Mario Heller

Accuracy of the LPM tracking system considering dynamic position changes

Abstract This study investigates the accuracy of the tracking system LPM (Local Position Measurement). The goal was to determine detailed error values of the system in the context of sports performance analyses. Six moderately trained male soccer players (amateur level) performed 276 runs on three different courses at six different speeds. Additionally, ten small-sided game plays were carried out. All runs and game plays were recorded with the LPM tracking system and the motion capture system VICON simultaneously. VICON served as the reference system. The absolute error of all LPM position estimations was on average 23.4±20.7 cm. The estimation for average velocities varied between 0.01 km h−1 and 0.23 km h−1, the maximum speed estimations differed by up to 2.71 km h−1. In addition, the results showed that the accuracy of the LPM system is highly dependent on the instantaneous dynamics of the player and decreases in the margins of the observation field. These dependencies were quantified. Considering commonly used applications of position tracking systems in sports (Leser, Ogris, & Baca, 2011), the accuracy of LPM is acceptable for position and velocity estimations. The system provides valuable results for average velocities but seems to be far less reliable when dealing with high dynamic movements and measuring instantaneous velocities.

Feedback Systems in Rowing

On-land feedback devices using rowing ergometers provide an alternative for on-water systems. In order not to draw incorrect conclusions it is essential to compare the rowers’ technique in the boat to that on the ergometer. Units for measuring reaction forces in the boat and at the ergometer have been constructed. Similarities in the reaction forces at the foot stretcher could be found for elite rowers.

Muscle co-contraction around the knee when walking with unstable shoes

Walking with unstable shoes has been discussed to decrease joint loading. Typical estimates of joint loading using an inverse dynamic approach only account for net joint moments, not considering the potential role of muscular co-contraction. Therefore, the purpose of this study was to compare muscular co-contraction levels when walking with two different unstable shoe constructions (rocker-bottom and toning shoes) compared to walking with regular shoes. For each shoe condition, 12 healthy subjects walked with both, a regular shoe and with an unstable shoe at self-selected walking speed at a 10-m walkway. Surface EMG data of selected muscles were recorded and time normalized for calculating co-contraction indices (CCI) for opposing muscle groups. Results showed an increase of co-contraction primarily for vastii and gastrocnemius muscles for the first and second half of stance when walking with an unstable shoe construction. Therefore, when using an inverse dynamic approach to analyze joint loading differences between regular shoes and unstable shoes, one should be cautious in interpreting the data, as these methods base their estimates of joint moments upon the net joint torque.

Perception of muscular effort in multiple sclerosis.

BACKGROUND Resistance exercise is effective in improving muscle strength and preventing muscle weakness in multiple sclerosis (MS) patients. Control of resistance training intensity based on perceived muscular effort is applicable to healthy individuals, yet there is no evidence of its utility for MS patients. OBJECTIVE To compare perception of muscular effort in MS patients to healthy controls. METHODS Based on their perception of muscular effort, twenty-five MS patients and twenty-eight controls adjusted static elbow extension tasks according to five levels on the OMNI-Resistance Exercise Scale. Elbow extension strength and muscle activity were measured via load cell dynamometer and surface electromyography (EMG) and related to each participants maximal voluntary contraction (MVC) strength and muscle activity. Two-way analysis of variance was used to evaluate statistical significance. RESULTS There were no statistically significant differences between MS patients and healthy controls, they produced similar relative torque values (F1 = 0.196; p > 0.05) and extensor muscle activities (F(2,617) = 1.556; p > 0.05) across all effort levels. CONCLUSION No differences were found in the perception of muscular effort in MS patients and the age-matched control group. Future studies should explore, whether rating of perceived exertion is an effective instrument to control resistance training intensity in MS patients.

On-target trajectories and the final pull in archery

Abstract At the end of the aiming phase, an archer pulls the arrow back a little bit before he releases the shot. This pulling back of the arrow is called the “final pull”. Simultaneous with the final pull, the archer has to hold the bow calm. The aim of this paper was to examine the motion of the bow and the final pull in highly skilled archers. From a technological point of view, we wished to develop a system to measure the draw-length in the final pull that could be used during archers’ normal training. Seven archers (two males, five females), all of whom were participants at the Junior World Championships and German National Championships, performed 66 shots indoors at a target 30 m away. Each archer shot the same bow as used in competition. On-target trajectories of the aim point movement were measured. Also, the alterations of the draw-length in the final pull were determined. The results suggest that irregularities in the final pull have a negative influence on archers’ scores. Intra-individually, a smaller range of motion of the bow in the last second before the shot appears to have a positive influence on archers’ scores.

Spectral parameters of surface electromyography and performance in swim bench exercises during the training of elite and junior swimmers

Abstract Spectral parameters of surface electromyography (EMG) are used to assess intramuscular coordination in terms of fatigue and motor unit recruitment. The aim of the present study was to examine changes in performance and EMG spectral parameters of the propulsive muscles during a swim bench exercise in swimmers to determine the intra-individual effects of different training periods in the normal training process. Ten swimmers of different ages and standards were investigated in a longitudinal study. Electromyograms of the relevant muscles (triceps longum, triceps lateralis, and latissimus dorsi) were recorded during the tests, and spectral parameters calculated using time-variant spectral analysis. In the elite swimmers, we observed variation in performance throughout the training season with respect to training load, whereas for the junior swimmers there was a trend to improve performances irrespective of training load. Correlations with performance were observed for the median frequencies of the triceps longus for the elite athletes. Performances and frequencies were increased in the taper period, whereas they were reduced after periods of high training loads. For the junior swimmers, no such correlations were observed. Based on our results, spectral parameters could provide information about the fatigue of the neuromuscular system of elite swimmers during periods of high training loads and enhanced intramuscular coordination in the taper period before competition.

Lightweight design optimization of a Bow Riser in Olympic Archery applying evolutionary computing

Recurve bows that are used in competitions like the Olympic Games are high-technology products. Good risers are lightweight but retain a high stiffness. The aim of this study was to design a riser with a stiffness comparable to that of the lightest riser currently used by the archers of the German National Archery Team, but with a considerably reduced weight. We computed the loads that are applied to a riser of a drawn recurve bow (the RADIAN model used by the German team) and created a 3-D solid CAD model of a riser with 24 variable parameters. We used evolutionary computing to optimize the 24 parameters of the model according to these criteria. We selected the most optimal riser out of the 1650 CAD models generated, manufactured it, and had it tested by three archers of the German National Archery Team. The mass of our manufactured riser is 871g, which is 243g or 22% less mass than the RADIAN riser.

Identification of temporal factors related to shot performance for indoor recurve archery

ABSTRACT The purpose of this study was to investigate the temporal phases of the archery shot cycle that distinguish the arrows distance from centre, in an attempt to understand critical factors that affect performance. Fifteen archers of varying ability each performed 30 shots at 18 m. Fourteen potential predictor variables were measured for statistical modelling by stepwise multiple linear regression. The results show that pre-shot time (pre-performance routine), follow-through time (post-performance routine), aiming time, speed of the arrow and the %variation in clicker-release time, account for 7.7% of the variation in predicting shot performance. The results have implications for practice demonstrating factors that coaches should focus on to develop their athletes. Further work on pre-, but more importantly, post-performance routines are needed generally within sport research as they are lacking and have been shown to be important contributing factors in a number of sports.

Perception of Muscular Effort During Dynamic Elbow Extension in Multiple Sclerosis.

OBJECTIVE To investigate the perception of muscular effort in individuals with multiple sclerosis (MS) and healthy controls during dynamic contractions. DESIGN Case-control study. SETTING MS day care center. PARTICIPANTS Individuals with MS (n=28) and controls (n=28) (N=56). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Perceived muscular effort during dynamic elbow extensions was rated at 9 different weight intensities (10%-90% of 1-repetition maximum) in a single-blind, randomized order using the OMNI-Resistance Exercise Scale. Muscle activity of the triceps brachii muscle (lateral head) was measured via surface electromyography and normalized to maximal voluntary excitation. RESULTS According to OMNI-level ratings, significant main effects were found for the diagnostic condition (F=27.33, P<.001, η(2)=.11), indicating 0.7 (95% confidence interval [CI], 0.3-1.1) lower mean OMNI-level ratings for MS, and for the intensity level (F=46.81, P<.001, η(2)=.46), showing increased OMNI-level ratings for increased intensity levels for both groups. Furthermore, significant main effects were found for the diagnostic condition (F=16.52, P<.001, η(2)=.07), indicating 7.1% (95% CI, -8.6 to 22.8) higher maximal voluntary excitation values for MS, and for the intensity level (F=33.09, P<.001, η(2)=.36), showing higher relative muscle activities for increasing intensity levels in both groups. CONCLUSIONS Similar to controls, individuals with MS were able to differentiate between different intensities of weight during dynamic elbow extensions when provided in a single-blind, randomized order. Therefore, perceived muscular effort might be considered to control resistance training intensities in individuals with MS. However, training intensity for individuals with MS should be chosen at approximately 1 OMNI level lower than recommended, at least for dynamic elbow extension exercises.

Body Fat Percentage Extracted from 3-D Scans for Sports & Medical Science

Body scanning technologies are used in many applications, from anthropometric research to garment technology to biomechanics. While capturing a subject’s body shape and measurements is often the primary objective, 3-D body scan systems can potentially add more value in some applications by determining additional body characteristics. In sports and medical science those are body mass, body surface, or overall body fat percentage. To develop algorithms capable of calculating such values, an extensive survey was conducted in which subjects were scanned in various positions to develop a stable and practicable process that considers process-inherent perturbations. Also, additional values were collected and interviews conducted to correlate subjects’ diet and activity with body characteristics. As a result, a new method was developed that allows estimating overall body fat percentage based on 3-D scans. The new method was evaluated against widely used methodologies such as infrared interactance, skin fold measurements, and body impedance.