Repeated episodes of ischemia followed by reperfusion, commonly referred to as ischemic preconditioning (IPC), represent an endogenous protective mechanism that delays cell injury. IPC also increases blood Xow and improves endothelial function. We hypothesize that IPC will improve physical exercise performance and maximal oxygen consumption. The purpose of the study was to examine the eVect of ischemic preconditioning in leg skeletal muscles on cycling exercise performance in healthy individuals. Fifteen healthy, well-trained subjects performed two incremental maximal exercise tests on a bicycle ergometer. Power output, oxygen consumption, ventilation, respiratory quotient, and heart rate were measured continuously. Blood pressure and blood lactate were measured before and after the test. One exercise test was performed after the application of ischemic preconditioning, using a protocol of three series of 5-min ischemia at both legs with resting periods of 5 min in between. The other maximal cycling test served as a control. Tests were conducted in counterbalanced order, at least 1 week apart, at the same time of the day. The repeated ischemic periods signiWcantly increased maximal oxygen consumption from 56.8 to 58.4 ml/min per kg (P = 0.003). Maximal power output increased signiWcantly from 366 to 372 W (P = 0.05). Ischemic preconditioning had no eVect on ventilation, respiratory quotient, maximal heart rate, blood pressure or on blood lactate. Repeated short-term leg ischemia prior to an incremental bicycle exercise test improves maximal oxygen consumption by 3% and power output by 1.6%. This protocol, which is suggested to mimic the eVects of ischemic preconditioning, may have important implications for exercise performance.

Deconditioning is a risk factor for cardiovascular disease. The physiology of vascular adaptation to deconditioning has not been elucidated. The purpose of the present study was to assess the effects of bed rest deconditioning on vascular dimension and function of leg conduit arteries. In addition, the effectiveness of resistive vibration exercise as a countermeasure for vascular deconditioning during bed rest was evaluated. Sixteen healthy men were randomly assigned to bed rest (BR-Ctrl) or to bed rest with resistive vibration exercise (BR-RVE). Before and after 25 and 52 days of strict horizontal bed rest, arterial diameter, blood flow, flow-mediated dilatation (FMD), and nitroglycerin-mediated dilatation were measured by echo Doppler ultrasound. In the BR-Ctrl group, the diameter of the common femoral artery decreased by 13 +/- 3% after 25 and 17 +/- 1% after 52 days of bed rest (P < 0.001). In the BR-RVE group this decrease in diameter was significantly attenuated (5 +/- 2% after 25 days and 6 +/- 2% after 52 days, P < 0.01 vs. BR-Ctrl). Baseline blood flow did not change after bed rest in either group. After 52 days of bed rest, FMD and nitroglycerin-mediated dilatation of the superficial femoral artery were increased in both groups, possibly by increased nitric oxide sensitivity. In conclusion, bed rest deconditioning is accompanied by a reduction in the diameter of the conduit arteries and by an increased reactivity to nitric oxide. Resistive vibration exercise effectively attenuates the diameter decrease of leg conduit arteries after bed rest.

Flow-mediated dilatation (FMD) of the brachial and radial arteries is an important research tool for assessment of endothelial function in vivo, and is nitric oxide (NO) dependent. The leg skeletal muscle vascular bed is an important territory for studies in exercise physiology. However, the role of endothelial NO in the FMD response of lower limb arteries has never been investigated. The purpose of this study was to examine the contribution of NO to FMD in the superficial femoral artery in healthy subjects. Since physical inactivity may affect endothelial function, and therefore NO availability, spinal cord-injured (SCI) individuals were included as a model of extreme deconditioning. In eight healthy men (34 ± 13 years) and six SCI individuals (37 ± 10 years), the 5 min FMD response in the superficial femoral artery was assessed by echo-Doppler, both during infusion of saline and during infusion of the NO synthase blocker N G -monomethyl-L-arginine (L-NMMA). In a subset of the controls (n = 6), the 10 min FMD response was also examined using the same procedure. The 5 min FMD response in controls (4.2 ± 0.3%) was significantly diminished during L-NMMA infusion (1.0 ± 0.2%, P < 0.001). In SCI, L-NMMA also significantly decreased the FMD response (from 8.2 ± 0.4% during saline to 2.4 ± 0.5% during L-NMMA infusion). The hyperaemic flow response during the first 45 s after cuff deflation was lower in both groups during infusion of L-NMMA, but the effect of L-NMMA on FMD persisted in both groups after correction for the shear stress stimulus. The 10 min FMD was not affected by L-NMMA (saline: 5.4 ± 1.6%, L-NMMA: 5.6 ± 1.5%). Superficial femoral artery FMD in response to distal arterial occlusion for a period of 5 min is predominantly mediated by NO in healthy men and in the extremely deconditioned legs of SCI individuals.

.-The aim of the study was to assess endothelial function, measured by flow-mediated dilation (FMD), in an inactive extremity (leg) and chronically active extremity (arm) within one subject. Eleven male spinal cord-injured (SCI) individuals and eleven male controls (C) were included. Echo Doppler measurements were performed to measure FMD responses after 10 and 5 min of arterial occlusion of the leg (superficial femoral artery, SFA) and the arm (brachial artery, BA), respectively. A nitroglycerine spray was administered to determine the endothelium independent vasodilatation in the SFA. In the SFA, relative changes in FMD were significantly enhanced in SCI compared with C (SCI: 14.1 Ϯ 1.3%; C: 9.2 Ϯ 2.3%), whereas no differences were found in the BA (SCI: 12.5 Ϯ 2.9%; C: 14.2 Ϯ 3.3%). Because the FMD response is directly proportional to the magnitude of the stimulus, the FMD response was also expressed relative to the shear rate. No differences between the groups were found for the FMD-to-shear rate ratio in the SFA (SCI:0.061 Ϯ 0.023%/s Ϫ1 ; C: 0.049 Ϯ 0.024%/s Ϫ1 ), whereas the FMD-to-shear rate ratio was significantly decreased in the BA of SCI individuals (SCI: 0.037 Ϯ 0.01%/s Ϫ1 ; C: 0.061 Ϯ 0.027%/s Ϫ1 ). The relative dilatory response to nitroglycerine did not differ between the groups. (SCI: 15.6 Ϯ 2.0%; C: 13.4 Ϯ 2.3%). In conclusion, our results indicate that SCI individuals have a preserved endothelial function in the inactive legs and possibly an attenuated endothelial function in the active arms compared with controls. vascular endothelial function; deconditioning; ultrasound THE ENDOTHELIUM plays an essential role in vascular homeostasis and is able to respond to physical and chemical stimuli by the synthesis and release of vasoactive, thromboregulatory, and growth factor substances (37). Impaired endothelial function has been suggested as a key early event in the development of atherosclerosis, and a high correlation between endothelial dysfunction and risk factors for cardiovascular diseases, including hypertension, hypercholesterolemia, cigarette smoking, diabetes, and aging, has been reported (6 -8, 12, 29, 33, 47, 48). Besides the above-mentioned traditional risk factors, it is well known that physical inactivity is associated with an increased risk of developing cardiovascular diseases (32). However, at present, the relationship between inactivity and endothelial dysfunction is not clear. In individuals with paraplegia, the part of the body below the lesion level is paralyzed and thus extremely inactive (20,39). In contrast, the upper limbs are often relatively active because the arms are used for ambulation due to their wheelchair-bound life-style (43). A spinal cord injury (SCI), therefore, offers a unique "human model of nature" to assess peripheral vascular adaptations to inactivity (legs) and activity (arms) on endothelial function within one subject.Healthy vessels are capable of accommodating to an increase in blood flow by dilating the internal vessel diameter, a phenomenon called fl...

Given the increasing emphasis on performance of resistance exercise as an essential component of health, we evaluated, using a prospective longitudinal design, the potential for resistance training to affect arterial endothelial function. Twenty-eight men (23 +/- 3.9 yr old; mean +/- SE) engaged in 12 wk of whole body resistance training five times per week using a repeating split-body 3-day cycle. Brachial endothelial function was measured using occlusion cuff-induced flow-mediated dilation. After occlusion of the forearm for 4.5 min, brachial artery dilation and postocclusion blood flow was measured continuously for 15 and 70 s, respectively. Peak and 10-s postocclusion blood flow, shear rate, and brachial artery flow-mediated dilation (relative and normalized to shear rate) were measured pretraining (Pre), at 6 wk of training (Mid), and at 13 wk of training (Post). Results indicated an increase of mean brachial artery diameter by Mid and Post vs. Pre. Peak and 10-s postocclusion blood flow increased by Mid and remained elevated at Post; however, shear rates were not different at any time point. Relative and normalized flow-mediated dilation was also not different at any time point. This study is the first to show that peripheral arterial remodeling does occur with resistance training in healthy young men. In addition, the increase in postocclusion blood flow may indicate improved resistance vessel function. However, unlike studies involving endurance training, flow-mediated dilation did not increase with resistance training. Thus arterial adaptations with high-pressure loads, such as those experienced during resistance exercise, may be quite different compared with endurance training.

Physical inactivity or deconditioning is an independent risk factor for atherosclerosis and cardiovascular disease. In contrast to exercise, the vascular changes that occur as a result of deconditioning have not been characterized. We used 4 wk of unilateral lower limb suspension (ULLS) to study arterial and venous adaptations to deconditioning. In contrast to previous studies, this model is not confounded by denervation or microgravity. Seven healthy subjects participated in the study. Arterial and venous characteristics of the legs were assessed by echo Doppler ultrasound and venous occlusion plethysmography. The diameter of the common and superficial femoral artery decreased by 12% after 4 wk of ULLS. Baseline calf blood flow, as measured by plethysmography, decreased from 2.1 +/- 0.2 to 1.6 +/- 0.2 ml.min(-1).dl tissue(-1). Both arterial diameter and calf blood flow returned to baseline values after 4 wk of recovery. There was no indication of a decrease in flow-mediated dilation of the superficial femoral artery after ULLS deconditioning. This means that functional adaptations to inactivity are not simply the inverse of adaptations to exercise. The venous pressure-volume curve is shifted downward after ULLS, without any effect on compliance. In conclusion, deconditioning by 4 wk of ULLS causes significant changes in both the arterial and the venous system.

Study design: Pre-post training intervention. Objectives: To evaluate the effect of training intensity on physical capacity, lipid profile and insulin sensitivity in early rehabilitation of spinal cord injured (SCI) patients, and to assess the correlation between peak aerobic capacity (VO 2Peak ) and insulin sensitivity. Setting: Spinal Cord Rehabilitation Unit, Sunnaas Hospital, Nesoddtangen, Norway. Method: Six recently injured SCI individuals participated in the arm training intervention and were randomly admitted to a high-intensity (HI; 70-80% heart rate reserve (HRR)) and lowintensity (LI; 40-50% HRR) group. The 1 h interval training consisted of 3 min exercise bouts interspersed with 2 min of rest, three times a week for 8 weeks. In addition, a correlation coefficient was obtained between VO 2Peak and insulin sensitivity in 11 SCI patients. Results: The 8-week training program resulted in a significant increase in VO 2Peak and maximal power output (PO Max ) for the group as a whole (Po0.05). VO 2Peak increased significantly more and total cholesterol/high-density lipoprotein cholesterol (TC/HDL-C) ratio and triglycerids decreased significantly more in the HI group than in the LI group (P ¼ 0.05). Training-induced changes in insulin sensitivity were significantly different between the groups (P ¼ 0.05), which was due to a nonsignificant decline in insulin sensitivity in the HI group and a nonsignificant improvement in the LI group. A significant positive correlation was found between VO 2peak and insulin sensitivity (r ¼ 0.68, P ¼ 0.02). Conclusion:The interval arm training protocol as used in the present study enables recently injured SCI patients to do substantial work at a relatively high intensity. Results indicate that improvements in physical capacity and lipid profile were more pronounced in response to highintensity training. The significant correlation between maximal oxygen consumption and insulin sensitivity indicates that, as in the able-bodied population, peak aerobic capacity is a predictive value with regard to insulin sensitivity in SCI. Future studies with larger groups assessing the role of exercise intensity on insulin sensitivity in SCI are suggested.

The effect of resistance training on arterial stiffening is controversial. We tested the hypothesis that resistance training would not alter central arterial compliance. Young healthy men (age, 23 ± 3.9 (mean ± S.E.M.) years; n = 28,) were whole-body resistance trained five times a week for 12 weeks, using a rotating 3-day split-body routine. Resting brachial blood pressure (BP), carotid pulse pressure, carotid cross-sectional compliance (CSC), carotid initima-media thickness (IMT) and left ventricular dimensions were evaluated before beginning exercise (PRE), after 6 weeks of exercise (MID) and at the end of 12 weeks of exercise (POST). CSC was measured using the pressure-sonography method. Results indicate reductions in brachial (61.1 ± 1.4 versus 57.6 ± 1.2 mmHg; P < 0.01) and carotid pulse pressure (52.2 ± 1.9 versus 46.8 ± 2.0 mmHg; P < 0.01) PRE to POST. In contrast, carotid CSC, β-stiffness index, IMT and cardiac dimensions were unchanged. In young men, central arterial compliance is unaltered with 12 weeks of resistance training and the mechanisms responsible for cardiac hypertrophy and reduced arterial compliance are either not inherent to all resistance-training programmes or may require a prolonged stimulus.