A transcription-translation activation feedback circuit as a function of protein degradation, with the quality of protein mass adaptation related to the average functional load

A mathematical model-based approach to optimize loading schemes of isometric resistance training sessions

Individualized resistance training is necessary to optimize training results. A model-based optimization of loading schemes could provide valuable impulses for practitioners and complement the predominant manual program design by customizing the loading schemes to the trainee and the training goals. We compile a literature overview of model-based approaches used to simulate or optimize the response to single resistance training sessions or to long-term resistance training plans in terms of strength, power, muscle mass, or local muscular endurance by varying the loading scheme. To the best of our knowledge, contributions employing a predictive model to algorithmically optimize loading schemes for different training goals are nonexistent in the literature. Thus, we propose to set up optimal control problems as follows. For the underlying dynamics, we use a phenomenological model of the time course of maximum voluntary isometric contraction force. Then, we provide mathematical formulations of key performance indicators for loading schemes identified in sport science and use those as objective functionals or constraints. We then solve those optimal control problems using previously obtained parameter estimates for the elbow flexors. We discuss our choice of training goals, analyze the structure of the computed solutions, and give evidence of their real-life feasibility. The proposed optimization methodology is independent from the underlying model and can be transferred to more elaborate physiological models once suitable ones become available.

Artificial neural networks as a tool of modeling of training loads

This paper shows that extremely important element of forming speed capabilities is proper (quantitative) structure of exercise loads. This means that training means should be chosen from point of view of energy production in metabolic processes, which depends on the structure of training means from the information area and energy area, therefore on the character of work made, its intensity, duration of exercise, number of repetitions and duration of rest periods. From the training process effectiveness point of view, it is extremely important to find the correct tool for choosing means in given training cycle. The investigation results confirm the experiences of coaches and theorists of sport, that the structure of volume and intensity of exercise loads should be individually chosen with consideration of predispositions of separate athletes. Individualization of training is condition for its optimization.

Development of a three-dimensional multiscale agent-based tumor model: Simulating gene-protein interaction profiles, cell phenotypes and multicellular patterns in brain cancer

Experimental evidence suggests that epidermal growth factor receptor (EGFR)-mediated activation of the signaling protein phospholipase Cgamma plays a critical role in a cancer cell's phenotypic decision to either proliferate or to migrate at a given point in time. Here, we present a novel three-dimensional multiscale agent-based model to simulate this cellular decision process in the context of a virtual brain tumor. Each tumor cell is equipped with an EGFR gene-protein interaction network module that also connects to a simplified cell cycle description. The simulation results show that over time proliferative and migratory cell populations not only oscillate but also directly impact the spatio-temporal expansion patterns of the entire cancer system. The percentage change in the concentration of the sub-cellular interaction network's molecular components fluctuates, and, for the 'proliferation-to-migration' switch we find that the phenotype triggering molecular profile to some degree varies as the tumor system grows and the microenvironment changes. We discuss potential implications of these findings for experimental and clinical cancer research.

Modeling the residual effects and threshold saturation of training: a case study of Olympic swimmers

The aim of this study was to model the residual effects of training on the swimming performance and to compare a model that includes threshold saturation (MM) with the Banister model (BM). Seven Olympic swimmers were studied over a period of 4 +/- 2 years. For 3 training loads (low-intensity w(LIT), high-intensity w(HIT), and strength training w(ST)), 3 residual training effects were determined: short-term (STE) during the taper phase (i.e., 3 weeks before the performance [weeks 0, 1, and 2]), intermediate-term (ITE) during the intensity phase (weeks 3, 4, and 5), and long-term (LTE) during the volume phase (weeks 6, 7, and 8). ITE and LTE were positive for w(HIT) and w(LIT), respectively (p < 0.05). Low-intensity training load during taper was related to performances by a parabolic relationship (p < 0.05). Different quality measures indicated that MM compares favorably with BM. Identifying individual training thresholds may help individualize the distribution of training loads.

Simulating the impact of a molecular 'decision-process' on cellular phenotype and multicellular patterns in brain tumors

Experimental evidence indicates that human brain cancer cells proliferate or migrate, yet do not display both phenotypes at the same time. Here, we present a novel computational model simulating this cellular decision-process leading up to either phenotype based on a molecular interaction network of genes and proteins. The model's regulatory network consists of the epidermal growth factor receptor (EGFR), its ligand transforming growth factor-alpha (TGF alpha), the downstream enzyme phospholipaseC-gamma (PLC gamma) and a mitosis-associated response pathway. This network is activated by autocrine TGF alpha secretion, and the EGFR-dependent downstream signaling this step triggers, as well as modulated by an extrinsic nutritive glucose gradient. Employing a framework of mass action kinetics within a multiscale agent-based environment, we analyse both the emergent multicellular behavior of tumor growth and the single-cell molecular profiles that change over time and space. Our results show that one can indeed simulate the dichotomy between cell migration and proliferation based solely on an EGFR decision network. It turns out that these behavioral decisions on the single cell level impact the spatial dynamics of the entire cancerous system. Furthermore, the simulation results yield intriguing experimentally testable hypotheses also on the sub-cellular level such as spatial cytosolic polarization of PLC gamma towards an extrinsic chemotactic gradient. Implications of these results for future works, both on the modeling and experimental side are discussed.

Review Article: Sarcopenia: Causes, Consequences, and Preventions

With the onset of advancing age, muscle tissue is gradually lost, resulting in diminished mass and strength, a condition referred to as sarcopenia. The sequela of sarcopenia often contributes to frailty, decreased independence, and subsequently increased health care costs. The following was adapted from an introduction to the conference "Sarcopenia, Age-Related Muscle Loss-Causes, Consequences, and Prevention," sponsored by the Kronos Longevity Research Institute in June 2002. This brief review will introduce potential mechanisms that may contribute to sarcopenia, although no one mechanism has yet, and may not completely, define this process. The only agreed-upon intervention from these proceedings was regular physical exercise, stressing weight-training for elderly men and women. However, even those individuals who maintain their fitness through exercise do not appear to be immune to sarcopenia.

Effect of endurance training on blood lactate clearance after maximal exercise

The aim of this study was to measure serial changes in the rate of blood lactate clearance (gamma2) in response to sequential periods of training and detraining in four male triathletes aged 22-44 years. There were two major phases of training and taper, each lasting 4-5 weeks (training 1 = 5 weeks, taper 1 = 2 weeks, training 2 = 4 weeks and taper 2 = 2 weeks), in preparation for a triathlon competition. The training stimulus absorbed by each subject was carefully quantified from the duration and intensity of the training exercise. A serial weekly measure of each trainee's physical response to training was evaluated as the peak power, termed a 'criterion performance', developed by a subject during a 30 W x min(-1) ramp cycle ergometer test to exhaustion each week. During 30 min of recovery after this test, 13 samples of venous blood were drawn sequentially from a subject to measure the blood lactate recovery curve. The rate constant of blood lactate clearance was estimated by a non-linear least-squares regression technique. In addition, the concurrent time to peak lactate concentration and the peak lactate concentration were also estimated to help define changing lactate kinetics. The criterion performance generally declined throughout each period of incremental training and improved during each taper period, rising iteratively in this way to be clearly above baseline by the end of the second taper. The blood lactate clearance rate increased transiently in early training before declining from the middle of the first training period to the middle of the first taper; thereafter, gamma2 increased above baseline in each trainee throughout the remaining first taper and the major portion of the second training period, decreasing only in the final criterion performance test. The time to peak lactate declined from baseline throughout all phases of training and taper. Peak blood lactate increased in all subjects to the end of the first taper before declining by the end of the second training period, rising again to baseline levels during the second taper. The change in gamma2 was examined relative to the work rate achieved in cycle ergometry above an initial baseline score (deltaCP) and against concurrent peak blood lactate. There was a clear upward shift in gamma2 above baseline throughout the first and second training and taper in two subjects; this was less clear in the remaining two subjects, each of whom had a lower deltaCP. We conclude that this indicates improved lactate clearance, manifest by the change in gamma2 induced by endurance training.

Comparison of soluble aminopeptidases in human cerebral cortex, skeletal muscle and kidney tissues

In an attempt to elucidate the cellular function of the soluble aminopeptidases (with which the majority of tissue aminopeptidase activity is usually associated) we have determined the distribution and characteristics of these enzymes in three functionally dissimilar human tissues (cerebral cortex, skeletal muscle and kidney cortex), using a systematic experimental approach. Following fractionation of brain, muscle or kidney soluble extracts via anion exchange chromatography, four aminopeptidase enzymes types (alanyl-, arginyl-, leucyl- and pyroglutamyl-) were identified; the absolute and relative activities for corresponding enzymes were similar in each tissue. Following further purification of each enzyme type from each tissue (via liquid chromatography/preparative electrophoresis), corresponding enzyme types were found to have similar characteristics (pH optimum of activity, action of enzyme effectors, substrate specificity and molecular mass). Since the same enzymes, with correspondingly similar distribution and characteristics are present in such functionally dissimilar tissues, it is suggested that the principal role for the soluble aminopeptidases (in contrast to the membrane-associated enzymes, which may function in the catabolism of neuropeptides) is in the final stages of the general intracellular protein catabolism cascade, via hydrolysis of oligopeptide intermediates to free amino acids.

The kinetics of mammalian gene expression

When rates of transcription from specific genes change, delays of variable length intervene before the corresponding mRNAs and proteins attain new levels. For most mammalian genes, the time required to complete transcription, processing, and transport of mRNA is much shorter than the period needed to achieve a new, steady-state level of protein. Studies of inducible genes have shown that the period required to attain new levels of individual mRNAs and proteins is related to their unique half-lives. The basis for this is a physical principle that predicts rates of accumulation of particles in compartmental systems. The minimum period required to achieve a new level is directly proportional to product half-lives because rates of decay control the ratio between the rate of synthesis and the concentration of gene products at steady state. This kinetic model suggests that sensitivity of gene products to degradation by ribonucleases and proteinases is an important determinant of the time scale of gene expression.