Using Cadence to Predict the Walk-to-Run Transition in Children and Adolescents: A Logistic Regression Approach.

The natural transition from walking to running occurs in adults at ≅140 steps/min. It is unknown when this transition occurs in children and adolescents. The purpose of this study was to develop a model to predict age- and anthropometry-specific preferred transition cadences in individuals 6-20 years of age. Sixty-nine individuals performed sequentially faster 5-min treadmill walking bouts, starting at 0.22 m/s and increasing by 0.22 m/s until completion of the bout during which they freely chose to run. Steps accumulated during each bout were directly observed and converted to cadence (steps/min). A logistic regression model was developed to predict preferred transition cadences using the best subset of parameters. The resulting model, which included age, sex, height, and BMI z-score, produced preferred transition cadences that accurately classified gait behaviour (k-fold cross-validated prediction accuracy =97.02%). This transition cadence ranged from 136-161 steps/min across the developmental age range studied. The preferred transition cadence represents a simple and practical index to predict and classify gait behaviour from wearable sensors in children, adolescents, and young adults. Moreover, herein we provide an equation and an open access online R Shiny app that researchers, practitioners, or clinicians can use to predict individual-specific preferred transition cadences.

The preferred walk to run transition speed in actual lunar gravity.

Quantifying the preferred transition speed (PTS) from walking to running has provided insight into the underlying mechanics of locomotion. The dynamic similarity hypothesis suggests that the PTS should occur at the same Froude number across gravitational environments. In normal Earth gravity, the PTS occurs at a Froude number of 0.5 in adult humans, but previous reports found the PTS occurred at Froude numbers greater than 0.5 in simulated lunar gravity. Our purpose was to (1) determine the Froude number at the PTS in actual lunar gravity during parabolic flight and (2) compare it with the Froude number at the PTS in simulated lunar gravity during overhead suspension. We observed that Froude numbers at the PTS in actual lunar gravity (1.39±0.45) and simulated lunar gravity (1.11±0.26) were much greater than 0.5. Froude numbers at the PTS above 1.0 suggest that the use of the inverted pendulum model may not necessarily be valid in actual lunar gravity and that earlier findings in simulated reduced gravity are more accurate than previously thought.

Effectiveness of a Variable-Speed Control Based on Auditory Feedback: Is It Possible?

PURPOSE: Variable-speed control in the field is challenging for motion science. Tests were performed to evaluate speed, Froude number, and oxygen consumption if these varied when using the same frequency of steps. The objective of this study was to evaluate the use of auditory feedback to control variable speed on the treadmill and track during acceleration cycles around the transition speed. METHODS: Twenty-four trained men participated. The protocol was based on 5 ramps of 50 seconds each around 80%, 90%, 100%, 110%, and 120% of the walking-running transition speed, recording the frequency of steps with a mobile phone during the treadmill test. The tests were replicated on the track using auditory feedback. RESULTS: When evaluating each speed of the protocols separately for the same frequency of steps, the average speed on the track was always higher on average at 54.7% compared to the laboratory (P < .050), and on the track, it was 16.2% higher than in the laboratory (P > .050). CONCLUSIONS: It cannot be considered that the same frequency of steps is equivalent to the same speed in the laboratory and on the track. These results point to the importance of reliable speed control during open field tests.

Combined Hip Angle Variability and RPE Could Determine Gait Transition in Elite Race Walkers.

The aim of this study was to investigate the role of energy cost in locomotion, specifically the rate of perceived exertion and movement variability in gait transition for eight race walkers (RW) and seven nonrace walkers (NRW). We hypothesized that a group of correlated variables could serve as combined triggers. Participants performed a preferred transition speed (PTS) test, exhibiting a higher PTS for RW (10.35 ± 0.28 km/hr) than for NRW (7.07 ± 0.69 km/hr), because RW engaged in race walking before switching to running. None of the variables increased before transition and dropped in PTS, which challenged the hypothesis of a unique transition variable in gait transitions. Principal component analysis showed that combined hip angle variability and rate of perceived exertion could determine gait transitions in elite RW and NRW. Thus, human gait transition may be triggered by a pool of determinant variables, rather than by a single factor.

Controlling the Temperature and Speed of the Phase Transition of VO2 Microcrystals.

We investigated the control of two important parameters of vanadium dioxide (VO2) microcrystals, the phase transition temperature and speed, by varying microcrystal width. By using the reflectivity change between insulating and metallic phases, phase transition temperature is measured by optical microscopy. As the width of square cylinder-shaped microcrystals decreases from ∼70 to ∼1 µm, the phase transition temperature (67 °C for bulk) varied as much as 26.1 °C (19.7 °C) during heating (cooling). In addition, the propagation speed of phase boundary in the microcrystal, i.e., phase transition speed, is monitored at the onset of phase transition by using the high-speed resistance measurement. The phase transition speed increases from 4.6 × 10(2) to 1.7 × 10(4) µm/s as the width decreases from ∼50 to ∼2 µm. While the statistical description for a heterogeneous nucleation process explains the size dependence on phase transition temperature of VO2, the increase of effective thermal exchange process is responsible for the enhancement of phase transition speed of small VO2 microcrystals. Our findings not only enhance the understanding of VO2 intrinsic properties but also contribute to the development of innovative electronic devices.

Preferred and energetically optimal transition speeds during backward human locomotion.

Some aspects of backward locomotion are similar to forward locomotion, while other aspects are not related to their forward counterpart. The backward preferred transition speed (BPTS) has never been directly compared to the energetically optimal transition speed (EOTS), nor has it been compared to the preferred transition speed (PTS) during forward locomotion. The purpose of this study was to determine whether the BPTS occurs at the EOTS, and to examine the relationship between the backward and forward preferred gait transition speeds. The preferred backward and forward transition speeds of 12 healthy, young subjects (7 males, 5 females) were determined after subjects were familiarized with forward and backward treadmill locomotion. On a subsequent day, subjects walked backward at speeds of 70, 80, 90, 100, and 110% of the BPTS and ran backward at speeds of 60, 75, 90, 100, and 120% of the BPTS while VO2 and RPE data were collected. After subtracting standing VO2, exercise VO2 was normalized to body mass and speed. For each subject, energy-speed curves for walking and running were fit to the normalized data points. The intersection of these curves was defined as the EOTS which was compared to the BPTS using a paired t-test (p < 0.05). RPE and VO2 at the BPTS were also compared between walking and running conditions, and the correlation between BPTS and PTS was calculated. The EOTS (1.85 ± 0.09 m·s(-1)) was significantly greater than the BPTS (1.63 ± 0.11 m·s(-1)). Even though RPE was equal for walking and running at the BPTS, VO2 was significantly greater when running. There was a strong correlation (r = 0.82) between the BPTS and the PTS. Similar to forward locomotion, the determinants of the BPTS must include factors other than metabolic energy. The gait transition during backward locomotion exhibits several similarities to its forward counterpart. Key PointsThe backward preferred transition speed (1.63 ± 0.11 m·s(-1)) was significantly less than the energetically optimal transition speed (1.85 ± 0.09 m·s(-1)), similar to what is observed during forward locomotion.RPE was equal for walking and running at the backward preferred transition speed.There was a strong correlation (r = 0.82) between the backward and forward preferred transition speeds.Similar to forward locomotion, the determinants of the BPTS must include factors other than metabolic energy.

Diurnal variation in gait characteristics and transition speed.

The aim of this study was to investigate the effect of time-of-day on Preferred Transition Speed (PTS) and spatiotemporal organization of walking and running movements. Twelve active male subjects participated in the study (age: 27.2 ± 4.9 years; height: 177.9 ± 5.4 cm; body mass: 75.9 ± 5.86 kg). First, PTS was determined at 08:00 h and 18:00 h. The mean of the two PTS recorded at the two times-of-day tested was used as a reference (PTSm). Then, subjects were asked to walk and run on a treadmill at three imposed speeds (PTSm, PTSm + 0.3 m.s(-1), and PTSm - 0.3 m.s(-1)) at 08:00 h and 18:00 h. Mean stride length, temporal stride, spatial stride variability, and temporal stride variability were used for gait analysis. The PTS observed at 08:00 h (2.10 ± 0.17 m.s(-1)) tends to be lower (p = 0.077) than that recorded at 18:00 h (2.14 ± 0.19 m.s(-1)). Stride lengths recorded while walking (p = 0.038) and running (p = 0.041) were shorter at 08:00 h than 18:00 h. No time-of-day effect was observed for stride frequency during walking and running trials. When walking, spatial stride variability (p = 0.020) and temporal stride variability (p = 0.028) were lower at 08:00 h than at 18:00 h. When running, no diurnal variation of spatial stride variability or temporal stride variability was detected.

The relationship between allometry and preferred transition speed in human locomotion.

The purpose of this study was to explore the relationships between preferred transition speed (PTS) and anthropometric characteristics, body composition and different human body proportions in males. In a sample of 59 male students, we collected anthropometric and body composition data and determined individual PTS using increment protocol. The relationships between PTS and other variables were determined using Pearson correlation, stepwise linear and hierarchical regression. Body ratios were formed as quotient of two variables whereby at least one significantly correlated to PTS. Circular and transversal (except bitrochanteric diameter) body dimensions did not correlate with PTS. Moderate correlations were found between longitudinal leg dimensions (foot, leg and thigh length) and PTS, while the highest correlation was found for lower leg length (r=.488, p<.01). Two parameters related to body composition showed weak correlation with PTS: body fat mass (r=-.250, p<.05) and amount of lean leg mass scaled to body weight (r=.309, p<.05). Segmental body proportions correlated more significantly with PTS, where thigh/lower leg length ratio showed the highest correlation (r=.521, p<.01). Prediction model with individual variables (lower leg and foot length) have explained just 31% of PTS variability, while model with body proportions showed almost 20% better prediction (R(2)=.504). These results suggests that longitudinal leg dimensions have moderate influence on PTS and that segmental body proportions significantly more explain PTS than single anthropometric variables.