Thorsten Sterzing

The biomechanics of kicking in soccer: A review

Abstract Kicking is the defining action of soccer, so it is appropriate to review the scientific work that provides a basis of our understanding of this skill. The focus of this review is biomechanical in nature and builds on and extends previous reviews and overviews. While much is known about the biomechanics of the kicking leg, there are several other aspects of the kick that have been the subject of recent exploration. Researchers have widened their interest to consider the kick beginning from the way a player approaches the ball to the end of ball flight, the point that determines the success of the kick. This interest has encapsulated characteristics of overall technique and the influences of the upper body, support leg and pelvis on the kicking action, foot–ball impact and the influences of footwear and soccer balls, ball launch characteristics and corresponding flight of the ball. This review evaluates these and attempts to provide direction for future research.

The Influence of Soccer Shoes on Kicking Velocity in Full-Instep Kicks

Soccer shoes enhance the traction required by the stance leg but decrease the quality of the ball contact during full-instep kicking. Shoe features that influence ball velocity include traction, foot protection, foot rigidity, and toe box height. Upper material and general comfort potentially affect ball velocity. In contrast, shoe weight and outsole stiffness do not influence ball velocity.

Sensitivity mapping of the human foot: thresholds at 30 skin locations.

Background: Mechanoreceptors in the skin provide sensory input for the central nervous system about foot placement and loading. This information is used by the brain to actively control or regain balance and is important to establish memory traces for subsequent movement. A sensitivity map of the human foot could help to understand the mechanisms of the foot as a sensory organ for movement adjustment and balance control. Materials and Methods: Touch and vibration perception threshold values from 30 plantar and dorsal foot locations were determined in more than 40 women and men between 20 and 35 years. Semmes Weinstein monofilaments and a vibrotactile neurothesiometer were used for skin sensitivity threshold detection. Results: Large sensitivity differences were present between the 30 different foot sites. Gender effects were not present for touch but women had better sensitivities for vibration (p < 0.01), especially on the dorsal aspect of the foot. Age, in our cohort of 20- to 35-year-olds, did not have an influence on vibration or touch sensitivity. The heel had the highest detection thresholds for touch but was very sensitive for vibration stimuli. Compared to the dorsum, the plantar foot was substantially more sensitive, especially for vibration detection. Conclusion: The results suggest that primarily the fast adapting plantar mechanoreceptors are important in assisting balance control during human locomotion. Clinical Relevance: The sensitivity map of the foot will help in understanding the function of the foot as a sensory organ and could be useful in creating footwear for better balance control and for the design of comfortable shoes.

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.

The influence of soccer shoe design on playing performance: a series of biomechanical studies

Contrary to the large amount of literature results for running footwear surprisingly little research has been published for soccer shoes. Therefore, this contribution will summarize established knowledge and discuss future possibilities in soccer shoe design, based on biomechanical research. Game analyses over the years demonstrate that soccer has become increasingly faster and is more powerful than ever. Comfortable footwear, providing high traction and good stability for fast accelerations, stops and turns are the most desirable features that soccer players want from their shoes. From questionnaires, listing desirable shoe properties, injury protection received only a low priority for both, female and male soccer players. Originating from the priority list of players several biomechanical studies were performed to study possible influences of soccer shoe design on performance. It was found that soccer shoe design can have a substantial influence on sprinting performance, improve kicking accuracy, and influences maximum kicking velocity. The challenge in future soccer shoe design will not only be a combination of these performance related properties but also to include injury protection features.

Reliability of a basketball specific testing protocol for footwear fit and comfort perception

This study introduces a method for evaluating fit and comfort perception of basketball footwear by using a basketball specific course (BSC) and to examine respective inter-day reliability. Methods: The BSC incorporated a sequence of acceleration, deceleration, lateral shuffling, lay-up, backward running, jumping, and landing movements. Nineteen university basketball players provided their perception scores of four fit and seven comfort items after going through the BSC. Six footwear conditions were counterbalanced. Perception scores were analysed by repeated measures ANOVAs (comfort) or Friedman tests (fit) as VAS and Likert scales were applied. Significance level was set at p < 0.05. For reliability analysis, a retest (day 2) was performed 2 weeks after using the identical protocol of the first test day (day 1). Two-way repeated measures ANOVAs and intraclass correlation coefficients (ICC) of shoe ratings were used to determine inter-day effect and inter-day reliability. Results: Shoe effects on comfort were found for heel cushioning, forefoot cushioning, collar, medial–lateral control, and overall comfort in either one or both test days. Shoe effects on fit (heel region) were only identified on day 2. No inter-day effect was found for all fit and comfort perception measurements. All comfort items showed substantial inter-day reliability (ICC, 0.61 to 0.8). Only one fit item (shoe length) showed almost perfect reliability (ICC > 0.80) while the others showed moderate reliability (ICC, 0.41 to 0.6). Conclusion: Differences in basketball footwear fit and comfort perception were identified when performing the BSC testing protocol. The current protocol demonstrated substantial reliability for evaluating comfort perception but only moderate reliability for evaluating fit perception in most cases, indicating that distinct testing protocols for comfort and fit perception need to be considered for respective testing.

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.

Systematically modified crash-pad reduces impact shock in running shoes

The purpose of this study was to compare the effect of (a) crash-pad thickness and (b) midsole height at the heel to reduce heel impact load during running. Twenty male runners performed heel-toe runs in four different shoe conditions. While three shoe conditions had systematic changes in crash-pad thickness without changing general heel height, a fourth shoe condition differed only in overall heel height. Kinetic and kinematic running variables were quantified by using a force platform and an electrogoniometer. Data were collected for five valid running trials at a constant running speed of 3.5 ± 0.1 m s−1. Kolmogorov–Smirnov tests, a one-way repeated measures ANOVA (P < 0.05) as well as effect sizes (η 2) were calculated for all variables. The findings of this study showed that (a) increasing crash-pad thickness resulted in reduced impact variables without influencing traditional rearfoot motion variables. Furthermore, reduced heel height (b) is influencing predominantly rearfoot stability. Consequently, crash-pad modification can be used to improve cushioning properties without influences on rearfoot stability. Furthermore, crash-pad modification allows reducing shoe weight while maintaining cushioning properties.