The future of performance-related sports biomechanics research

Biomechanical role can vary depending on the conditions of the motor task

Expert players in throwing sports may reduce the variability of projectile arrival position by systematically relating release parameters (e.g., release position, velocity, and angular velocity of the projectile). Reducing the variability of the projectile arrival position is often believed to increase the success rate of throwing task, but it may not be always true. Here, we experimentally illustrate that the systematic relationship between release parameters that reduce the variability of the ball arrival position may not increase the number of hitting trials during a throwing task. Furthermore, we demonstrate that the role of the release parameters in increasing successful trials can vary depending on the target size. Each participant threw balls at two different-sized targets (small and large target conditions). Additionally, they alternately threw balls with overhead and sidearm throwing for both the small and large targets. Our results showed that the release position and velocity in the left-right direction reduced the variability of the ball arrival position and increased the successful trials in the small target condition. In the large target condition, the two release parameters reduced the variability of the ball arrival position, but they did not increase the successful trials. Consequently, reducing the variability of the ball arrival position did not always equate to an increase in successful trials, as it depended on the target size. These findings indicate that the role of the release parameters in increasing hitting trials is not constant but varies depending on the condition of the motor task.

Computer simulation on the cueing movements in cue sports: a validation study

Background

Simulation models have been applied to analyze daily living activities and some sports movements. However, it is unknown whether the current upper extremity musculoskeletal models can be utilized for investigating cue sports movements to generate corresponding kinematic and muscle activation profiles. This study aimed to test the feasibility of applying simulation models to investigate cue sports players' cueing movements with OpenSim. Preliminary muscle forces would be calculated once the model is validated.

Methods

A previously customized and validated unimanual upper extremity musculoskeletal model with six degrees of freedom at the scapula, shoulder, elbow, and wrist, as well as muscles was used in this study. Two types of cueing movements were simulated: (1) the back spin shot, and (2) 9-ball break shot. Firstly, kinematic data of the upper extremity joints were collected with a 3D motion capture system. Using the experimental marker trajectories of the back spin shot on 10 male cue sports players, the simulation on the cueing movements was executed. The model was then validated by comparing the model-generated joint angles against the experimental results using statistical parametric mapping (SPM1D) to examine the entire angle-time waveform as well as t-tests to compare the discrete variables (e.g., joint range of motion). Secondly, simulation of the break shot was run with the experimental marker trajectories and electromyographic (EMG) data of two male cue sports players as the model inputs. A model-estimated muscle activation calculation was performed accordingly for the upper extremity muscles.

Results

The OpenSim-generated joint angles for the back spin shot corresponded well with the experimental results for the elbow, while the model outputs of the shoulder deviated from the experimental data. The discrepancy in shoulder joint angles could be due to the insufficient kinematic inputs for the shoulder joint. In the break shot simulation, the preliminary findings suggested that great shoulder muscle forces could primarily contribute to the forward swing in a break shot. This suggests that strengthening the shoulder muscles may be a viable strategy to improve the break shot performance.

Conclusion

It is feasible to cater simulation modeling in OpenSim for biomechanical investigations of the upper extremity movements in cue sports. Model outputs can help better understand the contributions of individual muscle forces when performing cueing movements.

Artificial Intelligence Approach in Biomechanics of Gait and Sport: A Systematic Literature Review

Background

Artificial neural network helps humans in a wide range of activities, such as sports.

Objective

This paper aims to investigate the effect of artificial intelligence on decision-making related to human gait and sports biomechanics, using computer-based software, and to investigate the impact of artificial intelligence on individuals' biomechanics during gait and sports performance.

Material and Methods

This review was conducted in compliance with the PRISMA guidelines. Abstracts and citations were identified through a search based on Science Direct, Google Scholar, PubMed, Elsevier, Springer Link, Web of Science, and Scopus search engines from 1995 up to 2023 to obtain relevant literature about the impact of artificial intelligence on biomechanics. A total of 1000 articles were found related to biomechanical characteristics of gait and sport and 26 articles were directly pertinent to the subject.

Results

The extent of the application of artificial intelligence in sports biomechanics in various fields. In addition, various variables in the fields of kinematics, kinetics, and the field of time can be investigated based on artificial intelligence. Conventional computational techniques are limited by the inability to process data in its raw form. Artificial Intelligence (AI) and Machine Learning (ML) techniques can handle complex and high-dimensional data.

Conclusion

The utilization of specialized systems and neural networks in gait analysis has shown great potential in sports performance analysis. Integrating AI into this field would be a significant advancement in sport biomechanics. Coaches and athletes can develop more precise training regimens with specialized performance prediction models.

Evaluation of the Foot Center of Pressure Estimation from Pressure Insoles during Sidestep Cuts, Runs and Walks

Estimating the foot center of pressure (CoP) position by pressure insoles appears to be an interesting technical solution to perform motion analysis beyond the force platforms surface area. The aim of this study was to estimate the CoP position from Moticon® pressure insoles during sidestep cuts, runs and walks. The CoP positions assessed from force platform data and from pressure insole data were compared. One calibration trial performed on the force platforms was used to localize the insoles in the reference coordinate system. The most accurate results were obtained when the motion performed during the calibration trial was similar to the motion under study. In such a case, mean accuracy of CoP position have been evaluated to 15±4mm along anteroposterior (AP) axis and 8.5±3mm along mediolateral (ML) axis for sidestep cuts, 18±5mm along AP axis and 7.3±4mm along ML axis for runs, 15±6mm along AP axis and 6.6±3mm along ML axis for walks. The accuracy of the CoP position assesment from pressure insole data increased with the vertical force applied to the pressure insole and with the number of pressure cells involved.

An EMG-Based Constitutive Law for Force Generation in Skeletal Muscle - Part II: Model Validation On the Ankle Joint Complex

This study evaluates the predictive ability of the skeletal muscle force model derived previously within the ankle joint complex. The model is founded in dimensional analysis, using electromyography and the muscle force-length, force-velocity, and force-frequency curves as inputs. Seventeen subjects (8 males, 9 females) performed five different exercises that activated the primary muscles crossing the ankle joint. Motion capture, force plate, and electromyography data were collected during these exercises. A constant, Km, was calculated for each muscle of each subject using four of the five exercises. The fifth exercise was used to validate the results by treating the moments due to muscle forces as known and all other components in Euler's second law as unknown. While muscle forces cannot be directly validated in vivo, methods can be developed to test these values with reasonable confidence. This study compared moments about the ankle joint due to the calculated muscle forces to the sum of the moments due to all other sources and the kinematic terms in the second Newton-Euler equation of rigid body motion. Average percent errors for each subject ranged from 4.2% to 15.5% with an average percent error across all subjects of 8.2% while maximum percent errors for each subject ranged from 33.3% to 78.0% with an overall average maximum of 52.4%. Future work will examine sensitivity analyses to identify potential simplifications to the model and solution process and will validate the model on a more complex joint.

Three-dimensional data-tracking simulations of sprinting using a direct collocation optimal control approach

Biomechanical simulation and modelling approaches have the possibility to make a meaningful impact within applied sports settings, such as sprinting. However, for this to be realised, such approaches must first undergo a thorough quantitative evaluation against experimental data. We developed a musculoskeletal modelling and simulation framework for sprinting, with the objective to evaluate its ability to reproduce experimental kinematics and kinetics data for different sprinting phases. This was achieved by performing a series of data-tracking calibration (individual and simultaneous) and validation simulations, that also featured the generation of dynamically consistent simulated outputs and the determination of foot-ground contact model parameters. The simulated values from the calibration simulations were found to be in close agreement with the corresponding experimental data, particularly for the kinematics (average root mean squared differences (RMSDs) less than 1.0° and 0.2 cm for the rotational and translational kinematics, respectively) and ground reaction force (highest average percentage RMSD of 8.1%). Minimal differences in tracking performance were observed when concurrently determining the foot-ground contact model parameters from each of the individual or simultaneous calibration simulations. The validation simulation yielded results that were comparable (RMSDs less than 1.0° and 0.3 cm for the rotational and translational kinematics, respectively) to those obtained from the calibration simulations. This study demonstrated the suitability of the proposed framework for performing future predictive simulations of sprinting, and gives confidence in its use to assess the cause-effect relationships of technique modification in relation to performance. Furthermore, this is the first study to provide dynamically consistent three-dimensional muscle-driven simulations of sprinting across different phases.

A Review of Forward-Dynamics Simulation Models for Predicting Optimal Technique in Maximal Effort Sporting Movements

The identification of optimum technique for maximal effort sporting tasks is one of the greatest challenges within sports biomechanics. A theoretical approach using forward-dynamics simulation allows individual parameters to be systematically perturbed independently of potentially confounding variables. Each study typically follows a four-stage process of model construction, parameter determination, model evaluation, and model optimization. This review critically evaluates forward-dynamics simulation models of maximal effort sporting movements using a dynamical systems theory framework. Organismic, environmental, and task constraints applied within such models are critically evaluated, and recommendations are made regarding future directions and best practices. The incorporation of self-organizational processes representing movement variability and “intrinsic dynamics” remains limited. In the future, forward-dynamics simulation models predicting individual-specific optimal techniques of sporting movements may be used as indicative rather than prescriptive tools within a coaching framework to aid applied practice and understanding, although researchers and practitioners should continue to consider concerns resulting from dynamical systems theory regarding the complexity of models and particularly regarding self-organization processes.

The validation of a swimming turn wall-contact-time measurement system: a touchpad application reliability study

The effectiveness of the swimming turn is highly influential to overall performance in competitive swimming. The push-off or wall contact, within the turn phase, is directly involved in determining the speed the swimmer leaves the wall. Therefore, it is paramount to develop reliable methods to measure the wall-contact-time during the turn phase for training and research purposes. The aim of this study was to determine the concurrent validity and reliability of the Pool Pad App to measure wall-contact-time during the freestyle and backstroke tumble turn. The wall-contact-times of nine elite and sub-elite participants were recorded during their regular training sessions. Concurrent validity statistics included the standardised typical error estimate, linear analysis and effect sizes while the intraclass correlating coefficient (ICC) was used for the reliability statistics. The standardised typical error estimate resulted in a moderate Cohen's d effect size with an R² value of 0.80 and the ICC between the Pool Pad and 2D video footage was 0.89. Despite these measurement differences, the results from this concurrent validity and reliability analyses demonstrated that the Pool Pad is suitable for measuring wall-contact-time during the freestyle and backstroke tumble turn within a training environment.

Validity of a portable force platform for assessing biomechanical parameters in three different tasks

The aim of this study was to determine the precision and accuracy of the vertical and anterior-posterior force components of the portable PASCO PS-2142 force plate. Impulse, peak force, and time to peak force were assessed and compared to a gold standard force plate in three different tasks: vertical jump, forward jump, and sprint start. Two healthy male participants performed ten trials for each task, resulting in 60 trials. Data analyses revealed good precision and accuracy for the vertical component of the portable force plate, with relative bias and root mean square (RMS) error values nearly the same in all tasks for the impulse, time to peak force, and peak force parameters. Precision and accuracy of the anterior-posterior component were lower for the impulse and time to peak force, with relative bias and RMS error values nearly the same between tasks. Despite the lower precision and accuracy of the anterior-posterior component of the portable force plate, these errors were systematic, reflecting a good repeatability of the measure. In addition, all variables presented good agreement between the portable and gold standard platforms. Our results provide a good perspective for using the aforementioned portable force plate in sports and clinical biomechanics.

An isovelocity dynamometer method to determine monoarticular and biarticular muscle parameters

This study aimed to determine whether subject-specific individual muscle models for the ankle plantar flexors could be obtained from single joint isometric and isovelocity maximum torque measurements in combination with a model of plantar flexion. Maximum plantar flexion torque measurements were taken on one subject at six knee angles spanning full flexion to full extension. A planar three-segment (foot, shank and thigh), two-muscle (soleus and gastrocnemius) model of plantar flexion was developed. Seven parameters per muscle were determined by minimizing a weighted root mean square difference (wRMSD) between the model output and the experimental torque data. Valid individual muscle models were obtained using experimental data from only two knee angles giving a wRMSD score of 16 N m, with values ranging from 11 to 17 N m for each of the six knee angles. The robustness of the methodology was confirmed through repeating the optimization with perturbed experimental torques (± 20%) and segment lengths (± 10%) resulting in wRMSD scores of between 13 and 20 N m. Hence, good representations of maximum torque can be achieved from subject-specific individual muscle models determined from single joint maximum torque measurements. The proposed methodology could be applied to muscle-driven models of human movement with the potential to improve their validity.

Biomechanical approaches to understanding the potentially injurious demands of gymnastic-style impact landings

Gymnasts are exposed to a high incidence of impact landings due to the execution of repeated dismount performances. Biomechanical research can help inform recent discussions surrounding a proposed rule change in potentially injurious gymnastic dismounting. The review examines existing understanding of the mechanisms influencing the impact loads incurred in gymnastic-style landings achieved using biomechanical approaches. Laboratory-based and theoretical modelling research of inherent and regulatory mechanisms is appraised. The integration of the existing insights into injury prevention interventions studies is further considered in the appraisals. While laboratory-based studies have traditionally been favoured, the difficulty in controlling and isolating mechanisms of interest has partially restricted the understanding gained. An increase in the use of theoretical approaches has been evident over the past two decades, which has successfully enhanced insight into less readily modified mechanisms. For example, the important contribution of mass compositions and 'tuned' mass coupling responses to impact loading has been evidenced. While theoretical studies have advanced knowledge in impact landing mechanics, restrictions in the availability of laboratory-based input data have suppressed the benefits gained. The advantages of integrating laboratory-based and theoretical approaches in furthering scientific understanding of loading mechanisms have been recognised in the literature. Since a multi-mechanism contribution to impact loading has been evident, a deviation away from studies examining isolated mechanisms may be supported for the future. A further scientific understanding of the use of regulatory mechanisms in alleviating a performer's inherent injury predisposition may subsequently be gained and used to inform potential rule changes in gymnastics. While the use of controlled studies for providing scientific evidence for the effectiveness of gymnastics injury counter measures has been advocated over the past decade, a lack of information based on randomised controlled studies or actual evaluation of counter measures in the field setting has been highlighted. The subsequent integration of insight into biomechanical risk factors of landing with clinical practice interventions has been recently advocated.

Evaluation of a Subject-Specific, Torque-Driven Computer Simulation Model of One-Handed Tennis Backhand Ground Strokes

A torque-driven, subject-specific 3-D computer simulation model of the impact phase of one-handed tennis backhand strokes was evaluated by comparing performance and simulation results. Backhand strokes of an elite subject were recorded on an artificial tennis court. Over the 50-ms period after impact, good agreement was found with an overall RMS difference of 3.3° between matching simulation and performance in terms of joint and racket angles. Consistent with previous experimental research, the evaluation process showed that grip tightness and ball impact location are important factors that affect postimpact racket and arm kinematics. Associated with these factors, the model can be used for a better understanding of the eccentric contraction of the wrist extensors during one-handed backhand ground strokes, a hypothesized mechanism of tennis elbow.

Determination of football pitch locations from video footage and official pitch markings

The ability to determine a specific location on a football (soccer) pitch from television footage would provide a cost-effective method of obtaining competition-specific information on many professional and international teams. This study presents the accuracy and reliability of a new method of calculating ball location from simulated television coverage and known pitch markings. The coordinates of 99 markers of known location on a football pitch were digitized from video. An intersection point was determined from the equations of two lines that form pitch markings and the relationship from this point to other known pitch coordinates was calculated using a curve-fitting based method. Average error between known and reconstructed measures was 0.21 m for pitch width and 0.11 m for pitch length from a view simulating television coverage. Inter- and intra-rater reliability analyses showed researchers could consistently reconstruct pitch locations to within less than half a metre. The accuracy and reliability of this method will be sufficient for most practical uses in an applied sport environment, although the level of accuracy required will depend on the specific application. This method could be applied to other sports to determine specific locations on a pitch or court or to improve current competition analysis systems.

Perceptions of elite coaches and sports scientists of the research needs for elite coaching practice

A major objective of sports scientists and elite coaches is the enhancement of athletic performance. Despite this common goal, there is a general perception that research in sports science does not meet the needs of coaches. A study using survey and interview examined the perceptions of elite coaches and sports science researchers in Australia regarding the research needs of elite coaching. Congruence was found between coaches and researchers regarding research practice at the elite level. Both groups held common perceptions on the importance and application of research, the methods by which research questions are determined, and the qualities valued in elite coaches and sports science researchers. However, elite coaches perceived a need for more research in the area of sports psychology, dissemination of research findings via coaching clinics and sports-specific magazines, and the use of more appropriate "lay" language in information dissemination.

Runners do not push off the ground but fall forwards via a gravitational torque

The relationship between the affect and timing of the four forces involved in running (gravity, ground reaction force, muscle force, and potential strain energy) is presented. These forces only increase horizontal acceleration of the centre of mass during stance but not flight. The current hierarchical models of running are critiqued because they do not show gravity, a constant force, in affect during stance. A new gravitational model of running is developed, which shows gravity as the motive force. Gravity is shown to cause a torque as the runner's centre of mass moves forward of the support foot. Ground reaction force is not a motive force but operates according to Newton's third law; therefore, the ground can only propel a runner forward in combination with muscle activity. However, leg and hip extensor muscles have consistently proven to be silent during leg extension (mid-terminal stance). Instead, high muscle-tendon forces at terminal stance suggest elastic recoil regains most of the centre of mass's height. Therefore, the only external motive force from mid-terminal stance is gravity via a gravitational torque, which causes a horizontal displacement. The aim of this paper is to establish a definitive biomechanical technique (Pose method) that is easily taught to runners (Romanov, 2002): falling forwards via a gravitational torque while pulling the support foot rapidly from the ground using the hamstring muscles.

A profile of sports science research (1983–2003)

A majority of sports science research is undertaken in universities and dedicated research centres, such as institutes of sport. Reviews of literature analysing and categorising research have been carried out, but categories identified have been limited to research design and data gathering techniques. Hence there is a need to include categories such as discipline, subjects and targeted sport. A study was conducted using document analysis method to gather data that described and categorised performance-based sports science research projects in Australian universities and institutes of sport. An instrument was designed that could be used by researchers to analyse and profile research in the area of sports science. The instrument contained six categories: targeted sport, primary study area, participant type, research setting, methodology and data gathering techniques. Research documents analysed consisted of 725 original unpublished research reports/theses. Results showed that over two-thirds of research projects were targeted to specific sports and, of this group, nearly half involved four sports: cycling, rowing, athletics and swimming. Overall, physiology was the most researched scientific discipline. The most frequently used research method was experimental design, and the most frequently used data gathering technique was physiological (performance) measures. Two-thirds of research was conducted in laboratory settings, and nearly half of the research was conducted with elite or sub-elite athletes as participants/subjects. The findings of this study provide an overall synopsis of performance-based sports science research conducted in Australia over the last 20 years, and should be of considerable importance in the ongoing development of sports science research policy in Australia.

Evaluation of a torque-driven model of jumping for height

This study used an optimization procedure to evaluate an 8-segment torque-driven subject-specific computer simulation model of the takeoff phase in running jumps for height. Kinetic and kinematic data were obtained on a running jump performed by an elite male high jumper. Torque generator activation timings were varied to minimize the difference between simulation and performance in terms of kinematic and kinetic variables subject to constraints on the joint angles at takeoff to ensure that joints remained within their anatomical ranges of motion. A percentage difference of 6.6% between simulation and recorded performance was obtained. Maximizing the height reached by the mass center during the flight phase by varying torque generator activation timings resulted in a credible height increase of 90 mm compared with the matching simulation. These two results imply that the model is sufficiently complex and has appropriate strength parameters to give realistic simulations of running jumps for height.

Strategies in preflight for an optimal Yurchenko layout vault

An optimal Yurchenko layout vault of an elite female gymnast was identified by Koh et al. [2003. A predicted optimal performance of the Yurchenko layout vault in women's artistic gymnastics. Journal of Applied Biomechanics 19, 187-204] to require a combination of an increased body angle at horse contact and increased angular momentum for postflight than was recorded experimentally. However, the individual effect of each of these variables to producing the optimal vault is not known. The purpose of the study was to determine an appropriate strategy to teaching the optimal Yurchenko layout vault. Separate optimisations were carried out to investigate how each of these variables would change in order to produce the optimal vault identified by Koh et al. (2003). A combined optimal parameter selection and optimal control approach was used. The results suggest that when the body angle of attack at horse impact was kept low, pre-flight angular momentum had to be increased, with further gains during horse impact, to produce an optimal vault. This strategy of increasing solely the level of angular momentum needed for optimum postflight may not be attainable realistically. On the other hand, employing a larger body angle of attack required an increase in angular momentum during impact but which was attainable. Both optimisations show that increasing the vertical CM horse takeoff velocity is essential for postflight height and distance. The strategy to enhance performance should thus focus on maintaining an appropriate CM pre-flight velocity, a high level of angular momentum during pre-flight and to contact the horse with a large body angle of attack.

Nutrition on match day

What players should eat on match day is a frequently asked question in sports nutrition. The recommendation from the available evidence is that players should eat a high-carbohydrate meal about 3 h before the match. This may be breakfast when the matches are played around midday, lunch for late afternoon matches, and an early dinner when matches are played late in the evening. The combination of a high-carbohydrate pre-match meal and a sports drink, ingested during the match, results in a greater exercise capacity than a high-carbohydrate meal alone. There is evidence to suggest that there are benefits to a pre-match meal that is composed of low-glycaemic index (GI) carbohydrate foods rather than high-GI foods. A low-GI pre-match meal results in feelings of satiety for longer and produces a more stable blood glucose concentration than after a high-GI meal. There are also some reports of improved endurance capacity after low-GI carbohydrate pre-exercise meals. The physical demands of soccer training and match-play draw heavily on players' carbohydrate stores and so the benefits of good nutritional practices for performance and health should be an essential part of the education of players, coaches, and in particular the parents of young players.

Physiological and mechanical response to soccer-specific intermittent activity and steady-state activity

The aim of this study was to quantify response to a soccer-specific intermittent (INT) treadmill protocol based on notational analysis of match-play. Ten male semiprofessional football players (age 24.7 +/- 4.4 yr, body mass 77.1 +/- 8.3 kg, VO2max 63.0 +/- 4.8 ml x kg x min(-1)) completed the 90 minute INT protocol and a steady-state (SS) protocol eliciting the same distance covered. Physiological (heart rate [HR], ratings of perceived exertion [RPE], blood lactate concentration, salivary cortisol concentration) and mechanical (electromyography [EMG] of biceps femoris and rectus femoris) responses were obtained at 15 minute intervals throughout each protocol. The physiological and mechanical responses were typically greater during the INT protocol than during the SS protocol, tending to increase as a function of exercise duration. The INT activity profile induces cumulative mechanical load on the musculoskeletal system. The increased incidence of injury toward the latter stages of match-play is attributed to compromised movement mechanics, rather than physiological strain.

Determination of subject-specific model parameters for visco-elastic elements

The determination of subject-specific model parameter values is necessary in order for a computer simulation model of human motion to be evaluated quantitatively. This study used an optimisation procedure along with a kinematically driven simulation model of the contact phase in running jumps to determine the elastic parameters of segmental wobbling masses and the foot-ground interface. Kinetic and kinematic data were obtained on running jumps for height and distance performed by an elite male high jumper. Stiffness and damping coefficients of the visco-elastic elements in the model were varied until the difference between simulation and performance was minimised. Percentage differences of 6% and 9% between the simulated and recorded performances were obtained in the jumps for height and distance, respectively. When the parameters obtained from the jump for height were used in a simulation of the jump for distance (and vice versa), there was poor agreement with the recorded jump. On the other hand, a common set of visco-elastic parameters were obtained using the data from both recorded jumps resulting in a mean difference of only 8% (made up of 7% and 10%) between simulation and performance that was almost as good as the individual matches. Simulations were not overly sensitive to perturbations of the common set of visco-elastic parameters. It is concluded that subject-specific elastic parameters should be calculated from more than a single jump in order to provide a robust set of values that can be used in different simulations.

Carbohydrates and fat for training and recovery

An important goal of the athlete's everyday diet is to provide the muscle with substrates to fuel the training programme that will achieve optimal adaptation for performance enhancements. In reviewing the scientific literature on post-exercise glycogen storage since 1991, the following guidelines for the training diet are proposed. Athletes should aim to achieve carbohydrate intakes to meet the fuel requirements of their training programme and to optimize restoration of muscle glycogen stores between workouts. General recommendations can be provided, preferably in terms of grams of carbohydrate per kilogram of the athlete's body mass, but should be fine-tuned with individual consideration of total energy needs, specific training needs and feedback from training performance. It is valuable to choose nutrient-rich carbohydrate foods and to add other foods to recovery meals and snacks to provide a good source of protein and other nutrients. These nutrients may assist in other recovery processes and, in the case of protein, may promote additional glycogen recovery when carbohydrate intake is suboptimal or when frequent snacking is not possible. When the period between exercise sessions is < 8 h, the athlete should begin carbohydrate intake as soon as practical after the first workout to maximize the effective recovery time between sessions. There may be some advantages in meeting carbohydrate intake targets as a series of snacks during the early recovery phase, but during longer recovery periods (24 h) the athlete should organize the pattern and timing of carbohydrate-rich meals and snacks according to what is practical and comfortable for their individual situation. Carbohydrate-rich foods with a moderate to high glycaemic index provide a readily available source of carbohydrate for muscle glycogen synthesis, and should be the major carbohydrate choices in recovery meals. Although there is new interest in the recovery of intramuscular triglyceride stores between training sessions, there is no evidence that diets which are high in fat and restricted in carbohydrate enhance training.

A Predicted Optimal Performance of the Yurchenko Layout Vault in Women’s Artistic Gymnastics

The Yurchenko layout vault is the base vault from which more advanced forms of the Yurchenko family of vaults have evolved. The purpose of the study was to predict an individual’s optimal Yurchenko layout vault by modifying selected critical mechanical variables. The gymnast’s current performance characteristics were determined using the Peak-Motus video analysis system. Body segment parameters were determined using the elliptical zone mathematical modeling technique of Jensen (1978). A 5-segment computer simulation model was personalized for the gymnast comprising the hands, upper limbs, upper trunk, lower trunk, and lower limbs. Symmetry was assumed, as the motion was planar in nature. An objective function was identified which translated the subjective points-evaluation scheme of the Federation of International Gymnastics (FIG) Code of Points to an analytic expression that was mathematically tractable. The objective function was composed of performance variables that, if maximized, would result in minimal points being deducted and bonus points being allocated. A combined optimal control and optimal parameter selection approach was applied to the model to determine an optimum technique. The predicted optimal vault displayed greater postflight amplitude and angular momentum when compared with the gymnast’s best trial performance. Increased angular velocity, and consequently greater angular momentum at impact and greater shoulder flexion angle at impact with the horse, were related with this optimum technique. The impact phase therefore serves to increase the angular momentum during horse contact. Since the optimized parameters at impact with the horse were within the accepted physical capacity limits observed for the individual, the predicted vault is viable.

Accuracy of Scaling and DLT Reconstruction Techniques for Planar Motion Analyses

Numerous planar analyses of sports activities have utilized scaling techniques to convert image coordinates into real-space locations. While in certain circumstances, such as competition, the camera must be elevated above the activity and its tilt accounted for, the influence of tilt on reconstruction accuracy using scaling is currently unreported. A modification of the direct linear transformation (2D-DLT) which considers only the vertical plane provides an alternative approach for planar reconstruction. This study compared the reconstruction accuracy between scaling and 2D-DLT over a range of tilt angles throughout a 6-m horizontal field of view. Four calibration and 30 reconstruction markers of known locations in a vertical plane were videotaped from nine positions to provide tilt angles varying between –2° and +6°. Both techniques were used to estimate real-space locations for the reconstruction markers, and accuracy was calculated by comparing known and reconstructed locations. The smallest reconstruction errors were obtained using 2D-DLT and were unaffected by camera tilt. The scaling technique produced significantly larger (p < 0.01) errors than 2D-DLT, with the exception of 0° and +1° of tilt, and there was a detrimental effect on accuracy as the magnitude of tilt increased. The largest variations in reconstruction errors were associated with scaling, with markers at the extremes of the image showing the largest errors. The 2D-DLT approach provided accurate reconstruction data for planar analyses across the field of view and throughout the range of tilt angles, and should be preferred over scaling techniques.

Determining Subject-Specific Torque Parameters for Use in a Torque-Driven Simulation Model of Dynamic Jumping

This paper describes a method for defining the maximum torque that can be produced at a joint from isovelocity torque measurements on an individual. The method is applied to an elite male gymnast in order to calculate subject-specific joint torque parameters for the knee joint. Isovelocity knee extension torque data were collected for the gymnast using a two-repetition concentric-eccentric protocol over a 75° range of crank motion at preset crank angular velocities ranging from 20 to 250°s–1. During these isovelocity movements, differences of up to 35° were found between the angle of the dynamometer crank and the knee joint angle of the participant. In addition, faster preset crank angular velocities gave smaller ranges of isovelocity motion for both the crank and joint. The simulation of an isovelocity movement at a joint angular velocity of 150°s–1 showed that, for realistic series elastic component extensions, the angular velocity of the joint can be assumed to be the same as the angular velocity of the contractile component during most of the isovelocity trial. Fitting an 18-parameter exponential function to experimental isovelocity joint torque/ angle/ angular velocity data resulted in a surface that was well behaved over the complete range of angular velocities and within the specified range of joint angles used to calculate the surface.

Statistical methods for assessing measurement error (reliability) in variables relevant to sports medicine

Minimal measurement error (reliability) during the collection of interval- and ratio-type data is critically important to sports medicine research. The main components of measurement error are systematic bias (e.g. general learning or fatigue effects on the tests) and random error due to biological or mechanical variation. Both error components should be meaningfully quantified for the sports physician to relate the described error to judgements regarding 'analytical goals' (the requirements of the measurement tool for effective practical use) rather than the statistical significance of any reliability indicators. Methods based on correlation coefficients and regression provide an indication of 'relative reliability'. Since these methods are highly influenced by the range of measured values, researchers should be cautious in: (i) concluding acceptable relative reliability even if a correlation is above 0.9; (ii) extrapolating the results of a test-retest correlation to a new sample of individuals involved in an experiment; and (iii) comparing test-retest correlations between different reliability studies. Methods used to describe 'absolute reliability' include the standard error of measurements (SEM), coefficient of variation (CV) and limits of agreement (LOA). These statistics are more appropriate for comparing reliability between different measurement tools in different studies. They can be used in multiple retest studies from ANOVA procedures, help predict the magnitude of a 'real' change in individual athletes and be employed to estimate statistical power for a repeated-measures experiment. These methods vary considerably in the way they are calculated and their use also assumes the presence (CV) or absence (SEM) of heteroscedasticity. Most methods of calculating SEM and CV represent approximately 68% of the error that is actually present in the repeated measurements for the 'average' individual in the sample. LOA represent the test-retest differences for 95% of a population. The associated Bland-Altman plot shows the measurement error schematically and helps to identify the presence of heteroscedasticity. If there is evidence of heteroscedasticity or non-normality, one should logarithmically transform the data and quote the bias and random error as ratios. This allows simple comparisons of reliability across different measurement tools. It is recommended that sports clinicians and researchers should cite and interpret a number of statistical methods for assessing reliability. We encourage the inclusion of the LOA method, especially the exploration of heteroscedasticity that is inherent in this analysis. We also stress the importance of relating the results of any reliability statistic to 'analytical goals' in sports medicine.

An Examination of Kinematic Variability of Motion Analysis in Sprint Hurdles

Eight trials each of 7 athletes (4 women and 3 men) were videotaped and digitized in order to investigate the variation sources and kinematic variability of video motion analysis in sprint hurdles. Mean coefficients of variation (CVs) of individuals ranged from 1.0 to 92.2% for women and from 1.2 to 209.7% for men. There were 15 and 14 variables, respectively, in which mean CVs revealed less than 5% variation. In redigitizing, CVs revealed <1.0% for 12 variables for the women's trials and 10 variables for the men's trials. These results, together with variance components (between-subjects, within-subject, and redigitizing), showed that one operator and the analysis system together produced repeatable values for most of the variables. The most repeatable variables by this combination were displacement variables. However, further data processing (e.g., differentiation) appeared to have some unwanted effects on repeatability. Regarding the athletes' skill, CVs showed that athletes can reproduce most parts of their performance within certain (reasonably low) limits.

The biomechanics of the human in flight

I used a computer simulation model of aerial movement to investigate the techniques for producing and controlling rotations of the human body during free flight. I found that the rotational motion can change from a twisting somersault to a nontwisting somersault by flexing at the hips at a suitable time. Twist may be produced in the aerial phase by means of asymmetrical movements of arms or hips, which result in a tilting of the longitudinal axis away from the plane perpendicular to the angular momentum vector. Asymmetrical movements may also remove the tilt and stop the twist. Elite performances of twisting somersaults are characterized by a large contribution from aerial twisting techniques. A progression of movements is presented for learning a double somersault with one and a half twists in the second somersault.

Current issues in the mechanics of athletic activities. A position paper

This position paper reviews current research topics in the study of athletic activities, which biomechanists would consider to be important or contentious issues, and focuses on critically evaluating what needs to be done in future research. It concludes that there remain many unresolved issues in the mechanics of athletic activities, many of which overlap with other disciplines. These issues relate to injury mechanisms, the control and co-ordination of movement, and ways of providing biomechanical feedback to enhance performance in athletic activities. Research to address these important issues will increasingly become more question than discipline orientated, must focus more on mechanisms than description, and will involve teams of researchers interacting on interdisciplinary problems.

Reliability of variables in the kinematic analysis of spring hurdles

The purpose of this study was to investigate the reliability of kinematic variables in spring hurdles and to find out how many trials are needed to achieve reliable data. Seven British National level athletes in sprint hurdles were videotaped and all eight trials of each athlete were digitized from two camera views to produce three dimensional coordinates. The reliability of 28 kinematic variables across eight trials ranged from 0.54 to 1.00 for females and from 0.00 to 0.99 for males. The number of trials needed to reach a certain reliability level was evaluated using Spearman-Brown prophecy formula, and in the worst case (horizontal velocity lost for males) 78 trials would be needed to reach 0.90 reliability. The results showed reasonably high reliability, and the values for the female trials were generally higher than the male trials. The relative height of the hurdles enforces a more demanding clearance for males that can lead to increased variation within the subjects and thus lowered reliability. Subsequently, the results indicate that often more than one trial is needed to provide accurate quantitative results of the technique.

The use of artificial intelligence in the analysis of sports performance: a review of applications in human gait analysis and future directions for sports biomechanics

Computers have played an important supporting role in the development of experimental and theoretical sports biomechanics. The role of the computer now extends from data capture and data processing through to mathematical and statistical modelling and simulation and optimization. This paper seeks to demonstrate that elevation of the role of the computer to involvement in the decision-making process, through the use of artificial intelligence techniques, would be a potentially rewarding future direction for the discipline. In the absence of significant previous work in this area, this paper reviews experiences in a parallel field of medical informatics, namely gait analysis. Research into the application of expert systems and neural networks to gait analysis is reviewed, observations made and comparisons drawn with the biomechanical analysis of sports performance. Brief explanations of the artificial intelligence techniques discussed in the paper are provided. The paper concludes that the creation of an expert system for a specific well-defined sports technique would represent a significant advance in the development of sports biomechanics.