Consecutive Strides Research Articles

Effect of Body-Weight-Support Running on Lower-Limb Biomechanics.

Study Design Controlled laboratory study. Background Body-weight-support (BWS) running is increasing in popularity, despite limited evidence of its effects on running mechanics. Objectives To determine the effect of increasing BWS on lower-limb biomechanics during lower-body positive-pressure (LBPP) treadmill running. Methods Fourteen male recreational runners completed 15 randomized trials on an LBPP treadmill at 5 levels of BWS and 3 velocities (1-minute trials with 3-minute recovery). Knee and ankle kinematic data were recorded continuously via electrogoniometry. Synchronous in-shoe plantar-pressure data identified stride onset and quantified foot-segment forces. Data were recorded during the final 30 seconds of each trial and averaged over 10 consecutive stride cycles. Results Higher levels of BWS resulted in significantly (P<.001) increased stride duration, reduced stride frequency, and reduced ground contact time (GCT). In addition, normalized GCT (GCT/stride duration) was significantly reduced (P<.001), indicating increased flight time. Increasing BWS resulted in significant reductions (P<.001) in peak knee flexion and dorsiflexion and reduced overall knee and ankle range of motion during the stance phase. Conclusion Running on an LBPP treadmill alters lower-limb kinematics, resulting in reduced ankle and knee joint range of motion. In addition, increased BWS alters stride characteristics, resulting in shorter GCT and longer flight time. Clinicians must be aware of lower-limb kinematic alterations to provide safe and effective parameters for rehabilitation involving LBPP treadmills. J Orthop Sports Phys Ther 2016;46(9):784-793. doi:10.2519/jospt.2016.6503.

Differences in the Rate of Locomotor Adapation of Anterior Cruciate Ligament Reconstructed Individuals

Even after ACL reconstruction and extensive therapy neuromuscular function and gait impairment often persists. These abnormalities and asymmetries may place individuals at risk for reinjury and degenerative joint disorders. These lingering defecits may arise because of reduced abilities to adapt the locomotor system following ACLR. PURPOSE: To investigate the locomotor adaptive capabilities of individuals who have undergone an ACLR. METHODS: We imposed novel locomotor constraints on a group of 20 ACLR individuals and 20 age-matched healthy young adults (HYA) by having them walk on a split-belt treadmill where one belt moved at twice the speed of the other belt (1.5 m/s:0.75 m/s) and then again in the opposite configuration. We collected motion capture data to determine spatiotemporal parameters during the first 200 strides of the adaptation period. The adaptation period was divided into 20 epochs containing ten consecutive strides. Step length asymmetry was determined for each stride and then the rate of adaptation of step length asymmetry was compared between groups by comparing (SLA) during each epoch using a repeated measures ANOVA. SLA=(Fast-Slow)/(Fast+Slow) RESULTS: There was a significant (p-value < 0.05) overall group by epoch interaction and post hoc comparisons show that the ACLR individuals (Mean±SE, -0.051±0.07) have greater persisting SLA at the fourth epoch as compared to HYA (-0.029±0.07). CONCLUSIONS: Our results indicate that ACLR individuals may require more practice to adapt to locomotor perturbations than healthy controls. Future research in characterizing the mechanisms that underlie these differences in the rate of adaptation could be important for designing rehabilitation strategies.

Effective Force Application Between Various Stride Frequencies While Running at Constant Velocity

Effective force application (EFA) is calculated as a ratio of horizontal force to resultant force (EFA=FH/FRes x100)), where EFA is the effectiveness of force application. EFA has been measured in sprinting, but not running at submaximal constant velocities using different stride frequencies. PURPOSE: To examine EFA while running a constant velocity using different stride frequencies. METHODS: Participants (n=6, 69.7± 14.8 kg) ran at their preferred running speed at ±5%, ±10%, and ±15% of their preferred stride frequency on a force instrumented treadmill (Bertec, Columbus, OH). Participants ran for 5 minutes at each stride frequency (intermittently directed by metronome), where 4-30s trials were collected with the metronome off for each trial collection. EFA was calculated for 20 consecutive strides with the average EFA over stance, during braking, and during propulsive phases. A repeated measures ANOVA was performed to analyze the differences in EFA, EFA Brake, and EFA Propulsive (α=0.05). RESULTS: EFA, EFA Brake, and EFA Propulsive were not different (p>0.05) between stride frequencies. Mean EFA of 0%, +5%, +10%, +5%, -5%, -10%, -15% EFA values were 6.81 ±2.20, 6.32 ±1.21, 5.77 ±1.47, 5.56 ±1.47, 6.23 ±1.41, 6.44 ±1.73, 5.95 ±1.79, respectively. Mean EFA Brake of 0%, +5%, +10%, +5%, -5%, -10%, -15% EFA values were -8.3 ±1.4, -8.67 ± 1.5, -8.87 ±1.79, -8.61 ±1.89, -8.63 ±1.36, -8.72 ±1.27, -8.65 ±1.06, respectively. Mean EFA Propulsive of 0%, +5%, +10%, +5%, -5%, -10%, -15% EFA values were 19.8 ±1.50, 20.63 ±1.51, 19.83 ±1.25, 19.45 ±1.12, 20.15 ±0.84, 20.33 ±.59, 20.01 ±0.77, respectively CONCLUSION: EFA was not influenced by stride frequency changes during constant velocity, even when braking and propulsive EFA phases were analyzed separately. Since EFA calculation is analogous to angle of force application, despite variations in stride frequency and stride length, the angle of force is maintained when running velocity is constant. More studies are required to determine if EFA can be intentionally manipulated to optimize performance.

Temporal, but not Directional, Prior Knowledge Shortens Muscle Reflex Latency in Response to Sudden Transition of Support Surface During Walking.

The central nervous system takes advantage of prior knowledge about potential upcoming perturbations for modulating postural reflexes. There are two distinct aspects of prior knowledge: spatial and temporal. This study investigated how each of spatial and temporal prior knowledge contributes to the shortening of muscle response latency. Eleven participants walked on a split-belt treadmill and perturbed by sudden acceleration or deceleration of the right belt at right foot contact. Spatial prior knowledge was given by instruction of possible direction (e.g., only acceleration) of upcoming perturbation at the beginning of an experimental session. Temporal prior knowledge was given to subjects by warning tones at foot contact during three consecutive strides before the perturbation. In response to acceleration perturbation, reflexive muscle activity was observed in soleus (SOL) and gastrocnemius (GAS) muscles. Onset latency of the GAS response was shorter (72 ms vs. 58 ms) when subjects knew the timing of the upcoming perturbation, whereas the latency was independent of directional prior knowledge. SOL onset latency (44 ms) was not influenced by directional nor temporal prior knowledge. Although spinal neural circuit that mediates short-latency reflex was not influenced by the prior knowledge, excitability in supra-spinal neural circuit that mediates medium- and long-latency reflex might be enhanced by knowing the timing of the upcoming perturbation.

A Novel Approach to Determine Strides, Ice Contact, and Swing Phases During Ice Hockey Skating Using a Single Accelerometer.

This study presents a new approach for automated identification of ice hockey skating strides and a method to detect ice contact and swing phases of individual strides by quantifying vibrations in 3D acceleration data during the blade-ice interaction. The strides of a 30-m forward sprinting task, performed by 6 ice hockey players, were evaluated using a 3D accelerometer fixed to a hockey skate. Synchronized plantar pressure data were recorded as reference data. To determine the accuracy of the new method on a range of forward stride patterns for temporal skating events, estimated contact times and stride times for a sequence of 5 consecutive strides was validated. Bland-Altman limits of agreement (95%) between accelerometer and plantar pressure derived data were less than 0.019 s. Mean differences between the 2 capture methods were shown to be less than 1 ms for contact and stride time. These results demonstrate the validity of the novel approach to determine strides, ice contact, and swing phases during ice hockey skating. This technology is accurate, simple, effective, and allows for in-field ice hockey testing.

The effect of self-paced speed and virtual reality on treadmill gait in children with cerebral palsy

Kinetic outcomes are an essential part of clinical gait analysis, and can be collected for many consecutive strides using instrumented treadmills. However, the validity of treadmill kinetic outcomes has not been demonstrated for children with cerebral palsy (CP). In this study we compared ground reaction forces (GRF), center of pressure, and hip, knee and ankle moments, powers and work, between overground (OG) and self-paced treadmill (TM) walking for 11 typically developing (TD) children and 9 children with spastic CP. Considerable differences were found in several outcome parameters. In TM, subjects demonstrated lower ankle power generation and more absorption, and increased hip moments and work. This shift from ankle to hip strategy was likely due to a more backward positioning of the hip and a slightly more forward trunk lean. In mediolateral direction, GRF and hip and knee joint moments were increased in TM due to wider step width. These findings indicate that kinetic data collected on a TM cannot be readily compared with OG data in TD children and children with CP, and that treadmill-specific normative data sets should be used when performing kinetic gait analysis on a treadmill.

Kinetic comparison of walking on a treadmill versus over ground in children with cerebral palsy

Kinetic outcomes are an essential part of clinical gait analysis, and can be collected for many consecutive strides using instrumented treadmills. However, the validity of treadmill kinetic outcomes has not been demonstrated for children with cerebral palsy (CP). In this study we compared ground reaction forces (GRF), center of pressure, and hip, knee and ankle moments, powers and work, between overground (OG) and self-paced treadmill (TM) walking for 11 typically developing (TD) children and 9 children with spastic CP. Considerable differences were found in several outcome parameters. In TM, subjects demonstrated lower ankle power generation and more absorption, and increased hip moments and work. This shift from ankle to hip strategy was likely due to a more backward positioning of the hip and a slightly more forward trunk lean. In mediolateral direction, GRF and hip and knee joint moments were increased in TM due to wider step width. These findings indicate that kinetic data collected on a TM cannot be readily compared with OG data in TD children and children with CP, and that treadmill-specific normative data sets should be used when performing kinetic gait analysis on a treadmill.

How to Sync to the Beat of a Persistent Fractal Metronome without Falling Off the Treadmill?

In rehabilitation, rhythmic acoustic cues are often used to improve gait. However, stride-time fluctuations become anti-persistent with such pacing, thereby deviating from the characteristic persistent long-range correlations in stride times of self-paced walking healthy adults. Recent studies therefore experimented with metronomes with persistence in interbeat intervals and successfully evoked persistent stride-time fluctuations. The objective of this study was to examine how participants couple their gait to a persistent metronome, evoking persistently longer or shorter stride times over multiple consecutive strides, without wandering off the treadmill. Twelve healthy participants walked on a treadmill in self-paced, isochronously paced and non-isochronously paced conditions, the latter with anti-persistent, uncorrelated and persistent correlations in interbeat intervals. Stride-to-stride fluctuations of stride times, stride lengths and stride speeds were assessed with detrended fluctuation analysis, in conjunction with an examination of the coupling between stride times and stride lengths. Stride-speed fluctuations were anti-persistent for all conditions. Stride-time and stride-length fluctuations were persistent for self-paced walking and anti-persistent for isochronous pacing. Both stride times and stride lengths changed from anti-persistence to persistence over the four non-isochronous metronome conditions, accompanied by an increasingly stronger coupling between these gait parameters, with peak values for the persistent metronomes. These results revealed that participants were able to follow the beat of a persistent metronome without falling off the treadmill by strongly coupling stride-length fluctuations to the stride-time fluctuations elicited by persistent metronomes, so as to prevent large positional displacements along the treadmill. For self-paced walking, in contrast, this coupling was very weak. In combination, these results challenge the premise that persistent metronomes in gait rehabilitation would evoke stride-to-stride dynamics reminiscent of self-paced walking healthy adults. Future studies are recommended to include an analysis of the interrelation between stride times and stride lengths in addition to the correlational structure of either one in isolation.

Identification of mouse gaits using a novel force-sensing exercise wheel.

The gaits that animals use can provide information on neurological and musculoskeletal disorders, as well as the biomechanics of locomotion. Mice are a common research model in many fields; however, there is no consensus in the literature on how (and if) mouse gaits vary with speed. One of the challenges in studying mouse gaits is that mice tend to run intermittently on treadmills or overground; this paper attempts to overcome this issue with a novel exercise wheel that measures vertical ground reaction forces. Unlike previous instrumented wheels, this wheel is able to measure forces continuously and can therefore record data from consecutive strides. By concatenating the maximum limb force at each time point, a force trace can be constructed to quantify and identify gaits. The wheel was three dimensionally printed, allowing the design to be shared with other researchers. The kinematic parameters measured by the wheel were evaluated using high-speed video. Gaits were classified using a metric called “3S” (stride signal symmetry), which quantifies the half wave symmetry of the force trace peaks. Although mice are capable of using both symmetric and asymmetric gaits throughout their speed range, the continuum of gaits can be divided into regions based on the frequency of symmetric and asymmetric gaits; these divisions are further supported by the fact that mice run less frequently at speeds near the boundaries between regions. The boundary speeds correspond to gait transition speeds predicted by the hypothesis that mice move in a dynamically similar fashion to other legged animals.

Identifying stride-to-stride control strategies in human treadmill walking.

Variability is ubiquitous in human movement, arising from internal and external noise, inherent biological redundancy, and from the neurophysiological control actions that help regulate movement fluctuations. Increased walking variability can lead to increased energetic cost and/or increased fall risk. Conversely, biological noise may be beneficial, even necessary, to enhance motor performance. Indeed, encouraging more variability actually facilitates greater improvements in some forms of locomotor rehabilitation. Thus, it is critical to identify the fundamental principles humans use to regulate stride-to-stride fluctuations in walking. This study sought to determine how humans regulate stride-to-stride fluctuations in stepping movements during treadmill walking. We developed computational models based on pre-defined goal functions to compare if subjects, from each stride to the next, tried to maintain the same speed as the treadmill, or instead stay in the same position on the treadmill. Both strategies predicted average behaviors empirically indistinguishable from each other and from that of humans. These strategies, however, predicted very different stride-to-stride fluctuation dynamics. Comparisons to experimental data showed that human stepping movements were generally well-predicted by the speed-control model, but not by the position-control model. Human subjects also exhibited no indications they corrected deviations in absolute position only intermittently: i.e., closer to the boundaries of the treadmill. Thus, humans clearly do not adopt a control strategy whose primary goal is to maintain some constant absolute position on the treadmill. Instead, humans appear to regulate their stepping movements in a way most consistent with a strategy whose primary goal is to try to maintain the same speed as the treadmill at each consecutive stride. These findings have important implications both for understanding how biological systems regulate walking in general and for being able to harness these mechanisms to develop more effective rehabilitation interventions to improve locomotor performance.

Comparison Between Inertial Sensors and Motion Capture System to Quantify Flexion‐Extension Motion in the Back of a Horse

IntroductionThe development of miniaturized inertial sensor technology (IMU) opens new possibilities to assess equine back motion in real‐life situations. The consistency of IMU for measuring dorsoventral displacement of the back has been assessed but orientation has not. The aim of this study was to assess accuracy and consistency of miniaturized inertial sensors for quantification of flexion‐extension of the equine back, compared to motion capture (mocap) as a gold standard.MethodsOne sound horse was trotted (3.5 m/s) and cantered (9 m/s) on a treadmill with synchronized mocap and IMU data collection. The amplitudes of two flexion‐extension angles were calculated between 3 IMUs (T12‐T16‐L2) and with a triad of markers linked to each IMU during 15 consecutive strides for two recordings at each gait. Consistency of sensor measurements was assessed using Lin correlation coefficient.ResultsThoracic and thoracolumbar angles showed respectively a Lin correlation coefficient of 0.96 (excellent) and 0.87 (good). The difference (mean ± SD) between IMU and mocap were, respectively for the thoracic and thoracolumbar angles, 0.57 ± 0.44 and 0.65 ± 0.47 degrees during trotting, and 0.83 ± 0.67 and 0.63 ± 0.44 degrees during canter.ConclusionsAngle values calculated with IMU data showed acceptable accuracy consistency for quantification of flexion‐extension movement in a horse's back. These results are encouraging for future development of the method in real‐life situations where mocap systems are unsuited for the quantification of back movements.Ethical Animal ResearchNone declared. Sources of funding: The authors thank the Institut Français du Cheval et de l′Equitation, the Association Nationale de la Recherche et de la Technologie and the Conseil Régional d′Aquitaine for financial support, the Pôle Hippolia for logistical support, and CIRALE for loaning the treadmill and the horse. Competing interests: none.

Variations in Muscle Activity of Vastus Lateralis and Gastrocnemius Lateralis with Increasing Draft Load

IntroductionMinimal research has examined the effect of draft loading on equine muscle activity. It is hypothesised that increases in draft load of 10 and 20% body mass (BM) will increase EMG intensity and duration of vastus lateralis (VL) and gastrocnemius lateralis (GL) during walk.MethodsData were collected from six Irish Cob geldings (11 ± 4 years; height: 1.47 ± 0.05 m; BM: 490 ± 65 kg) all trained to draft‐load. A modified lorry tyre was used as a loading platform. Surface EMG electrodes were positioned over VL and GL. An accelerometer placed on the left hind hoof collected kinematic data. EMG and accelerometer data at a draft load equivalent to 0 (zero load), 10 and 20% BM were recorded as the horses were led at walk in a 20 m straight line. A stopwatch determined mean speed over 20 m. Mean kinematic and EMG values were determined for 10 consecutive strides. EMG intensities were normalised to each horse. Kolmogorov‐Smirnov test explored data normality. Friedman test (P&lt;0.05) compared between conditions. A pair‐wise Wilcoxon signed ranks test identified where the differences lay.ResultsData for one horse was excluded because of poor accelerometer data. The remaining horses (n = 5) maintained a constant velocity (1.10 ± 0.02 m/s {SD}) between conditions (P&gt;0.7). VL and GL increased their muscular activity in terms of EMG intensity and duration of contraction with increasing draft load from 0 to 10% and 10 to 20% BM (P = 0.04; n = 5).ConclusionsDraft loading can be utilised for strength training following injury or to improve athletic performance.Ethical Animal ResearchThe study was approved by the Royal Veterinary College Ethics Committee. Sources of funding: Royal Veterinary College. Competing interests: none.

Variability of human gait: Long-range autocorrelations and fluctuation magnitude of stride duration

Human locomotion is a rhythmic process whose variability can be investigated in two different ways. The magnitude of the stride duration fluctuation can be addressed by classical mathematical methods (coefficients of variation) and are usually computed on about ten cycles. Fluctuation dynamics between strides can be characterized using the autocorrelation function computed by combining analysis of the Hurst exponent and of power spectral density over a large number of consecutive cycles (>=512) (Crevecoeur, J Neurosci Methods 2010). These analyses show that stride duration does not fluctuate at random but in a very complex way. Indeed, consecutive strides are characterized by correlations that can span over a large number of strides reflecting a centrally controlled behavior. Long-range autocorrelations are present among stride duration variability on level ground and on treadmill (Bollens, Gait&Posture 2010). They are not influenced by gait speed and subject age whereas coefficients of variation were inversely related to walking speed and the age of the subjects (Bollens, Neuroscience 2012). Long-range autocorrelations seem robust, being influenced by neither dual task walking nor backward walking (Bollens, Ann Biomed Eng 2013). Fluctuation magnitude and dynamics could be complementary tools for more complete gait characterization, in research and in clinical practice.

A Test of the Metabolic Cost of Cushioning Hypothesis during Unshod and Shod Running

This study aimed to investigate the effects of surface and shoe cushioning on the metabolic cost of running. In running, the leg muscles generate force to cushion the impact with the ground. External cushioning (surfaces or shoes) may reduce the muscular effort needed for cushioning and thus reduce metabolic cost. Our primary hypothesis was that the metabolic cost of unshod running would decrease with a more cushioned running surface. We also hypothesized that because of the counteracting effects of shoe cushioning and mass, unshod running on a hard surface would have approximately the same metabolic cost as running in lightweight, cushioned shoes. To test these hypotheses, we attached 10- and 20-mm-thick slats of the same foam cushioning used in running shoe midsoles to the belt of a treadmill that had a rigid deck. Twelve subjects who preferred a midfoot strike pattern and had substantial barefoot/minimalist running experience ran without shoes on the normal treadmill belt and on each thickness of foam. They also ran with lightweight, cushioned shoes on the normal belt. We collected V˙O2 and V˙CO2 to calculate the metabolic power demand and used a repeated-measures ANOVA to compare between conditions. Compared to running unshod on the normal belt, running unshod on the 10-mm-thick foam required 1.63% ± 0.67% (mean ± SD) less metabolic power (P = 0.034) but running on the 20-mm-thick foam had no significant metabolic effect. Running with and without shoes on the normal belt had similar metabolic power demands, likely because the beneficial energetic effects of cushioning counterbalanced the detrimental effects of shoe mass. On average, surface and shoe cushioning reduce the metabolic power required for submaximal running.

Variability of Human Gait: Effect of Backward Walking and Dual-Tasking on the Presence of Long-Range Autocorrelations

Information from the central and peripheral nervous systems is continuously integrated to produce a stable gait pattern. However, stride duration fluctuates in a complex manner in healthy subjects, exhibiting long-range autocorrelations that can span over hundreds of consecutive strides. The present study was conducted to explore the mechanisms controlling the long-term fluctuation dynamics of gait. In the first part of the study, stride duration variability was evaluated on a treadmill during forward (FW) and backward walking (BW). Despite the modification of the biomechanical constraints imposed on the locomotor system, the characteristics of the long-range autocorrelations remained unchanged in both modes of locomotion (FW: H=0.79±0.04 and α=0.58±0.13; BW: H=0.79±0.11 and α=0.53±0.25). In the second part of the study, stride duration variability was assessed while the subjects were performing a dual-task paradigm that combined gait and mental calculation. The long-term variability of stride duration was similar during usual walking (H=0.80±0.06 and α=0.57±0.13) and in dual-tasking (H=0.77±0.06 and α=0.52±0.16), whereas walking altered the performance of the cognitive task. Hence, the biomechanical and cognitive interferences imposed in the present study were not sufficient to induce a modification of the long-range autocorrelations highlighted in walking variability. These observations underline the robustness of the long-range autocorrelations.

Toward ambulatory balance assessment: Estimating variability and stability from short bouts of gait

Stride-to-stride variability and local dynamic stability of gait kinematics are promising measures to identify individuals at increased risk of falling. This study aimed to explore the feasibility of using these metrics in clinical practice and ambulatory assessment, where only a small number of consecutive strides are available. The concurrent validity and reliability were assessed compared to more continuous walking. Twenty young adults walked continuously for 500m, as well as 36 bouts of 20m while wearing an accelerometer (DynaPort MiniMod) on the trunk. Within-day reliability was high for stride time variability, mediolateral trunk variability and local dynamic stability, while between-day reliability was low for both variability estimates and moderate for local dynamic stability. Stride time variability and mediolateral trunk variability were increased when walking short bouts and did not correlate well with the longer walking trials. Local dynamic stability did correlate highly between the long and short bouts trials, and 15 bouts of eight strides appeared to be sufficient for valid estimation. These results imply task-specific differences and low reliability of variability estimates rendering them unsuitable for application to short bouts of gait, while local dynamic stability can be readily employed.

A note on the force of whip impacts delivered by jockeys using forehand and backhand strikes

The Australian Racing Board makes a distinction under its Rules of Racing concerning whip use between forehand and backhand whip action that is critically important: before the final 100 m of a race, the whip shall be used in a forehand manner neither in consecutive strides nor on more than 5 occasions. This seems to imply that backhand whip use is less closely scrutinized, which may have profound implications for horse welfare. We used pressure-detection pads to examine the force on the impact of 288 whip strikes (left forehand, left backhand, right forehand, and right backhand; n = 72 each) in batches of 12 consecutive strikes by 6 right-handed jockeys based in Victoria, a state in which thoroughbred racing is always conducted in a counterclockwise direction. The mean latency (±standard error of the mean) to complete each series of 12 strikes was 6.89 ± 0.44 seconds. The mean for force was 46.90 ± 5.39 N. Significant differences in force emerged between individual jockeys and in most interactions between jockey, hand and action. This highlights the problems the industry has in trying to enforce equity in whip use to satisfy punters while at the same time giving reassurances about horse welfare. The current results show that action (forehand vs. backhand) does not influence force on impact when using the nondominant hand. However, when using the dominant hand, these jockeys struck with more force in the backhand (P = 0.02). This result challenges the current focus on welfare concerns around forehand whip strikes. It should inform any review of the rules around whip use because it may help to avoid any unjustified focus on either forehand whip use or backhand whip use. This would help to inform the debate around levels of impact on fatigued horses when they are being struck for a perceived sporting gain.

Effects of Foot Strike on Low Back Posture, Shock Attenuation, and Comfort in Running

Barefoot running (BF) is gaining popularity in the running community. Biomechanical changes occur with BF, especially when initial contact changes from rearfoot strike (RFS) to forefoot strike (FFS). Changes in lumbar spine range of motion (ROM), particularly involving lumbar lordosis, have been associated with increased low back pain. However, it is not known if changing from RFS to FFS affects lumbar lordosis or low back pain. The purpose of this study was to determine whether a change from RFS to FFS would change lumbar lordosis, influence shock attenuation, or change comfort levels in healthy recreational/experienced runners. Forty-three subjects performed a warm-up on the treadmill where a self-selected foot strike pattern was determined. Instructions on running RFS/FFS were taught, and two conditions were examined. Each condition consisted of 90 s of BF with RFS or FFS, order randomly assigned. A comfort questionnaire was completed after both conditions. Fifteen consecutive strides from each condition were extracted for analyses. Statistically significant differences between FFS and RFS shock attenuation (P < 0.001), peak leg acceleration (P < 0.001), and overall lumbar ROM (P = 0.045) were found. There were no statistically significant differences between FFS and RFS in lumbar extension or lumbar flexion. There was a statistically significant difference between FFS and RFS for comfort/discomfort of the comfort questionnaire (P = .007). There were no statistically significant differences between other questions or the average of all questions. Change in foot strike from RFS to FFS decreased overall ROM in the lumbar spine but did not make a difference in flexion or extension in which the lumbar spine is positioned. Shock attenuation was greater in RFS. RFS was perceived a more comfortable running pattern.

Step-to-step variability in treadmill walking: influence of rhythmic auditory cueing.

While walking, human beings continuously adjust step length (SpL), step time (SpT), step speed (SpS = SpL/SpT) and step width (SpW) by integrating both feedforward and feedback mechanisms. These motor control processes result in correlations of gait parameters between consecutive strides (statistical persistence). Constraining gait with a speed cue (treadmill) and/or a rhythmic auditory cue (metronome), modifies the statistical persistence to anti-persistence. The objective was to analyze whether the combined effect of treadmill and rhythmic auditory cueing (RAC) modified not only statistical persistence, but also fluctuation magnitude (standard deviation, SD), and stationarity of SpL, SpT, SpS and SpW. Twenty healthy subjects performed 6×5 min. walking tests at various imposed speeds on a treadmill instrumented with foot-pressure sensors. Freely-chosen walking cadences were assessed during the first three trials, and then imposed accordingly in the last trials with a metronome. Fluctuation magnitude (SD) of SpT, SpL, SpS and SpW was assessed, as well as NonStationarity Index (NSI), which estimates the dispersion of local means in the times series (SD of 20 local means over 10 steps). No effect of RAC on fluctuation magnitude (SD) was observed. SpW was not modified by RAC, what is likely the evidence that lateral foot placement is separately regulated. Stationarity (NSI) was modified by RAC in the same manner as persistent pattern: Treadmill induced low NSI in the time series of SpS, and high NSI in SpT and SpL. On the contrary, SpT, SpL and SpS exhibited low NSI under RAC condition. We used relatively short sample of consecutive strides (100) as compared to the usual number of strides required to analyze fluctuation dynamics (200 to 1000 strides). Therefore, the responsiveness of stationarity measure (NSI) to cued walking opens the perspective to perform short walking tests that would be adapted to patients with a reduced gait perimeter.

Neural oscillators triggered by loading and hip orientation can generate activation patterns at the ankle during walking in humans

Spinal pattern generators (SPGs), which are neural networks without a central input from the brain may be responsible for controlling locomotion. In this study, we used neural oscillators to examine the rhythmic patterns generated at the ankle during walking. Seven healthy male subjects were requested to walk at their normal self-selected speed on a treadmill. Force measurements acquired from pressure insoles, electromyography and kinematic data were captured simultaneously. The SPG model consisted of a simple oscillator made up of two neurons; one neuron will activate an ankle extensor and the other will activate an ankle flexor. The outputs of the oscillator represented the muscle activation of each muscle. A nonlinear least squares algorithm was used to determine a set of parameters that would optimise the differences between model output and experimental data. Insole forces and hip angles of six consecutive strides were used as inputs to the model, which generated outputs that closely fitted experimental data. Our results showed that it is possible to reproduce muscle activations using neural oscillators. A close correlation between simulated and measured muscle activations indicated that spinal control should not be underestimated in models of human locomotion.