Seawater strontium isotopes, Acid rain, and the cretaceous-tertiary boundary.

A large bolide impact at the end of the Cretaceous would have produced significant amounts of nitrogen oxides by shock heating of the atmosphere. The resulting acid precipitation would have increased continental weathering greatly and could be an explanation for the observed high ratio of strontium-87 to strontium-86 in seawater at about this time, due to the dissolution of large amounts of strontium from the continental crust. Spikes to high values in the seawater strontium isotope record at other times may reflect similar episodes.

Cubanite: A New Sulfide Phase in CI Meteorites.

Cubanite (CuFe(2)S(3)), previously unobserved in meteorites, has been discovered in two carbonaceous chondrites, Orgueil and Alais. The association of this mineral with low-copper pyrrhotite suggests that it formed in a low-temperature environment on the meteorite parent body.

East pacific rise: hot springs and geophysical experiments.

Hydrothermal vents jetting out water at 380 degrees +/- 30 degrees C have been discovered on the axis of the East Pacific Rise. The hottest waters issue from mineralized chimneys and are blackened by sulfide precipitates. These hydrothermal springs are the sites of actively forming massive sulfide mineral deposits. Cooler springs are clear to milky and support exotic benthic communities of giant tube worms, clams, and crabs similar to those found at the Galápagos spreading center. Four prototype geophysical experiments were successfully conducted in and near the vent area: seismic refraction measurements with both source (thumper) and receivers on the sea floor, on-bottom gravity measurements, in situ magnetic gradiometer measurements from the submersible Alvin over a sea-floor magnetic reversal boundary, and an active electrical sounding experiment. These high-resolution determinations of crustal properties along the spreading center were made to gain knowledge of the source of new oceanic crust and marine magnetic anomalies, the nature of the axial magma chamber, and the depth of hydrothermal circulation.

Acute reversal of the enhanced insulin action in trained athletes. Association with insulin receptor changes.

We studied the effect of aerobic training and detraining on insulin-stimulated glucose disposal and on erythrocyte insulin receptor binding. Seven endurance-trained athletes were studied at 12 h, 60 h, and 7 days after cessation of training and compared with three untrained, age- and weight-matched controls. The metabolic clearance rate of glucose as measured by the euglycemic clamp technique was 15.6 +/- 1.8 ml/kg/min (mean +/- SEM) in the trained subjects 12 h after the last bout of exercise compared with 7.8 +/- 1.2 ml/kg/min in the untrained control group. When the trained subjects refrained from physical training, the metabolic clearance rate decreased to 10.1 +/- 1.0 ml/kg/min at 60 h and further to 8.5 +/- 0.5 ml/kg/min after 7 days of detraining. The percentage of specific insulin binding to young erythrocytes (density 1.089-1.092), isolated by density gradient centrifugation, decreased from 10.4 +/- 0.9 at 12 h after the last exercise to 8.1 +/- 0.7%/3 X 10(9) cells after 60 h of detraining (P less than 0.001). The decrease in insulin binding to erythrocytes was almost entirely accounted for by a decrease in the number of insulin receptors. We conclude that the increase in peripheral insulin action seen in trained athletes is rapidly reversed, possibly by a mechanism separate from other phenomena associated with chronic training. The parallel findings of decreased in vivo insulin action and decreased insulin binding in young erythrocytes suggest that modulation of in vivo insulin response by detraining may be at least partially mediated by changes in insulin receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of double labeling and photo CD for morphometric analysis of injured skeletal muscle.

We used computer-assisted analysis of myofiber cross-sectional areas to measure skeletal muscle responses to injury and disease. We developed a simple, inexpensive method for measuring myofiber size in human muscle samples using Kodak photo compact discs (CDs) as the image source. The photo CD serves as a permanent image storage medium and provides a high-resolution image that can be used to detect small myofibers. The use of double labeling for dystrophin and desmin allowed positive identification of both degenerating and regenerating fibers in a single biopsy specimen.

Aldosterone and prolactin response to exercise in the heat in circumpubertal boys.

Thermoregulatory responses to exercise in the heat, especially sweating pattern, differ between children and adults. To determine whether such differences may be related to hormonal responses and to assess the possible association between this response and physical maturation, three groups of circumpubertal boys cycled at 50% of maximal O2 uptake (three 20-min bouts with 10 min of rest between bouts) in 42 degrees C at 20% relative humidity. On the basis of Tanner staging, 11 were prepubertal (PP), 12 midpubertal (MP), and 7 late pubertal (LP). Water ingestion was encouraged to minimize dehydration. Venous blood was sampled before and immediately after the session. Changes in heart rate, rectal temperature, and percent decrease in plasma volume did not differ among groups. There was no change in plasma osmolality in any of the groups. Resting testosterone concentrations were higher with increased level of physical maturity (PP = 0.4 +/- 0.1, MP = 8.2 +/- 1.9, LP = 13.8 +/- 1.2 nmol/l; P less than 0.05). In all groups, both aldosterone (ALD) and prolactin (PRL) markedly increased after exercise in the heat (ALD: PP = 161 +/- 40 vs. 1,289 +/- 263, MP = 173 +/- 47 vs. 1,245 +/- 153, LP = 250 +/- 76 vs. 1,681 +/- 400 pmol/l; PRL: PP = 8.1 +/- 1.2 vs. 24.9 +/- 4.2, MP = 8.8 +/- 1.0 vs. 22.0 +/- 8.9, LP = 8.4 +/- 0.8 vs. 39.0 +/- 3.6 micrograms/l; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute changes in high-density lipoprotein cholesterol with exercise of different intensities.

The purpose of this study was to investigate the acute effects of exercise on plasma high-density lipoprotein cholesterol (HDL-C) and to determine whether the magnitude of this response would be affected by the intensity of the exercise. Twelve men (19-41 yr) ran an equivalent distance (9-12 km) on a treadmill on two separate occasions. On one occasion the exercise was performed at a speed that elicited 60% of the subject's maximal O2 uptake (VO2max), and on the other occasion exercise was performed at a speed that elicited 90% of VO2max. Changes in total cholesterol, triglycerides (TG), HDL-C, HDL apoprotein A (HDL-A), HDL saturation, lactate (LA), and free fatty acids (FFA) were measured during the course of each run, and all values were corrected for changes in plasma volume as indicated by hematocrit. There were significant increases (P less than 0.01) in HDL-C, HDL-A, and HDL saturation with exercise at both intensities, but greater increases in HDL-C (25 vs. 14%) and HDL-A (18 vs. 8%) were observed with the higher intensity exercise. Plasma FFA and TG did not differ between conditions, but LA concentrations rose significantly during the high-intensity exercise. These results indicate that increases in HDL components can occur with a relatively moderate exercise session and that the magnitude of these increases are directly related to the exercise intensity.

Influence of protein intake and training status on nitrogen balance and lean body mass.

The present study examined the effects of training status (endurance exercise or body building) on nitrogen balance, body composition, and urea excretion during periods of habitual and altered protein intakes. Experiments were performed on six elite bodybuilders, six elite endurance athletes, and six sedentary controls during a 10-day period of normal protein intake followed by a 10-day period of altered protein intake. The nitrogen balance data revealed that bodybuilders required 1.12 times and endurance athletes required 1.67 times more daily protein than sedentary controls. Lean body mass (density) was maintained in bodybuilders consuming 1.05 g protein.kg-1.day-1. Endurance athletes excreted more total daily urea than either bodybuilders or controls. We conclude that bodybuilders during habitual training require a daily protein intake only slightly greater than that for sedentary individuals in the maintenance of lean body mass and that endurance athletes require daily protein intakes greater than either bodybuilders or sedentary individuals to meet the needs of protein catabolism during exercise.

Contractile adaptations in the human triceps surae after isometric exercise.

Ultrastructural and twitch contractile characteristics of the human triceps surae were determined in seven healthy but very sedentary subjects before and after 16 wk of unilateral isometric training at 100% maximal voluntary contraction. After training, twitch contraction time decreased by approximately 20%. One-half relaxation time, peak twitch torque, and percent fiber type in any of the muscles of the triceps surae complex were not changed by training. Type I and type II fiber areas increased in the soleus by approximately 30%, but only type II fibers showed an increased in area in the lateral gastrocnemius (40%). Despite such changes in fiber area, the volume density of the sarcoplasmic reticulum-transverse tubular (SR) network averaged 3.2 +/- 0.6 and 5.9 +/- 0.9% in type I and type II fibers, respectively, before and after training in the two heads of the gastrocnemius. Type I SR fraction increased to 3.5 +/- 1.2% after training in the soleus; however, correlations were not significant between the change in the volume density of SR and the change in twitch contraction time (R = 0.46, P = 0.45) or the change in one-half relaxation time (R = -0.68, P = 0.08). The results demonstrate that isometric training at 100% maximal voluntary contraction induced changes in twitch contraction time that were not directly related to changes in the volume density of SR in fibers of the triceps surae.

Postactivation potentiation, fiber type, and twitch contraction time in human knee extensor muscles.

In small mammals, muscles with shorter twitch contraction times and a predominance of fast-twitch, type II fibers exhibit greater posttetanic twitch force potentiation than muscles with longer twitch contraction times and a predominance of slow-twitch, type I fibers. In humans, the correlation between potentiation and fiber-type distribution has not been found consistently. In the present study, postactivation potentiation (PAP) was induced in the knee extensors of 20 young men by a 10-s maximum voluntary isometric contraction (MVC). Maximal twitch contractions of the knee extensors were evoked before and after the MVC. A negative correlation (r = -0. 73, P < 0.001) was found between PAP and pre-MVC twitch time to peak torque (TPT). The four men with the highest (HPAP, 104 +/- 11%) and lowest (LPAP, 43 +/- 7%) PAP values (P < 0.0001) underwent needle biopsies of vastus lateralis. HPAP had a greater percentage of type II fibers (72 +/- 9 vs. 39 +/- 7%, P < 0.001) and shorter pre-MVC twitch TPT (61 +/- 12 vs. 86 +/- 7 ms, P < 0.05) than LPAP. These data indicate that, similar to the muscles of small mammals, human muscles with shorter twitch contraction times and a higher percentage of type II fibers exhibit greater PAP.

Reduced strength after passive stretch of the human plantarflexors.

The purpose of this study was to assess strength performance after an acute bout of maximally tolerable passive stretch (PS(max)) in human subjects. Ten young adults (6 men and 4 women) underwent 30 min of cyclical PS(max) (13 stretches of 135 s each over 33 min) and a similar control period (Con) of no stretch of the ankle plantarflexors. Measures of isometric strength (maximal voluntary contraction), with twitch interpolation and electromyography, and twitch characteristics were assessed before (Pre), immediately after (Post), and at 5, 15, 30, 45, and 60 min after PS(max) or Con. Compared with Pre, maximal voluntary contraction was decreased at Post (28%) and at 5 (21%), 15 (13%), 30 (12%), 45 (10%), and 60 (9%) min after PS(max) (P < 0.05). Motor unit activation and electromyogram were significantly depressed after PS(max) but had recovered by 15 min. An additional testing trial confirmed that the torque-joint angle relation may have been temporarily altered, but at Post only. These data indicate that prolonged stretching of a single muscle decreases voluntary strength for up to 1 h after the stretch as a result of impaired activation and contractile force in the early phase of deficit and by impaired contractile force throughout the entire period of deficit.

Interaction between concurrent strength and endurance training.

To assess the effects of concurrent strength (S) and endurance (E) training on S and E development, one group (4 young men and 4 young women) trained one leg for S and the other leg for S and E (S+E). A second group (4 men, 4 women) trained one leg for E and the other leg for E and S (E+S). E training consisted of five 3-min bouts on a cycle ergometer at a power output corresponding to that requiring 90-100% of oxygen uptake during maximal exercise (VO2 max). S training consisted of six sets of 15-20 repetitions with the heaviest possible weight on a leg press (combined hip and knee extension) weight machine. Training was done 3 days/wk for 22 wk. Needle biopsy samples from vastus lateralis were taken before and after training and were examined for histochemical, biochemical, and ultrastructural adaptations. The nominal S and E training programs were "hybrids", having more similarities as training stimuli than differences; thus S made increases (P less than 0.05) similar to those of S+E in E-related measures of VO2max (S, S+E: 8%, 8%), repetitions with the pretraining maximal single leg press lift [1 repetition maximum (RM)] (27%, 24%), and percent of slow-twitch fibers (15%, 8%); and S made significant, although smaller, increases in repetitions with 80% 1 RM (81%, 152%) and citrate synthase (CS) activity (22%, 51%). Similarly, E increased knee extensor area [computed tomography (CT) scans] as much as E+S (14%, 21%) and made significant, although smaller, increases in leg press 1 RM (20%, 34%) and thigh girth (3.4%, 4.8%). When a presumably stronger stimulus for an adaptation was added to a weaker one, some additive effects occurred (i.e., increases in 1 RM and thigh girth that were greater in E+S than E; increases in CS activity and repetitions with 80% 1 RM that were greater in S+E than S). When a weaker, although effective, stimulus was added to a stronger one, addition generally did not occur. Concurrent S and E training did not interfere with S or E development in comparison to S or E training alone.

Changes in human skeletal muscle ultrastructure and force production after acute resistance exercise.

Muscle ultrastructure and contractile properties were examined before and after a single bout of resistance exercise (8 sets of 8 repetitions at 80% of 1 repetition maximum). Eight untrained males performed the concentric (Con) phase of arm-curl exercise with one arm and the eccentric (Ecc) phase with the other arm. Needle biopsies were obtained from biceps brachii before exercise (Base), immediately postexercise from each arm (post-Con and post-Ecc), and 48 h postexercise from each arm (48 h-Con and 48 h-Ecc). Electron microscopy was used to quantify the presence of disrupted fibers in each sample. Analysis of variance revealed a greater (P < or = 0.05) proportion of disrupted fibers in post-Con, post-Ecc, 48 h-Con, and 48 h-Ecc samples compared with Base. Significantly more fibers were disrupted in post-Ecc (82%) and 48 h-Ecc (80%) samples compared with post-Con (33%) and 48 h-Con (37%), respectively. Voluntary and evoked strength measurements recovered to Base values within 24 h in the Con arm but remained depressed (P < or = 0.05) for 72-96 h in the Ecc arm. These data indicate that both the raising and lowering phases of weightlifting produced myofibrillar disruption, with the greatest disruption occurring during the lowering phase.

Left ventricular response in healthy young men during heavy-intensity weight-lifting exercise.

We examined cardiac volumes (using echocardiography), intra-arterial blood pressure (BP), and intrathoracic pressure (ITP) in healthy males performing leg press exercise to failure at 95% of their maximum dynamic strength. Compared with preexercise, during the lifting phase of exercise, end-diastolic volume (EDV; 147 +/- 8 to 103 +/- 7 ml) and end-systolic volume (ESV; 54 +/- 5 to 27 +/- 4 ml) decreased (P < 0.05); heart rate (82 +/- 6 to 143 +/- 5 beats/min), systolic BP (160 +/- 6 to 270 +/- 21 Torr), diastolic BP (91 +/- 2 to 183 +/- 18 Torr), ITP (0.8 +/- 0.8 to 57.8 +/- 24 Torr), and peak systolic BP/ESV (SBP/ESV; 3.0 +/- 0.3 to 11.0 +/- 1.5 Torr/ml) increased (P < 0.05); and stroke volume decreased (94 +/- 3 to 77 +/- 4 ml; P > 0.05). Full knee extension was associated with most values returning to preexercise levels except for ESV (38 +/- 7 ml), heart rate (130 +/- 9 beats/min), and ITP (-12.5 +/- 2.1 Torr). During the lowering phase, significant decreases in EDV to 105 +/- 14 ml and ESV to 27 +/- 7 ml were observed with increases in systolic BP to 207 +/- 23 Torr, diastolic BP to 116 +/- 8 Torr, and SBP/ESV to 10.0 +/- 2.5 Torr/ml. Stroke volume decreased to 78 +/- 9 ml (P > 0.05). Thus rapid changes in cardiac volumes, contractility, and pressure occur during weight lifting that are related to different phases of the lift.

Sweat lactate in exercising children and adolescents of varying physical maturity.

This study attempts to explain some of the individual variability in sweating pattern by comparing prepubescents and pubescents. Sweating rate and muscular anaerobic capacity are higher in adults than in children; thus we hypothesized that sweat gland anaerobic metabolism, as reflected by lactate excretion, might be higher with advanced physical maturity (PM). Lactate concentration in sweat ([LAC]sw) was measured at various stages of PM in boys who exercised in the heat. The subjects were divided into three groups on the basis of Tanner staging: prepubertal (PP, n = 16), midpubertal (MP, n = 15), and late pubertal (LP, n = 5). Subjects cycled at 50% of maximal O2 uptake for three 20-min bouts, with 10-min rest periods, in 42 degrees C and 18% relative humidity. Sweat samples were harvested, and population density of activated sweat glands was determined after each exercise bout. [LAC]sw during bout 1 was higher in PP than in LP [PP = 22.2 +/- 2.2, MP = 19.5 +/- 1.4, LP = 14.3 +/- 1.3 (SE) mmol/l]. In all groups, [LAC]sw decreased during subsequent bouts, and there were no intergroup differences in [LAC]sw during bout 3 (PP = 11.2 +/- 0.4, MP = 10.6 +/- 0.5, LP = 9.7 +/- 0.2 mmol/l). [LAC]sw was inversely related to sweating rate. Lactate excretion rate per gland was greater with the increase in PM (PP = 61.0 +/- 8.2, MP = 79.1 +/- 11.3, LP = 99.9 +/- 11.0 pmol/min; P = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Voluntary strength and muscle characteristics in untrained men and women and male bodybuilders.

Eight untrained women (F), 13 untrained men (M), and 11 male bodybuilders (BB) did maximal elbow flexions on an isokinetic dynamometer at velocities of 30, 120, 180, 240, and 300 degrees/s, from which impact torque (IT), peak torque (PT), and work (W) were measured. Biceps and total flexor cross-sectional area (CSA) were measured by computerized tomographic scanning. Muscle fiber area, fiber composition, and collagen volume density were determined from single needle biopsies of biceps brachii. Biceps fiber number was estimated as the ratio of biceps CSA (corrected for connective tissue) to mean fiber area. PT and W decreased at higher velocities in M and BB but not in F; consequently, the correlation between CSA and PT and W was lower at 300 degrees/s (r = 0.58, 0.60) than 30 degrees/s (r = 0.80, 0.79). The ratio of PT to flexor CSA was similar in all groups at 30 degrees/s, whereas F had greater ratios than M and BB at the remaining velocities. F had greater W/CSA ratios than M and BB at all velocities. IT increased at higher velocities in all groups; the increase was greater in F and M than in BB. In contrast to PT and W, the correlation between IT and CSA was greater at 300 degrees/s (r = 0.67) than 30 degrees/s (r = 0.58), and there were no differences among groups in the IT/CSA ratios. Flexor CSA correlated negatively with the ratio of IT, PT, and W to CSA. Muscle fiber composition failed to correlate with any measure of strength. M and BB had greater biceps area, fiber number, and fiber area than F.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting blood pressure during heavy weight lifting and static contractions.

Brachial arterial pressure was directly recorded in 31 healthy male volunteers through protocols examining the effects of the Valsalva maneuver, muscle size and strength, contraction force, contraction type (concentric, isometric, eccentric), changes in joint angle, and muscle fatigue on the blood pressure response to resistance exercise. Weight lifting at the same relative intensity produced similar increases in blood pressure, regardless of individual differences in muscle size or strength. Concentric, isometric, or eccentric exercise at the same relative intensity caused similar increases despite differences in force production. In weight lifting, the greatest increase in blood pressure occurred at the joint angle corresponding to the weakest point in the strength curve and the least at the angle corresponding to the strongest point. Isometric contractions of the same relative intensity at different joint angles produced identical blood pressures despite differences in absolute force production. When subjects attempted to maintain a maximum isometric contraction for 45 s, the blood pressure increase remained the same despite a marked diminution in force. Thus the magnitude of the blood pressure response depends on the degree of effort or central command and not actual force production. A brief Valsalva maneuver, which exaggerates the increase in blood pressure, is unavoidable when desired force production exceeds approximately 80% maximum voluntary contraction.

Evaluation of protein requirements for trained strength athletes.

Leucine kinetic and nitrogen balance (NBAL) methods were used to determine the dietary protein requirements of strength athletes (SA) compared with sedentary subjects (S). Individual subjects were randomly assigned to one of three protein intakes: low protein (LP) = 0.86 g protein.kg-1.day-1, moderate protein (MP) = 1.40 g protein.kg-1.day-1, or high protein (HP) = 2.40 g protein.kg-1.day-1 for 13 days for each dietary treatment. NBAL was measured and whole body protein synthesis (WBPS) and leucine oxidation were determined from L-[1-13C]leucine turnover. NBAL data were used to determine that the protein intake for zero NBAL for S was 0.69 g.kg-1.day-1 and for SA was 1.41 g.kg-1.day-1. A suggested recommended intake for S was 0.89 g.kg-1.day-1 and for SA was 1.76 g.kg-1.day-1. For SA, the LP diet did not provide adequate protein and resulted in an accommodated state (decreased WBPS vs. MP and HP), and the MP diet resulted in a state of adaptation [increase in WBPS (vs. LP) and no change in leucine oxidation (vs. LP)]. The HP diet did not result in increased WBPS compared with the MP diet, but leucine oxidation did increase significantly, indicating a nutrient overload. For S the LP diet provided adequate protein, and increasing protein intake did not increase WBPS. On the HP diet leucine oxidation increased for S. These results indicated that the MP and HP diets were nutrient overloads for S. There were no effects of varying protein intake on indexes of lean body mass (creatinine excretion, body density) for either group. In summary, protein requirements for athletes performing strength training are greater than for sedentary individuals and are above current Canadian and US recommended daily protein intake requirements for young healthy males.

Physiological effects of tapering in highly trained athletes.

This study examined some of the physiological and performance effects of three different tapers in highly trained athletes. After 8 wk of training, nine male middle-distance runners were randomly assigned to one of three different 7-day tapers: a high-intensity low-volume taper (HIT), a low-intensity moderate-volume taper (LIT), or a rest-only taper (ROT). After the first taper, subjects resumed training for 4 wk and performed a second taper and then resumed training for 4 wk and completed the remaining taper, so that each subject underwent all three tapers. Performance was measured before and after each taper by a treadmill run to fatigue at a velocity equivalent each subject's best 1,500-m time. Voluntary isometric strength and evoked contractile properties of the quadriceps were measured before and after each taper, as were muscle glycogen concentration and citrate synthase activity (from needle biopsies) and total blood and red cell volume by 125I and 51Cr tagging. Maximal O2 consumption was unaffected by all three tapers, but running time to fatigue increased significantly after HIT (+22%). It was unaffected by LIT (+6%) and ROT (-3%) procedure. Citrate synthase activity increased significantly with HIT and decreased significantly with ROT. Muscle glycogen concentration increased significantly after ROT and HIT, and strength increased after all three tapers. Total blood volume increased significantly after HIT and decreased after ROT.(ABSTRACT TRUNCATED AT 250 WORDS)

Gender differences in leucine kinetics and nitrogen balance in endurance athletes.

The current Canadian Recommended Nutrient Intake (RNI) for protein (0.86 g.kg-1.day-1) makes no allowance for an effect of habitual physical activity. In addition, Tarnopolsky et al. (J. Appl. Physiol. 68: 302-308, 1990) showed that males may catabolize more protein than females consequent to endurance exercise. We examined nitrogen (N) balance and leucine kinetics during submaximal endurance exercise to determine the adequacy of the current Canadian RNI for protein for male and female endurance athletes. Athletes were matched for equal training volume, competitive status, and conditioning and were fed diets isoenergetic with their habitual intake, containing protein at the Canadian RNI. Subjects were adapted to the diet for 10 days before completing a 3-day measurement of N balance. N balance showed that the RNI was inadequate for females (-15.9 +/- 6.0 mg.kg-1.day-1) and males (-26.3 +/- 11.0 mg.kg-1.day-1). Leucine kinetics during exercise were determined for each subject on day 3 of the N balance experiment by use of a primed continuous infusion of L-[1-13C]leucine and the reciprocal pool model. Exercise resulted in a significant (P < 0.01) increase in leucine oxidation for both groups. Males oxidized a greater amount of leucine during the infusion than females (P < 0.01). Leucine flux also increased significantly (P < 0.01) during exercise in both groups. We conclude that the current Canadian RNI for protein is inadequate for those who chronically engage in endurance exercise.(ABSTRACT TRUNCATED AT 250 WORDS)