Validity and reliability of a novel 3D ultrasound approach to assess static lengths and the lengthening behavior of the gastrocnemius medialis muscle and the Achilles tendon in vivo.

PURPOSE: Human muscle-tendon units (MTUs) are highly plastic and undergo changes in response to specific diseases and disorders. To investigate the pathological changes and the effects of therapeutic treatments, the use of valid and reliable examination methods is of crucial importance. Therefore, in this study, a simple 3D ultrasound approach was developed and evaluated with regard to: (1) its validity in comparison to magnetic resonance imaging (MRI) for the assessment of the gastrocnemius medialis (GM) MTU, muscle belly, and Achilles tendon lengths; and (2) its reliability for static and dynamic length measurements. METHODS: Sixteen participants were included in the study. To evaluate the validity and reliability of the novel 3D ultrasound approach, two ultrasound measurement sessions and one MRI assessment were performed. By combining 2D ultrasound and 3D motion capture, the tissue lengths were assessed at a fixed ankle joint position and compared to the MRI measurements using Bland-Altman plots. The intra-rater and inter-rater reliability for the static and dynamic length assessments was determined using the coefficient of variation, standard error of measurement (SEM), minimal detectable change (MDC95), and intraclass correlation coefficient (ICC). RESULTS: The 3D ultrasound approach slightly underestimated the length when compared with MRI by 0.7%, 1.5%, and 1.1% for the GM muscle belly, Achilles tendon, and MTU, respectively. The approach showed excellent intra-rater as well as inter-rater reliability, with high ICC (≥ 0.94), small SEM (≤ 1.3 mm), and good MDC95 (≤ 3.6 mm) values, with even better reliability found for the static length measurements. CONCLUSION: The proposed 3D ultrasound approach was found to be valid and reliable for the assessment of the GM MTU, muscle belly, and Achilles tendon lengths, as well as the tissue lengthening behavior, confirming its potential as a useful tool for investigating the effects of training interventions or therapeutic treatments (e.g., surgery or conservative treatments such as stretching and orthotics). LEVEL OF EVIDENCE: Level II.

Joint Flexibility and Isometric Strength Parameters Are Not Relevant Determinants for Countermovement Jump Performance.

Vertical jumps are of great importance as a performance predictor for many types of sports that require speed and agility. However, to date, it is not clear if flexibility and/or the strength of the different leg muscles are determinants for countermovement jump (CMJ) performance. Therefore, the purpose of this study was to relate isometric maximum voluntary contraction (MVC) torque and the flexibility of various muscle groups of the lower body with CMJ performance. Thirty-six healthy male volunteers participated in this study. The participants performed MVCs of the knee extensors, knee flexors, and plantar flexors on a dynamometer. Moreover, range of motion of the hip flexors and plantar flexors was assessed with 3D motion capture, and the range of motion of the knee flexors (hamstrings) was assessed with a Sit n' Reach® box. CMJs were assessed with a force platform. The correlation analysis revealed a significant moderate correlation of CMJ height with the flexibility of the hip flexors (rP = -0.39) and plantar flexors (rP = 0.47), but not the knee flexors. Moreover, we found that absolute MVC values are not related to CMJ height. However, we did find that knee extensor MVC relative to body mass is significantly related to CMJ height (rP = 0.33) with a moderate magnitude. Although we found significant correlations, the magnitudes of correlations vary between trivial and large according to a 90% confidence interval. Thus, this indicates that range of motion or strength of the assessed leg muscles can explain CMJ performance only to a limited extent.

Covid-19 Has Turned Home Advantage Into Home Disadvantage in the German Soccer Bundesliga.

The main factors for home advantage (HA), quantified by the number of points won at home expressed as a percentage of all points, are believed to be crowd support, territoriality, familiarity, and travel fatigue. In 2020, the German Soccer Bundesliga interrupted its championship due to the Covid-19 pandemic after 25 rounds and the last nine rounds were played without audience. This unique situation allowed studying the effect of spectators on the team's performance and the referee's decisions. We hypothesized a decrease in HA and a more balanced distribution of fouls and disciplinary cards in the games without audience (GWOA) compared to the games with audience (GWA). We evaluated n = 223 GWA and n = 83 GWOA of the season 2019/20 and all games of the preceding season 2018/19 to analyze the distribution of game outcomes (wins, losses, and draws) and HA. We analyzed the number of fouls, disciplinary cards, and penalty kicks. We found significant differences in HA between GWA (HA = 54.35%) and GWOA (HA = 44.1%) as well as GWOA and games of 2018/19 (HA = 57.63%). The distribution of game outcomes in GWOA did not differ from GWA but differed significantly from 2018/19 (p = 0.031). The distribution of fouls showed a significant difference to equal distribution in GWA [home: 2,595 (48.56%); away: 2,749 (51.44%)] but not in GWOA [home: 1,067 (50.54%); away: 1,044 (49.46%)]. In the GWOA, we counted 178 (51.1%, home) and 170 (48.9%, away) cards, representing a significant difference in the distribution to GWA [home: 405 (44.85%); away: 498 (55.15%)]. The number of red cards differed significantly from an equal distribution for GWA (14 home and 28 away) but not for GWOA (eight home and seven away). In the last nine rounds without audience, we observed more home losses (36) than home wins (27). Hence, the Covid-19 lock-down led to a home disadvantage. One reason for this surprising result could be that the home team is missing an important familiar aspect when playing in their empty stadium without social support from their home audience. Furthermore, both teams know about the HA thus the away team could be more motivated in this unusual situation.

Model-based analysis of fatigued human knee extensors : Effects of isometrically induced fatigue on Hill-type model parameters and ballistic contractions.

This study investigated the effect of isometrically induced fatigue on Hill-type muscle model parameters and related task-dependent effects. Parameter identification methods were used to extract fatigue-related parameter trends from isometric and ballistic dynamic maximum voluntary knee extensions. Nine subjects, who completed ten fatiguing sets, each consisting of nine 3 s isometric maximum voluntary contractions with 3 s rest plus two ballistic contractions with different loads, were analyzed. Only at the isometric task, the identified optimized model parameter values of muscle activation rate and maximum force generating capacity of the contractile element decreased from [Formula: see text] to [Formula: see text] Hz and from [Formula: see text] to [Formula: see text] N, respectively. For all tasks, the maximum efficiency of the contractile element, mathematically related to the curvature of the force-velocity relation, increased from [Formula: see text] to [Formula: see text]. The model parameter maximum contraction velocity decreased from [Formula: see text] to [Formula: see text] m/s and the stiffness of the serial elastic element from [Formula: see text] to [Formula: see text] N/mm. Thus, models of fatigue should consider fatigue dependencies in active as well as in passive elements, and muscle activation dynamics should account for the task dependency of fatigue.

PFA-100 closure times in preoperative screening in 500 pediatric patients.

Three to five percent of patients undergoing surgery have either an acquired or congenital platelet defect or von Willebrand disease (vWD). The predictive value of preoperative coagulation screening is questionable. PFA-100 is now routinely used in preoperative screening in our pediatric outpatient service. We wanted to assess whether the PFA-100 would help to identify patients with primary haemostatic defects or if the additional use of PFA-100 would add to the problem of unnecessary pathologic preoperative laboratory values resulting in delay of surgical procedure. We investigated 500 children consecutively seen in our outpatient service before surgery. Blood cell count, aPTT, PFA-100 closure times (CT) were done in all patients. If abnormalities were found, the patient was presented to a haemostatic expert. vWF:AG, R:Cof and factor VIII were analysed in all patients with prolonged closure times and APTT values. One hundred twenty-six patients (25.2%) showed abnormalities in APTT and/or PFA-100. Further investigations in 89 of these 126 patients did not yield a specific diagnosis; neither diagnostic criteria for impaired haemostasis were found by questionnaire. None of these 89 patients had a bleeding complication during surgery. Forty-eight patients showed prolonged CTs. Twelve patients with low vWF:AG were detected, 10 of these patients were found by PFA-100. Four of these patients did present with normal APTT values. Our study shows that similar to the APTT the PFA-100 is probably only a good screening method when a haemostatic defect in a patient is clinically likely, especially to screen forVWD, and the test should not be used in general unselective screening.

Biomechanical muscle properties and angiotensin-converting enzyme gene polymorphism: a model-based study.

Previous studies reported an association of angiotensin-converting enzyme (ACE) I/D gene polymorphism with physical performance. The study was based on the hypothesis that certain individual biomechanical muscle properties could be associated with ACE genotype and that they could influence athletes' physical performance. Movement-independent individual biomechanical muscle properties of 62 sports students were determined by applying a mathematical model to experimental data. Subjects exerted concentric and isometric contractions at a leg-press. The model was based on a Hill-type muscle model, a function describing the geometrical arrangement of human leg extensor muscles, and an exponential function describing muscle activation. Mouthwash samples were taken to determine the ACE genotypes. Several combinations of experimentally determined biomechanical properties served as input variables for a discriminant analysis. We were able to show that individual biomechanical muscle properties correlated with ACE I/D gene polymorphism. With a combination of certain individual muscle parameters based on a Hill-type muscle model, we were able to separate three individual ACE genotypes (II, ID, DD) in a significant way (P<0.03) and correctly classify 89% of the cases using a discriminant analysis. We conclude that local biomechanical muscle properties are influenced by ACE genotype.