Walk-run Transition Research Articles

Effects of walking, running, and skipping under simulated reduced gravity using the NASA Active Response Gravity Offload System (ARGOS)

Past research efforts have focused on the energy difference between altered locomotion methods in reduced gravity at different speeds, suggesting that skipping is energetically more efficient than walking and running in these environments. While skipping may be more beneficial from an energy standpoint, the full range of reasons behind the gait transition and locomotion selection have not been researched. This includes damage to the leg muscles, which is partially prevented by a transition from walking to running locomotion methods known as the walk-run transition. In a space environment, these factors will play a role in astronaut health and injury prevention. Participants walked, ran, and skipped on a treadmill for this study while being supported by an analog for activity on other planets called the Active Response Gravity Offload System (ARGOS). These intervals were performed under 1g, then under simulated 0.38g, and 0.17g conditions to simulate gravity conditions on Mars and the Moon. Electromyography was used to monitor muscle activation, along with the Vicon motion capture system for 3D motion analysis. Results show that there are significant changes (p <0.05) in activation of the TA and MG under simulated Martian and Lunar gravity conditions, as well as significant changes (p <0.05) in dorsiflexion and plantar flexion under several conditions. These findings suggest that there are fundamental changes in the way humans move in these reduced gravity environments and that the effect these changes have on the body should be included in the development of astronaut training regimen and equipment development. These changes may affect safety issues associated with locomotion, including increased trip and fall risks. Additionally, the reduction of energy expenditure demonstrated in this study, as well as detrimental effects from gait asymmetry on muscle growth, may prove to be counterproductive to efforts meant to reduce muscle and bone degradation in reduced gravity environments. The efficacy of running or skipping as preferred methods of locomotion in reduced gravity environments are yet to be sufficiently supported by gait analysis.

Why do we transition from walking to running? Energy cost and lower leg muscle activity before and after gait transition under body weight support.

BackgroundMinimization of the energetic cost of transport (CoT) has been suggested for the walk-run transition in human locomotion. More recent literature argues that lower leg muscle activities are the potential triggers of the walk-run transition. We examined both metabolic and muscular aspects for explaining walk-run transition under body weight support (BWS; supported 30% of body weight) and normal walking (NW), because the BWS can reduce both leg muscle activity and metabolic rate.MethodsThirteen healthy young males participated in this study. The energetically optimal transition speed (EOTS) was determined as the intersection between linear CoT and speed relationship in running and quadratic CoT-speed relationship in walking under BWS and NW conditions. Preferred transition speed (PTS) was determined during constant acceleration protocol (velocity ramp protocol at 0.00463 m·s−2 = 1 km·h−1 per min) starting from 1.11 m·s−1. Muscle activities and mean power frequency (MPF) were measured using electromyography of the primary ankle dorsiflexor (tibialis anterior; TA) and synergetic plantar flexors (calf muscles including soleus) before and after the walk-run transition.ResultsThe EOTS was significantly faster than the PTS under both conditions, and both were faster under BWS than in NW. In both conditions, MPF decreased after the walk-run transition in the dorsiflexor and the combined plantar flexor activities, especially the soleus.DiscussionThe walk-run transition is not triggered solely by the minimization of whole-body energy expenditure. Walk-run transition is associated with reduced TA and soleus activities with evidence of greater slow twitch fiber recruitment, perhaps to avoid early onset of localized muscle fatigue.

The scaling or ontogeny of human gait kinetics and walk-run transition: The implications of work vs. peak power minimization

A simple model is developed to find vertical force profiles and stance durations that minimize either limb mechanical work or peak power demands during bipedal locomotion. The model predicts that work minimization is achieved with a symmetrical vertical force profile, consistent with previous models and observations of adult humans, and data for 487 participants (predominantly 11–18 years old) required to walk at a range of speeds at a Science Fair. Work minimization also predicts the discrete walk-run transition, familiar for adult humans. In contrast, modeled peak limb mechanical power demands are minimized with an early skew in vertical ground reaction force that increases with speed, and stance durations that decrease steadily with speed across the work minimizing walk-run transition speed. The peak power minimization model therefore predicts a continuous walk-run gait transition that is quantitatively consistent with measurements of younger children (1.1–4.7 years) required to locomote at a range of speeds but free to select their own gaits.

The influence of speed and size on avian terrestrial locomotor biomechanics: Predicting locomotion in extinct theropod dinosaurs.

How extinct, non-avian theropod dinosaurs moved is a subject of considerable interest and controversy. A better understanding of non-avian theropod locomotion can be achieved by better understanding terrestrial locomotor biomechanics in their modern descendants, birds. Despite much research on the subject, avian terrestrial locomotion remains little explored in regards to how kinematic and kinetic factors vary together with speed and body size. Here, terrestrial locomotion was investigated in twelve species of ground-dwelling bird, spanning a 1,780-fold range in body mass, across almost their entire speed range. Particular attention was devoted to the ground reaction force (GRF), the force that the feet exert upon the ground. Comparable data for the only other extant obligate, striding biped, humans, were also collected and studied. In birds, all kinematic and kinetic parameters examined changed continuously with increasing speed, while in humans all but one of those same parameters changed abruptly at the walk-run transition. This result supports previous studies that show birds to have a highly continuous locomotor repertoire compared to humans, where discrete ‘walking’ and ‘running’ gaits are not easily distinguished based on kinematic patterns alone. The influences of speed and body size on kinematic and kinetic factors in birds are developed into a set of predictive relationships that may be applied to extinct, non-avian theropods. The resulting predictive model is able to explain 79–93% of the observed variation in kinematics and 69–83% of the observed variation in GRFs, and also performs well in extrapolation tests. However, this study also found that the location of the whole-body centre of mass may exert an important influence on the nature of the GRF, and hence some caution is warranted, in lieu of further investigation.

Interplay between Stride Velocity, Stride Frequency and Stride Length in Human Gait Transition

This paper presents the results of studying human gait transition outside the laboratory setting on a treadmill by means of wearable sensor technology. Combined inertial measurement and pressure sensor units embedded in footwear were employed to analyze the movement of the lower limbs during walk-run and run-walk transitions. Experimental data from 20 subjects was used to study three parameters - stride velocity, stride length and stride frequency. We focused on seven strides centered around the transition stride, that is, the stride in-between walking and running that has only a single floating phase. Three subjects underwent additional testing on a treadmill to capture the differences in kinematics between the two environments. The stride frequency varied least with both a subject’s individual transition behavior and the environment. The former can be concluded from the standard deviations evaluated for each stride, which were lower for stride frequency than for velocity and length. The latter was derived by comparing the results from within and outside the laboratory: Stride frequency shifted similarly in both cases, mainly within 2-4 strides, to the attractor of the new gait. Velocity profiles differed, with acceleration being more uniform and much lower on the treadmill. Stride lengths were inversely proportional: In the walk-run transition, when the belt of the treadmill was sped up, stride lengths decreased. In the run-walk transition, when the belt was slowed down, stride lengths increased. This phenomenon is attributable mainly to the dominant nature of the stride frequency, which forces changes in stride length in order to fulfill the velocity constraint. A non-laboratory environment lacks such a constraint, thus giving rise to free transition behavior. Stride frequency, being easy to measure, is well suited to analyzing and defining gait in a practical context.

Using step width to compare locomotor biomechanics between extinct, non-avian theropod dinosaurs and modern obligate bipeds.

How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width-the mediolateral (transverse) distance between successive footfalls-was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods (p < 0.001), as well as the five tallest bird species studied (p < 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk-run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history.

Locomotion Mode Affects the Physiological Strain during Exercise at Walk-Run Transition Speed inElderly Men

This study investigated cardiorespiratory responses and rating of perceived exertion (RPE) during prolonged walking and running exercise performed at the walk-run transition speed (WRTS) in untrained healthy elderly men. 20 volunteers (mean±SE, age: 68.4±1.2 yrs; height: 170.0±0.02 cm; body mass: 74.7±2.3 kg) performed the following bouts of exercise: a) maximal cardiopulmonary exercise test (CPET); b) specific protocol to detect WRTS; and c) two 30-min walking and running bouts at WRTS. Expired gases were collected during exercise bouts via the Ultima CardiO2 metabolic analyzer. Compared to walking, running at the WRTS resulted in higher oxygen uptake (>0.27 L·min-1), pulmonary ventilation (>7.7 L·min-1), carbon dioxide output (>0.23 L·min-1), heart rate (>15 beats·min-1), oxygen pulse (>0.88 15 mL·beats-1), energy expenditure (>27 kcal) and cost of oxygen transport (>43 mL·kg-1·km-1·bout-1). The increase of overall and local RPEs with exercise duration was similar across locomotion modes (P<0.001). In all participants, %HRR and %VO2R throughout walking and running bouts were around or above the gas exchange threshold. In conclusion, elderly men exhibited higher cardiorespiratory responses during 30-min bouts of running than walking at WRTS. Nevertheless, walking corresponded to relative metabolic intensities compatible with preservation or improvement of cardiorespiratory fitness and should be preferable over running at WRTS in the untrained elderly characterized by poor fitness and reduced exercise tolerance.

Preferred gait and walk-run transition speeds in ostriches measured using GPS-IMU sensors.

The ostrich (Struthio camelus) is widely appreciated as a fast and agile bipedal athlete, and is a useful comparative bipedal model for human locomotion. Here, we used GPS-IMU sensors to measure naturally selected gait dynamics of ostriches roaming freely over a wide range of speeds in an open field and developed a quantitative method for distinguishing walking and running using accelerometry. We compared freely selected gait-speed distributions with previous laboratory measures of gait dynamics and energetics. We also measured the walk-run and run-walk transition speeds and compared them with those reported for humans. We found that ostriches prefer to walk remarkably slowly, with a narrow walking speed distribution consistent with minimizing cost of transport (CoT) according to a rigid-legged walking model. The dimensionless speeds of the walk-run and run-walk transitions are slower than those observed in humans. Unlike humans, ostriches transition to a run well below the mechanical limit necessitating an aerial phase, as predicted by a compass-gait walking model. When running, ostriches use a broad speed distribution, consistent with previous observations that ostriches are relatively economical runners and have a flat curve for CoT against speed. In contrast, horses exhibit U-shaped curves for CoT against speed, with a narrow speed range within each gait for minimizing CoT. Overall, the gait dynamics of ostriches moving freely over natural terrain are consistent with previous lab-based measures of locomotion. Nonetheless, ostriches, like humans, exhibit a gait-transition hysteresis that is not explained by steady-state locomotor dynamics and energetics. Further study is required to understand the dynamics of gait transitions.

Physiological strain to prolonged exercise bouts at the walk-run transition speeds depends on locomotion mode in healthy untrained men.

This study compared the physiological strain induced by prolonged walking and running performed at the walk-run transition speed (WRTS) in healthy untrained men. Twenty volunteers (age: 28±5.01years; height: 174.0 ±0.3cm; body mass: 74.5±0.6kg) underwent the following: (a) ramp-incremental maximal cardiopulmonary exercise test (CPET); (b) specific protocol to detect the WRTS; and (c) two 30-min walking and running bouts at WRTS (mean±SD: 6.9±0.06km/h). Expired gases were collected during exercise bouts via the metabolic cart. A significant effect of locomotion mode (F=4.8, P<0.001) was observed with running resulting in higher cardiorespiratory responses than walking at the WRTS (oxygen uptake: mean difference=0.26L/min; pulmonary ventilation: mean difference=5.53L/min; carbon dioxide output: mean difference=0.32L/min; heart rate: mean difference=13 beats/min; total energy expenditure: mean difference=59kcal). The rating of perceived exertion was similar across locomotion modes (mean difference=0.3; P=0.490). In conclusion, running promoted greater cardiorespiratory responses than walking at the WRTS in untrained healthy men. These data might have practical impact on aerobic training performed at intensities corresponding to WRTS.

Neuromuscular effort predicts walk-run transition speed in normal and adapted human gaits.

Often, humans and other animals move in a manner that minimizes energy costs. It is more economical to walk at slow speeds, and to run at fast speeds. Here, we asked whether humans select a gait that minimizes neuromuscular effort under novel and unfamiliar conditions, by imposing interlimb asymmetry during split-belt treadmill locomotion. The walk-run transition speed changed markedly across different gait conditions: forward, backward, hybrid (one leg forward, one leg backward) and forward with speed differences (one leg faster than the other). Most importantly, we showed that the human walk-run transition speed across conditions was predicted by changes in neuromuscular effort (i.e. summed leg muscle activations). Our results for forward gait and forward gait with speed differences suggest that human locomotor patterns are optimized under both familiar and novel gait conditions by minimizing the motor command for leg muscle activation.

Estimation of Walk-Run Transition Speed and Oxygen Consumption on Planets of Solar System

The present work has analyzed and discussed the effect of gravitational force on the walk-run transition speed on the planets of the solar system. A walk-run transition speed at different gravity level has been calculated. Our results suggested that by increasing gravity level, the walk-run transition speed occurred at faster speed whereas the corresponding Froude numbers remain constant in normal and high gravities. The most significant effect of gravity on the Froude number was observed for the planets with gravity lower than the earth. In addition, the rates of oxygen consumption at the walk-run transition speed for these celestial objects have been predicted. The results showed that the rate of oxygen consumption for the planets are at the highest for those which have a gait transition at Froude number of greater than 0.5.

Vaulting mechanics successfully predict decrease in walk-run transition speed with incline.

There is an ongoing debate about the reasons underlying gait transition in terrestrial locomotion. In bipedal locomotion, the ‘compass gait’, a reductionist model of inverted pendulum walking, predicts the boundaries of speed and step length within which walking is feasible. The stance of the compass gait is energetically optimal—at walking speeds—owing to the absence of leg compression/extension; completely stiff limbs perform no work during the vaulting phase. Here, we extend theoretical compass gait vaulting to include inclines, and find good agreement with previous observations of changes in walk–run transition speed (approx. 1% per 1% incline). We measured step length and frequency for humans walking either on the level or up a 9.8 per cent incline and report preferred walk–run, walk–compliant-walk and maximum walk–run transition speeds. While the measured ‘preferred’ walk–run transition speed lies consistently below the predicted maximum walking speeds, and ‘actual’ maximum walking speeds are clearly above the predicted values, the onset of compliant walking in level as well as incline walking occurs close to the predicted values. These findings support the view that normal human walking is constrained by the physics of vaulting, but preferred absolute walk–run transition speeds may be influenced by additional factors.

Gait transitions in simulated reduced gravity

Gravity has a strong effect on gait and the speed of gait transitions. A gait has been defined as a pattern of locomotion that changes discontinuously at the transition to another gait. On Earth, during gradual speed changes, humans exhibit a sudden discontinuous switch from walking to running at a specific speed. To study the effects of altered gravity on both the stance and swing legs, we developed a novel unloading exoskeleton that allows a person to step in simulated reduced gravity by tilting the body relative to the vertical. Using different simulation techniques, we confirmed that at lower gravity levels the transition speed is slower (in accordance with the previously reported Froude number ∼0.5). Surprisingly, however, we found that at lower levels of simulated gravity the transition between walking and running was generally gradual, without any noticeable abrupt change in gait parameters. This was associated with a significant prolongation of the swing phase, whose duration became virtually equal to that of stance in the vicinity of the walk-run transition speed, and with a gradual shift from inverted-pendulum gait (walking) to bouncing gait (running).

Walk-Run Transition Speed Training as an Efficient Exercise Adjunct to Dietary Restriction in the Management of Obesity: A Prospective Intervention Pilot Study

Objective: The aim of this study was to test the utility of preferred walk-run transition speed (WRTS) in exercise training adjunct to dietary restriction for obesity management in healthy obese women. Materials and Methods: 37 obese women (age: 35 ± 9 years, body mass index (BMI): 34.9 ± 4.6 kg/m²) were assigned to an intervention pilot study during 6 months of restricted diet alone (RD) followed by 6 months of RD combined with WRTS (RD and WRTS) as a training exercise. Body mass, waist circumference (WC), fat mass (FM), fat free mass (FFM), active cell mass (ACM), fasting glucose, serum lipids (triacylglycerol (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), apo-lipoproteins A1 (ApoA1) and B (ApoB)], leptin and insulin concentrations, and HOMA-IR were assessed at baseline (T0), at the end of the RD alone (T1), and at the end of the RD and WRTS programme (T2). Results: Mean weight loss was 8.6 ± 4.9 kg and 2.2 ± 2.9 kg for (T0-T1) and (T1-T2), respectively. Significant BMI and WC reductions were reported at T1 and T2. FM decreased significantly both with RD and with RD and WRTS training whereas FFM and ACM increased with RD and WRTS training only. TG decreased significantly with the two phases of the programme. A significant increase in HDL-C, and a decrease in LDL-C and TC/HDL-C ratio were noticed with RD and WRTS training. Heart rate monitored in training improved significantly after RD and WRTS training. A significant relationship (r = 0.542, p < 0.02) was demonstrated between reductions in serum leptin and insulin concentrations observed with both RD and WRTS training. Conclusion: The addition of WRTS training to RD promoted a greater reduction in body mass, WC, FM, leptin and insulin concentrations, improved metabolic and cardiovascular risk factors, and enhanced cardiovascular fitness.

Variability of cardio-respiratory, electromyographic, and perceived exertion responses at the walk-run transition in a sample of young men controlled for anthropometric and fitness characteristics

The cardio-respiratory (heart rate, HR; oxygen uptake, VO(2;) expired carbon dioxide, VCO(2); ventilation, VE), electromyographic (EMG; medial gastrocnemius, vastus lateralis, rectus femoralis, and anterior tibialis), and perceived exertion (PE) responses during a protocol for the determination of the walk-run transition speed (WRTS) were investigated. From an initial sample of 453 volunteers, 12 subjects matched for age, anthropometric characteristics [height, weight, lower limb length (LLL)], cardio-respiratory fitness (peak oxygen consumption, VO(2peak); ventilatory threshold, VT; maximal HR), and habitual physical activity levels were selected (age = 18.6 ± 0.5 years; height = 174.5 ± 1.4 cm; weight = 66.4 ± 1.1 kg; LLL = 83.3 ± 1.2 cm, VO(2peak) = 52.2 ± 2.2 ml kg(-1) min(-1); VT = 39.8 ± 2.6 ml kg(-1) min(-1)). The highly reproducible WRTS determination protocol (ICC = 0.92; p < 0.0001) consisted in 2-min warm-up at 5.5 km h(-1) followed by increments of 0.1 km h(-1) every 15 s. Between-subjects variability of the measured variables during 24 walking and 12 running velocities (from 80 to 120% of WRTS) was compared to WRTS variation. The coefficient of variation for WRTS was 7.8%, which was within the range of variability for age, anthropometric variables, VO(2peak), and maximal HR (from 5 to 12%). Cardio-respiratory responses at WRTS had a greater variation (VO(2) about 50%; VE/VCO(2) about 35%; VE/VO(2) about 45%; HR about 30%). The highest variation was found for PE (from 70 to 90%) whereas EMG variables showed the lowest variation (from 25 to 30%). Linear regression between EMG series and VO(2) data showed that VO(2) reflected the increase in muscle activity only before the WRTS. These results support the hypothesis that the walk-run transition phenomenon is determined by mechanical variables such as limb length and its relationship to biomechanical model rather than by metabolic factors.

Walk–run transition in young and older adults: with special reference to the cardio-respiratory responses

Cardio-respiratory responses of young and older subjects performing walking and running protocols at the walk-run transition speed (WRT) were compared. A total of 26 volunteers assigned to younger (YG, 24 +/- 3 years) and older (OG, 64 +/- 6 years) groups underwent a protocol to determine the WRT used in 6-min walking and running protocols. Oxygen uptake (VO(2)), ventilation (V (E)), expired carbon dioxide (VCO(2)), heart rate (HR) and perceived exertion (RPE) were assessed. Oxygen pulse (O(2) pulse) and respiratory exchange ratio (RER) were calculated. The WRT was not different between groups (OG: 6.84 +/- 0.69 km h(-1) vs. YG: 7.04 +/- 0.77 km h(-1), P = 0.62). No between-group differences were found within a given gait pattern for VO(2) (P = 0.061) and VCO(2) (P = 0.076). However, VO(2) (P = 0.0022) and VCO(2) (P = 0.0041) increased in OG when running, remaining stable in YG (VO(2): P = 0.622; VCO(2): P = 0.412). The VE was higher in OG compared to YG in walking (P = 0.030) and running (P = 0.004) protocols. No age-related (P = 0.180) or locomotion (P = 0.407) effects were found for RER. The HR increased in OG and between-group difference was detected while running (P = 0.003). No within- (P = 0.447) or between-group (P = 0.851) difference was found for O(2) pulse. The net VO(2) increased from walking to running in OG (P < 0.0001) but not in YG (P = 0.53), while RPE was lower in YG (P = 0.041) but stable in OG (P = 0.654). In conclusion, the WRT speed was similar across the age groups. However, the VO(2) and VCO(2) increase from walking to running was larger for OG than YG. The HR, VE and RPE were also higher when running in OG compared to YG. Therefore, the locomotion strategy had different impacts on the metabolic demand of older and younger subjects.

Respostas cardiorrespiratórias e perceptivas para as mesmas velocidades de caminhada e corrida

It is possible that different forms of locomotion, when carried out at the same speed, may have a distinct influence on the physiological and perceptual responses to exercise.To compare the cardiorespiratory responses and the subjective perception of the effort to walk and run at the same speed, as determined from the walk-run transition speed (WRTS).From an initial sample of 453 subjects enrolled in the compulsory military service, 12 young adult men were selected and carefully homogenized as to age, sex, anthropometric characteristics, aerobic condition and experience in a treadmill. In preliminary sessions, the individual WRTS was determined. Thereafter, on three different days, the subjects walked and ran in balanced order, in each of the following speeds: WRTS; WRTS - 0.5 km/h; WRTS + 0.5 km/h, so as to obtain exhaled gases, heart rate (HR) and perception of effort measurements.The protocol for WRTS detection was highly reproducible (r = 0.92, p <0.05). In an intensity of exercise above the WRTS, the perceived effort, the HR, and the ventilatory variables-VE, VO2, VCO2 and R-showed higher values during walking than during running (p <0.05), whereas at the WRTS and at the speed of 0.5 km/h below WRTS, the form of locomotion did not affect the cardiorespiratory and perceptual variables (p > 0.05).Walking at a speed above the WRTS tends to be more stressful to the subject, from a physiological and perceptual point of view. It seems appropriate to individualize the WRTS and standardize the form of locomotion for determining a more accurate and physiological intensity of the aerobe exercises.

The Apollo Number: Space Suits, Self-Support, and the Walk-Run Transition

BackgroundHow space suits affect the preferred walk-run transition is an open question with relevance to human biomechanics and planetary extravehicular activity. Walking and running energetics differ; in reduced gravity (<0.5 g), running, unlike on Earth, uses less energy per distance than walking.Methodology/Principal FindingsThe walk-run transition (denoted *) correlates with the Froude Number (Fr = v2/gL, velocity v, gravitational acceleration g, leg length L). Human unsuited Fr* is relatively constant (∼0.5) with gravity but increases substantially with decreasing gravity below ∼0.4 g, rising to 0.9 in 1/6 g; space suits appear to lower Fr*. Because of pressure forces, space suits partially (1 g) or completely (lunar-g) support their own weight. We define the Apollo Number (Ap = Fr/M) as an expected invariant of locomotion under manipulations of M, the ratio of human-supported to total transported mass. We hypothesize that for lunar suited conditions Ap* but not Fr* will be near 0.9, because the Apollo Number captures the effect of space suit self-support. We used the Apollo Lunar Surface Journal and other sources to identify 38 gait events during lunar exploration for which we could determine gait type (walk/lope/run) and calculate Ap. We estimated the binary transition between walk/lope (0) and run (1), yielding Fr* (0.36±0.11, mean±95% CI) and Ap* (0.68±0.20).Conclusions/SignificanceThe Apollo Number explains 60% of the difference between suited and unsuited Fr*, appears to capture in large part the effects of space suits on the walk-run transition, and provides several testable predictions for space suit locomotion and, of increasing relevance here on Earth, exoskeleton locomotion. The knowledge of how space suits affect gait transitions can be used to optimize space suits for use on the Moon and Mars.

Comparing two devices of suspended treadmill walking by varying body unloading and Froude number

In rehabilitation, treadmill walking with body weight support is commonly used to reduce loads on lower extremities. (1) However, gait pattern alterations during unloading at constant Froude number are infrequently reported. (2) Furthermore, differences between two common devices for unloading are not well known. Therefore, we investigated two devices; a waist-high chamber with increased pressure called Lower Body Positive Pressure (LBPP), and a harness system (LiteGait), considered a standard system for unloading the lower body. Four gait parameters (cadence, normalized stride length, duty factor, and leg angle at touch down), heart rate, and comfort level were monitored in 12 healthy volunteers. Subjects walked at three body weight (BW) conditions (100%, 66%, and 33% BW) and three Froude numbers (Fr), which refer to a dimensionless speed reflecting slow walking (Fr = 0.09), comfortable walking (Fr = 0.25), and walk–run transition (Fr = 0.5). Absolute treadmill speed was determined using Froude numbers reflecting dynamically similar motions during unloading. We found that (1) the normal gait pattern is altered during unloading at a constant Froude number. In rehabilitation, physical therapists should be aware that normal gait pattern may not need to be maintained during unloaded treadmill walking. (2) Gait parameters were not different when comparing LBPP to harness supported walking. However, heart rate was lower and comfort higher during unloaded LBPP ambulation compared to suspended harness walking. Therefore, suspended LBPP walking may be more appropriate for patients with cardiovascular disease and for conditions at high unloading.

Influence of Shock Waves and Muscle Activity at Initial Contact on Walk–Run Transition Evaluated by Two Models

The walk-run transition (WRT) is a well-described phenomenon without any known cause; however, mechanical variables related to human gait have been associated with the WRT. This study tested the hypothesis that shock waves in the tibia and 3rd lumbar vertebra in addition to activity of tibialis anterior, vastus lateralis, and erector spinae muscles could be responsible for the WRT. Thirty subjects walked and ran on a treadmill at 80%, 90%, 100%, 110%, and 120% of preferred transition speed. Shock waves were measured with skin-mounted accelerometers and muscle activity by surface electromyography. The influence on the WRT was analyzed with two models. The shock waves and muscle activity tended to a significant increase (p < .05) for both walking and running with increased speed. The only factor that appeared to be involved in the WRT mechanism was the activity of the tibialis anterior; however, this was only confirmed by one of the two models. The use of different models to analyze the same data for the WRT triggers may give different results; thus, a standard model is required to investigate the influence of given factors on biological phenomena.