Gait transitions of persons with and without intellectual disability

Prediction of walk-to-run transition using stride frequency: A test-retest reliability study

The transition from walking to running has previously been predicted to occur at a point where the stride frequency starts getting closer to the running attractor than to the walking attractor. The two behavioural attractors were considered to be represented by the freely chosen stride frequencies during unrestricted treadmill walking and running. The aim of the present study was to determine the relative and absolute test-retest reliability of the predicted walk-to-run transition stride frequency. Healthy individuals (n=25) performed walking and running on a treadmill in a day-to-day test-retest design. The two behavioral attractors were determined during walking and running at freely chosen velocities and stride frequencies. Subsequently, the walk-to-run transition stride frequency was predicted using camera recordings and a previously reported equation for prediction. The walk-to-run transition occurred at a velocity of 7.7±0.5kmh^-1 at day 1 as well as at day 2. Besides, the predicted walk-to-run transition stride frequencies were 69.7±3.3 strides min^-1 and 70.5±3.4 strides min^-1 on day 1 and day 2, respectively (p=0.08). A further comparison between the predicted walk-to-run transition stride frequencies at day 1 and day 2 showed an ICC_3,1 of 0.89, which indicated almost perfect relative reliability. The absolute reliability was reflected by a%-value of the standard error of the measurement (SEM%) of 1.6% and a%-value of the smallest real difference (SRD%) of 4.4%. In conclusion, the predicted walk-to-run transition stride frequency can be considered reliable across days.

The role of stride frequency for walk-to-run transition in humans

It remains unclear why humans spontaneously shift from walking to running at a certain point during locomotion at gradually increasing velocity. We show that a calculated walk-to-run transition stride frequency (70.6 ± 3.2 strides min⁻¹) agrees with a transition stride frequency (70.8 ± 3.1 strides min⁻¹) predicted from the two stride frequencies applied during treadmill walking and running at freely chosen velocities and freely chosen stride frequencies. The agreement is based on Bland and Altman’s statistics. We found no essential mean relative difference between the two transition frequencies, i.e. −0.5% ± 4.2%, as well as limits of agreement of −8.7% and 7.7%. The particular two freely chosen stride frequencies used for prediction are considered behavioural attractors. Gait is predicted to be shifted from walking to running when the stride frequency starts getting closer to the running attractor than to the walking attractor. In particular, previous research has focussed on transition velocity and optimisation theories based on minimisation of, e.g., energy turnover or biomechanical loadings of the legs. Conversely, our data support that the central phenomenon of walk-to-run transition during human locomotion could be influenced by behavioural attractors in the form of stride frequencies spontaneously occurring during behaviourally unrestricted gait conditions of walking and running.

Development of a walking aerobic capacity test for structural firefighters

Firefighting requires high fitness to perform job tasks and minimize risk of job-related cardiac death. To reduce this risk, the International Association of Firefighters has recommended firefighters possess a VO2max ≥ 42 ml·kg-1·min-1. This recommendation is not universally applied because existing screening tests require costly equipment and do not accommodate firefighters unable to run. The purpose of this study was to develop a walking test to predict VO2max in firefighters using a standard treadmill. Thirty-eight male firefighters wore a vest weighing 20% of their body weight and performed a walking VO2max test on a standard treadmill. Walking speed was dependent on leg length and ranged from 3.6 to 4.3 mph. The test began with a 3-minute warm-up, after which the speed was increased to test speed. Every minute thereafter, the grade increased 1% until participants reached exhaustion. For cross-validation, 13 firefighters also performed a running VO2max test. The average test time was 16.95 ± 2.57 minutes (including warm-up) and ranged between 8 and 22 minutes. Average VO2max was 48.4 ± 6.5 ml·kg-1·min-1. Stepwise linear regression included time as the only significant independent variable explaining 76% of the variance in VO2max (p < 0.001). The standard error of the estimate was 3.2 ml·kg-1·min-1. The equation derived is: VO2max (ml·kg·min-1) = 11.373 + time (minute) × 2.184. On average, VO2max values measured while walking were 4.62 ± 5.86 ml·kg-1·min-1, lower than running values. This test has good potential for predicting VO2max among structural firefighters, and minimal equipment needs make it feasible for fire departments to administer.

The influence of dual-task conditions on movement in young adults with and without Down syndrome

This investigation compared spatial and temporal movement parameters of a sample of young adults with Down syndrome (DS) (N=12) and individuals without disabilities (IWD) (N=12) under dual-task conditions. Subjects performed a walking task at a preferred speed in isolation and again while holding a plate and cup, carrying tray and cups, talking on a phone, or buttoning a shirt. Spatial and temporal values were compared using a 2 (group) × 5 (conditions) repeated measures analysis of variance. Analysis of spatial components separately indicated that step length, step width, stride length and stride width revealed significant group and condition interactions (p ≤.01). Temporal components yielded significance in velocity and single-leg support time (p ≤.01). The current results support the notion that along with impairments to qualitative motor skills, individuals with DS are also impaired in higher order executive functioning (EF), as measured by a dual-task paradigm. It was concluded that movements are less efficient and functional in individuals with DS when an additional task is encountered while walking. We theorized that the motor program was sufficient for general locomotion but was not sufficiently developed to allow individuals with DS to modify or alter their movements to changing cognitive conditions that increasingly taxed EF. As gait and balance are trainable in this population, we recommend developing appropriate exercise and motor skill interventions during childhood and adolescents to increase strength, stability, and more "robust" ambulatory motor schema.

Evaluation of gait and slip parameters for adults with intellectual disability

Adults with intellectual disability (ID) experience more falls than their non-disabled peers. A gait analysis was conducted to quantify normal walking, and an additional slip trial was performed to measure slip response characteristics for adults with ID as well as a group of age- and gender-matched controls. Variables relating to gait pattern, slip propensity, and slip severity were assessed to compare the differences between groups. The ID group was found to have significantly slower walking speed, shorter step lengths, and increased knee flexion angles at heel contact. These gait characteristics are known to reduce the likelihood of slip initiation in adults without ID. Despite a more cautious gait pattern, however, the ID group exhibited greater slip distances indicating greater slip severity. This study suggests that falls in this population may be due to deficient slip detection or insufficient recovery response.

Effects of Down syndrome on three-dimensional motion during walking at different speeds

The inherent joint laxity and muscle hypotonia of adults with Down syndrome (DS) may result in reduced gait stability and increased energetic cost. These factors vary as a function of walking speed and may be reflected in gait patterns. The present study therefore examined whether the three-dimensional motion of the body center of mass (COM) and stepping characteristics differ between adults with and without DS as a function of speed. Fifteen adults with DS and 15 adults without DS underwent a series of treadmill walking trials. Walking speeds were determined as Froude numbers, based on leg length. Participants walked at Froude numbers of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and, for adults without DS, 0.7. Whole-body kinematic data were collected for 30-35 steps at each speed. Across speeds, adults with DS showed greater and more variable mediolateral COM motion than adults without DS. COM anteroposterior velocity and vertical motion did not differ in range between groups, but were more variable in adults with DS. Adults with DS also showed smaller-duration steps and varied their step widths and step lengths more than adults without DS. The results suggest a gait pattern with lesser stability and greater energetic cost among adults with DS.