Ezio Preatoni

Movement variability and skills monitoring in sports

The aim of this paper was to present a review on the role that movement variability (MV) plays in the analysis of sports movement and in the monitoring of the athletes skills. MV has been traditionally considered an unwanted noise to be reduced, but recent studies have re-evaluated its role and have tried to understand whether it may contain important information about the neuro-musculo-skeletal organisation. Issues concerning both views of MV, different approaches for analysing it and future perspectives are discussed. Information regarding the nature of the MV is vital in the analysis of sports movements/motor skills, and the way in which these movements are analysed and the MV subsequently quantified is dependent on the movement in question and the issues the researcher is trying to address. In dealing with a number of issues regarding MV, this paper has also raised a number of questions which are still to be addressed.

Motor variability in sports: A non-linear analysis of race walking

Abstract This aim of this study was to analyse the nature of movement variability and to assess whether entropy measures may represent a valuable synthetic index of neuromuscular organization. The regularity of kinematic/kinetic time series during race walking, the changes in the structure of intra-individual variability over the test session, and the influence of athletic skill in (inter)national rank athletes were investigated. Motion analysis techniques were used. Sample entropy (SampEn) was adopted to examine fluctuations in lower limb angles and ground reaction forces. The regularity of both original and surrogate time series was assessed and compared, by estimating SampEn, to verify the presence of non-linear features in movement variability. SampEn was statistically lower in the original data than in surrogates. In contrast, the regularity of time series did not change significantly throughout the subsequent intra-individual repetitions. Hip and ankle joint angles and vertical ground reaction force manifested increased entropy for skilled athletes. Results suggest that race walking variability was not only the product of random noise but also contained information about the inherent propriety of the neuro-musculo-skeletal system. Furthermore, they provide some indications about neuromuscular control of the lower limb joints during race walking gait, and about the differences between more and less skilled individuals.

Acute effect of different minimalist shoes on foot strike pattern and kinematics in rearfoot strikers during running

Abstract Despite the growing interest in minimalist shoes, no studies have compared the efficacy of different types of minimalist shoe models in reproducing barefoot running patterns and in eliciting biomechanical changes that make them differ from standard cushioned running shoes. The aim of this study was to investigate the acute effects of different footwear models, marketed as “minimalist” by their manufacturer, on running biomechanics. Six running shoes marketed as barefoot/minimalist models, a standard cushioned shoe and the barefoot condition were tested. Foot–/shoe–ground pressure and three-dimensional lower limb kinematics were measured in experienced rearfoot strike runners while they were running at 3.33 m · s−1 on an instrumented treadmill. Physical and mechanical characteristics of shoes (mass, heel and forefoot sole thickness, shock absorption and flexibility) were measured with laboratory tests. There were significant changes in foot strike pattern (described by the strike index and foot contact angle) and spatio-temporal stride characteristics, whereas only some among the other selected kinematic parameters (i.e. knee angles and hip vertical displacement) changed accordingly. Different types of minimalist footwear models induced different changes. It appears that minimalist footwear with lower heel heights and minimal shock absorption is more effective in replicating barefoot running.

Injury and biomechanical perspectives on the rugby scrum: a review of the literature

As a collision sport, rugby union has a relatively high overall injury incidence, with most injuries being associated with contact events. Historically, the set scrum has been a focus of the sports medicine community due to the perceived risk of catastrophic spinal injury during scrummaging. The contemporary rugby union scrum is a highly dynamic activity but to this point has not been well characterised mechanically. In this review, we synthesise the available research literature relating to the medical and biomechanical aspects of the rugby union scrum, in order to (1) review the injury epidemiology of rugby scrummaging; (2) consider the evidence for specific injury mechanisms existing to cause serious scrum injuries and (3) synthesise the information available on the biomechanics of scrummaging, primarily with respect to force production. The review highlights that the incidence of acute injury associated with scrummaging is moderate but the risk per event is high. The review also suggests an emerging acknowledgement of the potential for scrummaging to lead to premature chronic degeneration injuries of the cervical spine and summarises the mechanisms by which these chronic injuries are thought to occur. More recent biomechanical studies of rugby scrummaging confirm that scrum engagement forces are high and multiplanar, but can be altered through modifications to the scrum engagement process which control the engagement velocity. As the set scrum is a relatively ‘controlled’ contact situation within rugby union, it remains an important area for intervention with a long-term goal of injury reduction.

A modified prebind engagement process reduces biomechanical loading on front row players during scrummaging:a cross-sectional study of 11 elite teams.

Aim Biomechanical studies of the rugby union scrum have typically been conducted using instrumented scrum machines, but a large-scale biomechanical analysis of live contested scrummaging is lacking. We investigated whether the biomechanical loading experienced by professional front row players during the engagement phase of live contested rugby scrums could be reduced using a modified engagement procedure. Methods Eleven professional teams (22 forward packs) performed repeated scrum trials for each of the three engagement techniques, outdoors, on natural turf. The engagement processes were the 2011/2012 (referee calls crouch-touch-pause-engage), 2012/2013 (referee calls crouch-touch-set) and 2013/2014 (props prebind with the opposition prior to the ‘Set’ command; PreBind) variants. Forces were estimated by pressure sensors on the shoulders of the front row players of one forward pack. Inertial Measurement Units were placed on an upper spine cervical landmark (C7) of the six front row players to record accelerations. Players’ motion was captured by multiple video cameras from three viewing perspectives and analysed in transverse and sagittal planes of motion. Results The PreBind technique reduced biomechanical loading in comparison with the other engagement techniques, with engagement speed, peak forces and peak accelerations of upper spine landmarks reduced by approximately 20%. There were no significant differences between techniques in terms of body kinematics and average force during the sustained push phase. Conclusions Using a scrum engagement process which involves binding with the opposition prior to the engagement reduces the stresses acting on players and therefore may represent a possible improvement for players’ safety.

Engagement techniques and playing level impact the biomechanical demands on rugby forwards during machine-based scrummaging

Objectives This cross-sectional study investigated the factors that may influence the physical loading on rugby forwards performing a scrum by studying the biomechanics of machine-based scrummaging under different engagement techniques and playing levels. Methods 34 forward packs from six playing levels performed repetitions of five different types of engagement techniques against an instrumented scrum machine under realistic training conditions. Applied forces and body movements were recorded in three orthogonal directions. Results The modification of the engagement technique altered the load acting on players. These changes were in a similar direction and of similar magnitude irrespective of the playing level. Reducing the dynamics of the initial engagement through a fold-in procedure decreased the peak compression force, the peak downward force and the engagement speed in excess of 30%. For example, peak compression (horizontal) forces in the professional teams changed from 16.5 (baseline technique) to 8.6 kN (fold-in procedure). The fold-in technique also reduced the occurrence of combined high forces and head-trunk misalignment during the absorption of the impact, which was used as a measure of potential hazard, by more than 30%. Reducing the initial impact did not decrease the ability of the teams to produce sustained compression forces. Conclusions De-emphasising the initial impact against the scrum machine decreased the mechanical stresses acting on forward players and may benefit players’ welfare by reducing the hazard factors that may induce chronic degeneration of the spine.

Method for Movement and Gesture Assessment (MMGA) in Ergonomics

We present a technique for the ergonomic assessment of motor tasks and postures. It is based on movement analysis and it integrates the perceived discomfort scores for joints motions and the time involvement of the different body districts. It was tested on 8 subjects performing reaching movements. The experimental protocol was designed to have an a priori expected comfort ranking, namely, higher values in presence of more uncomfortable tasks. The validation of the Method for Movement and Gesture Assessment (MMGA) in the ergonomic evaluation of a reaching task gave promising results and showed the effectiveness of the index. Possible applications of the method might be the integration into CAD tools and human motion simulation to provide an early comparative evaluation of the ergonomics of the prototyping process and workplace redesign in industry.

Spinal muscle activity in simulated rugby union scrummaging is affected by different engagement conditions.

Biomechanical studies of rugby union scrummaging have focused on kinetic and kinematic analyses, while muscle activation strategies employed by front‐row players during scrummaging are still unknown. The aim of the current study was to investigate the activity of spinal muscles during machine and live scrums. Nine male front‐row forwards scrummaged as individuals against a scrum machine under “crouch‐touch‐set” and “crouch‐bind‐set” conditions, and against a two‐player opposition in a simulated live condition. Muscle activities of the sternocleidomastoid, upper trapezius, and erector spinae were measured over the pre‐engagement, engagement, and sustained‐push phases. The “crouch‐bind‐set” condition increased muscle activity of the upper trapezius and sternocleidomastoid before and during the engagement phase in machine scrummaging. During the sustained‐push phase, live scrummaging generated higher activities of the erector spinae than either machine conditions. These results suggest that the pre‐bind, prior to engagement, may effectively prepare the cervical spine by stiffening joints before the impact phase. Additionally, machine scrummaging does not replicate the muscular demands of live scrummaging for the erector spinae, and for this reason, we advise rugby union forwards to ensure scrummaging is practiced in live situations to improve the specificity of their neuromuscular activation strategies in relation to resisting external loads.

An integrated measurement system for analysing impact biomechanics in the rugby scrum

As part of a wider project investigating the biomechanics of the rugby scrum within rugby union, the focus of the present study was to design, realise and test an unobtrusive measurement system for assessing the kinematics and kinetics of rugby forwards while scrummaging on the pitch in realistic environmental conditions. Currently the study investigates one forward pack (eight players) scrummaging against an instrumented scrum machine, a training aid used widely throughout rugby. The measurement system integrates three different subsystems for: (1) measuring forces exerted by players; (2) capturing players’ movements; and, (3) triggering/synchronising all the sensors involved in (1) and (2). Applied three-dimensional forces were measured by strain gauge circuits attached to each pusher arm of the machine and then summed to produce the components of overall force. Multiple camera views allowed the recording and subsequent analysis of player movements, in the primary transverse (50 Hz and 200 Hz) and sagittal (50 Hz) planes of motion. A control system executed pre-recorded audio commands to players with consistent timings, sent trigger pulses to acquisition devices and collected analogue data at 500 Hz. The overall system has been applied successfully in the field to record data from rugby union forward packs across a range of playing levels and initial results confirm that the measurement system will be useful for its desired purpose to compare the biomechanics of different scrum engagement techniques.

Towards a Biomarker of Motor Adaptation: Integration of Kinematic and Neural Factors

We propose an experimental protocol for the integrated study of motor adaptation during target-based movements. We investigated how motor adaptation affects both cerebral activity and motor performance during the preparation and execution of a pointing task, under different conditions of external perturbation. Electroencephalography (EEG) and movement analysis were simultaneously recorded from 16 healthy subjects enrolled in the study. EEG signal was preprocessed by means of independent component analysis and empirical mode decomposition based Hilbert Huang transform, in order to extract event-related synchronization (ERS) and desynchronization (ERD) parameters. Movement analysis provided several kinematic indexes, such as movement durations, average jerk, and inter-quartile-ranges. Significant correlations between score, neural, and kinematic parameters were found. Specifically, the duration of the going phase of movement was found to correlate with synchronization in the beta brain rhythm, in both the planning and executive phases of movement. Inter-quartile ranges and average jerk showed correlations with executive brain parameters and ERS/ERDcueBeta, respectively. Results indicate the presence of links between the primary motor cortex and the farthest ending point of the upper limb. In the present study, we assessed significant relationship between neural and kinematic descriptors of motor adaptation, during a protocol requiring short-term learning, through the modulation of the external perturbations.