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The vibration serviceability problems induced by the coupling vibration of lightweight footbridges is a research focus. Much research has been conducted in recent years, yet the attenuation of the coupling vibration subjected to a low-density crowd is still challenging. To investigate the coupling vibration between a moving crowd and aluminum alloy footbridge due to synchronous excitation, orthogonal crowd load tests were carried out on a simply supported aluminum alloy footbridge with a span of 34.8 m. Load tests with different numbers of pedestrians and step frequencies were conducted to obtain vibration frequency and peak acceleration of the footbridge. The comparative analysis reveals that vibration serviceability under certain conditions of synchronous excitation was not in accordance with German footbridges guidelines or British standards. Synchronous excitation of low-density crowds may lead to a marked decline in pedestrian comfort. A two degrees of freedom (TDOF) human dynamic model with a supporting mass of human body was applied to establish a crowd-footbridge coupling system. The numerical results are in agreement with experimental data, which validates the finite element model of the footbridge. Further numerical analysis was conducted to investigate the coupling vibration response of the footbridge subjected to low-density crowd below 1 person/m2. The results show that the coupling effect is minor when the mass ratio is 0.12–0.3. When the mass ratio is 0.3–0.46, the coupling vibration is significant. Therefore, the coupling vibration of lightweight aluminum alloy footbridge deserves attention in design when subjected to low-density crowds. The evaluation of vibration serviceability is advised to be conducted according to the requirements of peak acceleration given in footbridge specifications. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the reliability, validity, and sensitivity of spatiotemporal parameters, during sprint skating, of bandy players. Thirty-two well-trained male bandy players (age: 17.8 ± 1.2 years; height: 1.80 ± 0.06 m; body mass: 75.7 ± 1.2 kg) participated in this study. They performed two 80 m linear skating sprints. To calculate the velocities and obtain glide-by-glide spatiotemporal variables, nine timing gates and two skate-mounted inertial measurement units (IMUs) were synchronized and used. The spatiotemporal variables at each step included the glide time, glide length, double support time, double support length, step length, and step frequency. All the spatiotemporal variables were analyzed separately: averaged over 80 m, during the acceleration, and the maximal steady-state phases. The relative and absolute reliability of the spatiotemporal parameters were good (ICC > 0.70; CV < 10%), except for the step frequency during the steady-state phase. The spatiotemporal parameters showed "good" to "satisfactory" sensitivity during the acceleration phase and whole sprint, and "marginal" sensitivity during the steady-state phase. Content validity was confirmed by a low percentage of the shared variance (17.9–34.3%) between the spatiotemporal parameters obtained during the acceleration and steady-state phases. A "stepwise" regression significantly predicted the steady-state skating velocity from the spatiotemporal metrics obtained during the acceleration [F(5,26) = 8.34, p < 0.001, adj. R2 = 0.62] and steady-state phases [F(5,26) = 13.6, p < 0.01, R2 = 0.67]. Only the step frequency obtained in the acceleration phase significantly predicted the maximal skating velocity (p < 0.01), while the glide length and step frequency derived during the steady-state phase significantly added to the prediction (p < 0.01). In conclusion, the spatiotemporal parameters, obtained by two skate-mounted IMUs, were shown to be reliable and sensitive measures of sprint skating, and they could be used to provide independent information for the different skating phases. The maximal skating velocity could be predicted from the spatiotemporal parameters, with longer gliding and more frequent steps as the most significant determinants. [ABSTRACT FROM AUTHOR]

The step characteristics of the starting motion of international-level skeleton athletes were investigated in official races as well as the relationship between the start and finish times. The starting motion of 26 male athletes was recorded with four video cameras in Intercontinental and Europe Cups, 2018 and their starting motion was analysed by a three-dimensional direct linear transformation method. The start time showed significant correlation with the finish time (ρ = 0.87, p < 0.001), as well as the sled speed at the 4 m (ρ = −0.43, p = 0.029) and 9 m (ρ = −0.79, p < 0.001) marks. The athletes were divided into two types according to the sled position and the foot for the 1st step: ipsilateral type and contralateral type. The sled speed of the ipsilateral type athletes in the 1st step was higher than that of the contralateral-type athletes. Step length from the 2nd to 5th and 7th steps showed a significant negative correlation with the start time (ρ = −0.70 to −0.46, p = 0.001 to 0.032). The international-level skeleton athletes gained a shorter start time due to a large running speed by acquiring the large SL. [ABSTRACT FROM AUTHOR]

We aimed to examine the validity of estimating spatiotemporal and ground reaction force (GRF) parameters during resisted sprinting using a robotic loading device (1080 Sprint). Twelve male athletes (age: 20.9 ± 2.2 years; height: 174.6 ± 4.2 cm; weight: 69.4 ± 6.1 kg; means ± SDs) performed maximal resisted sprinting with three different loads using the device. The step frequency and length and step‐averaged velocity, anteroposterior GRF (Fap), and the ratio of Fap to resultant GRF (RF) were estimated using the velocity and towing force data measured using the device. Simultaneously, the corresponding values were measured using a 50‐m force plate system. The proportional and fixed biases of the estimated values against those measured using the force plate system were determined using ordinary least product (OLP) regression analysis. Proportional and fixed biases were observed for most variables. However, the proportional bias was small or negligible except for the step frequency. Conversely, the fixed bias was small for step‐averaged velocity (0.11 m/s) and step length (0.04 m), whereas it was large for step frequency (0.54 step/s), Fap (16N), and RF (2.22%). For all variables except step frequency, the prediction intervals in the OLP regression dramatically decreased when the corresponding values were smoothed using a two‐step moving average. These results indicate that by using the velocity and force data recorded in the loading device, most of the spatiotemporal and GRF variables during resisted sprinting can be estimated with some correction of the fixed bias and data smoothing using the two‐step moving average. [ABSTRACT FROM AUTHOR]

The aim of the present study was to examine whether full leg-length compression tights modify physiological and kinematic measures during treadmill running at a competitive race pace in moderately trained runners. Thirteen males and five females completed two 15-minute running tests at a speed corresponding to a recent race time wearing compression tights or loose-fitting running shorts. Running economy (RE) was determined by oxygen consumption and carbon dioxide expiration during the final 3 minutes of treadmill running. Muscle oxygenation, skin temperature, heart rate (HR), vertical oscillation, step frequency and ground contact time (GCT) were measured continuously. GCT was shorter with compression compared with control trials (p = 0.03), however, no differences in RE, muscle oxygenation, vertical oscillation, step frequency, HR or skin temperature were revealed. Despite a shorter GCT with compression tights, the findings suggest that moderately trained runners do not benefit nor limit physiological responses at a competitive race pace. [ABSTRACT FROM AUTHOR]

Is step frequency (SF) related to running economy and how? This is the main question we have tried to answer in this study. It is a well-known biomechanical variable used in scientific and practical analysis of running technique. A systematic review was carried out to analyse available literature of the field. Scopus, Web of Science and ScienceDirect databases were used for article search. In total 249 articles matched defined queries and after exclusion, 12 were used in the review. After analysis of the review, our hypothesis remained unconfirmed. In some cases, step frequency affected the running economy, while in others it did not have a direct impact on it. It might be that SF cannot be considered in isolation from other biomechanical characteristics and it cannot be analysed as a universal criterion for improving running technique and economy. [ABSTRACT FROM AUTHOR]

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This study aimed to evaluate individual variations in running kinematics at various running intensities by considering the potential differences in runners' abilities. It is essential to recognize that running kinematic dynamics may not remain identical at different intensities, even among runners with similar performance abilities. To avoid assumptions based solely on group data, this study focused on individual variations as a key objective. The research involved three male runners who demonstrated similar 3000 m running times, ranging from 9:02 to 9:08 min. These participants underwent a series of running tests on a leveled treadmill, during which comprehensive measurements of running kinematics, heart rate, and blood lactate values were recorded. The running velocity was in the range of 12-20 km/h, and nine individual tests were conducted with a randomized order of velocities. Analysis of the heart rate data revealed variations in exercise response both within and between individuals. However, among these three runners, general physiological responses, including the heart rate and lactate concentration, were similar. This study shows that running velocity significantly affects various kinematic characteristics of running such as the step length, step frequency, contact time, and flight time. The findings indicate that with an increase in the running velocity, there is a corresponding increase in the step length and stride frequency, a decrease in the contact time, and an increase in the flight time. Furthermore, a strong positive correlation between the step length and running velocity is observed; there is also a general trend of stride frequency increasing with higher running velocity, although this result is not always statistically significant. In conclusion, this study highlights the importance of considering individual variations in running kinematics when assessing the effects of different running intensities. [ABSTRACT FROM AUTHOR]

This paper discusses the derivation of a set of dynamic load factors for calculation of walking response on the basis of measurements made during a biomechanics research carried out with young adults. Firstly, a quite large number of experimental data on single footstep force were collected. The single footstep forces were then superimposed to generate the force time history for a continuous walk. This was followed by the transformation of the resultant force to the frequency domain from which the dynamic load factors for the first ten harmonics of a pacing rate can be extracted. A statistical analysis was employed on the dynamic load factors to acquire their design values in terms of the 90-th or 95-th percentile. The waking force function recommended by various design guides and that developed in the paper were then used in a comprehensive finite element model to predict the vibration level of a building floor. Current design guides on floor vibration normally suggest using four harmonics in the walking force whereas load factors for ten harmonics were developed in this paper. The acceleration response of the floor was found to increase by 5-33 % when walking harmonics beyond the fourth harmonic were considered. The inclusion of higher harmonics would therefore lead to a more conservative estimation of the floor response.

Intelligent lower-limb prostheses aims to make amputees walk more comfortably and symmetrically which requires the dynamic altering of gait parameters such as walking speed. Some solutions have been proposed such as direct integration and machine learning methods. The former updates walking speed once after an entire gait cycle and the latter collects large amounts of gait data which are unfriendly to lower-limb amputees. Only by using an inertial measurement unit (IMU) placed on the thigh, this paper proposes a novel online walking speed estimation method to determine the walking speed rapidly and accurately in real-time. A step frequency estimator based on the phase variable and a stride estimator based on the inverted pendulum model is designed to determine the walking speed together. The proposed method is evaluated on a public open-source dataset and the gait data were collected in the lab to verify the effectiveness for able-bodied and prosthetic wearers. The experiment results show that the walking speed estimator offers higher accuracy (RMSE of the able-bodied dataset: 0.051 ± 0.016 m/s, RMSE of the prosthetic wearers' dataset: 0.036 ± 0.021 m/s) than the previous works with a real-time frequency of 100 Hz. The results also show that the proposed method has good performances both in static speeds and dynamic speed tracking without much data collection before being applied. [ABSTRACT FROM AUTHOR]

Is step frequency (SF) related to running economy and how? This is the main question we have tried to answer in this study. It is a well-known biomechanical variable used in scientific and practical analysis of running technique. A systematic review was carried out to analyse available literature of the field. Scopus, Web of Science and ScienceDirect databases were used for article search. In total 249 articles matched defined queries and after exclusion, 12 were used in the review. After analysis of the review, our hypothesis remained unconfirmed. In some cases, step frequency affected the running economy, while in others it did not have a direct impact on it. It might be that SF cannot be considered in isolation from other biomechanical characteristics and it cannot be analysed as a universal criterion for improving running technique and economy.

Purpose: This study aimed at comparing the predictive accuracy of the power law (PL), 2-parameter hyperbolic (HYP) and linear (LIN) models on elite 1-h track running performance, and evaluating pacing profile and running pattern of the men's best two 1-h track running performances of all times. Methods: The individual running speed–distance profile was obtained for nine male elite runners using the three models. Different combinations of personal bests times (3000 m-marathon) were used to predict performance. The level of absolute agreement between predicted and actual performance was evaluated using intraclass correlation coefficient (ICC), paired t test and Bland–Altman analysis. A video analysis was performed to assess pacing profile and running pattern. Results: Regardless of the predictors used, no significant differences (p > 0.05) between predicted and actual performances were observed for the PL model. A good agreement was found for the HYP and LIN models only when the half-marathon was the longest event predictor used (ICC = 0.718–0.737, p < 0.05). Critical speed (CS) was highly dependent on the predictors used. Unlike CS, PLV20 (i.e., the running speed corresponding to a 20-min performance estimated using the PL model) was associated with 1-h track running performances (r = 0.722–0.807, p < 0.05). An even pacing profile with minimal changes of step length and frequency was observed. Conclusions: The PL model may offer the more realistic 1-h track running performance prediction among the models investigated. An even pacing might be the best strategy for succeeding in such running events. [ABSTRACT FROM AUTHOR]

Sprinting and dribbling a ball are considered essential for success in team sports, such as soccer. The purpose of the present study was to examine straight line (SL) and changes of direction (COD) sprinting and dribbling abilities after a standing and a flying starting position. Twelve amateur U12 male soccer players participated in the study. The participants were tested in four different sprinting conditions. The first consisted of 15 m SL sprinting and dribbling test by standing position; the second consisted of 15 m SL sprinting and dribbling test by flying start. The third condition consisted of 15 m COD sprinting and dribbling test by standing position, and the fourth condition consisted of 15 m COD sprinting and dribbling test by flying start. T-tests analysis indicated significant differences between SL sprinting and dribbling sprinting tests (P < 0.05) and between standing and flying start positions (P < 0.05). Step frequency was higher for sprinting tests (P < 0.05). Moreover, the results showed that step length was longer when players had a standing position (P < 0.05). These findings emphasize the importance for trainers to add parts without ball, focused on the development of certain fitness and running components. [ABSTRACT FROM AUTHOR]

Background: The duty factor (reflecting the ratio of stance to flight time) is an important variable related to running performance, economy, and injury risk. According to the dual-axis model, the duty factor and the cadence are sufficient to describe an individual's running style at a certain speed. To test this model, one should be able to modulate both variables independently. While acoustic pacing is an established method for cadence modulation, no such method is available for duty-factor modulation.Research Questions: Can people modulate their duty factor based on verbal instructions to change either their stance or flight time without changing their cadence? And, if so, which instruction is most effective?Methods: Twelve participants ran on an instrumented treadmill and completed four training blocks starting with a baseline trial and ending with a performance trial in which they followed verbal instructions to both increase and decrease their stance and flight time. Acoustic pacing at their preferred cadence was present during the first part of each trial. We calculated the duty factor and cadence for paced and non-paced parts of each trial, assessed the effectiveness of the instructions aimed at changing the duty factor, and examined the effects of instructions and acoustic pacing on cadence using Bayesian statistics.Results: The duty factor changed in intended directions with verbal instructions to increase and decrease the stance and flight time (18.04 ≤ BF10 ≤ 4954.42), without differences between the instructions or during and after acoustic pacing. The instructions and acoustic pacing did not result in a consistent change in cadence (0.40 ≤ BF10 ≤ 2.59).Significance: Runners can change their duty factor through verbal instructions pertaining to stance or flight time, without clear concomitant effects on cadence. Running styles can thus be altered with verbal instructions to change stance or flight time for duty-factor modulation, optionally combined with acoustic pacing to prescribe cadence. [ABSTRACT FROM AUTHOR]

The request of material savings in bridge constructions leads to the development towards slender and lightweight structures, which are more sensitive to human-induced vibrations caused by walking pedestrians. The resulting accelerations do not endanger the structural safety, but can be perceived as unpleasant for the user and must therefore be restricted within the limit state of serviceability. For this purpose, the guidelines define acceleration intervals, called as "comfort levels" (CL), which evaluate the comfort of the pedestrians, given the maximum acceleration of the bridge. The model for human-induced loads in the design guideline is based on conservative and deterministic simplifications. In particular, the uncertainties in the human gait parameters are neglected. The main objective of this paper is to develop an uncertain load model for walking pedestrians based on Fourier series. The aleatory and epistemic uncertainties in the human gait parameters are quantified with appropriate uncertainty models relying on available data. In a dynamical finite element analysis, the model is used to simulate groups of pedestrians randomly walking over a bridge to calculate the resulting acceleration amplitudes. The approach is applied to a single span beam and to a real world footbridge using a 3D finite element model. The results are then evaluated within the CLs, enabling new assessment methods. • Uncertainty quantification for human-induced loads. • Introduction of a Fuzzy Fourier load model for walking pedestrians. • Simulation of human-induced vibrations of a real world footbridge with polymorphic uncertain data. • New assessment methods for the footbridges comfort level. [ABSTRACT FROM AUTHOR]

Intelligent lower-limb prostheses aims to make amputees walk more comfortably and symmetrically which requires the dynamic altering of gait parameters such as walking speed. Some solutions have been proposed such as direct integration and machine learning methods. The former updates walking speed once after an entire gait cycle and the latter collects large amounts of gait data which are unfriendly to lower-limb amputees. Only by using an inertial measurement unit (IMU) placed on the thigh, this paper proposes a novel online walking speed estimation method to determine the walking speed rapidly and accurately in real-time. A step frequency estimator based on the phase variable and a stride estimator based on the inverted pendulum model is designed to determine the walking speed together. The proposed method is evaluated on a public open-source dataset and the gait data were collected in the lab to verify the effectiveness for able-bodied and prosthetic wearers. The experiment results show that the walking speed estimator offers higher accuracy (RMSE of the able-bodied dataset: 0.051 ± 0.016 m/s, RMSE of the prosthetic wearers‘ dataset: 0.036 ± 0.021 m/s) than the previous works with a real-time frequency of 100 Hz. The results also show that the proposed method has good performances both in static speeds and dynamic speed tracking without much data collection before being applied.

We tested the hypothesis that restricting either step frequency (SF) or stride length (SL) causes a decrease in ventilatory response with limited breath frequency during sinusoidal walking. In this study, 13 healthy male and female volunteers (mean ± SD; age: 21.5 ± 1.8 years, height: 168 ± 7 cm, weight: 61.5 ± 8.3 kg) participated. The walking speed was sinusoidally changed between 50 and 100 m⋅min–1 with periods from 10 to 1 min. Using a customized sound system, we fixed the SF at 120 steps⋅min–1 with SL variation (0.83–0.41 m) (SF fix ) or fixed the SL at 0.7 m with SF variation (143–71 steps⋅min–1) (SL fix ) during the subjects' sinusoidal walking. Both the subjects' preferred locomotion pattern without a sound system (Free) and the unprompted spontaneous locomotor pattern for each subject (Free) served as the control condition. We measured breath-by-breath ventilation [tidal volume (VT) and breathing frequency (B f)] and gas exchange [CO2 output ( V. CO2), O2 uptake ( V. O2)]. The amplitude (Amp) and the phase shift (PS) of the fundamental component of the ventilatory and gas exchange variables were calculated. The results revealed that the SF fix condition decreased the Amp of the B f response compared with SL fix and Free conditions. Notably, the Amp of the B f response under SF fix was reduced by less than one breath at the periods of 5 and 10 min. In contrast, the SL fix condition resulted in larger Amps of B f and V. E responses as well as Free. We thus speculate that the steeper slope of the V. E - V. CO2 relationship observed under the SL fix might be attributable to the central feed-forward command or upward information from afferent neural activity by sinusoidal locomotive cadence. The PSs of the V. E , V. O2, and V. CO2 responses were unaffected by any locomotion patterns. Such a sinusoidal wave manipulation of locomotion variables may offer new insights into the dynamics of exercise hyperpnea. [ABSTRACT FROM AUTHOR]

Background: Different approaches have been implemented to calculate stepping cadence (steps/min) that vary in the time demominator used. Given the differences in how stepping intensity are calculated, it is unclear if they are more so associated with total step counts.Research Objective: This study compared three methods of calculating stepping cadence and determined their relationship with total step counts.Methods: 132 participants (74♀; 35 ± 20 years; body mass index: 24.9 ± 4.0 kg•m-2) wore an activPAL monitor 24-hr/day for up to 8-d (total: 869-d). The total steps/day, time spent stepping (0.1 s resolution; to calculate bout stepping rate), time spent stepping in 60 s epochs (step accumulation), and awake time (awake cadence) were determined. Each cadence method (in steps/min) were compared via Spearman's rank correlation. The relationships versus total step count were determined, and the strength of these relationships compared between cadence measures (95% confidence interval of correlation differences).Results: Bout stepping rate (85 ± 14 steps/min) was larger than step accumulation (34 ± 12 steps/min) and awake cadence (10 ± 5 steps/min, both: P < 0.001). Step accumulation was positively strongly related to bout stepping rate (ρ = 0.813; P < 0.001) whereas awake cadence was weakly related to bout stepping rate (ρ = 0.496; P < 0.001). Step accumulation (ρ = 0.634; P < 0.001) and awake cadence (ρ = 0.964; P < 0.001) were more related to step counts than bout stepping rate (ρ = 0.497; P < 0.001; 95% confidence intervals of correlation differences: step accumulation=0.10-0.17, awake cadence: 0.42-0.52).Significance: Without a precise measure of time spent stepping, stepping cadence is lower using the step accumulation and awake cadence methods. Step accumulation and awake cadence are more related to total step counts than bout stepping rate. Bout stepping rate outcomes reflect continuous stepping rate, does not rely on a preset epoch, and may have less overlap with step counts, which may have implications for determining the unique contributions of step count versus stepping cadence on health outcomes. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that restricting either step frequency (SF) or stride length (SL) causes a decrease in ventilatory response with limited breath frequency during sinusoidal walking. In this study, 13 healthy male and female volunteers (mean ± SD; age: 21.5 ± 1.8 years, height: 168 ± 7 cm, weight: 61.5 ± 8.3 kg) participated. The walking speed was sinusoidally changed between 50 and 100 m⋅min–1 with periods from 10 to 1 min. Using a customized sound system, we fixed the SF at 120 steps⋅min–1 with SL variation (0.83–0.41 m) (SFfix) or fixed the SL at 0.7 m with SF variation (143–71 steps⋅min–1) (SLfix) during the subjects’ sinusoidal walking. Both the subjects’ preferred locomotion pattern without a sound system (Free) and the unprompted spontaneous locomotor pattern for each subject (Free) served as the control condition. We measured breath-by-breath ventilation [tidal volume (VT) and breathing frequency (Bf)] and gas exchange [CO2 output (V.CO2), O2 uptake (V.O2)]. The amplitude (Amp) and the phase shift (PS) of the fundamental component of the ventilatory and gas exchange variables were calculated. The results revealed that the SFfix condition decreased the Amp of the Bf response compared with SLfix and Free conditions. Notably, the Amp of the Bf response under SFfix was reduced by less than one breath at the periods of 5 and 10 min. In contrast, the SLfix condition resulted in larger Amps of Bf and V.E responses as well as Free. We thus speculate that the steeper slope of the V.E-V.CO2 relationship observed under the SLfix might be attributable to the central feed-forward command or upward information from afferent neural activity by sinusoidal locomotive cadence. The PSs of the V.E, V.O2, and V.CO2 responses were unaffected by any locomotion patterns. Such a sinusoidal wave manipulation of locomotion variables may offer new insights into the dynamics of exercise hyperpnea.

This study aimed to characterise the push phase kinematics in skeleton sport and explore the relationship between kinematic indicators and push performance. Nine male Chinese skeleton athletes performed three 15-metre pushes on an indoor simulated push track. Kinematic data were recorded with a 3-dimensional motion system (VICON; UK) consisting of 14 cameras sampling at a rate of 200 Hz. The linear relationships between the kinematic indicators and push performance were determined by Pearson correlation analysis. Statistical significance was set at p ≤ 0.05. Step velocity (SV), step length (SL), toe-off distance (TOD), and toe-off angle (TOA) were significantly different between the inside and outside foot in the first four steps. Positively significant correlations were found between touchdown distance (TD), touchdown angle (TA), and SV in step 1 (r = 0.696; r = 0.682), and negative correlations were found between contact time (CT), TOA, and SV in step 1 and step 4, respectively (r = −0.839; r = −0.763). Effective acceleration was achieved by shortening contact, increasing TA and TD in the first step, and maintaining a relatively small TOA and a relatively long TOD in the steps 2 to 4. [ABSTRACT FROM AUTHOR]

Abstract Objective This study examined the relationship between leg bone length and sprint performance in sprinters. The leg bone lengths in 28 100-m specialized sprinters and 28 400-m specialized sprinters were measured using magnetic resonance imaging. The lengths of the upper and lower leg bones were assessed by calculating the lengths of the femur and tibia, respectively. To minimize differences in body size among participants, both bone lengths were normalized to body height. The ratio of the tibial length to femoral length was calculated to evaluate the interaction between the lengths of the upper and lower leg bones. International Amateur Athletic Federation (IAAF) scores, based on the personal best times of the sprinters in each group were used as parameters for sprint performance. Results There were no significant correlations between absolute and relative lengths of the femur and tibia and IAAF scores in both 100-m and 400-m sprinters. By contrast, the ratio of the tibial length to femoral length correlated significantly with IAAF score in 400-m sprinters (r = 0.445, P = 0.018), but not 100-m sprinters. These findings suggest that the leg bone lengths may play an important role in achieving superior long sprint performance in 400-m specialized sprinters.

Older adults and neurological populations tend to walk with slower speeds, more gait variability, and a higher metabolic cost. This higher metabolic cost could be related to their increased gait variability, but this relationship is still unclear. The purpose of this study was to determine how increased step length variability affects the metabolic cost of waking. Eighteen healthy young adults completed a set of 5-minute trials of treadmill walking at 1.20 m/s while we manipulated their step length variability. Illuminated rectangles were projected onto the surface of a treadmill to cue step length variabilities of 0, 5 and 10% (coefficient of variation). Actual step lengths and their variability were tracked with reflective markers on the feet, while metabolic cost was measured using indirect calorimetry. Changes in metabolic cost across habitual walking (no projections) and the three variability conditions were analyzed using a linear mixed effects model. Metabolic power was largest in the 10% condition (4.30 ± 0.23 W/kg) compared to 0% (4.16 ± 0.18 W/kg) and habitual (3.98 ± 0.25 W/kg). The participant's actual step length variability did not match projected conditions for 0% (3.10%) and 10% (7.03%). For every 1% increase in step length variability, there is an 0.7% increase in metabolic cost. Our results demonstrate an association between the metabolic cost of walking and gait step length variability. This suggests that increased gait variability contributes to a portion of the increased cost of walking seen in older adults and neurological populations., Competing Interests: Competing interests The authors declare no competing or financial interests.

Purpose: To examine the influence of induced changes in the morphology of the leg by adding mass on the optimal step length (OSL) in experienced runners to get more insight into parameters that influence preferred step length (PSL) and OSL. Methods: Thirteen experienced male runners (mean age 26.9 ± 6.1 y, height 183.7 ± 7.1 cm, mass 71.8 ± 5.9 kg) ran on a treadmill in 3 different conditions: unloaded (UL), loaded with 2 kg mass at the ankles (MA), and loaded with 2 kg mass at the hips (MH) at 7 different step lengths (SLs). SL deviations were expressed as deviations in relative leg length (%LL) from the individual PSL: 0%LL, ±5%LL, ±10%LL, and ±15%LL. Trials lasted 8 min, and 8 min of rest was given between trials. Oxygen uptake (V02) was expressed as a fraction of V02 at PSL + 0%LL in the unloaded condition (%V02). The %SL with the lowest value of %V02 was considered the OSL for this group of participants. Results: OSL at the UL condition was 6% shorter than PSL. The MA condition resulted in a 7%LL larger OSL than at UL and MH (P < .05). Conclusions: The mass distribution of the leg is a determinant of the OSL. As a consequence of the added mass to the ankles, OSL was 7%LL longer. Morphological characteristics of the leg might therefore play an important role in determining the runner's individual optimal SL. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop a normative sample of step frequency and step length during maximal sprinting in amputee sprinters. We analyzed elite-level 100-m races of 255 amputees and 93 able-bodied sprinters, both men and women, from publicly-available Internet broadcasts. For each sprinter's run, the average forward velocity, step frequency, and step length over the 100-m distance were analyzed by using the official record and number of steps in each race. The average forward velocity was greatest in able-bodied sprinters (10.04 ± 0.17 m/s), followed by bilateral transtibial (8.77 ± 0.27 m/s), unilateral transtibial (8.65 ± 0.30 m/s), and transfemoral amputee sprinters (7.65 ± 0.38 m/s) in men. Differences in velocity among 4 groups were associated with step length (able-bodied vs transtibial amputees) or both step frequency and step length (able-bodied vs trans-femoral amputees). Although we also found that the velocity was greatest in able-bodied sprinters (9.10 ± 0.14 m/s), followed by unilateral transtibial (7.08 ± 0.26 m/s), bilateral transtibial (7.06 ± 0.48 m/s), and transfemoral amputee sprinters (5.92 ± 0.33 m/s) in women, the differences in the velocity among the groups were associated with both step frequency and step length. Current results suggest that spatiotemporal parameters during a 100-m race of amputee sprinters is varied by amputation levels and sex. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the reliability of the spatiotemporal determinants of maximal sprinting speed in boys over single and multiple steps. Fifty-four adolescent boys (age = 14.1 ± 0.7 years [range = 12.9-15.7 years]; height = 1.63 ± 0.09 m; body mass = 55.3 ± 13.3 kg; -0.31 ± 0.90 age from Peak Height Velocity (PHV) in years; mean ± s) volunteered to complete a 30 m sprint test on 3 occasions over a 2-week period. Speed, step length, step frequency, contact time, and flight time were assessed via an optical measurement system. Speed and step characteristics were obtained from the single-fastest step and average of the 2 and 4 fastest consecutive steps. Pairwise comparison of consecutive trials revealed the coefficient of variation (CV) for speed was greater in 4-step (CV = 7.3 & 7.5%) compared with 2-step (CV = 4.2 & 4.1 %) and 1-step (CV = 4.8 & 4.6%) analysis. The CV of step length, step frequency and contact time ranged from 4.8 to 7.5% for 1-step, 3.8-5.0% for 2-step and 4.2-7.5% for 4-step analyses across all trials. An acceptable degree of reliability was achieved for the spatiotemporal and performance variables assessed in this study. Two-step analysis demonstrated the highest degree of reliability for the key spatiotemporal variables, and therefore may be the most suitable approach to monitor the spatiotemporal characteristics of maximal sprint speed in boys. [ABSTRACT FROM AUTHOR]

The purpose of this study was to compare step-by-step kinematics of unresisted and resisted 10-m sprints measured with the Optojump or Musclelab on elite sprinters. Six subjects (age 30.0 ± 5.1 years, body mass 76.3 ± 5.3 kg, body height 1.79 ± 0.09 m, and 100-m personal best 10.51 ± 0.3 s) performed 2 unresisted and 2 sets of 2 resisted (10 and 20% of body mass) 30-m sprints in random order (6 sprints in total) in 1 session in which kinematics of the first 10 m were measured with the Optojump and Musclelab. The main finding was that there were no significant differences between the measurements made with the Optojump and Musclelab systems. In addition, it was possible to discriminate most kinematic variables per step of the first 10 m when different loads (10 and 20% of body mass) had to be pulled during the 30-m sprints. The variations in sprint times associated with changes in the resistance provided by the dynaSpeed were mainly caused by a decrease in step length as the resistance increased. It was concluded that the 2 systems are valid and could help coaches, researchers, and athletes by providing more detailed information about possible changes to kinematics during training and sprinting with different resistances. [ABSTRACT FROM AUTHOR]

This study compared the kinematics (step and joint) and muscle activity of unresisted and active resisted 30 m sprints with different loads (10–40% body mass) in experienced male and female sprinters. Step kinematics were measured using a laser gun and contact mat in 28 male and female participants during unresisted 30 m sprint, and sprints with 10–40% of body mass (BM) active resistance, while peak angular velocities of lower limb was measured, together with muscle activation of nine muscles. Increased resisted loads resulted in slower 30 m times, as a result of lower step velocity mainly caused by shorter step lengths and frequencies, flight times and longer contact times, with a greater effect on women than on men. These step kinematic differences, due to increasing load were accompanied with lower peak joint movements. However, gender differences were only found for peak plantar flexion with unresisted and 10% BM resisted sprints. Furthermore, increasing load decreased calf and hamstring muscles activity, while medial vastus activity increased. Based upon these findings, it was concluded that when introducing active resisted sprints, women should sprint with approximately 10% less active loads than men to have equal step and joint kinematics development over the sprint distance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Objective: This study examined the relationship between leg bone length and sprint performance in sprinters. The leg bone lengths in 28 100-m specialized sprinters and 28 400-m specialized sprinters were measured using magnetic resonance imaging. The lengths of the upper and lower leg bones were assessed by calculating the lengths of the femur and tibia, respectively. To minimize differences in body size among participants, both bone lengths were normalized to body height. The ratio of the tibial length to femoral length was calculated to evaluate the interaction between the lengths of the upper and lower leg bones. International Amateur Athletic Federation (IAAF) scores, based on the personal best times of the sprinters in each group were used as parameters for sprint performance. Results: There were no significant correlations between absolute and relative lengths of the femur and tibia and IAAF scores in both 100-m and 400-m sprinters. By contrast, the ratio of the tibial length to femoral length correlated significantly with IAAF score in 400-m sprinters (r = 0.445, P = 0.018), but not 100-m sprinters. These findings suggest that the leg bone lengths may play an important role in achieving superior long sprint performance in 400-m specialized sprinters. [ABSTRACT FROM AUTHOR]

The resource scheduling strategy of the existing cognitive radar imaging system only performs resource scheduling from one dimension that distance (waveform design) or azimuth, which doesn't adequately allocate and utiliize radar system resources. Therefore, a two-dimeniional resource adaptive scheduling algorithm is proposed for the stepped frequency inverse synthetic aperture radar imaging system to improve the efficiency of the radar system based on the recognition of target's features and according to the principle of compressed sensing, the proposed algorithm calculates the pulse resources required for two-dimensional sparse imaging of targets. Then, according to the two-dimensional resource scheduling model, the two-dimensional pulse resources are adaprively allocated to realize the alternate observation of the target. Two-dimensional image of target is obtained by the sparse imaging algorithm. Finally, the feasibility of the algorithm is verified by stimulation, and more imaging tasks can be performed compared with the traditional algorithm in the case of resource saturation. [ABSTRACT FROM AUTHOR]

This study aimed to clarify the relative growth in thigh muscle size and sprint performance in children from 3 to 15 years. A total of 902 children performed a 30-m sprint test. Sprint time was measured by a photocell system. Muscle thicknesses of thigh anterior and posterior were determined by using a B-mode ultrasound. For 431 children, step frequency (SF) and step length (SL) during the sprint running were also analyzed with the films, and corrected by leg length. Using an allometry equation based on body height, relative growth of thigh muscle size and sprint performance was estimated. In both boys and girls, there was a breakpoint (BP) at which the rate of development in sprint velocity changes, and the rate of development was slower after the BP. On the other hand, the rate of growth in thigh muscle size after the BP was superior to that before the point, except of thigh posterior in boys. Regardless of sex, the rate of development in SL index after the BP became to be lower with increasing body height, whereas SF index relatively increased. These current findings indicate that in boys and girls, the rate of development in sprint velocity becomes to be lower above a certain body height, and the relative slow development may result from those in SF and SL. [ABSTRACT FROM AUTHOR]

This study examined the relationship between step characteristics and race time in a 5000-m race. Twenty-one male Japanese endurance runners performed a 5000-m race. Step length, step frequency, contact time, and flight time of two gait cycles (i.e., four consecutive ground contacts) were measured every 400-m by using high-speed video image. Moreover, step length was normalized to body height to minimize the effect of body size. In addition to step characteristics on each lap, the averages of all laps and the per cent change from the first half to the second half were calculated. The average step frequency and step length normalized to body height correlated significantly with the 5000-m race time (r = −0.611, r = −0.575, respectively, p < 0.05 for both). Per cent changes in contact time and step length correlated significantly with the 5000-m race time (r = 0.514, r = −0.486, respectively, p < 0.05 for both). These findings suggest that, in addition to higher step frequency and step length normalized to body height, smaller changes in step length during a given race may be an important step characteristic to achieving superior race performance in endurance runners.

Background: Female triple jumping is a relatively new athletics event. A limited number of researchers have focused on comparing male and female jumpers competing in international events, resulting in scarce findings in the literature regarding gender differences of the determinants of triple jump performance. Objective: The aim of the study was to examine the possible gender differences in the approach step characteristics, the spatiotemporal parameters of the separate phases of the triple jump as performed by athletes participating in sub-elite international events. Methods: The male and female participants of the 2015 European Team Championships triple jump event were recorded with a panning video camera. Approach speed was measured using photocells. Kinematical parameters were extracted using the APAS WIZARD 13.3.0.3 software. The relationships between the examined parameters and the actual triple jump performance were examined with Pearson's correlation analysis. Repeated measures ANOVA and chi-square statistical tests were run to examine the significance of the differences between genders. Results: Approach speed significantly correlated with the actual jumping distance in both males and females (p

This investigation examined step-by-step kinematics of sprint running acceleration. Using a randomised counterbalanced approach, 37 female team handball players (age 17.8 ± 1.6 years, body mass 69.6 ± 9.1 kg, height 1.74 ± 0.06 m) performed resisted, assisted and unloaded 20-m sprints within a single session. 20-m sprint times and step velocity, as well as step length, step frequency, contact and flight times of each step were evaluated for each condition with a laser gun and an infrared mat. Almost all measured parameters were altered for each step under the resisted and assisted sprint conditions (η2 ≥ 0.28). The exception was step frequency, which did not differ between assisted and normal sprints. Contact time, flight time and step frequency at almost each step were different between 'fast' vs. 'slow' sub-groups (η2 ≥ 0.22). Nevertheless overall both groups responded similarly to the respective sprint conditions. No significant differences in step length were observed between groups for the respective condition. It is possible that continued exposure to assisted sprinting might allow the female team-sports players studied to adapt their coordination to the 'over-speed' condition and increase step frequency. It is notable that step-by-step kinematics in these sprints were easy to obtain using relatively inexpensive equipment with possibilities of direct feedback. [ABSTRACT FROM AUTHOR]

In this work, we developed a smart wearable device for gait speed measurement with dual wireless communication on the feet by using an inertia measurement unit (IMU) sensor. To discover step counts and speed information, pitch and yaw angles were calculated successfully from IMU signals using a Kalman filter and a moving average algorithm. Walking step counts were calculated using the sensor; the results demonstrated almost zero errors and averaged more than 90% accuracy in walking and running measurements. The observable speed for two-foot indication and adapted variation can be implemented on the sensor to gauge walking and running speeds for different subjects. Step counts and the swing frequency were tested and compared with results over a treadmill using a commercial chip in the insole of a shoe. Experimental results were validated using fast Fourier transform from the acquired pitch angle history. The pitch and yaw angles of users' tibias can be used as controllable monitoring tags for personal health information in the future. [ABSTRACT FROM AUTHOR]

In this study, kinematic and kinetic data for 14 test subjects walking on a treadmill were recorded to verify a damped bipedal inverted pendulum (DBIP) model. The verification aim was for the DBIP model to match the step frequency and first harmonic dynamic load factor (DLF 1) extracted from the measured data, as these are key parameters of interest in civil engineering applications. The verification was conducted in several phases. First, kinematic data from 39 markers attached to the human body were used to get the trajectory of body's centre of mass (BCoM). This trajectory, in conjunction with the vertical and longitudinal ground reaction forces (GRFs) were then used to plot the leg force – leg length relationship. Linear curve fitting yielded the spring stiffness and spring length parameters. These parameters, together with the body mass and damping coefficient, were fed into the DBIP model to identify initial conditions for the motion of BCoM leading to the stable periodic gait. For the 14 test subjects, the model produced excellent agreement with the measured step frequency and DLF 1 , while relative error for the walking speed was between - 12. 6 % and 2.0%. The simulated waveform of the vertical BCoM displacement was found to match the measured signal well. In addition, match between simulated and measured GRF profiles was satisfactory except for one test subject. Regression functions have been established for estimating model parameters, based on which step-by-step procedures have then been proposed for modelling a pedestrian within the population. The results suggest that the DBIP succeeds in modelling pedestrians walking on rigid level surfaces. In the next step the model should be considered for modelling pedestrians on vibrating civil engineering structures. [ABSTRACT FROM AUTHOR]