Energy cost and muscular activity required for propulsion during walking.

We reasoned that with an optimal aiding horizontal force, the reduction in metabolic rate would reflect the cost of generating propulsive forces during normal walking. Furthermore, the reductions in ankle extensor electromyographic (EMG) activity would indicate the propulsive muscle actions. We applied horizontal forces at the waist, ranging from 15% body weight aiding to 15% body weight impeding, while subjects walked at 1.25 m/s. With an aiding horizontal force of 10% body weight, 1) the net metabolic cost of walking decreased to a minimum of 53% of normal walking, 2) the mean EMG of the medial gastrocnemius (MG) during the propulsive phase decreased to 59% of the normal walking magnitude, and yet 3) the mean EMG of the soleus (Sol) did not decrease significantly. Our data indicate that generating horizontal propulsive forces constitutes nearly half of the metabolic cost of normal walking. Additionally, it appears that the MG plays an important role in forward propulsion, whereas the Sol does not.     

Energy cost of walking and running at extreme uphill and downhill slopes.

The costs of walking (Cw) and running (Cr) were measured on 10 runners on a treadmill inclined between -0.45 to +0.45 at different speeds. The minimum Cw was 1.64 +/- 0.50 J. kg(-1). m(-1) at a 1.0 +/- 0.3 m/s speed on the level. It increased on positive slopes, attained 17.33 +/- 1.11 J. kg(-1). m(-1) at +0.45, and was reduced to 0.81 +/- 0.37 J. kg(-1). m(-1) at -0.10. At steeper slopes, it increased to reach 3.46 +/- 0.95 J. kg(-1). m(-1) at -0.45. Cr was 3.40 +/- 0.24 J. kg(-1). m(-1) on the level, independent of speed. It increased on positive slopes, attained 18.93 +/- 1.74 J. kg(-1). m(-1) at +0.45, and was reduced to 1.73 +/- 0.36 J. kg(-1). m(-1) at -0.20. At steeper slopes, it increased to reach 3.92 +/- 0.81 J. kg(-1). m(-1) at -0.45. The mechanical efficiencies of walking and running above +0.15 and below -0.15 attained those of concentric and eccentric muscular contraction, respectively. The optimum gradients for mountain paths approximated 0.20-0.30 for both gaits. Downhill, Cr was some 40% lower than reported in the literature for sedentary subjects. The estimated maximum running speeds on positive gradients corresponded to those adopted in uphill races; on negative gradients they were well above those attained in downhill competitions.     

Energy cost and muscular activity required for leg swing during walking.

To investigate the metabolic cost and muscular actions required for the initiation and propagation of leg swing, we applied a novel combination of external forces to subjects walking on a treadmill. We applied a forward pulling force at each foot to assist leg swing, a constant forward pulling force at the waist to provide center of mass propulsion, and a combination of these foot and waist forces to evaluate leg swing. When the metabolic cost and muscle actions were at a minimum, the condition was considered optimal. We reasoned that the difference in energy consumption between the optimal combined waist and foot force trial and the optimal waist force-only trial would reflect the metabolic cost of initiating and propagating leg swing during normal walking. We also reasoned that a lower muscle activity with these assisting forces would indicate which muscles are normally responsible for initiating and propagating leg swing. With a propulsive force at the waist of 10% body weight (BW), the net metabolic cost of walking decreased to 58% of normal walking. With the optimal combination, a propulsive force at the waist of 10% BW plus a pulling force at the feet of 3% BW the net metabolic cost of walking further decreased to 48% of normal walking. With the same combination, the muscle activity of the iliopsoas and rectus femoris muscles during the swing phase was 27 and 60% lower, respectively, but the activity of the medial gastrocnemius and soleus before swing did not change. Thus our data indicate that approximately 10% of the net metabolic cost of walking is required to initiate and propagate leg swing. Additionally, the hip flexor muscles contribute to the initiation and propagation leg swing.     

Energy cost of treadmill and floor walking at self-selected paces

Oxygen uptake-velocity regression equations were developed for floor and level treadmill walking by having two groups of men, aged 19-29 years (n = 20) and 55-66 years (n = 22), walk at four self-selected paces, from "rather slowly" to "as fast as possible". A two-variable quadratic model relating VO2 (ml X kg-1 X min-1) to velocity (m X s-1) was adopted for prediction purposes. However, age and fatness significantly (P less than 0.05) interacted with treadmill walking speed, while age alone significantly interacted with floor speed. In addition, a significant difference was found between the energy cost of floor and treadmill walking. For example at the normal walking speed of 1.33 m X s-1, the energy cost for the treadmill (age 55-66 years) was 10.58 ml X kg-1 X min-1 and for the floor, 11.04 ml X kg-1 X min-1 (P less than 0.05). Four quadratic equations are therefore presented, one each for floor and treadmill in each of the two age-groups. The percent variance explained was between 87 and 95% for each of these equations.     

Speed training with body weight unloading improves walking energy cost and maximal speed in 75- to 85-year-old healthy women.

This randomized controlled study was designed to prove the hypothesis that a novel approach to high-speed interval training, based on walking on a treadmill with the use of body weight unloading (BWU), would have improved energy cost and speed of overground walking in healthy older women. Participants were randomly assigned to either the exercise group (n = 11, 79.6 +/- 3.7 yr, mean +/- SD) or the nonintervention control group (n = 11, 77.6 +/- 2.3 yr). During the first 6 wk, the exercise group performed walking interval training on the treadmill with 40% BWU at the maximal walking speed corresponding to an intensity close to heart rate at ventilatory threshold (T(vent) walking speed). Each session consisted of four sets of 5 min of walking (three 1-min periods at T(vent) walking speed, with two 1-min intervals at comfortable walking speed in between each period at T(vent) walking speed) with 1-min interval between each set. Speed was increased session by session until the end of week 6. BWU was then progressively reduced to 10% during the last 6 wk of intervention. After 12 wk, the walking energy cost per unit of distance at all self-selected overground walking speeds (slow, comfortable, and fast) was significantly reduced in the range from 18 to 21%. The exercise group showed a 13% increase in maximal walking speed and a 67% increase in mechanical power output at T(vent) after the training program. The novel "overspeed" training approach has been demonstrated to be effective in improving energy cost and speed of overground walking in healthy older women.     

Energy cost of balance control during walking decreases with external stabilizer stiffness independent of walking speed

Human walking requires active neuromuscular control to ensure stability in the lateral direction, which inflicts a certain metabolic load. The magnitude of this metabolic load has previously been investigated by means of passive external lateral stabilization via spring-like cords. In the present study, we applied this method to test two hypotheses: (1) the effect of external stabilization on energy cost depends on the stiffness of the stabilizing springs, and (2) the energy cost for balance control, and consequently the effect of external stabilization on energy cost, depends on walking speed. Fourteen healthy young adults walked on a motor driven treadmill without stabilization and with stabilization with four different spring stiffnesses (between 760 and 1820 N m⁻¹) at three walking speeds (70%, 100%, and 130% of preferred speed). Energy cost was calculated from breath-by-breath oxygen consumption. Gait parameters (mean and variability of step width and stride length, and variability of trunk accelerations) were calculated from kinematic data. On average external stabilization led to a decrease in energy cost of 6% (p<0.005) as well as a decrease in step width (24%; p<0.001), step width variability (41%; p<0.001) and variability of medio-lateral trunk acceleration (12.5%; p<0.005). Increasing stabilizer stiffness increased the effects on both energy cost and medio-lateral gait parameters up to a stiffness of 1260 N m⁻¹. Contrary to expectations, the effect of stabilization was independent of walking speed (p=0.111). These results show that active lateral stabilization during walking involves an energetic cost, which is independent of walking speed.     

Effect of walking speed changes on tibialis anterior EMG during healthy gait for FES envelope design in drop foot correction.

Functional electrical stimulation may be used to correct hemiplegic drop foot. An optimised stimulation envelope to reproduce the EMG pattern observed in the tibialis anterior (TA) during healthy gait has been proposed by O'Keeffe et al. [O'Keeffe, D.T., Donnelly, A.E., Lyons, G.M., 2003. The development of a potential optimised stimulation intensity envelope for drop foot applications. IEEE Transactions on Neural Systems and Rehabilitation Engineering]. However this envelope did not attempt to account for changes in TA activity with walking speed. The objective of this paper was to provide data to enable the specification of an algorithm to control the adaptation of an envelope with walking speed. Ten young healthy subjects walked on a treadmill at 11 different walking speeds while TA EMG was recorded. The results showed that TA EMG recorded around initial contact and at toe off changed with walking speed. At the slowest velocities, equivalent to hemiplegic walking, the toe-off burst (TOB) of EMG activity had larger peak amplitude than that of the heel-strike burst (HSB). The peak amplitude ratio of TOB:HSB was 1:0.69 at the slowest speed compared to, 1:1.18 and 1:1.5 for the self-selected and fastest speed, respectively. These results suggest that an FES envelope, which produces larger EMG amplitude for the TOB than the HSB, would be more appropriate at walking speeds typical of hemiplegic patients.     

Determination of microgram quantities of protein in 65-80 percent salt solutions

Due to the necessity of determining microgram quantities of protein in 65–80% salt solutions, a combination of gel filtration and low-ultraviolet absorption of proteins was investigated as a possible solution to this problem. Such a system is described and includes a spectrophotometer equipped with a strip-chart recorder to continuously monitor a Sephadex G-25 column. Also the construction of a flow meter, and the proper method of applying samples to the column when they are in high-salt solutions is described. A wavelength of 220 nm was selected over lower wavelengths because of greater light intensity and less stray light. At this wavelength the absorption of proteins seems to be less sensitive to changes in the composition of one amino acid, such as tryptophan, and more closely related to the total content of aromatic residues and the number of peptide bonds. Excellent results were obtained when the areas of the eluting protein peaks, but not the peak heights, were used to quantitatively measure 7–50 μg of protein. Although this method cannot be easily adapted for routine analysis of very large numbers of samples, it has the advantage of being more sensitive than the Lowry method and allows for the accurate determination of microgram quantities of protein in solvent systems that would preclude the use of other methods.     

Biomechanics of overground vs. treadmill walking in healthy individuals.

The goal of this study was to compare treadmill walking with overground walking in healthy subjects with no known gait disorders. Nineteen subjects were tested, where each subject walked on a split-belt instrumented treadmill as well as over a smooth, flat surface. Comparisons between walking conditions were made for temporal gait parameters such as step length and cadence, leg kinematics, joint moments and powers, and muscle activity. Overall, very few differences were found in temporal gait parameters or leg kinematics between treadmill and overground walking. Conversely, sagittal plane joint moments were found to be quite different, where during treadmill walking trials, subjects demonstrated less dorsiflexor moments, less knee extensor moments, and greater hip extensor moments. Joint powers in the sagittal plane were found to be similar at the ankle but quite different at the knee and hip joints. Differences in muscle activity were observed between the two walking modalities, particularly in the tibialis anterior throughout stance, and in the hamstrings, vastus medialis and adductor longus during swing. While differences were observed in muscle activation patterns, joint moments and joint powers between the two walking modalities, the overall patterns in these behaviors were quite similar. From a therapeutic perspective, this suggests that training individuals with neurological injuries on a treadmill appears to be justified.     

Predicting the metabolic cost of incline walking from muscle activity and walking mechanics

The goal of this study was to identify which muscle activation patterns and gait features best predict the metabolic cost of inclined walking. We measured muscle activation patterns, joint kinematics and kinetics, and metabolic cost in sixteen subjects during treadmill walking at inclines of 0%, 5%, and 10%. Multivariate regression models were developed to predict the net metabolic cost from selected groups of the measured variables. A linear regression model including incline and the squared integrated electromyographic signals of the soleus and vastus lateralis explained 96% of the variance in metabolic cost, suggesting that the activation patterns of these large muscles have a high predictive value for metabolic cost. A regression model including only the peak knee flexion angle during stance phase, peak knee extension moment, peak ankle plantarflexion moment, and peak hip flexion moment explained 89% of the variance in metabolic cost; this finding indicates that kinematics and kinetics alone can predict metabolic cost during incline walking. The ability of these models to predict metabolic cost from muscle activation patterns and gait features points the way toward future work aimed at predicting metabolic cost when gait is altered by changes in neuromuscular control or the use of an assistive technology.     

Minimizing center of mass vertical movement increases metabolic cost in walking.

A human walker vaults up and over each stance limb like an inverted pendulum. This similarity suggests that the vertical motion of a walker's center of mass reduces metabolic cost by providing a mechanism for pendulum-like mechanical energy exchange. Alternatively, some researchers have hypothesized that minimizing vertical movements of the center of mass during walking minimizes the metabolic cost, and this view remains prevalent in clinical gait analysis. We examined the relationship between vertical movement and metabolic cost by having human subjects walk normally and with minimal center of mass vertical movement (flat-trajectory walking). In flat-trajectory walking, subjects reduced center of mass vertical displacement by an average of 69% (P = 0.0001) but consumed approximately twice as much metabolic energy over a range of speeds (0.7-1.8 m/s) (P = 0.0001). In flat-trajectory walking, passive pendulum-like mechanical energy exchange provided only a small portion of the energy required to accelerate the center of mass because gravitational potential energy fluctuated minimally. Thus, despite the smaller vertical movements in flat-trajectory walking, the net external mechanical work needed to move the center of mass was similar in both types of walking (P = 0.73). Subjects walked with more flexed stance limbs in flat-trajectory walking (P < 0.001), and the resultant increase in stance limb force generation likely helped cause the doubling in metabolic cost compared with normal walking. Regardless of the cause, these findings clearly demonstrate that human walkers consume substantially more metabolic energy when they minimize vertical motion.     

Effect of walking speed and severity of hip osteoarthritis on gait variability

Gait analysis in orthopaedic and neurological examinations is important; however, few studies assess gait variability at different walking speeds in patients with varying degrees of hip osteoarthritis. We aimed to clarify (1) how different controlled speeds and (2) various severities of hip osteoarthritis influence gait variability. Gait variability was described by the standard deviation (SD) of the spatial–temporal and mean standard deviation (MeanSD) of angular parameters. The spatial positions of the anatomical points for calculating gait parameters were determined in 20 healthy elderly controls and 20 patients with moderate and 20 patients with severe hip osteoarthritis with a zebris CMS-HS ultrasound-based motion analysis system at three walking speeds. The SD of the spatial–temporal and MeanSD of angular parameters of gait, which together describe gait variability, significantly depended on speed and osteoarthritis severity. The lowest variability in the gait was found near the self-selected walking speeds. Hip joint degeneration significantly worsened variability on the affected side, with non-affected joints and the pelvis compensating by increasing flexibility and adapting to step-by-step motions. Particular attention must be paid to improving gait stability and the reliability of limb movements in the presence of and increasing severity of osteoarthritis.     

Electromyographic analysis of walking in water in healthy humans

This study was designed to describe and clarify muscle activities which occur while walking in water. Surface electromyography (EMG) was used to evaluate muscle activities in six healthy subjects (mean age, 23.3 +/- 1.4 years) while they walked on a treadmill in water (with or without a water current) immersed to the level of the xiphoid process, and while they walked on a treadmill on dry land. The trials in water utilized the Flowmill which has a treadmill at the base of a water flume. Integrated EMG analysis was conducted for the quantification of muscle activities. In order to calculate the %MVC, the measurement of maximal voluntary contraction (MVC) of each muscle was made before the gait analysis, thus facilitating a comparison of muscle activities while walking in water with those on dry land. The %MVCs obtained from each of the tested muscles while walking in water, both with and without a water current, were all found to be lower than those obtained while walking on dry land at a level of heart rate response similar to that used when walking on dry land. Furthermore, the %MVCs while walking in water with a water current tended to be greater when compared to those while walking in water without a water current. In conclusion, the present study demonstrated that muscle activities while walking in water were significantly decreased when compared to muscle activities while walking on dry land, that muscle activities while walking in water tended to be greater with a water current than without, and that the magnitude of the muscle activity in water was relatively small in healthy humans. This information is important to design water-based exercise programs that can be safely applied for rehabilitative and recreational purposes.     

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   

Muscle mechanical advantage of human walking and running: implications for energy cost.

Muscular forces generated during locomotion depend on an animal's speed, gait, and size and underlie the energy demand to power locomotion. Changes in limb posture affect muscle forces by altering the mechanical advantage of the ground reaction force (R) and therefore the effective mechanical advantage (EMA = r/R, where r is the muscle mechanical advantage) for muscle force production. We used inverse dynamics based on force plate and kinematic recordings of humans as they walked and ran at steady speeds to examine how changes in muscle EMA affect muscle force-generating requirements at these gaits. We found a 68% decrease in knee extensor EMA when humans changed gait from a walk to a run compared with an 18% increase in hip extensor EMA and a 23% increase in ankle extensor EMA. Whereas the knee joint was extended (154-176 degrees) during much of the support phase of walking, its flexed position (134-164 degrees) during running resulted in a 5.2-fold increase in quadriceps impulse (time-integrated force during stance) needed to support body weight on the ground. This increase was associated with a 4.9-fold increase in the ground reaction force moment about the knee. In contrast, extensor impulse decreased 37% (P < 0.05) at the hip and did not change at the ankle when subjects switched from a walk to a run. We conclude that the decrease in limb mechanical advantage (mean limb extensor EMA) and increase in knee extensor impulse during running likely contribute to the higher metabolic cost of transport in running than in walking. The low mechanical advantage in running humans may also explain previous observations of a greater metabolic cost of transport for running humans compared with trotting and galloping quadrupeds of similar size.     

Effects of obesity and sex on the energetic cost and preferred speed of walking.

The metabolic energy cost of walking is determined, to a large degree, by body mass, but it is not clear how body composition and mass distribution influence this cost. We tested the hypothesis that walking would be most expensive for obese women compared with obese men and normal-weight women and men. Furthermore, we hypothesized that for all groups, preferred walking speed would correspond to the speed that minimized the gross energy cost per distance. We measured body composition, maximal oxygen consumption, and preferred walking speed of 39 (19 class II obese, 20 normal weight) women and men. We also measured oxygen consumption and carbon dioxide production while the subjects walked on a level treadmill at six speeds (0.50-1.75 m/s). Both obesity and sex affected the net metabolic rate (W/kg) of walking. Net metabolic rates of obese subjects were only approximately 10% greater (per kg) than for normal-weight subjects, and net metabolic rates for women were approximately 10% greater than for men. The increase in net metabolic rate at faster walking speeds was greatest in obese women compared with the other groups. Preferred walking speed was not different across groups (1.42 m/s) and was near the speed that minimized gross energy cost per distance. Surprisingly, mass distribution (thigh mass/body mass) was not related to net metabolic rate, but body composition (% fat) was (r2= 0.43). Detailed biomechanical studies of walking are needed to investigate whether obese individuals adopt novel energy saving mechanisms during walking.     

Energy cost and energy sources in karate

Energy costs and energy sources in karate (wado style) were studied in eight male practitioners (age 23.8 years, mass. 72.3 kg, maximal oxygen consumption (VO_2max) 36.8 ml · min^–1 · kg^–1) performing six katas (formal, organized movement sequences) of increasing duration (from approximately. 10 s to approximately 80 s). Oxygen consumption (VO₂) was determined during pre-exercise rest, the exercise period and the first 270 s of recovery in five consecutive expired gas collections. A blood sample for lactate (la^–) analysis was taken 5 min after the end of exercise. The overall amount of O₂ consumed during the exercise and in the following recovery increased linearly with the duration of exercise (t) from approximately 1.51 (for t equal to 10.5 s (SD 1.6)) to approximately 5.81, for t equal to 81.5 s (SD 1.0). The energy release from la^– production (VO_21a ^–) calculated assuming that an increase of 1 mmol · l^–1 la^– corresponded to a VO₂ of 3 mlO₂ · kg^–1 was negligible for t equal to or less than 20 s and increased to 17.3 ml · kg^–1 (la^– = 5.8 mmol · l^–1 above resting values) for t equal approximately to 80 s. The overall energy requirement (VO_2eq) as given by the sum of VO₂ and VO_2la ^– was described by VO_2eq = 0.87 + 0.071 · t (n = 64; r ² = 0.91), where VO_2eq is in litres and t in seconds. This equation shows that the metabolic power (VO_2eq · t ^–1) for this karate style is very high: from approximately 9.51 · min^–1 for t equal to 10 s to approximately 4.91 · min^–1 for t equal to 80 s, i.e. from 3.5 to 1.8 times the subjects' VO_2max. The fraction of VO_2eq derived from the amount of O₂ consumed during the exercise increased from 11% for t equal to 10 s to 41 % for t equal to 80 s whereas VO_21a ^– was negligible far t equal to or less than 20 s and increased to 13 % o for t equal to 80 s. The remaining fraction (from 90% for t equal to 10 s to 46% for t equal to 80 s), corresponding to the amount of O₂ consumed in the recovery after exercise, is derived from anaerobic alactic sources, i.e. from net splitting of high energy phosphates during the exercise.     

Energy cost of galactoside transport to Escherichia coli.

Energy reserves of Escherichia coli can be depleted by our previously reported procedure to a level such that even the "downhill" transport of o-nitrophenyl-beta-D-galactopyranoside (ONPG) is completely dependent upon the exogenous energy supply. The ONPG concentration is high externally to the cells and is low intracellular because of the action of cytoplasmic beta-galactosidase. In the present work, depleted cell suspensions have been infused at low, steady rates with glucose and other energy sources while measurements of transport were being made. Comparing the rate of ONPG transport with the rate of introduction of glucose under conditions where the chosen glucose infusion rate limits transport, we find that 89 molecules of ONPG are transported per molecule of fully oxidized glucose. This transport yield is constant over a 6.5-fold range in rate of glucose addition. This constancy over a range of infusion rates implies that transport is the major cellular function under these special conditions. The yield value if 89 is in the agreement with the predicitions of 76 from Mitchell's chemiosmotic theory and constitutes an independent proff of its validity, since all the other proposed mechanisms of engery coupling predict much smaller yields. The lag from the start of glucose infusion into the reaction cuvette, to the extrapolated time at which a steady rate of transport and concomitant hydrolysis are achieved, is short (approximately 1 min). Similarly, the time after the infusion is stopped until the rate of transport returns to the background rate is also short. The latter implies that the energy metabolism is directed almost entirely to transport and/or other ongoing cellular processes and not to repair or renewal of an energy-independent, facilitated diffusion system.     

The relative cost of bent-hip bent-knee walking is reduced in water

The debate about how early hominids walked may be characterised as two competing hypotheses: They moved with a fully upright (FU) gait, like modern humans, or with a bent-hip, bent-knee (BK) gait, like apes. Both have assumed that this bipedalism was almost exclusively on land, in trees or a combination of the two. Recent findings favoured the FU hypothesis by showing that the BK gait is 50–60% more energetically costly than a FU human gait on land. We confirm these findings but show that in water this cost differential is markedly reduced, especially in deeper water, at slower speeds and with greater knee flexion. These data suggest that the controversy about australopithecine locomotion may be eased if it is assumed that wading was a component of their locomotor repertoire and supports the idea that shallow water might have been an environment favourable to the evolution of early forms of “non-optimal” hominid bipedalism.