Lumbar and abdominal muscle activity during walking in subjects with chronic low back pain: Support of the “guarding” hypothesis?

It has been hypothesized that changes in trunk muscle activity in chronic low back pain (CLBP) reflect an underlying “guarding” mechanism, which will manifest itself as increased superficial abdominal – and lumbar muscle activity. During a functional task like walking, it may be further provoked at higher walking velocities. The purpose of this cross sectional study was to investigate whether subjects with CLBP show increased co-activation of superficial abdominal – and lumbar muscles during walking on a treadmill, when compared to asymptomatic controls. Sixty-three subjects with CLBP and 33 asymptomatic controls walked on a treadmill at different velocities. Surface electromyography data of the erector spinae, rectus abdominis and obliquus abdominis externus muscles were obtained and averaged per stride. Results show that, compared to asymptomatic controls, subjects with CLBP have increased muscle activity of the erector spinae and rectus abdominis, but not of the obliquus abdominis externus. These differences in trunk muscle activity between groups do not increase with higher walking velocities. In conclusion, the observed increased trunk muscle activity in subjects with CLBP during walking supports the guarding hypothesis.     

Energy expenditure of bipedal walking is higher than that of quadrupedal walking in Japanese macaques

The authors previously compared energetic costs of bipedal and quadrupedal walking in bipedally trained macaques used for traditional Japanese monkey performances (Nakatsukasa et al. 2004 Am. J. Phys. Anthropol. 124:248-256). These macaques used inverted pendulum mechanics during bipedal walking, which resulted in an efficient exchange of potential and kinetic energy. Nonetheless, energy expenditure during bipedal walking was significantly higher than that of quadrupedal walking. In Nakatsukasa et al. (2004 Am. J. Phys. Anthropol. 124:248-256), locomotor costs were measured before subjects reached a steady state due to technical limitations. The present investigation reports sequential changes of energy consumption during 15 min of walking in two trained macaques, using carbon dioxide production as a proxy of energy consumption, as in Nakatsukasa et al. (2004 Am. J. Phys. Anthropol. 124:248-256). Although a limited number of sessions were conducted, carbon dioxide production was consistently greater during bipedal walking, with the exception of some irregularity during the first minute. Carbon dioxide production gradually decreased after 1 min, and both subjects reached a steady state within 10 min. Energy expenditure during bipedalism relative to quadrupedalism differed between the two subjects. It was considerably higher (140% of the quadrupedal walking cost) in one subject who walked with more bent-knee, bent-hip gaits. This high cost strongly suggests that ordinary macaques, who adopt further bent-knee, bent-hip gaits, consume a far greater magnitude of energy during bipedal walking.     

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.     

Subject-specific axes of the ankle joint complex

The aim of this study was to use a two-axis ankle joint model and an optimisation process (van den Bogert et al., 1994) to calculate and compare the talocrural and subtalar hinge axes for non-weight-bearing ankle motion, weight-bearing ankle motion, and walking in normal, healthy adult subjects and to see which of the first two sets of axes better fit the walking data. Motion data for the foot and shank were collected on eight subjects whilst they performed the activities mentioned. After choosing the best marker sets for motion tracking, a two-hinge ankle joint model was fit to the motion data. Ankle joint ranges of motion were also calculated. It was found that the model fit the experimental data well, with non-weight-bearing motion achieving the best fit. Despite this, the calculated axis orientations were highly variable both between motion types and between subjects. No significant difference between the fit of the non-weight-bearing and weight-bearing models to the walking data was found, which implies that either set of functional axes is adequate for modeling walking; however, the subtalar deviation angle was significantly closer for the weight-bearing activity and walking than for the non-weight-bearing activity and walking, which suggests that it is marginally better to use the weight-bearing functional motions. The results lead to questions about the appropriateness of the two-hinge ankle model for use in applications in which the behaviour of the individual joints of the ankle complex, rather than simply the relative motion of the leg and foot, is important.     

Differences in muscle function during walking and running at the same speed

Individual muscle contributions to body segment mechanical energetics and the functional tasks of body support and forward propulsion in walking and running at the same speed were quantified using forward dynamical simulations to elucidate differences in muscle function between the two different gait modes. Simulations that emulated experimentally measured kinesiological data of young adults walking and running at the preferred walk-to-run transition speed revealed that muscles use similar biomechanical mechanisms to provide support and forward propulsion during the two tasks. The primary exception was a decreased contribution of the soleus to forward propulsion in running, which was previously found to be significant in walking. In addition, the soleus distributed its mechanical power differently to individual body segments between the two gait modes from mid- to late stance. In walking, the soleus transferred mechanical energy from the leg to the trunk to provide support, but in running it delivered energy to both the leg and trunk. In running, earlier soleus excitation resulted in it working in synergy with the hip and knee extensors near mid-stance to provide the vertical acceleration for the subsequent flight phase in running. In addition, greater power output was produced by the soleus and hip and knee extensors in running. All other muscle groups distributed mechanical power among the body segments and provided support and forward propulsion in a qualitatively similar manner in both walking and running.     

The physiological cost of carrying light and heavy loads

Nine subjects walked on a treadmill with load weights equal to 10% and 40% of body weight carried on the back. Although the speed of the treadmill was selected so that the measured oxygen consumption (VO2) was the same for both load conditions, the heavier load placed an extra strain on the cardiopulmonary system and was perceived by all subjects as harder work than the lighter load. When the subjects worked at their own pace, walking on a level road or climbing stairs with load weights equal to 10% and 40% of body weight, they compensated for the heavier load by decreasing walking speed or climbing rate. Although the energy costs calculated from walking speed, body and load weight for self-paced walking and the external work of stair climbing were the same for both load conditions, the heavier load was again perceived as harder work. These findings are discussed as they relate to the definition of acceptable load weights.     

Do highly trained monkeys walk like humans? A kinematic study of bipedal locomotion in bipedally trained Japanese macaques

In this study, we examined the kinematics of bipedal walking in macaque monkeys that have been highly trained to stand and walk bipedally, and compared them to the kinematics of bipedal walking in ordinary macaques. The results revealed that the trained macaques walked with longer and less frequent strides than ordinary subjects. In addition, they appear to have used inverted pendulum mechanics during bipedal walking, which resulted in an efficient exchange of potential and kinetic energy. These gait characteristics resulted from the relatively more extended hindlimb joints of the trained macaques. By contrast, the body of the ordinary macaques translated downward during the single-limb stance phase due to more flexed hindlimb joints. This resulted in almost in-phase fluctuations of potential and kinetic energy, which indicated that energy transformation was less efficient in the ordinary macaques. The findings provide two insights into the early stage of the evolution of human bipedalism. First, the finding that training considerably improved bipedal walking a posteriori may explain why the very first bipeds that might not yet have been morphologically adapted to bipedal walking continued to walk bipedally. The evolutionary transition from quadrupedalism to bipedalism might not be as difficult as has been envisioned. In addition, the finding that macaques, which are phylogenetically distant from humans and in which bipedal walking is unlike human walking, could develop humanlike gait characteristics with training, provides strong support for the commonly held but unproven idea that the characteristics of the human gait are advantageous to human bipedalism.     

Energy exchange between subject and belt during treadmill walking

Treadmill walking aims to simulate overground walking, but intra-stride belt speed variations of treadmills result in some interaction between treadmill and subject, possibly obstructing this aim. Especially in self-paced treadmill walking, in which the belt speed constantly adjusts to the subject, these interactions might affect the gait pattern significantly. The aim of this study was to quantify the energy exchange between subject and treadmill, during the fixed speed (FS) and self-paced (SP) modes of treadmill walking. Eighteen subjects walked on a dual-belt instrumented treadmill at both modes. The energy exchange was calculated as the integration of the product of the belt speed deviation and the fore-aft ground reaction force over the stride cycle. The total positive energy exchange was 0.44 J/stride and the negative exchange was 0.11 J/stride, which was both less than 1.6% of the performed work on the center of mass. Energy was mainly exchanged from subject to treadmill during both the braking and propulsive phase of gait. The two treadmill modes showed a similar pattern of energy exchange, with a slightly increased energy exchange during the braking phase of SP walking. It is concluded that treadmill walking is only mildly disturbed by subject-belt interactions when using instrumented treadmills with adequate belt control.     

Energy of gait in below-knee casts with different soles

This study aims to provide some guidelines for the use of soles on below-knee walking casts. Whole-body energy changes during the single limb support phase of the gait cycle have been quantified in twenty volunteer subjects fitted with below-knee casts and each wearing one of five soles in turn. Simple gait analysis was carried out with a Kistler force plate and an Apple II microcomputer, the date were sampled at 50 Hz. Three commerical soles and two ‘home made’ ones were used; it was generally found that the commercial products produced a more energy efficient gait. Some recommendations are included regarding the design of soles to be used in this clinically demanding situation.     

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.     

Physiological and metabolic responses to a hill walk.

The physiological and metabolic demands of hill walking have not been studied systematically in the field despite the potentially deleterious physiological consequences of activity sustained over an entire day. On separate occasions, 13 subjects completed a self-paced hill walk over 12 km, consisting of a range of gradients and terrain typical of a mountainous walk. During the hill walk, continuous measurements of rectal (T(re)) and skin (T(sk)) temperatures and of respiratory gas exchange were made to calculate the total energy expenditure. Blood samples, for the analysis of metabolites and hormones, were taken before breakfast and lunch and immediately after the hill walk. During the first 5 km of the walk (100- to 902-m elevation), T(re) increased (36.9 +/- 0.2 to 38.5 +/- 0.4 degrees C) with a subsequent decrease in mean T(sk) from this time point. T(re) decreased by approximately 1.0 degrees C during a 30-min stop for lunch, and it continued to decrease a further 0.5 degrees C after walking recommenced. The total energy intake from both breakfast and lunch [5.6 +/- 0.7 (SE) MJ] was lower than the energy expended [14.5 +/- 0.5 (SE) MJ; P < 0.001] during the 12-km hill walk. Despite the difference in energy intake and expenditure, blood glucose concentration was maintained. The major source of energy was an enhanced fat oxidation, probably from adipose tissue lipolysis reflected in high plasma nonesterified fatty acid concentrations. The major observations were the varying thermoregulatory responses and the negative energy balance incurred during the hill walk. It is concluded that recreational hill walking can constitute a significant metabolic and thermoregulatory strain on participants.     

Bionic ankle-foot prosthesis normalizes walking gait for persons with leg amputation

Over time, leg prostheses have improved in design, but have been incapable of actively adapting to different walking velocities in a manner comparable to a biological limb. People with a leg amputation using such commercially available passive-elastic prostheses require significantly more metabolic energy to walk at the same velocities, prefer to walk slower and have abnormal biomechanics compared with non-amputees. A bionic prosthesis has been developed that emulates the function of a biological ankle during level-ground walking, specifically providing the net positive work required for a range of walking velocities. We compared metabolic energy costs, preferred velocities and biomechanical patterns of seven people with a unilateral transtibial amputation using the bionic prosthesis and using their own passive-elastic prosthesis to those of seven non-amputees during level-ground walking. Compared with using a passive-elastic prosthesis, using the bionic prosthesis decreased metabolic cost by 8 per cent, increased trailing prosthetic leg mechanical work by 57 per cent and decreased the leading biological leg mechanical work by 10 per cent, on average, across walking velocities of 0.75-1.75 m s(-1) and increased preferred walking velocity by 23 per cent. Using the bionic prosthesis resulted in metabolic energy costs, preferred walking velocities and biomechanical patterns that were not significantly different from people without an amputation.     

The effect of repeated bouts of backward walking on physiologic efficiency

Previous studies have demonstrated an increased energy expenditure with novel tasks. With practice, the energy cost decreases as the body more efficiently recruits motor units. This study examined whether one becomes more efficient after repeated bouts of backward walking. The subjects were 7 healthy subjects between the ages of 23 and 49 years. A backward walking speed was calculated to elicit a VO(2) equal to 60% of the VO(2)max. There were 18 training sessions at the prescribed walking speed 3 d x wk(-1) for 20 min x d(-1). The backward walking speed required to elicit a fixed VO(2) increased between weeks 4 and 6 of the training period. This finding suggests that backward walking is indeed a novel task and that motor learning occurs as a result of practice, leading to a more efficient recruitment of motor units.     

Nonexercise movement in elderly compared with young people

The association between free-living daily activity and aging is unclear because nonexercise movement and its energetic equivalent, nonexercise activity thermogenesis, have not been exhaustively studied in the elderly. We wanted to address the hypothesis that free-living nonexercise movement is lower in older individuals compared with younger controls matched for lean body mass. Ten lean, healthy, sedentary elderly and 10 young subjects matched for lean body mass underwent measurements of nonexercise movement and body posture over 10 days using sensitive, validated technology. In addition, energy expenditure was assessed using doubly labeled water and indirect calorimetry. Total nonexercise movement (acceleration arbitrary units), standing time, and standing acceleration were significantly lower in the elderly subjects; this was specifically because the elderly walked less distance per day despite having a similar number of walking bouts per day compared with the young individuals. The energetic cost of basal metabolic rate, thermic effect of food, total daily energy expenditure, and nonexercise activity thermogenesis were not different between the elderly and young groups. Thus, the energetic cost of walking in the elderly may be greater than in the young. Lean, healthy elderly individuals may have a biological drive to be less active than the young.     

Modeling and optimal control of an energy-storing prosthetic knee

Advanced prosthetic knees for transfemoral amputees are currently based on controlled damper mechanisms. Such devices require little energy to operate, but can only produce negative or zero joint power, while normal knee joint function requires alternative phases of positive and negative work. The inability to generate positive work may limit the user's functional capabilities, may cause undesirable adaptive behavior, and may contribute to excessive metabolic energy cost for locomotion. In order to overcome these problems, we present a novel concept for an energy-storing prosthetic knee, consisting of a rotary hydraulic actuator, two valves, and a spring-loaded hydraulic accumulator. In this paper, performance of the proposed device will be assessed by computational modeling and by simulation of functional activities. A computational model of the hydraulic system was developed, with methods to obtain optimal valve control patterns for any given activity. The objective function for optimal control was based on tracking of joint angles, tracking of joint moments, and the energy cost of operating the valves. Optimal control solutions were obtained, based on data collected from three subjects during walking, running, and a sit-stand-sit cycle. Optimal control simulations showed that the proposed device allows near-normal knee function during all three activities, provided that the accumulator stiffness was tuned to each activity. When the energy storage mechanism was turned off in the simulations, the system functioned as a controlled damper device and optimal control results were similar to literature data on human performance with such devices. When the accumulator stiffness was tuned to walking, simulated performance for the other activities was sub-optimal but still better than with a controlled damper. We conclude that the energy-storing knee concept is valid for the three activities studied, that modeling and optimal control can assist the design process, and that further studies using human subjects are justified.     

Effects of arm swing on mechanical parameters of human gait

The aim of this study was to investigate the influence of the upper limb swing on human gait. Measurements were performed on 52 subjects by using the Elite system with two cameras and a Kistler force platform. The recording of trajectories of characteristic body points on the subjects and the measurement of ground reaction forces have been performed at normal walking and at walking with emphasised rhythmic upper limb swing. The trajectory of the whole body mass centre, central dynamic moments of inertia and ground reaction forces have been calculated for every subject and mean curves of the entire group have been determined for walking with the natural and the emphasised upper limb swing. The determined mean values of normalised mechanical parameters have been compared and differences between the gait with the natural and the emphasised upper limb swing have been described.     

Modular control of human walking: A simulation study

Recent evidence suggests that performance of complex locomotor tasks such as walking may be accomplished using a simple underlying organization of co-active muscles, or “modules”, which have been assumed to be structured to perform task-specific biomechanical functions. However, no study has explicitly tested whether the modules would actually produce the biomechanical functions associated with them or even produce a well-coordinated movement. In this study, we generated muscle-actuated forward dynamics simulations of normal walking using muscle activation modules (identified using non-negative matrix factorization) as the muscle control inputs to identify the contributions of each module to the biomechanical sub-tasks of walking (i.e., body support, forward propulsion, and leg swing). The simulation analysis showed that a simple neural control strategy involving five muscle activation modules was sufficient to perform the basic sub-tasks of walking. Module 1 (gluteus medius, vasti, and rectus femoris) primarily contributed to body support in early stance while Module 2 (soleus and gastrocnemius) contributed to both body support and propulsion in late stance. Module 3 (rectus femoris and tibialis anterior) acted to decelerate the leg in early and late swing while generating energy to the trunk throughout swing. Module 4 (hamstrings) acted to absorb leg energy (i.e., decelerate it) in late swing while increasing the leg energy in early stance. Post-hoc analysis revealed an additional module (Module 5: iliopsoas) acted to accelerate the leg forward in pre- and early swing. These results provide evidence that the identified modules can act as basic neural control elements that generate task-specific biomechanical functions to produce well-coordinated walking.     

The relationship between physical fitness and ambulatory activity in very elderly women with normal functioning and functional limitations

The effect of daily ambulatory activity on physical fitness has not yet been identified by quantitatively measuring the time spent on the intensity levels of ambulatory activity in elderly women over 75 with different functional capacity levels. The subjects consisted of 147 elderly women over 75 years old (82.8±4.3 years old) who were all capable of performing basic daily activities by themselves. Physical fitness was measured for 7 items (handgrip strength, knee extensor strength, postural stability, stepping, one-legged standing time with eyes open, 10 m walking, and the Timed Up and Go Test). The subjects wore a triaxial accelerometer for 2 consecutive weeks to measure their daily physical activities. The functional capacity level was assessed by the Tokyo Metropolitan Institute of Gerontology Index of Competence. The subjects were divided into two groups, a group with a score ≥10 points (high functional capacity group, n=59) and a score <10 points (low functional capacity group, n=88), and the relationship between physical fitness and physical activity was examined in both groups. In both the high and low functional capacity groups, 10 m walking, the Timed Up and Go Test, and one-legged standing time with eyes open significantly correlated with either the total steps/day or the ambulatory activity intensity. In the high functional capacity group, the knee extensor strength also significantly correlated with the total steps/day and moderate ambulatory activity. It is suggested that very elderly women with a reduced functional capacity should maintain their mobility by simply increasing their daily ambulatory activity.     

Individual limb work does not explain the greater metabolic cost of walking in elderly adults.

Elderly adults consume more metabolic energy during walking than young adults. Our study tested the hypothesis that elderly adults consume more metabolic energy during walking than young adults because they perform more individual limb work on the center of mass. Thus we compared how much individual limb work young and elderly adults performed on the center of mass during walking. We measured metabolic rate and ground reaction force while 10 elderly and 10 young subjects walked at 5 speeds between 0.7 and 1.8 m/s. Compared with young subjects, elderly subjects consumed an average of 20% more metabolic energy (P=0.010), whereas they performed an average of 10% less individual limb work during walking over the range of speeds (P=0.028). During the single-support phase, elderly and young subjects both conserved approximately 80% of the center of mass mechanical energy by inverted pendulum energy exchange and performed a similar amount of individual limb work (P=0.473). However, during double support, elderly subjects performed an average of 17% less individual limb work than young subjects (P=0.007) because their forward speed fluctuated less (P=0.006). We conclude that the greater metabolic cost of walking in elderly adults cannot be explained by a difference in individual limb work. Future studies should examine whether a greater metabolic cost of stabilization, reduced muscle efficiency, greater antagonist cocontraction, and/or a greater cost of generating muscle force cause the elevated metabolic cost of walking in elderly adults.     

Effects of aging and arm swing on the metabolic cost of stability in human walking

To gain insight into the mechanical determinants of walking energetics, we investigated the effects of aging and arm swing on the metabolic cost of stabilization. We tested two hypotheses: (1) elderly adults consume more metabolic energy during walking than young adults because they consume more metabolic energy for lateral stabilization, and (2) arm swing reduces the metabolic cost of stabilization during walking in young and elderly adults. To test these hypotheses, we provided external lateral stabilization by applying bilateral forces (10% body weight) to a waist belt via elastic cords while young and elderly subjects walked at 1.3m/s on a motorized treadmill with arm swing and with no arm swing. We found that the external stabilizer reduced the net rate of metabolic energy consumption to a similar extent in elderly and young subjects. This reduction was greater (6-7%) when subjects walked with no arm swing than when they walked normally (3-4%). When young or elderly subjects eliminated arm swing while walking with no external stabilization, net metabolic power increased by 5-6%. We conclude that the greater metabolic cost of walking in elderly adults is not caused by a greater cost of lateral stabilization. Moreover, arm swing reduces the metabolic cost of walking in both young and elderly adults likely by contributing to stability.