Biomedical subjects

A Hreljac

Publications and source records attributed to A Hreljac.

9 recordsLinked to original sources

PubMed2000

Phase determination during normal running using kinematic data.

Algorithms to predict heelstrike and toe-off times during normal running at subject-selected speeds, using only kinematic data, are presented. To assess the accuracy of these algorithms, results are compared with synchronised force platform recordings from ten subjects performing ten trials each. Using a single 180 Hz camera, positioned in the sagittal plane, the average RMS error in predicting heelstrike times is 4.5 ms, whereas the average RMS error in predicting toe-off times is 6.9 ms. Average true errors (negative for an early prediction) are +2.4 ms for heelstrike and +2.8 ms for toe-off, indicating that systematic errors have not occurred. The average RMS error in predicting contact time is 7.5 ms, and the average true error in predicting contact time is 0.5 ms. Estimations of event times using these simple algorithms compare favourably with other techniques requiring specialised equipment. It is concluded that the proposed algorithms provide an easy and reliable method of determining event times during normal running at a subject selected pace using only kinematic data and can be implemented with any kinematic data-collection system.

Adult↗

PubMed2000

Algorithms to determine event timing during normal walking using kinematic data.

Algorithms to predict heelstrike and toeoff times during normal walking using only kinematic data are presented. The accuracy of these methods was compared with the results obtained using synchronized force platform recordings of two subjects walking at a variety of speeds for a total of 12 trials. Using a 60Hz data collection system, the absolute value errors (AVE) in predicting heelstrike averaged 4.7ms, while the AVE in predicting toeoff times averaged 5.6ms. True average errors (negative for an early prediction) were +1.2ms for both heelstrike and toeoff, indicating that no systematic errors occurred. It was concluded that the proposed algorithms provide an easy and reliable method of determining event times during walking when kinematic data are collected, with a considerable improvement in resolution over visual inspection of video records, and could be utilized in conjunction with any 2-D or 3-D kinematic data collection system.

Acceleration↗

PubMed2000

Stride smoothness evaluation of runners and other athletes.

The purpose of this study was to compare an objective measurement of smoothness between a group of runners and a group of non-runners during running and fast walking. Smoothness was quantified by evaluating the endpoint jerk-cost (JC) at the heel. Subjects walked at a speed of 1.75 m.s(-1) and ran at a speed of 3.35 m.s(-1) on a motor driven treadmill while 2-D kinematic data (60 Hz) were collected from a sagittal plane view. The runners were found to be smoother than the non-runners during both gait conditions, suggesting that this group was inherently smoother in gait related tasks. This study demonstrated that the smoothness of gait can be quantified objectively by evaluating the end-point JC at the heel, and that competitive runners tend to exhibit smoother strides than recreational runners during both running and fast walking.

Adult↗

PubMed2000

Evaluation of lower extremity overuse injury potential in runners.

INTRODUCTION: The purpose of this study was to identify biomechanical and anthropometric variables that contribute to overuse injuries in runners. METHODS: Comparisons were made between a group of runners who had sustained at least one overuse running injury and a group of runners who had been injury free throughout their running careers. Groups were well matched in important training variables. Synchronized kinetic and rearfoot kinematic variables of both feet were collected by filming subjects running over a force platform at a speed of 4 m x s(-1). RESULTS: The injury-free group demonstrated significantly greater posterior thigh (hamstring) flexibility, as measured by a standard sit and reach test. This was the only anthropometric variable in which the groups differed. Within each group, there were no significant differences between left and right foot landing for any biomechanical variable. Biomechanical variables that demonstrated significantly lower values for the injury free group were the vertical force impact peak and the maximal vertical loading rate, with the maximal rate of rearfoot pronation and the touchdown supination angle showing a trend toward being greater in the injury free group. CONCLUSION: These results suggest that runners who have developed stride patterns that incorporate relatively low levels of impact forces, and a moderately rapid rate of pronation are at a reduced risk of incurring overuse running injuries.

Adult↗

PubMed1998

Individual effects on biomechanical variables during landing in tennis shoes with varying midsole density.

The aim of this study was to determine whether individuals responded uniquely to three different pairs of tennis shoes that differed only in midsole hardness. Kinematic and kinetic data were collected while the subjects (n = 3) performed a stereotyped lateral movement wearing each of the three pairs of tennis shoes. The results were analysed statistically for each subject separately. Variables were identified as discriminators between shoes for individual subjects based upon the results of separate discriminant analyses. After these analyses, a multivariate analysis of variance (MANOVA) was used for each subject to determine whether the discriminator variables differed significantly between shoes. A scoring system was devised that used the results of the MANOVA to assign scores to shoes for each variable. Cumulative scores for shoes (for each subject) were compared to determine which shoe was best for a subject. The results indicated that each subject responded uniquely to the shoes, and each demonstrated a preference for a particular pair of shoes. A need for single-subject designs exists when evaluating variations in athletic shoes.

Biomechanical Phenomena↗

PubMed1995

Determinants of the gait transition speed during human locomotion: kinematic factors.

The overall purpose of this investigation was to examine whether any kinematic factors could be identified as determinants of the preferred transition speed (PTS) during human locomotion. Initially, a set of four criteria was established that must be satisfied by a variable in order to be considered a determinant of the PTS. Three of the criteria were able to be examined by searching previous literature in addition to being tested experimentally, while a fourth stringent criterion was tested during this study. The experimental hypothesis of this study was that selected variables would conform to the four criteria. An extensive literature search identified four variables that met the first three criteria. From these four variables, only one (maximum ankle angular velocity) was found that also met the fourth criterion, while another (maximum ankle angular acceleration) was very close to meeting all criteria. It was hypothesized that gait transitions are effected to prevent overexertion of the dorsiflexor muscles that perform at or near maximum capacity during fast walking (at the PTS).

Acceleration↗

PubMed1993

The relationship between smoothness and economy during walking.

The purpose of this study was to test a theoretical model (Stein et al. 1986) which suggested that minimizing the rate of metabolic energy consumption (VO2) is related to minimizing jerk (third derivative of position) during human movement. At a given speed of walking, VO2 has been shown to increase curvilinearly as stride length (SL) is varied from freely chosen stride length (FCSL). It was hypothesized that the jerk-cost, or JC (area under squared jerk curve), would exhibit similar behavior. Subjects (n = 24) walked (1.75 m.s-1) on a treadmill at FCSL, and at SL derivations at +/- 10 and +/- 20% of leg length from FCSL until steady-state VO2 was attained. Videotaping (60 Hz) in the sagittal plane and subsequent digitizing of relevant markers produced position coordinates which were smoothed and normalized in both distance and time before calculating the third time derivative to obtain two-dimensional JC values. The expected response of VO2 to deviations in SL was found (minimum at FCSL), but JC increased with SL except at the two longest SL conditions. A weak but statistically significant negative correlation was found between VO2 and JC, suggesting that smoothness and economy are not complementary performance criteria during walking.

Biomechanical Phenomena↗

PubMed1993

The relationship between smoothness and performance during the practice of a lower limb obstacle avoidance task.

The relationship between performance (movement time) and smoothness was examined as subjects (n = 8) practiced a simple lower limb obstacle avoidance task. Smoothness was quantified by endpoint 3D jerk-cost, partitioned into magnitudinal and directional components. Data were collected with two WATSMART cameras at a sampling rate of 200 Hz for three sets of two trial blocks, including trials 1, 2, 13, 14, 25, and 26. Ten practice trials were performed between blocks of recorded trials. A DLT method was used to reconstruct 3D position coordinates of the fifth metatarsal of the subject's right (dominant) foot, considered to be the endpoint. After the data were smoothed with a fourth order, zero lag Butterworth filter, the time period was normalized so that a comparison of jerk-cost could be made between trials. Very rapid decreases in both movement time and jerk-cost measures were followed by gradual decreases, indicating that the movement became smoother as performance improved. Correlation coefficients between movement time and the various components of jerk-cost ranged from 0.70 to 0.78, supporting the hypothesis that moving more smoothly enables a person to move more rapidly during an obstacle avoidance task.

Cybernetics↗

PubMed1993

Preferred and energetically optimal gait transition speeds in human locomotion.

A widespread assumption of previous researchers is that the gait transition during human locomotion takes place at speeds that minimize metabolic energy consumption. The primary purpose of this investigation was to determine, by direct measurements, whether changing gaits is actually an energy saving mechanism. The secondary purpose of the experiment was determine whether the sense of effort, as measured by a Rating of Perceived Exertion (RPE), was greater for walking or running at the preferred transition speed (PTS). Twenty young, healthy adults (10 males, 10 females) walked on a treadmill at five speeds ranging from 70-110% of their individually measured PTS, and ran at five speeds ranging from 90-130% of their PTS while VO2 was monitored to determine each individual's energetically optimal transition speed (EOTS). Although the EOTS found during this study (2.24 m.s-1) was significantly greater than the PTS (2.06 m.s-1), RPE was significantly greater while walking at the PTS (13.5) than running at the PTS (10.0), suggesting that the gait transition during human locomotion does not take place in order to minimize metabolic energy consumption.

Adult↗