Effect of countermovement on power–force–velocity profile

Purpose

To study the effect of a countermovement on the lower limb force–velocity (F–v) mechanical profile and to experimentally test the influence of F–v mechanical profile on countermovement jump (CMJ) performance, independently from the effect of maximal power output (P _max).

Methods

Fifty-four high-level sprinters and jumpers performed vertical maximal CMJ and squat jump (SJ) against five to eight additional loads ranging from 17 to 87 kg. Vertical ground reaction force data were recorded (1,000 Hz) and used to compute center of mass vertical displacement. For each condition, mean force, velocity, and power output were determined over the entire push-off phase of the best trial, and used to determine individual linear F–v relationships and P _max. From a previously validated biomechanical model, the optimal F–v profile maximizing jumping performance was determined for each subject and used to compute the individual mechanical F–v imbalance (Fv _IMB) as the difference between actual and optimal F–v profiles.

Results

A multiple regression analysis clearly showed (r ² = 0.952, P < 0.001, SEE 0.011 m) that P _max, Fv _IMB and lower limb extension range (h _PO) explained a significant part of the interindividual differences in CMJ performance (P < 0.001) with positive regression coefficients for P _max and h _PO and a negative one for Fv _IMB.

Conclusion

Compared to SJ, F–v relationships were shifted to the right in CMJ, with higher P _max, maximal theoretical force and velocity (+35.8, 20.6 and 13.3 %, respectively). As in SJ, CMJ performance depends on Fv _IMB, independently from the effect of P _max, with the existence of an individual optimal F–v profile (Fv _IMB having an even larger influence in CMJ).     

Methamphetamine-associated dysregulation of the hypothalamic–pituitary–thyroid axis

Methamphetamine and HIV impair thyroid function, but few studies have investigated their combined effects on thyroid dysregulation. This study examined the associations of methamphetamine use alone and in combination with HIV on thyroid function among men in South Florida. Measures of thyroid function in methamphetamine-using, HIV-infected (METH+HIV+; n?=?127) and HIV-negative (METH+HIV?; n?=?46) men who have sex with men (MSM) were compared to non-methamphetamine-using, HIV-negative men (METH?HIV?; n?=?136). Thyroid function was dysregulated in methamphetamine-using MSM, irrespective of HIV status. Both meth-using groups had greater odds of abnormal thyroid stimulating hormone levels and significantly higher mean free triiodothyronine (T3) levels. Elevated free T3 was associated with greater depressive symptoms. Overall, outcomes have important implications for assessment of thyroid function in methamphetamine users, particularly among those presenting with depression.     

Pathobiology of neutrophil–epithelial interactions

Polymorphonuclear neutrophils (PMNs) are innate immune system cells that play an essential role in eradicating invading pathogens. PMN migration to sites of infection/inflammation requires exiting the microcirculation and subsequent crossing of epithelial barriers in mucosa-lined organs such as the lungs and intestines. Although these processes usually occur without significant damage to surrounding host tissues, dysregulated/excessive PMN transmigration and resultant bystander-tissue damage are characteristic of numerous mucosal inflammatory disorders. Mechanisms controlling PMN extravasation have been well characterized, but the molecular details regarding regulation of PMN migration across mucosal epithelia are poorly understood. Given that PMN migration across mucosal epithelia is strongly correlated with disease symptoms in many inflammatory mucosal disorders, enhanced understanding of the mechanisms regulating PMN transepithelial migration should provide insights into clinically relevant tissue-targeted therapies aimed at ameliorating PMN-mediated bystander-tissue damage. This review will highlight current understanding of the molecular interactions between PMNs and mucosal epithelia and the associated functional consequences.     

Validation of an Information–Motivation–Behavioral Skills model of diabetes self-care (IMB-DSC)

Objective

Comprehensive behavior change frameworks are needed to provide guidance for the design, implementation, and evaluation of diabetes self-care programs in diverse populations. We applied the Information–Motivation–Behavioral Skills (IMB) model, a well-validated, comprehensive health behavior change framework, to diabetes self-care.

Methods

Patients with diabetes were recruited from an outpatient clinic. Information gathered pertained to demographics, diabetes knowledge (information); diabetes fatalism (personal motivation); social support (social motivation); and diabetes self-care (behavior). Hemoglobin A1C values were extracted from the patient medical record. Structural equation models tested the IMB framework.

Results

More diabetes knowledge (r = 0.22 p < 0.05), less fatalistic attitudes (r = −0.20, p < 0.05), and more social support (r = 0.27, p < 0.01) were independent, direct predictors of diabetes self-care behavior; and through behavior, were related to glycemic control (r = −0.20, p < 0.05).

Conclusions

Consistent with the IMB model, having more information (more diabetes knowledge), personal motivation (less fatalistic attitudes), and social motivation (more social support) was associated with behavior; and behavior was the sole predictor of glycemic control.

Practice implications

The IMB model is an appropriate, comprehensive health behavior change framework for diabetes self-care. The findings indicate that in addition to knowledge, diabetes education programs should target personal and social motivation to effect behavior change.     

Emergence and evolution of the renin–angiotensin–aldosterone system

The renin-angiotensin-aldosterone system (RAAS) is not the sole, but perhaps the most important volume regulator in vertebrates. To gain insights into the function and evolution of its components, we conducted a phylogenetic analysis of its main related genes. We found that important parts of the system began to appear with primitive chordates and tunicates and that all major components were present at the divergence of bony fish, with the exception of the Mas receptor. The Mas receptor first appears after the bony-fish/tetrapod divergence. This phase of evolutionary innovation happened about 400 million years ago. We found solid evidence that angiotensinogen made its appearance in cartilage fish. The presence of several RAAS genes in organisms that lack all the components shows that these genes have had other ancestral functions outside of their current role. Our analysis underscores the utility of sequence comparisons in the study of evolution. Such analyses may provide new hypotheses as to how and why in today's population an increased activity of the RAAS frequently leads to faulty salt and volume regulation, hypertension, and cardiovascular diseases, opening up new and clinically important research areas for evolutionary medicine.     

Mechanisms of Interstitial Flow-Induced Remodeling of Fibroblast–Collagen Cultures

Interstitial fluid flow, critical for macromolecular transport, was recently shown to drive fibroblast differentiation and perpendicular cell and matrix alignment in 3D collagen cultures. Here we explore the mechanisms underlying this flow-induced cell and collagen alignment. Cell and matrix alignment was assessed from 3D confocal reflectance stacks using a Fast Fourier Transform method. We found that human dermal and lung fibroblasts align perpendicular to flow in the range of 5–13 μm/s (0.1–0.3 dyn/cm²) in collagen; however, neither cells nor matrix fibers align in fibrin cultures, which unlike collagen, is covalently cross-linked and generally degraded by cell fibrinolysis. We also found that even acellular collagen matrices align weakly upon exposure to flow. Matrix alignment begins within 12 h of flow onset and continues, along with cell alignment, over 48 h. Together, these data suggest that interstitial flow first induces collagen fiber alignment, providing contact guidance for the cells to orient along the aligned matrix; later, the aligned cells further remodel and align their surrounding matrix fibers. These findings help elucidate the effects of interstitial flow on cells in matrices and have relevance physiologically in tissue remodeling and in tissue engineering applications.     

Nanostructuring of PEG–fibrinogen polymeric scaffolds

Recent studies have shown that nanostructuring of scaffolds for tissue engineering has a major impact on their interactions with cells. The current investigation focuses on nanostructuring of a biocompatible, biosynthetic polymeric hydrogel scaffold made from crosslinked poly(ethylene glycol)–fibrinogen conjugates. Nanostructuring was achieved by the addition of the block copolymer Pluronic^® F127, which self-assembles into nanometric micelles at certain concentrations and temperatures. Cryo-transmission electron microscopy experiments detected F127 micelles, both embedded within PEGylated fibrinogen hydrogels and in solution. The density of the F127 micelles, as well as their ordering, increased with increasing block copolymer concentration. The mechanical properties of the nanostructured hydrogels were investigated using stress-sweep rheological testing. These tests revealed a correlation between the block copolymer concentration and the storage modulus of the composite hydrogels. In vitro cellular assays confirmed that the increased modulus of the hydrogels did not limit the ability of the cells to form extensions and become spindled within the three-dimensional (3-D) hydrogel culture environment. Thus, altering the nanostructure of the hydrogel may be used as a strategy to control cellular behavior in 3-D through changes in mechanical properties of the environment.     

Inhibition of return in cue–target and target–target tasks

Inhibition of return (IOR), the term given for the slowing of a response to a target that appeared at the same location as a previously presented stimulus, has been studied with both target–target (TT; participants respond to each successive event) and cue–target (CT; participants only respond to the second of two events) tasks. Although both tasks have been used to examine the processes and characteristics of IOR, few studies have been conducted to understand if there are any differences in the processes that underlie the IOR that results from ignoring (CT paradigm) or responding to (TT paradigm) the first stimulus. The purpose of the present study was to examine the notion that IOR found in TT tasks represents “true” IOR whereas IOR found in CT tasks consist of both “true” IOR and response inhibition (Coward et al. in Exp Brain Res 155:124–128, 2004). Consistent with the pattern of effects found by Coward et al. (Exp Brain Res 155:124–128, 2004), IOR was larger in the CT task than in the TT task when a single detection response was required (Experiment 1). However, when participants completed one of two spatially-directed responses (rapid aiming movement to the location of the target stimulus), IOR effects from the CT and TT tasks were equal in magnitude (Experiment 2). Rather than CT tasks having an additional response inhibition component, these results suggest that TT tasks may show less of an inhibitory effect because of a facilitatory response repetition effect.     

Temporal frequency characteristics of synchrony–asynchrony discrimination of audio-visual signals

Temporal synchrony is a critical condition for integrating information presented in different sensory modalities. To gain insight into the mechanism underlying synchrony perception of audio-visual signals we examined temporal limits for human participants to detect synchronous audio-visual stimuli. Specifically, we measured the percentage correctness of synchrony-asynchrony discrimination as a function of audio-visual lag while changing the temporal frequency and/or modulation waveforms. Audio-visual stimuli were a luminance-modulated Gaussian blob and amplitude-modulated white noise. The results indicated that synchrony-asynchrony discrimination became nearly impossible for periodic pulse trains at temporal frequencies higher than 4 Hz, even when the lag was large enough for discrimination with single pulses (Experiment 1). This temporal limitation cannot be ascribed to peripheral low-pass filters in either vision or audition (Experiment 2), which suggests that the temporal limit reflects a property of a more central mechanism located at or before cross-modal signal comparison. We also found that the functional behaviour of this central mechanism could not be approximated by a linear low-pass filter (Experiment 3). These results are consistent with a hypothesis that the perception of audio-visual synchrony is based on comparison of salient temporal features individuated from within-modal signal streams.     

A Priori Identifiability of Distributed Models of Blood–Tissue Exchange

A priori identifiability deals with the uniqueness of the solution for the unknown parameters of a dynamic model from a given input–output experiment, and is a prerequisite for well posedness of parameter estimation from the data. Identifiability has been extensively investigated for lumped parameter, linear, and nonlinear dynamic models, in particular, compartmental models of biological systems. Much less attention has been devoted to distributed parameter model, in particular, those describing blood–tissue exchange, which are normally used to interpret regional multiple tracer dilution experiments. In this paper, we study a priori identifiability of distributed parameter models of transcapillary exchange, focusing first on a single capillary (one-region) model, then moving on to a single capillary–interstitial fluid (two-region) model, and finally to an organ model also describing flow heterogeneity. © 1999 Biomedical Engineering Society. PAC99: 8719Tt, 8710+e     

Effect of Cell–Cell Interactions on the Observable Strength of Adhesion of Sheets of Cells

Previous research in cellular adhesion has focused primarily on studying isolated cells under conditions where cells do not interact with each other. However, in vivo cells form sheets where both cell–substratum and cell–cell interactions contribute to the overall adhesive behavior. Our understanding of how cell–cell and cell–substratum interactions affect the overall process of cell adhesion in these situations is limited. To address this problem, we developed a systematic approach to evaluate how cell–cell and cell–substratum interactions affect the critical shear stress for detachment for semiconfluent and confluent sheets of cells. Our studies were based on subjecting cultures of adherent cells to a defined hydrodynamic flow in a radial-flow chamber with a gap height of 140 m. Using phase-contrast microscope imaging and analysis we measured shear-dependent patterns of detachment as a function of the extent of cell confluency. Our results show that the critical shear stress for detachment is maximum at intermediate extents of confluency of 10%–40%. These results have important implications for sodding vascular grafts and tissue engineering. © 1999 Biomedical Engineering Society. PAC99: 8718-h, 8719Rr