Effect Of Gait Speed Research Articles

Effects of Gait Speed and Sole Adjustment on Shoe–Floor Angles: Measurement Using Shoe-Type Sensor

Background: Assessment of walking with shoes is important for understanding different types of walking in various environments. Methods: In this study, a shoe-type sensor was used to demonstrate the shoe–floor angle in fifteen participants who walked on a treadmill under varying gait speed and sole adjustments, lifting one side of the sole. The shoe–floor angle in the sagittal; the angle of toe-up (θTup) and toe-down (θTdown) and frontal planes; and the angle of pronation (θPro) and supination (θSup) were calculated, and angles at the initial contact and maximum angles were extracted. Results: The results showed that most angles significantly increased with an increase in the gait speed (θTup and θTdown; p < 0.01 both, θPro and θSup; p < 0.02 and 0.04). Conversely, only the supination angle at the initial contact changed significantly, owing to the tilt of the sole (p < 0.01). Conclusion: Shoe movements were more strongly affected by gait speed than by sole adjustment.

Effect of Gait Speed and Dynamic Time-Warping on the prediction of Lower-Limb Joint Angles

Effect of Gait Speed and Dynamic Time-Warping on the prediction of Lower-Limb Joint Angles

Effect of gait speed on clinical outcomes after crural and pedal bypass in patients with chronic limb-threatening ischemia.

Many factors affect long-term outcomes after open bypass in patients with chronic limb-threatening ischemia (CLTI). Ambulatory status has been suggested to be associated with clinical outcomes, but there is limited knowledge on the effect of gait speed on outcomes. The purpose of this study is to evaluate the effect of gait speed assessed in a 6-min walk test (6MWT) on outcomes after crural and pedal bypass in patients with CLTI. A retrospective analysis was performed in patients with CLTI who underwent a 6MWT at 1month after crural and pedal bypass at a single center from 2014 to 2021. Comparisons were made between those with high gait speed (HG group, 6-min walk distance (6MWD) > 288m) and those with low gait speed (LG group, 6MWD ≤288m). The primary endpoint was survival, and the secondary endpoints were graft patency, limb salvage, wound healing, major adverse cardiovascular events (MACEs), and hospital outcomes. Of 104 patients with CLTI who underwent a 6MWT after crural and pedal bypass, 46 (44%) and 58 (56%) were placed in the HG and LG groups, respectively. The LG group was older (p < .001), had more female subjects (p = .006), and had a higher prevalence of cerebrovascular disease (p = .042) and tissue loss (p = .007). The median follow-up was 36 (22-57) months. The HG group had significantly higher 3-year primary patency (65% vs 42%, p = .013), 3-year secondary patency (87% vs 66%, p = .018), 3-year overall survival (89% vs 58%, p < .001), and 3-year freedom from MACE (79% vs 67%, p = .039). The 3-year limb salvage and 12-month wound healing rates did not differ between the groups. Gait speed in patients with CLTI after crural and pedal bypass was associated with survival, freedom from MACE, and graft patency but not with limb salvage and wound healing. A detailed study of walking ability in these patients may be needed in the future.

Just a matter of indexes: symmetry in walking

Gait symmetry is related to differences between the left and right side of the body and provides information about functional limitation due to pathology/injury [1]. Many metrics exist to quantify gait symmetry, differing for the considered data source and mathematical approach [1]. Although the body center of mass (BCoM) is the point that globally represents an individual’s movement, very few studies have focused on the quantification of gait symmetry from its trajectory (Simmetry Index, SI) [2]. Conversely, the use of the Harmonic Ratio and of its improved version (iHR) has gained great popularity in recent years [3], being extracted from trunk 3D accelerations easily measured by wearable inertial devices. The relationship between the SI and iHR, however, has not been quantified yet. The aim of this study is thus to investigate this relationship in healthy adults during walking at different speeds. Five healthy adults (2 women, 1.69±0.08 m, 29.8±2.8 y) participates to this study (CAR 101/2021). They walked for 60 s on a treadmill at six different speeds (from 0.55 to 1.95 m/s with step of 0.28 m/s). The trajectories of 18 markers located on the main joint centers [4] were collected by an optoelectronic system (Vicon, 200 Hz). Simultaneously, lower trunk 3D linear accelerations were measured by an inertial sensor (APDM Opal, 200 Hz). The 3D trajectory of the BCoM was estimated from marker trajectories as the weighted mean of an 11–segment model [4]. Gait symmetry was then quantified for each stride and each direction (antero-posterior AP, medio-lateral ML, cranio-caudal CC) using two indices: the Symmetry Index (SI) from the BCoM trajectory [2] and the iHR from the trunk accelerations [3]. Both iHR and SI are based on the harmonic content of the relevant signal and range from 100% (perfect symmetry) to 0% (total asymmetry). To assess the effect of walking speed on SI and iHR values, a two-way repeated measure ANOVA was performed after verifying for normal data distribution. A total number of 1572 strides were analyzed, with a minimum of 288 strides for each participant. SI and iHR significantly differed in all three directions for each velocity (p<0.01), except at 1.39, 1.67 and 1.95 m/s in the ML direction (Fig. 1). When considering the effect of gait speed on symmetry values, the latter significantly changed only for the AP and CC components (p<0.0001) ( Fig. 1 ). SI and iHR may provide substantial different information about the level of gait symmetry, with iHR characterized by greater values in AP and CC directions and smaller values in ML direction. Interestingly, gait symmetry increases with speed, at least up to 1.67 m/s, in AP and CC directions. This is not the case for the ML component: whereas SI slightly decreases with speed (p<0.05), the high variability of iHR, already discussed in the literature [4], does not allow to identify any clear trend. It is suggested to carefully describe the methodology used to assess gait symmetry, as the type of data and the method used may strongly influence the final outcome and, thus, its clinical interpretation.

Measuring Foot Progression Angle during Walking Using Force-Plate Data

Foot progression angle (FPA) is a gait-related clinical measurement commonly used for assessing the rotational profile of the lower extremity. This study examined the accuracy of two methods based on force-plate data for estimating FPA during walking by comparing them with a reference method using a motion capture system. Ten healthy adults performed a series of overground walking trials at three different speeds: slow, preferred and fast. FPA was estimated from two methods using data on center of pressure—one method previously reported in the literature, and a novel method proposed here. The FPA estimated by each of these two force-plate methods were compared with the reference FPA determined from kinematic data. Results showed that the novel force-plate method was more accurate and precise when measuring the FPA in the three speed conditions than the force-plate method previously reported in the literature. The mean absolute error obtained with this novel method was 3.3° ± 2.1° at slow speed, 2.0° ± 1.2° at preferred speed and 2.0° ± 1.2° at fast speed, with no significant effect of gait speed (p &gt; 0.05). These findings suggest that the novel force-plate method proposed here is valid for determining FPA during walking at various speeds. In the absence of kinematic data, this method constitutes an attractive alternative for measuring FPA.

Effect of Gait Speed on Recovery Motion from Tripping on a Treadmill

The analysis of the mechanism of fall avoidance motion is required to prevent fall-related injuries. To investigate the factors that affect fall avoidance motion, tripping was induced among 10 healthy male subjects during treadmill walking at gait speeds of 3.5 and 4.0 km/h. The posture of the subjects and ground reaction force of the recovery steps were recorded using a motion capture system and force plate to analyze the effect of gait speed on recovery motion. The gait parameters of the recovery steps were calculated and compared between gait speeds. Principal component analysis was performed to identify the parameters that represent the recovery motion and the magnitude of the first and second recovery steps, and the balance of recovery steps were extracted as defining characteristics. Of the 18 gait parameters, such as step time, five differed depending on gait speeds. However, the other gait parameters and all four principal components did not differ significantly with respect to gait speeds. Furthermore, the distribution of principal components and gait parameters across subjects and gait speeds suggested that the variability between trials was greater than the effect of gait speed and individual characteristics on recovery motion.

The Effects of Gait Speed and Psychomotor Speed on Risk for Depression and Anxiety in Older Adults with Medical Comorbidities.

Gait speed and psychomotor speed slow with age and may predict neuropsychiatric disease such as depression and anxiety. We explored the relative predictive values of gait speed, psychomotor slowing, and a composite index of these two measures on time to new episode depression or anxiety in older adults at risk for these common psychiatric conditions. Randomized controlled prevention trial with 15-month follow-up. University-based late-life mental health research clinic. Two hundred thirteen individuals, age 60+ years, with subsyndromal symptoms of depression or anxiety and one of the following risk factors for these common conditions: mild cognitive impairment, knee osteoarthritis, or disabilities requiring home-based care. Participants in each of the risk factor groups were randomized to a depression-specific preventive intervention or usual care. Gait speed: 4-m walk test from the Short Physical Performance Battery. Psychomotor speed: Coding task of the Repeatable Battery for the Assessment of Neuropsychological Status. We created a composite index of slowing by determining whether participants exceeded established cut-offs for slow performance in both gait speed (≤0.8 m/s) and psychomotor speed (<7 on the coding task). Time to new onset syndromal depression/anxiety was measured using research diagnostic criteria. Fifty-four participants developed syndromal depression/anxiety (19.5%) over the course of 15 months. Participants with slowing in both areas were over twice as likely to experience new onset depression/anxiety (hazard ratio (HR) = 2.11; 95% confidence interval (CI) = 1.02-4.40, P = .046) compared to participants with no slowing in either area. Slowed gait (HR = 1.88; 95% CI = 0.992-3.55; P = .052) or slowed psychomotor speed (HR = 0.60; 95% CI = 0.14-2.58; P = .488) alone did not increase risk for depression/anxiety. Evaluating both gait and psychomotor speed in older adults with medical comorbidities and sub-syndromal depression may predict incident mental illness and inform prevention planning. Future research is needed to validate our observations and explore shared neurobiological mechanisms that explain this elevated risk.

Effects of age and speed on the ankle\u2013foot system\u2019s power during walking

Structural and functional changes in the foot have been associated with age-related changes in gait mechanics, but walking speed may be a confounding factor in this relationship. The aim of this study was to investigate the effect of aging and speed on the ankle–foot power output during level walking. The effects of speed and aging on features of the mechanical power and work of the ankle and foot were quantified with a gait analysis of 24 young and 16 older individuals walking at different speeds. We observed gait speed having a significant effect on all the investigated features: peak power and positive and negative work of the ankle, foot, and sum of the ankle and foot (average effect size: 0.64 ± 0.22, from 0.26 to 0.87). We observed age having no effect on these same features (average effect size: 0.23 ± 0.12, from 0.03 to 0.39), with the exception of age’s effect when combined with speed on the negative work of the foot. We performed additional analysis to illustrate how the speed can become a confounding factor to the understanding of the age effect on the gait biomechanics. Based on the influence of gait speed on the mechanical power of the ankle–foot system, it is essential that studies control for the effect of gait speed if there is interest in understanding age-related effects, particularly when studying frail older individuals.

A prediction method of speed-dependent walking patterns for healthy individuals

BackgroundGait speed is one of the main biomechanical determinants of human movement patterns. However, in clinical gait analysis, the effect of gait speed is generally not considered, and people with disabilities are usually compared with able-bodied individuals even though disabled people tend to walk slower. Research questionsThis study proposes a simple way to predict the gait pattern of healthy individuals at a specific speed. MethodsThe method consists of creating a reference database for a range of gait speeds, and the gait-pattern prediction is implemented as follows: 1) the gait cycle is discretized from 0 to 100% for each variable, 2) a first or second-order polynomial is used to adjust the values of the reference dataset versus the corresponding gait speeds for each instant of the gait cycle to obtain the parameters of the regression, and 3) these regression parameters are then used to predict the new values of the gait pattern at any specific speed. Twenty-four healthy adults walked on the treadmill at eight different gait speeds, where the gait pattern was obtained by a 3D motion capture system and an instrumented treadmill. ResultsOverall, the predicted data presented good agreement with the experimental data for the joint angles and joint moments. SignificanceThese results demonstrated that the proposed prediction method can be used to generate more unbiased reference data for clinical gait analysis and might be suitably applied to other speed-dependent human movement patterns.

The reliability of gait variability measures for individuals with Parkinson’s disease and healthy older adults – The effect of gait speed

BackgroundStep-to-step variability is a marker of reduced motor control and a frequently studied outcome measure in neurodegenerative disorders such as Parkinson’s disease (PD) as compared to healthy older adults (HOA). To challenge motor control of gait, walking should be tested at different gait speeds. Good reliability is essential, and gait variability estimates show good reproducibility when sampled at normal gait speed. The aim was therefore to investigate if gait variability could be reliably sampled at slow and fast speeds for individuals with PD and HOA by evaluating test-retest reliability. Methods29 (14 males) subjects with idiopathic PD, Hoehn &Yahr 2 (n = 18) and 3, ≥ 60 years, and 25 age matched HOAwere included. Spatiotemporal gait data was collected (GAITRite) during slow, normal, and fast walking on two occasions. ResultsMeasurement error was lowest for gait variability estimates based on 40 steps in both groups. This was true across all speeds in HOA, but only for normal and fast gait speeds in the PD cohort. Due to increased homogeneity in the variability estimates intraclass correlation coefficients (ICC) were low for HOA, except for step width variability. In the PD cohort ICCs were good to excellent for temporal- and step width gait variability across speeds. ConclusionHOA demonstrated reliable gait variability estimates across all speeds, whereas Individuals with PD were reliable at normal and fast gait speeds only Estimates should be based on at least 40 steps. Step width variability was overall the most reliable variable across groups and speed conditions.

The effect of gait speed and gait phase to the allocation of attention during dual task gait.

[Purpose] The purpose of this study was to determine the change of allocation of attention caused by a difference in gait phase and gait speed. We also determined the relationship between attentional demand and gait automaticity change caused by the gait speed alteration. [Subjects and Methods] Ten male participated. Participants were instructed to perform the probe reaction time (RT) task during treadmill walking in four different gait speed conditions (60%, 80%, 100%, and 120% of preferred speed). Walking ratio in each gait speed conditions were calculated, and RTs and walking ratios were compared in each gait speed condition and in the single-support and double-support gait phase. [Results] RTs were significantly delayed with decline of gait speed. Walking ratio was significantly decreased in proportion of decrement of gait speed. There was no difference of gait phase between single-support and double-support phase. [Conclusion] This study showed that relationship between attentional load and deficit of gait automaticity. While gait phase didn’t influence attentional demand, and this result showed the characteristics of treadmill gait.

Variability of the Dynamic Stiffness of Foot Joints: Effect of Gait Speed.

Comparison of dynamic stiffness of foot joints was previously proposed to investigate pathologic situations with changes in the properties of muscle and passive structures. Samples must be controlled to reduce the variability within groups being compared, which may arise from different sources, such as gait speed or Foot Posture Index (FPI). Variability in the measurement of the dynamic stiffness of ankle, midtarsal, and metatarsophalangeal joints was studied in a controlled sample of healthy men with normal FPI, and the effect of gait speed was analyzed. In experiment 1, dynamic stiffnesses were obtained in three sessions, five trials per session, for each participant, taking the mean value across trials as representative of each session. In experiment 2, five trials were considered at slow, comfortable, and fast velocities. Similar intersession and intrasession errors and intraparticipant errors within sessions were found, indicating the goodness of using five trials per session for averaging. The intraparticipant and interparticipant variability data provided can be used to select the sample size in future comparative analyses. Significant differences with gait speed were observed in most dynamic stiffnesses considered, with a general rise when gait speed increased, especially at the midtarsal joint, this being attributed to an active modulation produced by the central nervous system. Differences with gait speed were higher than intrasession and intersession repeatability errors for the propulsion phases at the ankle and midtarsal joints; comparative analyses at these phases need more exhaustive control of gait speed to reduce the required sample size.

O24 Gait Profile Score in post-stroke subjects accounting for the effect of gait speed

O24 Gait Profile Score in post-stroke subjects accounting for the effect of gait speed

Effects of gait speed on the body’s center of mass motion relative to the center of pressure during over-ground walking

Preferred walking speed (PWS) reflects the integrated performance of the relevant physiological sub-systems, including energy expenditure. It remains unclear whether the PWS during over-ground walking is chosen to optimize one’s balance control because studies on the effects of speed on the body’s balance control have been limited. The current study aimed to bridge the gap by quantifying the effects of the walking speed on the body’s center of mass (COM) motion relative to the center of pressure (COP) in terms of the changes and directness of the COM-COP inclination angle (IA) and its rate of change (RCIA). Data of the COM and COP were measured from fifteen young healthy males at three walking speeds including PWS using a motion capture system. The values of IAs and RCIAs at key gait events and their average values over gait phases were compared between speeds using one-way repeated measures ANOVA. With increasing walking speed, most of the IA and RCIA related variables were significantly increased (p<0.05) but not for those of the frontal IA. Significant quadratic trends (p<0.05) with highest directness at PWS were found in IA during single-limb support, and in RCIA during single-limb and double-limb support. The results suggest that walking at PWS corresponded to the COM-COP control maximizing the directness of the RCIAs over the gait cycle, a compromise between the effects of walking speed and the speed of weight transfer. The data of IA and RCIA at PWS may be used in future assessment of balance control ability in people with different levels of balance impairments.

Toward goal-oriented robotic gait training: The effect of gait speed and stride length on lower extremity joint torques.

Robot-assisted gait training is becoming increasingly common to support recovery of walking function after neurological injury. How to formulate controllers capable of promoting desired features in gait, i.e. goals, is complicated by the limited understanding of the human response to robotic input. A possible method to formulate controllers for goal-oriented gait training is based on the analysis of the joint torques applied by healthy subjects to modulate such goals. The objective of this work is to understand how sagittal plane joint torque is affected by two important gait parameters: gait speed (GS) and stride length (SL). We here present the results obtained from healthy subjects walking on a treadmill at different speeds, and asked to modulate stride length via visual feedback. Via principal component analysis, we extracted the global effects of the two factors on the peak-to-peak amplitude of joint torques. Next, we used a torque pulse approximation analysis to determine optimal timing and amplitude of torque pulses that approximate the SL-specific difference in joint torque profiles measured at different values of GS. Our results show a strong effect of GS on the torque profiles in all joints considered. In contrast, SL mostly affects the torque produced at the knee joint at early and late stance, with smaller effects on the hip and ankle joints. Our analysis generated a set of torque assistance profiles that will be experimentally tested using gait training robots.

Inter-segmental motions of the foot: differences between younger and older healthy adult females

BackgroundAlthough accumulative evidence exists that support the applicability of multi-segmental foot models (MFMs) in evaluating foot motion in various pathologic conditions, little is known of the effect of aging on inter-segmental foot motion. The objective of this study was to evaluate differences in inter-segmental motion of the foot between older and younger adult healthy females during gait using a MFM with 15-marker set.MethodsOne hundred symptom-free females, who had no radiographic evidence of osteoarthritis, were evaluated using MFM with 15-marker set. They were divided into young (n = 50, 20–35 years old) and old (n = 50, 60–69 years old) groups. Coefficients of multiple correlations were evaluated to assess the similarity of kinematic curve. Inter-segmental angles (hindfoot, forefoot, and hallux) were calculated at each gait phase. To evaluate the effect of gait speed on intersegmental foot motion, subgroup analysis was performed according to the similar speed of walking.ResultsKinematic curves showed good or excellent similarity in most parameters. Range of motion in the sagittal (p < 0.001) and transverse (p = 0.001) plane of the hallux, and sagittal (p = 0.023) plane of the forefoot was lower in older females. The dorsiflexion (p = 0.001) of the hallux at terminal stance and pre-swing phases was significantly lower in older females. When we compared young and older females with similar speed, these differences remained.ConclusionsAlthough the overall kinematic pattern was similar between young and older females, reduced range of inter-segmental motion was observed in the older group. Our results suggest that age-related changes need to be considered in studies evaluating inter-segmental motion of the foot.

Abstract P162: Maintenance of Gait Speed in Elderly Men and Women Reduces Risk of Hospitalization Irrespective of the Extent of Coronary Artery Calcium

Introduction: Coronary artery disease (CAD) is a major contributor to medical costs in old age, including risk of hospitalization and risk of disability. Coronary artery calcium (CAC) is an accepted biomarker for CAD. Individuals lose their functionality with increasing age at different pace due to various reasons including chronic disease, such as CAD. Functional impairment, measured by gait speed, may be an important indicator of risk for hospitalization. We assessed the hypothesis that elderly people who maintain their gait speed are less likely to be hospitalized independent of CAD defined by CAC. Methods: Data from the population based AGES Reykjavik Study included 1208 men and 1660 women walking without aid, mean age 76.4 years (SD 4.9), were examined between 2002-2006 and 2007-2011. CAC was measured at visit one and gait speed at both visits. Hospital records were obtained for all participants. Hospital admission rates were estimated using age adjusted survival models according to baseline gait speed at [0.1-0.8), [0.8-1.0), [1.0-2.0) m/sec; change in gait speed (reduced, maintained or increased) and by CAC categories (0-300, and more than 300 Agatston units). Analysis was performed for men and women separately and the effect of adjusting for knee strength evaluated. Results: Both lower baseline and decreasing gait speed were associated with increased rate of hospitalization over five years follow-up. The rate ratio was slightly attenuated after adjustment for knee extension. When change in gait speed over five years period was examined, those who maintained or increased their gait speed had significantly lower age adjusted hospitalization rate for both men and women (Figure). This effect of gait speed was statistically significant for both CAC categories in all categories of gait speed (p&lt; 0.05). Conclusion: These results show that maintenance of gait speed even in those who walk at a slow gait speed benefit by less hospitalization even if they have considerable CAD and thus potentially reduce health care cost.

Effects of Aging on Arm Swing during Gait: The Role of Gait Speed and Dual Tasking.

Healthy walking is characterized by pronounced arm swing and axial rotation. Aging effects on gait speed, stride length and stride time variability have been previously reported, however, less is known about aging effects on arm swing and axial rotation and their relationship to age-associated gait changes during usual walking and during more challenging conditions like dual tasking. Sixty healthy adults between the ages of 30–77 were included in this study designed to address this gap. Lightweight body fixed sensors were placed on each wrist and lower back. Participants walked under 3 walking conditions each of 1 minute: 1) comfortable speed, 2) walking while serially subtracting 3’s (Dual Task), 3) walking at fast speed. Aging effects on arm swing amplitude, range, symmetry, jerk and axial rotation amplitude and jerk were compared between decades of age (30–40; 41–50; 51–60; 61–77 years). As expected, older adults walked slower (p = 0.03) and with increased stride variability (p = 0.02). Arm swing amplitude decreased with age under all conditions (p = 0.04). In the oldest group, arm swing decreased during dual task and increased during the fast walking condition (p<0.0001). Similarly, arm swing asymmetry increased during the dual task in the older groups (p<0.004), but not in the younger groups (p = 0.67). Significant differences between groups and within conditions were observed in arm swing jerk (p<0.02), axial rotation amplitude (p<0.02) and axial jerk (p<0.001). Gait speed, arm swing amplitude of the dominant arm, arm swing asymmetry and axial rotation jerk were all independent predictors of age in a multivariate model. These findings suggest that the effects of gait speed and dual tasking on arm swing and axial rotation during walking are altered among healthy older adults. Follow-up work is needed to examine if these effects contribute to reduced stability in aging.

異なる歩行速度が歩行時の足部の動きに及ぼす影響

〔目的〕異なる歩行速度が歩行時の足部の動きに及ぼす影響を明らかにするため，足部を後足部と前足部に分け，分析することとした．〔対象〕健常成人男性10名とした．〔方法〕歩行速度は，遅い，快適，最速とした．三次元動作解析装置を用い，下腿部に対する後足部（HF/TB），後足部に対する前足部（FF/HF）の角度を算出した．分析項目は，立脚期の最大角度変化量と最大角度値に至るタイミングとした．〔結果〕歩行速度の増加に伴い，HF/TBとFF/HFの最大底屈角度変化量が増大した．また，HF/TBの最大背屈角度値に至るタイミングが早まった．〔結語〕歩行速度が，特に後足部と前足部の最大底屈変化量と後足部の最大背屈角度に至るタイミングを調節していた．

Age differences in the required coefficient of friction during level walking do not exist when experimentally-controlling speed and step length.

The effects of gait speed and step length on the required coefficient of friction (COF) confound the investigation of age-related differences in required COF. The goals of this study were to investigate whether age differences in required COF during self-selected gait persist when experimentally-controlling speed and step length, and to determine the independent effects of speed and step length on required COF. Ten young and 10 older healthy adults performed gait trials under five gait conditions: self-selected, slow and fast speeds without controlling step length, and slow and fast speeds while controlling step length. During self-selected gait, older adults walked with shorter step lengths and exhibited a lower required COF. Older adults also exhibited a lower required COF when walking at a controlled speed without controlling step length. When both age groups walked with the same speed and step length, no age difference in required COF was found. Thus, speed and step length can have a large influence on studies investigating age-related differences in required COF. It was also found that speed and step length have independent and opposite effects on required COF, with step length having a strong positive effect on required COF, and speed having a weaker negative effect.