Variability in the response of different male subjects to the effect of marathon running on the increase in plasma high density lipoprotein

The acute effects of running a 42.2 km marathon race on the concentration and composition of the plasma lipoproteins were studied in 56 men of varying fitness, training experience, age and physical characteristics. There was no change in the mean concentration of total serum cholesterol, but a 10.9% increase (P less than 0.001) in the mean concentrations of high-density lipoprotein cholesterol (HDL-TC), representing an 11.1% increase (P less than 0.001) in the cholesteryl ester (CE) and 9.9% increase (P less than 0.001) in the unesterified cholesterol (UC) moieties of HDL. The ratio of total serum cholesterol to HDL-TC decreased significantly (P less than 0.001) during the exercise. Changes in lipoprotein concentrations during the marathon varied considerably between individual subjects, with a small proportion of subjects exhibiting relatively large increases or decreases in HDL-TC, HDL-CE and HDL-UC. Small sub-populations of runners were identified who showed abnormally large decreases in HDL-UC and abnormally small increases in HDL-CE relative to HDL-UC. A correlation (P less than 0.05) was found between the average weekly mileage of training and the increase in HDL-TC, whilst faster runners (finishing time less than 3 h; n = 13) had a significantly greater (P less than 0.02) increase in HDL-TC than slower runners (greater than 4 h; n = 14).(ABSTRACT TRUNCATED AT 250 WORDS)     

Constraints on the evolution of phenotypic plasticity: limits and costs of phenotype and plasticity

Phenotypic plasticity is ubiquitous and generally regarded as a key mechanism for enabling organisms to survive in the face of environmental change. Because no organism is infinitely or ideally plastic, theory suggests that there must be limits (for example, the lack of ability to produce an optimal trait) to the evolution of phenotypic plasticity, or that plasticity may have inherent significant costs. Yet numerous experimental studies have not detected widespread costs. Explicitly differentiating plasticity costs from phenotype costs, we re-evaluate fundamental questions of the limits to the evolution of plasticity and of generalists vs specialists. We advocate for the view that relaxed selection and variable selection intensities are likely more important constraints to the evolution of plasticity than the costs of plasticity. Some forms of plasticity, such as learning, may be inherently costly. In addition, we examine opportunities to offset costs of phenotypes through ontogeny, amelioration of phenotypic costs across environments, and the condition-dependent hypothesis. We propose avenues of further inquiry in the limits of plasticity using new and classic methods of ecological parameterization, phylogenetics and omics in the context of answering questions on the constraints of plasticity. Given plasticity''s key role in coping with environmental change, approaches spanning the spectrum from applied to basic will greatly enrich our understanding of the evolution of plasticity and resolve our understanding of limits.     

Effects of fluid, electrolyte and substrate ingestion on endurance capacity

The availability of carbohydrate (CHO) as a substrate for the exercising muscles is known to be a limiting factor in the performance of prolonged cycle exercise, and provision of exogenous CHO in the form of glucose can increase endurance capacity. The present study examined the effects of ingestion of fluids and of CHO in different forms on exercise performance. Six male volunteers exercised to exhaustion on a cycle ergometer at a workload which required approximately 70% of Vo2max. After one preliminary trial, subjects performed this exercise test on six occasions, one week apart. Immediately before exercise, and at 10-min intervals throughout, subjects ingested 100 ml of one of the following: control (no drink), water, glucose syrup, fructose syrup, glucose-fructose syrup or a dilute glucose-electrolyte solution. Each of the syrup solutions contained approximately 36 g CHO per 100 ml; the isotonic glucose-electrolyte solution contained 4 g glucose per 100 ml. A randomised Latin square order of administration of trials was employed. Expired air samples for determination of Vo2, respiratory exchange ratio and rate of CHO oxidation were collected at 15-min intervals. Venous blood samples were obtained before and after exercise. Subjects drinking the isotonic glucose-electrolyte solution exercised longer (90.8 (12.4) min, mean (SEM] than on the control test (70.2 (8.3) min; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of a 36 h fast followed by refeeding with glucose, glycerol or placebo on metabolism and performance during prolonged exercise in man

Five men were studied during exercise to exhaustion on an electrically braked cycle ergometer at 70% of VO2max. The four experimental treatments were as follows: fasted for 36 h (A); fasted (36 h) and refed with glucose (B) or glycerol (C); postabsorptive (overnight fast, D). In B and C the subjects were given a drink containing glucose or glycerol (1g per kg body weight) 45 min before starting exercise. A placebo drink was given 45 min before exercise on treatments A and D. Despite an increased availability of circulating free fatty acids, beta-hydroxybutyrate and glycerol exercise time to exhaustion was significantly lower after fasting (treatment A 77.7 +/- 6.8 min) compared with treatment D (119.5 +/- 5.8 min). Refeeding with glucose or glycerol did not significantly improve performance (92.4 +/- 11.8 min and 80.8 +/- 3.6 min respectively) compared with treatment A and lowered circulating levels of FFA and beta-HB during exercise compared with A. Despite the probability of low liver glycogen levels after fasting, none of the subjects became hypoglycaemic (blood glucose less than 4 mmol.l-1) during exercise and their blood lactate concentrations were not high at exhaustion. Plasma levels of branched chain amino acids (BCAA) decreased progressively during exercise on treatments A, B and C and were considerably lower at exhaustion compared with treatment D. Falling plasma concentrations of BCAA during prolonged exercise may be implicated in the generation of central fatigue.     

The decay of potentially lethal oxygen-dependent damage in fully hydrated Bacillus megaterium spores exposed to pulsed electron irradiation.

Using a stopped-flow mixing and pulsed irradiation apparatus, a study has been made of the decay, to a harmless form, of radiation-induced species which would otherwise be lethal to spores on contact with oxygen. Aqueous suspensions of Bacillus megaterium spores were irradiated with 600 krad of electrons given over approximately 1 s; at various times after irradiation oxygen in solution was added. As the interval between irradiation and introduction of oxygen increased, the fraction of spores surviving increased. For spores irradiated in a deoxygenated condition the decay of the potentially lethal species, reflected by this change in survival, proceeded as if two parallel first-order reactions with half-lives of 9 and 120 s operate. In contrast, for spores equilibrated with oxygen and then irradiated, the decay is described by a single first-order expression with an associated half-life similar to that of the faster of the two reactions operating in anoxia.