Thomas L. Milani

Perceptual and biomechanical variables for running in identical shoe constructions with varying midsole hardness

OBJECTIVE: Perceptual ratings of mechanical variables were compared with biomechanical variables that are related to running injuries. DESIGN: Eight identical running shoes with a relatively close range of midsole hardness were used. Ground reaction force (GRF), in-shoe pressure distribution and rearfoot motion were measured during running. Perceptual ratings were obtained after the running trials. BACKGROUND: Previous studies reported high correlations between cushioning perception and biomechanical variables for shoes that featured large differences in midsole hardness. METHODS: A 15-point categorical rating scale was used to judge impact severity, pressure magnitude and rearfoot motion in running. Rating scores were compared with biomechanical variables (GRF, pressure distribution and pronation values) using regression analyses. RESULTS: Regression analyses revealed high relations between different biomechanical variables and the perception scores. The best relation to perception was analysed for the median power frequency of the vertical GRF (r(2) = 0.97). A negative correlation (r(2) = 0.54) between the first impact of GRF and the perception of impact severity could be revealed. CONCLUSION: The present study suggests that the bodys sensory system seems to differentiate well between impacts of different frequency content. Based on perceptual abilities, subjects adapt their running style to avoid high heel impacts.

Transfer of tennis racket vibrations onto the human forearm

One of several factors suspected in the development of lateral epicondylitis, often referred to as tennis elbow, is the impact-induced vibration of the racket-and-arm system at ball contact. Using two miniature accelerometers at the wrist and the elbow of 24 tennis players, the effects of 23 different tennis racket constructions were evaluated in a simulated backhand stroke situation. The influences of body weight, skill level, and tennis racket construction onto the magnitude of vibrations at wrist and elbow were investigated. Amplitudes, integrals, and fourier components were used to characterize arm vibration. More than fourfold reductions in acceleration amplitude and integral were found between wrist and elbow. Off-center as compared with center ball impacts resulted in approximately three times increased acceleration values. Between subjects, body weight as well as skill level were found to influence arm vibration. Compared with proficient players, a group of less skilled subjects demonstrated increased vibration loads on the arm. Between different racket constructions, almost threefold differences in acceleration values could be observed. Increased racket head size as well as a higher resonance frequency of the racket were found to reduce arm vibration. The vibration at the arm after ball impact showed a strong inverse relationship (r = -0.88) with the resonance frequency of tennis rackets.

Use of Ground Reaction Force Parameters in Predicting Peak Tibial Accelerations in Running

Ground reaction force data and tibial accelerations from a skin-mounted transducer were collected during rearfoot running at 3.3 m/s across a force platform. Five repetitive trials from 27 subjects in each of 19 different footwear conditions were evaluated. Ground reaction force as well as tibial acceleration parameters were found to be useful for the evaluation of the cushioning properties of different athletic footwear. The good prediction of tibial accelerations by the maximum vertical force rate toward the initial force peak (r2 = .95) suggests that the use of a force platform is sufficient for the estimation of shock-absorbing properties of sport shoes. If an even higher prediction accuracy is required a regression equation with two variables (maximum force rate, median power frequency) may be used (r2 = .97). To evaluate the influence of footwear on the shock traveling through the body, a good prediction of peak tibial accelerations can be achieved from force platform measurements.

Dynamic plantar pressure distribution measurements in hemiparetic patients.

OBJECTIVE: A comparison of plantar pressure distribution of hemiparetic patients with a control group was performed to determine quantitative, objective and reproducible criteria for better assessment of hemiparetic gait. DESIGN: This empirical, descriptive study used a clinical sample of 18 hemiparetic patients and compared the data to previously published data from 111 healthy persons. BACKGROUND: Several biomechanical methods have been used in the past to evaluate and classify hemiplegic gait, for example kinetic, cinematographic, or electromyographic systems, but plantar pressure distribution measurement has not been studied. METHODS: Peak pressures were determined under the feet of 18 hemiparetic patients during stance phase using a capacitive pressure distribution platform (EMED-F01 system, Novel GmbH). RESULTS: Hemiparetic patients showed considerably lower peak pressures under all anatomical structures and an unexpected medial load shift in the forefoot. CONCLUSIONS: The grade of spasticity seems to be the most important cause for expression of the medial load shift. Individual pressure distribution gait analysis, as shown in an example, may improve assessment and therapy of hemiparetic patients. RELEVANCE: Plantar pressure distribution data from hemiparetic patients can be used for an analysis of lower extremity dysfunctions. This method may also be employed to assess objectively the success of drug treatment and/or other rehabilitation processes. In particular, individual plantar pressure data from patients will provide additional clinical information for rehabilitation physicians, therapists, and engineers.

Actual and perceived running performance in soccer shoes: A series of eight studies

Soccer shoes in general but especially their outsoles are important for running and consequently playing performance. This article aims to quantify running performance and perception of running performance due to type of footwear and surface condition by use of Functional Traction Courses (FTC). Soccer players were required to run through slalom and acceleration courses as fast as possible providing running time and perception of running time variables due to wearing different soccer footwear. A series of eight single studies featuring different types of soccer footwear and different surfaces was conducted. The influence of footwear (subject Means and SD) was analyzed by Repeated Measures ANOVA, followed by post-hoc t-tests when appropriate. Slalom running times were considerably affected by altered shoe/surface interface conditions, whereas acceleration running times were affected only to lesser extent. Running time perception of athletes generally reflected actual running performance. Running performance differed about 3% when altering stud type or stud geometry. Thus, players benefit by the appropriate choice of footwear for a given surface. Complete elimination of studs resulted in a running time difference of 26% compared to normal condition. Surface conditions may be responsible for up to 20% of performance differences. It is recommended to include FTC testing in the evaluation of soccer footwear to get an idea of potential running performance benefits for players.

Foot sole skin temperature affects plantar foot sensitivity

OBJECTIVE Factors like age and polyneuropathic diseases are known to influence foot sensitivity and are considered when applying quantitative sensory testing. However, the effects of temperature on foot sensitivity are controversial. Therefore, the aim of this study was to investigate the influence of different foot sole temperature on vibration sensitivity of healthy subjects. METHODS Forty healthy subjects (20 male, 20 female) were analyzed. Vibration thresholds were measured at three anatomical locations (Heel, 1st Metatarsal Head and Hallux) of both feet at 200Hz. Thresholds were measured at initial baseline temperature and after cooling/warming of the foot skin 5-6 degrees C. Comparisons between baseline and cooled/warmed thresholds as well as between genders were performed. RESULTS There were no significant differences in vibration thresholds when comparing men and women. Thresholds were significantly higher after skin cooling for at all anatomical locations. After skin warming, thresholds were significantly lower at all measured anatomical locations. CONCLUSIONS Small temperature changes significantly influence vibration sensitivity of healthy subjects and should be controlled during collection of foot sensitivity data. SIGNIFICANCE The control of temperature is an important factor to enhance the quality of data acquired with quantitative sensory testing.

Comprehensive evaluation of player-surface interaction on artificial soccer turf.

The purpose of this study was to evaluate the traction characteristics of four different stud configurations on Fédération Internationale de Football Association (FIFA) 2-Star, third-generation artificial soccer turf. The investigated stud configurations were hard ground design, firm ground design, soft ground design, and an experimental prototype. The concept of this study combines performance, perception, biomechanical, and mechanical testing procedures. Twenty-five soccer players took part in the different testing procedures. Variables of this study were: running times, subjective rankings/ratings, ground reaction forces, and mechanical traction properties. Statistical discrimination between the four stud configurations was shown for performance, perception, and biomechanical testing (p < 0.05). Unsuited stud configurations for playing on artificial turf are characterized by less plain distributed and pronounced studs.

Ultimate stress and age-dependent deformation characteristics of the iliotibial tract.

BACKGROUND AND AIMS To understand biomechanics of ligaments and tendons data on their material properties are necessary. The iliotibial tract is a suitable model for virtual pelvic or lower extremity ligaments due to its parallel fibers, which facilitates biomechanical testing. Here, we determined Youngs modulus (YM) as secant stiffness between defined limits of the iliotibial tract and correlated the data to ultimate stress (US) of the specimens and to age, gender and body weight of the body donors. MATERIALS AND METHODS Thirty eight specimens from 12 iliotibial tracts of 10 young donors (mean age 31.2±9.1 years) were investigated biomechanically. After preconditioning, YM were determined in the ranges of 0-4 and 4-11 N/mm² of applied stress and from 4N/mm² of applied stress to US. RESULTS YM of the specimens were 84.7±30.2 (0-4 N/mm²), 335.4±101.9 (4-11 N/mm²), and 369.1±191.5 (4 N/mm² to US) N/mm², respectively. The mean US was 35.8±16.4 N/mm². YM and US correlated closely in the ranges of 4-11 N/mm² (r=0.95) and 4 N/mm² to US (r=0.91). YM did not correlate to age, body weight or gender within these young donors. Concerning tissue behavior a decrease of YM, i.e. weakening, is more common than an increase of YM, i.e. stiffening, before specimen failure. Overall, YM of specimens from young donors were significantly lower compared to those of old donors. DISCUSSION AND CONCLUSIONS This is the first study providing age-dependent nonlinear stiffness properties of the iliotibial tract. YM is significantly lower in young than in old donors and is thus a subject of alteration during life time.

Detecting foot-to-ground contact from kinematic data in running

Determining foot touchdown and foot takeoff is an essential part of gait analysis protocols and is usually accomplished using force plate data and thresholds for the vertical component of the ground reaction force (GRF). It has been proposed that gait events can also be estimated from kinematic data, and several algorithms have already been published. However, many of these algorithms were designed and specified for application in walking gait only. Hence, the purpose of this paper is to present our newly developed foot contact algorithm (FCA) and compare its estimation accuracy for touchdown and takeoff to a selection of existing algorithms. Forty one subjects were analyzed in a laboratory setup recording ground reaction forces and 3D-kinematic data of the lower limbs during running in three different running shoes. Prediction error of touchdown and takeoff was quantified in relation to gold standard events determined from force-plate data. Out of the evaluated algorithms, only FCA was able to estimate touch down and take off with similar precision, and is recommended when analyzing running gait. Furthermore, we found no evidence that different running shoes influenced the prediction error for any of the used algorithms.

Whole body vibration training reduces plantar foot sensitivity but improves balance control of healthy subjects

The goal of this study was to investigate the effects of short-time whole body vibration (WBV) training on foot vibration sensitivity of healthy subjects. Furthermore, the effects of WBV on a balance task (one-leg stand) were also evaluated. 30 young healthy subjects participated in the study. Vibration perception thresholds and balance were measured prior and after a single session of a 4-min WBV training (27Hz, 2mm horizontal amplitude). Thresholds were measured at 200Hz at three anatomical locations of the plantar foot area (first and fifth metatarsal heads and heel). Body balance was quantified using the length as well as the area described by the center of pressure (COP) at quiet, one-leg standing. Whereas vibration thresholds significantly increased after WBV training at all measured locations, there was a significant decrease in the balance related parameters after WBV exercise. The results indicate that the above-threshold, sinusoidal vibration used during WBV training is not an adequate strategy to stimulate/improve vibration sensitivity. The improvements seen in balance after WBV are likely to have neuromuscular mechanisms as their main component rather than increased foot sensitivity.