclists were 118 +/- 8 min-1, 235 +/- 17 min-1 and 122 +/- 6 min-1, 242 +/- 12 min-1 respectively. The coefficient of variation of duplicate measurements of Wcap was found to be +/- 9%. Using data of Wilkie (1968) for muscle phosphagen and glycolytic stores (27 mmol.kg-1), it was estimated that the probable efficiency of the anaerobic processes during maximal cycling was 0.22. It was concluded that Wmax and Wcap are largely determined by body size and muscularity. The efficiency of anaerobiosis appears to be of the same order of magnitude as found for oxidative work.     

Margins of stability in young adults with traumatic transtibial amputation walking in destabilizing environments

Understanding how lower-limb amputation affects walking stability, specifically in destabilizing environments, is essential for developing effective interventions to prevent falls. This study quantified mediolateral margins of stability (MOS) and MOS sub-components in young individuals with traumatic unilateral transtibial amputation (TTA) and young able-bodied individuals (AB). Thirteen AB and nine TTA completed five 3-min walking trials in a Computer Assisted Rehabilitation ENvironment (CAREN) system under each of three test conditions: no perturbations, pseudo-random mediolateral translations of the platform, and pseudo-random mediolateral translations of the visual field. Compared to the unperturbed trials, TTA exhibited increased mean MOS and MOS variability during platform and visual field perturbations (p<0.010). AB exhibited increased mean MOS during visual field perturbations and increased MOS variability during both platform and visual field perturbations (p<0.050). During platform perturbations, TTA exhibited significantly greater values than AB for mean MOS (p<0.050) and MOS variability (p<0.050); variability of the lateral distance between the center of mass (COM) and base of support at initial contact (p<0.005); mean and variability of the range of COM motion (p<0.010); and variability of COM peak velocity (p<0.050). As determined by mean MOS and MOS variability, young and otherwise healthy individuals with transtibial amputation achieved lateral stability similar to that of their able-bodied counterparts during unperturbed and visually-perturbed walking. However, based on mean and variability of MOS, unilateral transtibial amputation was shown to have affected lateral walking stability during platform perturbations.     

The influence of the fixed negative charges on mechanical and electrical behaviors of articular cartilage under unconfined compression

Unconfined compression test has been frequently used to study the mechanical behaviors of articular cartilage, both theoretically and experimentally. It has also been used in explant and gel-cell-complex studies in tissue engineering. In biphasic and poroelastic theories, the effect of charges fixed on the proteoglycan macromolecules in articular cartilage is embodied in the apparent compressive Young's modulus and the apparent Poisson's ratio of the tissue, and the fluid pressure is considered to be the portion above the osmotic pressure. In order to understand how proteoglycan fixed charges might affect the mechanical behaviors of articular cartilage, and in order to predict the osmotic pressure and electric fields inside the tissue in this experimental configuration, it is necessary to use a model that explicitly takes into account the charged nature of the tissue and the flow of ions within its porous interstices. In this paper, we used a finite element model based on the triphasic theory to study how fixed charges in the porous-permeable soft tissue can modulate its mechanical and electrochemical responses under a step displacement in unconfined compression. The results from finite element calculations showed that: 1) A charged tissue always supports a larger load than an uncharged tissue of the same intrinsic elastic moduli. 2) The apparent Young's modulus (the ratio of the equilibrium axial stress to the axial strain) is always greater than the intrinsic Young's modulus of an uncharged tissue. 3) The apparent Poisson's ratio (the negative ratio of the lateral strain to the axial strain) is always larger than the intrinsic Poisson's ratio of an uncharged tissue. 4) Load support derives from three sources: intrinsic matrix stiffness, hydraulic pressure and osmotic pressure. Under the unconfined compression, the Donnan osmotic pressure can constitute between 13%-22% of the total load support at equilibrium. 5) During the stress-relaxation process following the initial instant of loading, the diffusion potential (due to the gradient of the fixed charge density and the associated gradient of ion concentrations) and the streaming potential (due to fluid convection) compete against each other. Within the physiological range of material parameters, the polarity of the electric potential depends on both the mechanical properties and the fixed charge density (FCD) of the tissue. For softer tissues, the diffusion effects dominate the electromechanical response, while for stiffer tissues, the streaming potential dominates this response. 6) Fixed charges do not affect the instantaneous strain field relative to the initial equilibrium state. However, there is a sudden increase in the fluid pressure above the initial equilibrium osmotic pressure. These new findings are relevant and necessary for the understanding of cartilage mechanics, cartilage biosynthesis, electromechanical signal transduction by chondrocytes, and tissue engineering.     

The influence of footwear on the electromyographic activity of selected lower limb muscles during walking

The purpose of this study was to compare the effects of a standard flexible shoe and a stability running shoe on lower limb muscle activity during walking. Twenty-eight young asymptomatic adults with flat-arched feet were recruited. While walking, electromyographic (EMG) activity was recorded from tibialis posterior and peroneus longus via intramuscular electrodes; and from tibialis anterior and medial gastrocnemius via surface electrodes. Three experimental conditions were assessed: (i) barefoot, (ii) a standard flexible shoe, (iii) a stability running shoe. Results showed significant differences for the peak amplitude and the time of peak amplitude for tibialis anterior, peroneus longus and medial gastrocnemius when comparing the three experimental conditions (p < 0.05). Significant differences were detected primarily between the barefoot and shoe conditions and with relatively small effect sizes for peroneus longus, tibialis anterior and medial gastrocnemius. Few significant differences were found between the two shoe styles. We discuss how these changes are most likely associated with the shoe upper bracing the foot, the shape of the shoe outer-sole and weight of the shoes. Further research is needed to investigate differences between these shoe styles when participants walk for longer distances (i.e. over 1000 m) and following fatigue.     

Energetics and passive dynamics of the ankle in downhill walking

This study investigated the energetics of the human ankle during the stance phase of downhill walking with the goal of modeling ankle behavior with a passive spring and damper mechanism. Kinematic and kinetic data were collected on eight male participants while walking down a ramp with inclination varying from 0° to 8°. The ankle joint moment in the sagittal plane was calculated using inverse dynamics. Mechanical energy injected or dissipated at the ankle joint was computed by integrating the power across the duration of the stance phase. The net mechanical energy of the ankle was approximately zero for level walking and monotonically decreased (i.e., became increasingly negative) during downhill walking as the slope decreased. The indication is that the behavior of the ankle is energetically passive during downhill walking, playing a key role in dissipating energy from one step to the next. A passive mechanical model consisting of a pin joint coupled with a revolute spring and damper was fit to the ankle torque and its parameters were estimated for each downhill slope using linear regression. The passive model demonstrated good agreement with actual ankle dynamics as indicated by low root-mean-square error values. These results indicate the stance phase behavior of the human ankle during downhill walking may be effectively duplicated by a passive mechanism with appropriately selected spring and damping characteristics.