Experimentelle Untersuchungen zur Optimierung der Belastungsmethodik im Schnellkrafttraining

Aktuelle Tendenzen im Leistungs- und Hochleistungssport deuten auf zunehmende Verkürzungen der Wettkampfvorbereitung im Jahreszyklus sportlichen Trainings aus unterschiedlichen Gründen hin. Diese veränderten Rahmenbedingungen sportlichen Trainings stellen erhöhte Anforderungen an die effektivere Gestaltung der Trai-ningsmethodik zur systematischen Leistungsentwicklung bei Sportlern (Wick, 2006). Vor diesem Hintergrund wurden neue Ansätze zur Effektivierung des Schnellkraft-trainings unter Nutzung veränderter neuronaler Muskelrekrutierung nach elektrischer Muskelstimulation untersucht. Aus den Untersuchungen von Akima et al. (2002) ist bekannt, dass nach elektrischer Stimulation eines Muskels aus einer Muskelgruppe das Nerv-Muskelsystem mit einer Veränderung der neuralen Ansteuerung der agonistisch wirkenden Muskeln bei will-kürlichen Kontraktionen reagiert. Dabei wurden sowohl hemmende (Sacco, Newberry, McFadden, Brown, & McComas, 1997) als auch verstärkende (Kinugasa, Yoshida, & Horii, 2005) motoneuronale Aktivierungen nach submaximalen Belastun-gen nachgewiesen. Das Ziel der Studie I war die Bedingungen für eine Auslösung der verstärkten Muskelaktivität bei unterschiedlichen Kontraktionsformen und Mus-kelgruppen zu untersuchen und daraus eine Belastungsmethode zur Steigerung der Schnellkraft theoretisch abzuleite

Active exoskeleton reduces erector spinae muscle activity during lifting

Musculoskeletal disorders (MSD) are a widespread problem, often regarding the lumbar region. Exoskeletons designed to support the lower back could be used in physically demanding professions with the intention of reducing the strain on the musculoskeletal system, e.g., by lowering task-related muscle activation. The present study aims to investigate the effect of an active exoskeleton on back muscle activity when lifting weights. Within the framework of the study, 14 subjects were asked to lift a 15 kg box with and without an active exoskeleton which allows the adjustment of different levels of support, while the activity of their M. erector spinae (MES) was measured using surface electromyography. Additionally, the subjects were asked about their overall rating of perceived exertion (RPE) during lifting under various conditions. Using the exoskeleton with the maximum level of support, the muscle activity was significantly lower than without exoskeleton. A significant correlation was found between the exoskeleton’s support level and the reduction of MES activity. The higher the support level, the lower the observed muscle activity. Furthermore, when lifting with the maximum level of support, RPE was found to be significantly lower than without exoskeleton too. A reduction in the MES activity indicates actual support for the movement task and might indicate lower compression forces in the lumbar region. It is concluded that the active exoskeleton supports people noticeably when lifting heavy weights. Exoskeletons seem to be a powerful tool for reducing load during physically demanding jobs and thus, their use might be helpful in lowering the risk of MSD

Locational and Directional Dependencies of Smooth Muscle Properties in Pig Urinary Bladder

The urinary bladder is a distensible hollow muscular organ, which allows huge changes in size during absorption, storage and micturition. Pathological alterations of biomechanical properties can lead to bladder dysfunction and loss in quality of life. To understand and treat bladder diseases, the mechanisms of the healthy urinary bladder need to be determined. Thus, a series of studies focused on the detrusor muscle, a layer of urinary bladder made of smooth muscle fibers arranged in longitudinal and circumferential orientation. However, little is known about whether its active muscle properties differ depending on location and direction. This study aimed to investigate the porcine bladder for heterogeneous (six different locations) and anisotropic (longitudinal vs. circumferential) contractile properties including the force-length-(FLR) and force-velocity-relationship (FVR). Therefore, smooth muscle tissue strips with longitudinal and circumferential direction have been prepared from different bladder locations (apex dorsal, apex ventral, body dorsal, body ventral, trigone dorsal, trigone ventral). FLR and FVR have been determined by a series of isometric and isotonic contractions. Additionally, histological analyses were conducted to determine smooth muscle content and fiber orientation. Mechanical and histological examinations were carried out on 94 and 36 samples, respectively. The results showed that maximum active stress (pact) of the bladder strips was higher in the longitudinal compared to the circumferential direction. This is in line with our histological investigation showing a higher smooth muscle content in the bladder strips in the longitudinal direction. However, normalization of maximum strip force by the cross-sectional area (CSA) of smooth muscle fibers yielded similar smooth muscle maximum stresses (165.4 ± 29.6 kPa), independent of strip direction. Active muscle properties (FLR, FVR) showed no locational differences. The trigone exhibited higher passive stress (ppass) than the body. Moreover, the bladder exhibited greater ppass in the longitudinal than circumferential direction which might be attributed to its microstructure (more longitudinal arrangement of muscle fibers). This study provides a valuable dataset for the development of constitutive computational models of the healthy urinary bladder. These models are relevant from a medical standpoint, as they contribute to the basic understanding of the function of the bladder in health and disease

Three-dimensional muscle architecture and comprehensive dynamic properties of rabbit gastrocnemius, plantaris and soleus: input for simulation studies

The vastly increasing number of neuro-muscular simulation studies (with increasing numbers of muscles used per simulation) is in sharp contrast to a narrow database of necessary muscle parameters. Simulation results depend heavily on rough parameter estimates often obtained by scaling of one muscle parameter set. However, in vivo muscles differ in their individual properties and architecture. Here we provide a comprehensive dataset of dynamic (n=6 per muscle) and geometric (three-dimensional architecture, n=3 per muscle) muscle properties of the rabbit calf muscles gastrocnemius, plantaris, and soleus. For completeness we provide the dynamic muscle properties for further important shank muscles (flexor digitorum longus, extensor digitorum longus, and tibialis anterior; n=1 per muscle). Maximum shortening velocity (normalized to optimal fiber length) of the gastrocnemius is about twice that of soleus, while plantaris showed an intermediate value. The force-velocity relation is similar for gastrocnemius and plantaris but is much more bent for the soleus. Although the muscles vary greatly in their three-dimensional architecture their mean pennation angle and normalized force-length relationships are almost similar. Forces of the muscles were enhanced in the isometric phase following stretching and were depressed following shortening compared to the corresponding isometric forces. While the enhancement was independent of the ramp velocity, the depression was inversely related to the ramp velocity. The lowest effect strength for soleus supports the idea that these effects adapt to muscle function. The careful acquisition of typical dynamical parameters (e.g. force-length and force-velocity relations, force elongation relations of passive components), enhancement and depression effects, and 3D muscle architecture of calf muscles provides valuable comprehensive datasets for e.g. simulations with neuro-muscular models, development of more realistic muscle models, or simulation of muscle packages

The difference between saying and doing when it comes to training volume: Effect of motives of sport activity, age, gender and pain on training volume [Der Unterschied zwischen Sagen und Tun beim Trainingsfleiß: Effekte von Motiven sportlicher Aktivität, Alter, Geschlecht und Schmerzen auf den Trainingsumfang sportlicher Aktivitäten]

Background Health, joy/fun, body shape and society are motives for physical exercise. So far, the impact of the strength of these factors on the training scope is unclear. The study aims to analyse the association between these motives, age, gender, back pain and training volume. Materials and methods In this study, 792 participants (68% women and 32% men, mean age 53.5 years, standard deviation 11.9, range 24–85 years) were asked about their motives for physical activities, their back pain and their volume of training. Regression analyses were performed to assess the effects of the motives on training volume. Results In women, the motives joy (B$_{joy}$ = 0.23, t = 3.6, p < 0.001, r = 0.25), body shape (B$_{body shape}$ = 0.127, t = 2.0, p = 0.05, r = 0.16) and age (B$_{age}$ = 0.03, t = 2.5, p = 0.01, r = 0.17) had small (age, body shape) to medium effects (joy) on training volume. In men, only back pain had a significant positive effect (B$_{back pain}$ = 1.4, t = 4.2, p < 0.001, r = 0.35) on training volume (strong effect). Discussion and conclusion For active women, the pleasure felt during training (intrinsic motivation) and the desire for a better figure (introjected regulation = meeting external requirements) promote the amount of training. For active men, the solution to the health problem is possibly in the foreground: the greater the problem (back pain), the higher the training volume. Presumably, they have made the experience that physical training reduces back pain

The Effect of Multidirectional Loading on Contractions of the M. Medial Gastrocnemius

Research has shown that compression of muscle can lead to a change in muscle force. Most studies show compression to lead to a reduction in muscle force, although recent research has shown that increases are also possible. Based on methodological differences in the loading design between studies, it seems that muscle length and the direction of transverse loading influence the effect of muscle compression on force production. Thus, in our current study we implement these two factors to influence the effects of muscle loading. In contrast to long resting length of the medial gastrocnemius (MG) in most studies, we use a shorter MG resting length by having participant seated with their knees at a 90° angle. Where previous studies have used unidirectional loads to compress the MG, in this study we applied a multidirectional load using a sling setup. Multidirectional loading using a sling setup has been shown to cause muscle force reductions in previous research. As a result of our choices in experimental design we observed changes in the effects of muscle loading compared to previous research. In the present study we observed no changes in muscle force due to muscle loading. Muscle thickness and pennation angle showed minor but significant increases during contraction. However, no significant changes occurred between unloaded and loaded trials. Fascicle thickness and length showed different patterns of change compared to previous research. We show that muscle loading does not result in force reduction in all situations and is possibly linked to differences in muscle architecture and muscle length

The Energy of Muscle Contraction. II. Transverse Compression and Work

In this study we examined how the strain energies within a muscle are related to changes in longitudinal force when the muscle is exposed to an external transverse load. We implemented a three-dimensional (3D) finite element model of contracting muscle using the principle of minimum total energy and allowing the redistribution of energy through different strain energy-densities. This allowed us to determine the importance of the strain energy-densities to the transverse forces developed by the muscle. We ran a series of in silica experiments on muscle blocks varying in initial pennation angle, muscle length, and external transverse load. As muscle contracts it maintains a near constant volume. As such, any changes in muscle length are balanced by deformations in the transverse directions such as muscle thickness or muscle width. Muscle develops transverse forces as it expands. In many situations external forces act to counteract these transverse forces and the muscle responds to external transverse loads while both passive and active. The muscle blocks used in our simulations decreased in thickness and pennation angle when passively compressed and pushed back on the load when they were activated. Activation of the compressed muscle blocks led either to an increase or decrease in muscle thickness depending on whether the initial pennation angle was less than or greater than 15°, respectively. Furthermore, the strain energy increased and redistributed across the different strain-energy potentials during contraction. The volumetric strain energy-density varied with muscle length and pennation angle and was reduced with greater transverse load for most initial muscle lengths and pennation angles. External transverse load reduced the longitudinal muscle force for initial pennation angles of β0 = 0°. Whereas for pennate muscle (β0 &gt; 0°) longitudinal force changed (increase or decrease) depending on the muscle length, pennation angle and the direction of the external load relative to the muscle fibres. For muscle blocks with initial pennation angles β0 ≤ 20° the reduction in longitudinal muscle force coincided with a reduction in volumetric strain energy-density

Einfluss verschiedener Oligo- und Polysaccharide auf das Wachstum ausgewählter Bakterienstämme

Es ist schon lange bekannt, dass Pro-, Prä- und Synbiotika einen positiven Einfluss auf die Gesundheit des Menschen haben. In dieser Diplomarbeit wurde die wachstumsfördernde Wirkung von verschiedenen Oligo- und Polysacchariden auf ausgewählte Bakterienstämme untersucht. Diese Saccharide wurden aus Agave, Topinambur, Knoblauch, Grünlilie, Kakteen und Pilzen gewonnen. Die ausgewählten Arten waren Lactobacillus acidophilus, Lactobacillus reuteri, Lactobacillus rhamnosus, Lactobacillus paracasei und Bifidobacterium animalis. Die Wachstumszunahme der Bakterien wurde mittels Trübungsmessung bestimmt. Im Rahmen dieser Untersuchungen konnte ein positiver Einfluss einiger Zucker festgestellt werden, der durch zusätzliche Bestimmung der koloniebildenden Einheiten auf Agarplatten bestätigt werden konnte

Methodological considerations for investigating the influence of neuromuscular electrical stimulation on pH heterogeneity

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