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Energy restriction (ER) has shown to be an effective 'anti-aging' factor in rodents, resulting in an increased life span and preventing or delaying the occurrence of many age-related diseases in rodents. As a part of a feasibility study on the potential application of ER in humans, we studied the effects of moderate ER on physical performance in 24 apparently healthy, non-obese middle-aged men. After two weeks of weight maintenance the ER group (n = 16) received 80% of their habitual energy intake, while a control group (n = g) still received their weight-maintaining diet for ten weeks. Physical performance (bicycle ergometer) was estimated by a maximal (until exhaustion) and a submaximal (30min at 60% of VO2max) exercise test. After the experimental period the subjects in ER group had a significantly shorter cycling time (Δ = 1.31 ± 1.14 vs - 0.45 ± 1.56 min, p = 0.01), and thus had a lower maximal power output (Δ = 4.3 ± 5.9 vs -6.3 ± 13.6 watt, p < 0.01) and maximal oxygen uptake (Δ = 0.03 ± 0.18 vs - 0.18 ± 0.32 1/min, p = 0.05) during the maximal exercise test, than the subjects in the control group. None of these changes correlated with weight loss. As in every exercise test, motivation could have played an important role. During the submaximal exercise test no significant changes between the two groups in HR, VO2, RER and FFA, glucose, lactate and catecholamine levels were observed. It is concluded that 10 weeks of moderate ER lead to a slight but significant decrease in maximal power output, which is not related to weight loss. Moreover, no changes on submaximal physical performance and on substrate metabolism have been observed although significant alterations in body weight (-7.4 ± 2.6 kg) occurred.

Een nieuwe methode is gevonden om lichamelijke vermoeidheid te meten in bewegende omgevingen. De methode houdt in dat de Maximaaltest, die daar onderdeel van is, niet in een stlstaande maar in een bewegende omgeving moet worden afegnomen.

The maximal power that muscles can generate is reduced at low muscle temperatures. However, in prolonged heavy exercise in the heat, a high core temperature may be the factor limiting performance. Precooling has been shown to delay the attainment of hyperthermia. It is still unclear if the whole body should be cooled or if the active muscles should be excluded from cooling in order to maintain muscle power. An experiment was performed to compare thermal strain and gross efficiency following whole body or partial body cooling. Eight well-trained participants performed 40 min of 60 % V·O2max cycling exercise in a 30 °C, 70 % relative humidity climatic chamber after four different precooling sessions in a water perfused suit: N (no precooling), CC (45 min whole body precooling), WC (45 min lower body precooling), and CW (45 min upper body precooling). The uncooled body part was warmed in such a way that the core temperature did not differ from that in session N. Gross efficiency was used to compare performance between the sessions since it indicates how much oxygen is needed for a certain external load. The gross efficiency did not differ significantly between the sessions. Differences in heat loss and heat storage were observed during the first 20 min of exercise. The evaporative heat loss in session WC (305 ± 67 W) and CW (284 ± 68 W) differed from session N (398 ± 77 W) and CC (209 ± 58 W). More heat was stored in session CC (442 ± 125 W) than in sessions WC (316 ± 39 W), CW (307 ± 63 W), and N (221 ± 65 W). It was confirmed that precooling reduces heat strain during exercise in the heat. No differences in heat strain and gross efficiency were observed between precooling of the body part with the exercising muscles and precooling of the tissues elsewhere in the body.

Purpose: To investigate the effect of guideline operationalization in terms of intensity threshold, bout duration, and days on the proportion of children meeting the health-related 60-min physical activity guideline using a subjective and an objective assessment method. Methods: Five hundred and twenty-one children (6-11 yr) completed a physical activity diary for at least 4 d. A subsample of 51 children simultaneously wore an ActiGraph (ActiGraph, Pensacola, FL) accelerometer. Time spent above moderate-intensity thresholds of 3 and 5 METs, respectively, for continuous bouts of at least 1, 5, and 10 min was calculated. For each intensity threshold and bout duration, the proportion of children meeting the 60-min guideline was calculated. A distinction was made between meeting the 60-min threshold on each assessment day and meeting this threshold on average across all assessment days. Results: The proportion of children meeting the 60-min guideline differed considerably by guideline operationalization and assessment method. It ranged from 3% to 86% using the diary and from 0% to 100% using the ActiGraph. Overall, a higher proportion of children met the guideline when the 3-MET intensity threshold was used compared with the 5-MET threshold and when a shorter bout duration was used compared with a longer bout duration. More children met the guideline on average across all assessment days compared with the guideline on each assessment day. In general, boys were found to be more active than girls, independent of guideline operationalization and assessment method. Conclusion: Meeting the 60-min guideline highly depends on guideline operationalization and assessment method. Consensus about how the guideline should be operationalized is needed to monitor the extent to which populations of children meet the guideline and to simplify comparison, between studies Copyright © 2008 by the American College of Sports Medicine.

Objective. Arterial pressure waveforms distort between brachial and finger arteries, causing differences mainly in systolic pressure. Distortion, reportedly, can be removed by applying a waveform filter to the finger pressure. Design. We analysed the data from two studies that detected discrepancies in systolic tracking between Finapres and brachial pressures. The first set comprised waveforms of seven volunteers during incremental bicycle exercise to exhaustion and the second set comprised waveforms of eight volunteers during increasing phenylephrine infusion. Methods. We applied the filter and compared 1 min averaged unfiltered and waveform-filtered finger and brachial pressures. Results. During exercise, finger systolic pressure overestimated brachial increasingly, from 7 (SD 10) mmHg at rest to 27 (17) mmHg at maximal exertion. Differences were reduced by waveform filtering from 3 (SD 9) mmHg at rest to 1 (SD 15) mmHg at maximal exertion. During phenylephrine infusion finger systolic pressure overestimated brachial pressure, but the magnitude of the overestimate decreased from 14(SD 15) mmHg at baseline to -1 (SD 16) mmHg at maximal rate. After waveform filtering over-estimation was an almost constant 6 (SD 11) mmHg. Median baroreflex sensitivities from brachial, unfiltered and waveform-filtered finger pressure were 5.8, 7.5 and 5.3 ms/mmHg and correlation increased after filtering. The results indicate improved systolic pressure tracking after waveform filtering. Conclusions. Finger pressure distortion follows a general pattern correctable by waveform filtering. Waveform filtering allows a 'brachial' view to be obtained from Finapres data.

Due to more stringent requirements to protect personnel against hazardous gasses, the inspiratory resistance of the present generation of respiratory protective devices tends to increase. Therefore an important question is to what extent inspiratory resistance may increase without giving problems during physical work. In this study the effects of three levels (0.24; 1.4 and 8.3 kPasl-1) of inspiratory resistance were tested on maximal voluntary performance. Nine male subjects performed a graded exercise test on a cycle ergometer with and without these three levels of inspiratory resistance. Oxygen consumption, heart rate, time to exhaustion and external work were measured. The results of these experiments showed that increasing inspiratory resistance led to a reduction of time to exhaustion (TTE) on a graded exercise test(GXT). Without inspiratory resistance the mean TTE was 11.9 min, the three levels of resistance gave the following mean TTE's: 10.7, 7.8 and 2.7 min. This study showed that TTE on a GXT can be predicted when physical fitness (VO 2-max) of the subject and inspiratory resistance are known. The metabolic rate of the subjects was higher with inspiratory resistance, but no differences were found between the three selected inspiratory loads. Other breathing parameters as minute ventilation, tidal volume, expiration time and breathing frequency showed no or minor differences between the inspiratory resistances. The most important conclusion of these experiments is that the overall workload increases due to an increase in inspiratory resistance

Background: It has been shown that endurance performance after one night of sleep deprivation is not compromised despite the feeling of fatigue and that, in contrast, performance in the heat deteriorates even though people may feel good. However, it is essentially unknown how the estimation of performance capabilities relate to actual performance. We hypothesized that endurance performance in the heat would be overestimated and performance after sleep deprivation would be underestimated. We also hypothesized that jumping performance will be underestimated in the heat. Methods: There were 11 fit (V̇ O2peak 52.0 ± 3.7 ml. kg -1. min -1 ) men, familiar with cycling, who performed a 20-min all-out cycling test (AO) and a vertical jump test (VJ) under four different conditions: a test trial at 24°C, at 11°C ambient temperature without (C) and with one night of sleep deprivation (CS), and at 31°C (H). The subjects estimated the performance prior to exercise in CS, C, and H. Results: AO performance was less for H (6.95 ± 0.36 km) than for C (7.68 ± 0.29 km) and CS (7.62 ± 0.33 km). The subjects underestimated AO performance for CS by 1.11 km and C by 0.42 km, but not for H. VJ was higher in the H condition, in contrast with subjects ' assessment. Discussion: We conclude that subjective estimates of performance are not in line with actual performance for endurance exercise after sleep deprivation and for explosive exercise in the heat. © by the Aerospace Medical Association, Alexandria, VA.

Objective: The aim of this study was to compare beat-to-beat changes in stroke volume (SV) estimated by two different pressure wave analysis techniques during orthostatic stress testing: pulse contour analysis and Modelflow, ie, simulation of a three-element model of aortic input impedance. Methods: A reduction in SV was introduced in eight healthy young men (mean age, 25; range, 19-32 y) by a 30-minute head-up tilt maneuver. Intrabrachial and noninvasive finger pressure were monitored simultaneously. Beat-to-beat changes in SV were estimated from intrabrachial pressure by pulse contour analysis and Modelflow. In addition, the relative differences in Modelflow SV obtained from intrabrachial pressure and noninvasive finger pressure were assessed. Results: Beat-to-beat changes in Modelflow SV from intrabrachial pressure were comparable with pulse contour measures. The relative difference between the two methods amounted to 0.1 ± 1% (mean ± SEM) and was not dependent on the duration of tilt. The difference between Modelflow applied to intrabrachial pressure and finger pressure amounted to -2.7 ± 1.3% (p = 0.04). This difference was not dependent on the duration of tilt or level of arterial pressure. Conclusions: Based on different mathematical models of the human arterial system, pulse contour and Modelflow compute similar changes in SV from intrabrachial pressure during orthostatic stress testing in young healthy men. The magnitude of the difference in SV derived from intrabrachial and finger pressure may vary among subjects; Modelflow SV from noninvasive finger pressure tracks fast and brisk changes in SV derived from intrabrachial pressure.

In pushing and pulling wheeled carts, the direction of force exertion may, beside the force magnitude, considerably affect musculoskeletal loading. This paper describes how force direction changes as handle height and force level change, and the effects this has on the loads on the shoulder and low back. Eight subjects pushed against or pulled on a stationary bar or movable cart at various handle heights and horizontal force levels while walking on a treadmill. The forces at the hands in the vertical and horizontal direction were measured by a force-transducer. The forces, body movements and anthropometric data were used to calculate the net joint torques in the sagittal plane in the shoulder and the lumbo-sacral joint. The magnitudes and directions of forces did not differ between the cart and the bar pushing and pulling. Force direction was affected by the horizontal force level and handle height. As handle height and horizontal force level increased, the pushing force direction changed from 45°(SD 3.3°) downward to near horizontal, while the pulling force direction changed from pulling upward by 14°(SD 15.3°) to near horizontal. As a result, it was found that across conditions the changes in force exertion were frequently reflected in changes in shoulder torque and low back torque although of a much smaller magnitude. Therefore, an accurate evaluation of musculoskeletal loads in pushing and pulling requires, besides a knowledge of the force magnitude, knowledge of the direction of force exertion with respect to the body.