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Every day, humans make countless decisions that require the integration of information about potential benefits (i.e. rewards) with other decision features (i.e. effort required, probability of an outcome or time delays). Here, we examine the overlap and dissociation of behavioral preferences and neural representations of subjective value in the context of three different decision features (physical effort, probability and time delays) in a healthy adult life span sample. While undergoing functional neuroimaging, participants (N = 75) made incentive compatible choices between a smaller monetary reward with lower physical effort, higher probability, or a shorter time delay versus a larger monetary reward with higher physical effort, lower probability, or a longer time delay. Behavioral preferences were estimated from observed choices, and subjective values were computed using individual hyperbolic discount functions. We found that discount rates were uncorrelated across tasks. Despite this apparent behavioral dissociation between preferences, we found overlapping subjective value-related activity in the medial prefrontal cortex across all three tasks. We found no consistent evidence for age differences in either preferences or the neural representations of subjective value across adulthood. These results suggest that while the tolerance of decision features is behaviorally dissociable, subjective value signals share a common representation across adulthood.
Studying the magnitude and kinetics of blood flow, oxygen extraction, and oxygen consumption at exercise onset and during the recovery from exercise can lead to insights into both the normal control of metabolism and blood flow and the disturbances to these processes in metabolic and cardiovascular diseases. The purpose of this study was to examine the on- and off-kinetics for oxygen delivery, extraction, and consumption as functions of submaximal contraction intensity. Eight healthy subjects performed four 1-min isometric dorsiflexion contractions, with two at 20% MVC and two at 40% MVC. During one contraction at each intensity, relative perfusion changes were measured by using arterial spin labeling, and the deoxyhemoglobin percentage (%HHb) was estimated using the spin- and gradient-echo sequence and a previously published empirical calibration. For the whole group, the mean perfusion did not increase during contraction. The %HHb increased from ∼28 to 38% during contractions of each intensity, with kinetics well described by an exponential function and mean response times (MRTs) of 22.7 and 21.6 s for 20 and 40% MVC, respectively. Following contraction, perfusion increased ∼2.5-fold. The %HHb, oxygen consumption, and perfusion returned to precontraction levels with MRTs of 27.5, 46.4, and 50.0 s, respectively (20% MVC), and 29.2, 75.3, and 86.0 s, respectively (40% MVC). These data demonstrate in human subjects the varied recovery rates of perfusion and oxygen consumption, along with the similar rates of %HHb recovery, across these exercise intensities.
Copyright © 2015 the American Physiological Society.
BACKGROUND - Leisure time exercise has been linked to lower circulating levels of inflammatory markers. Few studies have examined the association of nonexercise physical activity with markers of inflammation and oxidative stress.
METHODS - This cross-sectional analysis included 1005 Chinese women aged 40-70 years. Usual physical activity was assessed through in-person interviews using a validated physical activity questionnaire. Plasma proinflammatory cytokines and urinary F2-isoprostanes were measured. Multivariable linear models were used to evaluate the association of inflammatory and oxidative stress markers with nonexercise physical activity and its major components.
RESULTS - Nonexercise physical activity accounted for 93.8% of overall physical activity energy expenditure. Levels of nonexercise physical activity were inversely associated with circulating concentrations of interleukin (IL)-6 (Ptrend=0.004), IL-1β (Ptrend=0.03) and tumor necrosis factor-alpha (TNF-α) (Ptrend=0.01). Multivariable-adjusted concentrations of these cytokines were 28.2% for IL-6, 22.1% for IL-1β, and 15.9% for TNF-α lower in the highest quartile of nonexercise physical activity compared with the lowest quartile. Similar inverse associations were found for two major components of nonexercise physical activity, walking and biking for transportation, and household activity. No significant associations were observed between nonexercise physical activity and oxidative stress markers.
CONCLUSION - Daily nonexercise physical activity is associated with lower levels of systemic inflammation. This finding may have important public health implications because this type of activity is the main contributor to overall physical activity among middle-aged and elderly women.
BACKGROUND - The data existing in the literature regarding the safety of using regadenoson with symptom-limited exercise are limited, which motivated the authors to undertake this randomized study.
METHODS - We offered patients scheduled to undergo vasodilator stress nuclear myocardial perfusion imaging the opportunity to exercise instead. Patients who failed to reach target heart rate (THR) were randomized to (1) receive regadenoson at peak exercise or (2) stop exercise and receive regadenoson at rest. Patients who reached THR received a standard Tc-99m sestamibi injection with no regadenoson.
RESULTS - 200 patients were included (66% male, mean age 52.5 ± 13.6). 125 patients (62%) reached THR with exercise alone. All stress protocols were well tolerated, and there were no significant adverse events. There were no statistically significant differences in the extent of perfusion abnormalities, image quality, or rate of referral to cardiac catheterization within 60 days between the groups. In fully adjusted logistic regression models, beta-blocker use and diabetes remained significant univariate predictors of failure to reach THR (OR 0.21, 95% CI 0.1-0.5, P < .0001, OR 0.34, 95% CI 0.2-0.7, P = .004, respectively).
CONCLUSIONS - A protocol combining regadenoson at peak exercise in patients unable to reach THR with exercise is feasible, well-tolerated, and yields comparable imaging results to a standard regadenoson injection at rest. In addition, pharmacologic stress testing may be over-ordered in current clinical practice, as patients referred for such testing were often able to exercise.
Surface electromyography (EMG) can assess muscle recruitment patterns during cycling, but has limited applicability to studies of deep muscle recruitment and electrically stimulated contractions. We determined whether muscle recruitment timing could be inferred from MRI-measured transverse relaxation time constant (T(2)) changes and a cycle ergometer modified to vary power as a function of pedal angle. Six subjects performed 6 min of single-leg cycling under two conditions (E0°-230° and E90°-230°), which increased the power from 0°-230° and 90-230° of the pedal cycle, respectively. The difference condition produced a virtual power output from 0-180° (V0°-180°). Recruitment was assessed by integrating EMG over the pedal cycle (IEMG) and as the (post-pre) exercise T(2) change (ΔT(2)). For E0°-230°, the mean IEMG for vastus medialis and lateralis (VM/VL; 49.3 ± 3.9 mV·s; mean ± SE) was greater (P < 0.05) than that for E90°-230° (17.9 ± 1.9 mV·s); the corresponding ΔT(2) values were 8.7 ± 1.0 and 1.4 ± 0.5 ms (P < 0.05). For E0°-230° and E90°-230°, the IEMG values for biceps femoris/long head (BF(L)) were 37.7 ± 5.4 and 27.1 ± 5.6 mV·s (P > 0.05); the corresponding ΔT(2) values were 0.9 ± 0.9 and 1.5 ± 0.9 ms (P > 0.05). MRI data indicated activation of the semitendinosus and BF/short head for E0°-230° and E90°-230°. For V0°-180°, ΔT(2) was 7.2 ± 0.9 ms for VM/VL and -0.6 ± 0.6 ms for BF(L); IEMG was 31.5 ± 3.7 mV·s for VM/VL and 10.6 ± 7.0 mV·s for BF(L). MRI and EMG data indicate VM/VL activity from 0 to 180° and selected hamstring activity from 90 to 230°. Combining ΔT(2) measurements with variable loading allows the spatial and temporal patterns of recruitment during cycling to be inferred from MRI data.
Endothelial nitric oxide synthase (eNOS) is associated with a number of physiological functions involved in the regulation of metabolism; however, the functional role of eNOS is poorly understood. We tested the hypothesis that eNOS is critical to muscle cell signaling and fuel usage during exercise in vivo, using 16-wk-old catheterized (carotid artery and jugular vein) C57BL/6J mice with wild-type (WT), partial (+/-), or no expression (-/-) of eNOS. Quantitative reductions in eNOS expression ( approximately 40%) elicited many of the phenotypic effects observed in enos(-/-) mice under fasted, sedentary conditions, with expression of oxidative phosphorylation complexes I to V and ATP levels being decreased, and total NOS activity and Ca(2+)/CaM kinase II Thr(286) phosphorylation being increased in skeletal muscle. Despite these alterations, exercise tolerance was markedly impaired in enos(-/-) mice during an acute 30-min bout of exercise. An eNOS-dependent effect was observed with regard to AMP-activated protein kinase signaling and muscle perfusion. Muscle glucose and long-chain fatty acid uptake, and hepatic and skeletal muscle glycogenolysis during the exercise bout was markedly accelerated in enos(-/-) mice compared with enos(+/-) and WT mice. Correspondingly, enos(-/-) mice exhibited hypoglycemia during exercise. Thus, the ablation of eNOS alters a number of physiological processes that result in impaired exercise capacity in vivo. The finding that a partial reduction in eNOS expression is sufficient to induce many of the changes associated with ablation of eNOS has implications for chronic metabolic diseases, such as obesity and insulin resistance, which are associated with reduced eNOS expression.
UNLABELLED - Health benefits of physical activity (PA) during pregnancy have been noted, but women's perceptions of PA safety have been little studied.
OBJECTIVES - To examine associations among PA participation, safety perceptions, and demographic characteristics.
METHODS - Pregnant women were recruited from nine clinics in Grand Rapids, MI (USA) from April to October, 2006. Demographics, participation in moderate and vigorous PA, and perceived safety of both intensities (5-pt Likert scales) were reported. Logistic regression analyses were used to estimate associations.
RESULTS - Of 342 eligible women, 296 provided complete PA information. Most (88%) participated in some PA and felt moderate PA was safe (89%), but only 36% felt vigorous PA was safe. Feeling unsafe/unsure about moderate PA was associated with non-White race/ethnicity, low education, low income, not participating in moderate PA, and/or not intending to be active during pregnancy. Hispanic ethnicity, low education, nulliparity, and not participating in moderate or vigorous PA were associated with feeling unsafe/unsure about vigorous PA.
CONCLUSIONS - Pregnant women generally feel that moderate PA is safe, but are less certain about vigorous PA. More work is needed to inform pregnant women about the benefits of moderate PA, especially among non-White and low education/income populations.
The endothelium plays an essential role in maintaining vascular homeostasis, and it fulfills this role by modulating intracellular signaling and gene expression in response to chemical and mechanical stimuli. Assessing changes in endothelial gene expression is essential to understanding how physiological and pathophysiological processes modulate vascular homeostasis. Here we describe the use of molecular beacons to rapidly and quantitatively assess expression and 3'-polyadenylation of a gene that is important for vascular homeostasis, endothelial nitric oxide synthase (eNOS). Single- and dual-fluorescence resonance energy transfer (FRET) molecular beacon hybridization assays were developed to measure changes in mRNA levels and 3'-polyadenylation, respectively, in primary human endothelial cell cultures subjected to laminar shear stress or statin treatment. Optimized beacon hybridization assays took approximately 15 min to perform, and eNOS mRNA levels were validated by quantitative real-time RT-PCR. Competitive inhibition assays and posttranscriptional silencing of eNOS expression were used to verify the specificity of molecular beacon fluorescence. Finally, the dual-FRET method was used to assess eNOS polyadenylation in tissues isolated from mice subjected to exercise training. These data demonstrate that molecular beacons can be used to rapidly and efficiently measure endothelial gene expression and 3'-polyadenylation. This approach could easily be adapted for studies of other endothelial genes and has promise for applications in live endothelial cells.
INTRODUCTION - QT interval for a given heart rate differs between exercise and recovery (QT hysteresis) due to slow QT adaptation to changes in heart rate. We hypothesized that QT hysteresis is evident within stages of exercise and investigated which component of the QT contributes to hysteresis.
METHODS AND RESULTS - Nineteen healthy volunteers performed a staged exercise test (four stages, 3 min each). Continuous telemetry was analyzed with software to compare QT intervals in a rate-independent fashion. QRST complexes during each minute were sorted by RR interval, and complexes in bins of 20 ms width were signal-averaged. QT and QTp (onset of QRS to peak T wave) were measured, and terminal QT calculated (peak to end of T wave, Tpe = QT - QTp). QT, QTp, and Tpe at the same heart rate were compared between the first and last minute of each stage. QT shortened from the first to last minute of exercise in each stage (Stage I: 358 +/- 30 to 346 +/- 25 ms, P < 0.001; Stage II: 342 +/- 27 to 331 +/- 24 ms, P = 0.003; Stage III: 329 +/- 21 to 322 +/- 18 ms, P = 0.03; Stage IV: 313 +/- 22 to 303 +/- 23 ms, P = 0.005). QTp also shortened in each stage, while Tpe was unchanged.
CONCLUSION - QT hysteresis occurs during exercise in normals, and the major determinant is shortening of the first component of the T wave. Terminal repolarization (peak to end of T wave), a surrogate for transmural dispersion of repolarization, does not shorten significantly with exercise.
It has previously been observed that during isometric dorsiflexion exercise, the time course of T2-weighted signal intensity (SI) changes is spatially heterogeneous. The purpose of this study was to test the hypothesis that this spatial heterogeneity would increase at higher contraction intensities. Eight subjects performed 90-s isometric dorsiflexion contractions at 30% and 60% of maximum voluntary contraction (MVC) while T2-weighted (repetition time/echo time=4000/35 ms) images were acquired. SI was measured before, during and after the contractions in regions of interest (ROIs) in the extensor digitorum longus (EDL) muscle and the deep and superficial compartments of the tibialis anterior (D-TA and S-TA, respectively). For all ROIs at 30% MVC, SI changes were similar. The maximum postcontraction SI was greater than the SI during exercise. At 60% MVC, SI changes during contraction were greater in the S-TA than in the D-TA and EDL. For the EDL and D-TA, the maximum postcontraction SI was greater than those during exercise. For the S-TA, the maximum postcontraction change was greater than the changes at t=8, 20 and 56 s but not the end-exercise value. We conclude that spatial heterogeneity increases during more intense dorsiflexion contractions, possibly reflecting regional differences in perfusion or neural activation of the muscle.