Principal Component Analysis can Be Used to Discriminate Between Elite and Sub-Elite Kicking Performance.

Contemporary descriptions of motor control suggest that variability in movement can be indicative of skilled or unskilled performance. Here we used principal component analysis to study the kicking performance of elite and sub-elite soldiers who were highly familiar with the skill in order to compare the variability in the first and second principal components. The subjects kicked a force plate under a range of loaded conditions, and their movement was recorded using optical motion capture. The first principal component explained >92% of the variability across all kinematic variables when analyzed separately for each condition, and both groups and explained more of the variation in the movement of the elite group. There was more variation in the loading coefficient of the first principal component for the sub-elite group. In contrast, for the second principal component, there was more variation in the loading coefficient for the elite group, and the relative magnitude of the variation was greater than for the first principal component for both groups. These results suggest that the first principal component represented the most fundamental movement pattern, and there was less variation in this mode for the elite group. In addition, more of the variability was explained by the hip than the knee angle entered when both variables were entered into the same PCA, which suggests that the movement is driven by the hip.

Does a linear position transducer placed on a stick and belt provide sufficient validity and reliability of countermovement jump performance outcomes?

Manufacturers recommend that linear position transducers (LPTs) should be placed on the side of a barbell (or wooden dowel) to measure countermovement jump (CMJ) height, but the validity and reliability of this placement have not been compared to other attachment sites. Since this recommended attachment site is far from the centre of mass, a belt attachment where the LPT is placed between the feet may increase the validity and reliability of CMJ data. Thirty-six physical education students participated in the study (24.6 ± 4.3 years; 177.0 ± 7.7 cm; 77.2 ± 9.0 kg). Parameters from the two LPT attachments (barbell and belt) were simultaneously validated to force plate data, where the nature of bias was analysed (systematic vs random). The within-session and between-session reliability of both attachment sites were compared to force plate data using a test-retest protocol of two sets of 5 CMJs separated by 7 days. The LPT provided highly reliable and valid measures of peak force, mean force, mean power, and jump height, where the bias was mostly systematic (r2 > 0.7; ICC > 0.9). Peak velocity, mean velocity, and peak power were in very good agreement with the force plate and were highly reliable (r2 > 0.5; ICC > 0.7). Therefore, both attachment sites produced similar results with a systematic bias compared to force plate data. Thus, both attachment sites seem to be valid for assessing CMJs when the measuring tool and site remain consistent across measurements. However, if LPT data are to be compared to force plate data, recalculation equations should be used.

Kinematic Determinants of Front Kick Dynamics Across Different Loading Conditions.

INTRODUCTION: The efficiency of front kick is related to the kicking technique. Thus, the aim of this study was to find the kinematic determinants of front kick dynamics across different performance and loading levels (no load to 45-kg load). MATERIALS AND METHODS: Twenty-four elite and sub-elite professional military personnel (26.8 ± 10.1 years, 84.2 ± 5.4 kg, 181.1 ± 6.4 cm) performed six front kicks into a force plate across five different loading conditions. Three-dimensional kinematics of the kicks was quantified and included velocity of the hip (Vhip), velocity of the knee (Vknee), velocity of the shoulder (Vshoulder), velocity of the foot (Vfoot), angular velocity of the knee (AVknee), and angular velocity of the hip (AVhip). RESULTS: The main kinematic differences between the two groups were that the sub-elite group had an increased kick time for all loading conditions (P < .001) and a lower Vfoot (P = .05) and a decreased Vhip and Vshoulder (P < .05) in the highest load condition. Vhip and AVhip were the best predictors (up to R2 = 0.58; P = .020) of peak force and impact force during no-load or loaded kicking at the elite level. Typical predictors of impulse in the elite group were AVhip, Vhip, and Vshoulder and those in the sub-elite group were AVknee and Vfoot. CONCLUSIONS: The kinematic variables provide good predictions of kicking dynamics; however, the best predictor varies with the loading conditions and performance levels. Hip motion is the main differentiating factor.

Field-Based and Lab-Based Assisted Jumping: Unveiling the Testing and Training Implications.

Purpose: Assisted jumping can supplement resistance training and traditional plyometric training to increase vertical jump performance. However, as coaches may choose to make field-based decisions based on lab-based research, this study determined whether a field-based assisted jumping set-up results in different ground contact times (CT), take off forces (TOF), flight times (FT), and impact forces (IF) compared to a lab-based set-up. Methods: Eighteen active males (24.8 ± 3.0 yr; 178.8 ± 7.8 cm; 77.8 ± 7.8 kg) performed two sessions of assisted jumping: one with each hand holding a commercially available resistance band (1m) that was attached to a pull-up bar (FIELD), and the other with assistance from a custom-built system of ropes, pulleys, and long (3 m) elastic bands (LAB). With each set-up, subjects performed five sets of five countermovement jumps on a force plate. Each set was performed with either bodyweight (BW), 90, 80, 70, or 60% of BW, which was achieved by either grabbing higher or lower on the bands during FIELD, or by being pulled upward via a full-body harness during LAB. The order of each visit was counter-balanced, and the order of jumps within each visit was quasi-randomized. Data from the 90, 80, 70, and 60% trials for each set-up were then expressed relative to the data of BW jumps, and these relative values were then used for analysis. Results: CTFIELD was less than CTLAB at 80, 70, and 60%. FTFIELD was greater than FTLAB at 90 and 80%, but FTLAB became greater at 60%. TOF and IF remained unchanged during LAB, but TOFFIELD was consistently less than TOF during BW, with IFFIELD generally being greater than IFLAB. Conclusion: If the purpose of assisted jumping is to spend less time on the ground without decreasing force, systems with finite adjustments and longer bands like LAB should be used. However, shorter bands similar to FIELD may also be used; but due to the larger variability of assistance throughout the range of motion, such systems may alter the neuromuscular characteristics of the jump in other ways that should be investigated in future research.

A systematic review of the main factors that determine agility in sport using structural equation modeling.

While tests of basic motor abilities such as speed, maximum strength or endurance are well recognized, testing of complex motor functions such as agility remains unresolved in current literature. Therefore, the aim of this review was to evaluate which main factor or factor structures quantitatively determine agility. In methodological detail, this review focused on research that explained or described the relationships between latent variables in a factorial model of agility using approaches such as principal component analysis, factor analysis and structural equation modeling. Four research studies met the defined inclusion criteria. No quantitative empirical research was found that tried to verify the quality of the whole suggested model of the main factors determining agility through the use of a structural equation modeling (SEM) approach or a confirmatory factor analysis. From the whole structure of agility, only change of direction speed (CODS) and some of its subtests were appropriately analyzed. The combination of common CODS tests is reliable and useful to estimate performance in sub-elite athletes; however, for elite athletes, CODS tests must be specific to the needs of a particular sport discipline. Sprinting and jumping tests are stronger factors for CODS than explosive strength and maximum strength tests. The authors suggest the need to verify the agility factorial model by a second generation data analysis technique such as SEM.

Influence of SYSADOA group chemicals on progression of human knee joint osteoarthritis: new objective evaluation method - measuring of rheological properties in vivo.

OBJECTIVES: This study seeks to demonstrate the influence of pharmacological substances from the SYSADOA group on the progression of osteoarthritis in the human knee. The quantification methods were direct measurement of the rheological properties of the knee joints in vivo and standard WOMAC index questionnaires. MATERIALS AND METHODS: The drugs were administered orally to 34 probands with second degree gonarthrosis for 13 weeks. The untreated control group consisted of 10 probands. The rheological properties of the joints were determined by a biorheometer, and subjective assessment of the knees by patients (WOMAC) before and after medication, and for a further 13 weeks. Changes in the calculated parameters over time were compared. RESULTS: During the audited perioda slight deterioration in all of the parameters was observed in the untreated group. The treated group, however, improved in all the parameters and some indicators showed statistically significant differences. The positive effects of the SYSADOA persisted for 3 months after the end of treatments. Partial correlation was found between the results of the WOMAC questionnaire and the rheological measurements. CONCLUSIONS: This study shows the positive effects of the preparation on arthritic changes in the knee joint, but due to the large variance of the collected data, this conclusion is on the borderline of statistical significance. The method of measuring the rheological properties of the joints is suitable for evaluating the progression of OA.