Increase In Pmax Research Articles

Longitudinal Changes of Maximal Short-Term Peak Power in Girls and Boys during Growth

The aims of this study are twofold: first, to analyze the influence of age, body mass, and lean leg volume (LLV) on short-term leg peak power (Pmax) of young females and males during growth using multilevel regression analysis and, second, to compare the regression results of boys and girls. The individuals were 100 girls and 109 boys aged 7.5-17.5 yr old. Pmax, LLV, and mass were determined on two occasions using the cycling force-velocity test. The optimal force (Fopt) and pedaling frequency (Vopt) corresponded to the force and pedaling frequency at Pmax. It was observed that the increase of Pmax doesn't depend on gender until the age of 14. From that age, Pmax values are significantly lower in girls than in boys. In girls, LLV is the main predictor of Pmax variance (68%; P < 0.001), whereas in boys it is age (57%; P < 0.001). Results of ANCOVA were that for the same leg length (LL), Vopt is significantly (P < 0.001) higher in boys than in girls. It also indicated that for the same LLV, there are no significant (P > 0.05) gender differences of Fopt. These results illustrated that during the growth period, the increase of Pmax is significantly higher in boys than in girls. Qualitative muscular factors (Type II fiber, glycolytic ability, motor coordination, and motor unit activation) may account for the significantly higher Pmax production in boys than in girls. Precisely, the gender differences might be explained by neuromuscular determinants of contraction velocity. In conclusion, children should develop their neuromuscular determinants of contraction velocity rather than their lean leg volume.

Increased P wave dispersion and maximum P wave duration after hemodialysis.

Atrial fibrillation is a frequent arrhythmia in patients undergoing hemodialysis. The consequences of hemodialysis on P wave durations and P wave dispersion have not been fully understood. The objective of this study was to study the effect of dialysis on P wave maximum (Pmax), P wave minimum (Pmin), and P wave dispersion (Pd). We studied Pmax, Pmin, and Pd in 32 patients (17 men and 15 women, mean age 54 +/- 18 years) with chronic renal failure undergoing hemodialysis. The difference between maximum and minimum P wave duration was calculated and defined as P wave dispersion (Pd= Pmax- Pmin). There was a significant increase in Pmax at the end of dialysis compared to the beginning (98 +/- 13 ms vs. 125 +/- 12 ms, P < 0.001). Pmin did not show any significant change (71 +/- 11 ms vs. 73 +/- 10 ms, P = 0.42). Pd was significantly increased at the end of dialysis (27 +/- 9 ms vs. 52 +/- 11 ms, P < 0.001). There was a negative correlation between serum potassium, magnesium, phosphate, blood urea nitrogen, and creatinin at the end of dialysis and Pmax and Pd, respectively (P < 0.05). A weak positive correlation was found between serum calcium, bicarbonate at the end of dialysis and Pmax and Pd (P < 0.05). Hemodialysis ends with significant increase in P wave maximum duration and P wave dispersion, which might be responsible for the increased occurrence of atrial fibrillation in these groups of patients.

Effects of stem fraction on the optimization of biomass allocation and maximum photosynthetic capacity

SummaryA model was developed to examine effects of the stem biomass fraction on the optimal responses of plants to soil nitrogen availability.Our model predicts that the optimal leaf : root ratio and optimal photosynthetic capacity (Pmax) increase with soil N availability. For a given N availability, the optimal leaf : root ratio decreases and the optimalPmaxincreases with increasing stem fraction. As a result, the increase in optimal leaf : root ratio is smaller, and that in optimalPmaxis greater, in response to increasing N availability when stem fraction is large.To test these predictions we grew two herbs with different stem fractions:Polygonum cuspidatumSieb. et Zucc. andChenopodium albumL.Showing excellent agreement with the simulation results, the leaf N concentration and leaf : root ratio of the two herbs increased with increasing N availability, and leaf N concentration was larger forC. albumwith higher stem fraction thanP. cuspidatum.The general tendency for plants with larger stem fractions also to have greater leaf N concentrations andPmaxwas demonstrated for a wide range of temperate herbs. This suggests that stem fraction may be a source of variation inPmaxamong plants in the same functional group.

Does the photosynthetic light‐acclimation need change in leaf anatomy?

ABSTRACTThere is a strong correlation between leaf thickness and the light‐saturated rate of photosynthesis per unit leaf area (Pmax). However, when leaves are exposed to higher light intensities after maturation, Pmax often increases without increasing leaf thickness. To elucidate the mechanism with which mature leaves increase Pmax, the change in anatomical and physiological characteristics of mature leaves of Chenopodium album, which was transferred from low to high light condition, were examined. When compared with leaves subjected to low light continuously (LL leaves), the leaves transferred from low to high light (LH leaves) significantly increased Pmax. The transfer also increased the area of chloroplasts facing the intercellular space (Sc) and maintained a strong correlation between Pmax and Sc. The mesophyll cells of LL leaves had open spaces along cell walls where chloroplasts were absent, which enabled the leaves to increase Pmax when they were exposed to high light (LH). However, the LH leaves were not thick enough to allow further increase in Pmax to the level in HH leaves. Thus leaf thickness determines an upper limit of Pmax of leaves subjected to a change from low to high light conditions. Shade leaves would only increase Pmax when they have open space to accommodate chloroplasts which elongate after light conditions improve.

Effects of dissolved ammonium addition and host feeding with Artemia salina on photoacclimation of the hermatypic coral Stylophora pistillata

Effects of nutrient treatments on photoacclimation of the hermatypic coral Stylophora pistillata (Esper) were studied. Studies on photoacclimation of colonies from different light regimes in the field were evaluated and used to design laboratory experiments. Coral colonies were collected in the Gulf of Eilat (Israel) from January to March 1993. Exterior branches of colonies from different depths (1 to 40 m) displayed different trends in production characteristics at reduced and very low levels of illumination. From 24 ± 3% to 12 ± 2% of incident surface photosynthetic active radiation (PARo), zooxanthella population density and chlorophyll a+c per 106 zooxanthellae increased, a trend seen in the range of light levels optimal for coral growth (90 to 30% PARo). The Pmax of CO2 per 106 zooxanthellae decreased, while Pmax of CO2 per 103 polyps increased, indicating an increase in zooxanthella population density at low light levels. Proliferous zooxanthella frequency (PZF, a measure of zooxanthella division) declined significantly at light levels <18 ± 3% PARo. At the lowest levels of illumination (<5% PARo), zooxanthella population density decreased, as did the PZF; chl a+c per 106 zooxanthellae was unchanged. In 28-d experiments, exterior coral branches from the upper surfaces of colonies from 3 m depth (65 ± 4% PARo) were incubated in aquaria under bright (80 to 90% PARo), reduced (20 to 30% PARo), and extremely low (2 to 4% PARo) light intensities. At each light intensity, the corals were maintained in three feeding treatments: sea water (SW); ammonium enriched SW (SW + N); SW with Artemia salina nauplii (SW + A). An increase in Pmax of CO2 per 103 polyps was found in corals acclimated to reduced light (20 to 30% PARo) in nutrient-enriched SW, while in SW, where the increase in zooxanthella population density was smaller, it did not occur. Nutrient enrichments (SW + N at 2 to 4% PARo and SW + A at 20 to 30% PARo) increased zooxanthella population density, but had no effect on chl a+c per 106 zooxanthellae. Acclimation for 14 d to reduced (10 to 20% PARo) and extremely low (1 to 3% PARo) light intensities shifted 14C photoassimilation into glycerol and other compounds (probably glycerides), rather than sugars. Both ammonium addition and feeding with Artemia salina nauplii resulted in an increase in photosynthetic assimilation of 14C into amino acids. We conclude that acclimation to reduced light consists of two processes: an increase in photosynthetic pigments and in zooxanthella population density. Both processes require nitrogen, the increase in zooxanthella population density needing more; this adaptation is therefore limited in nitrogen-poor sea water.

Photosynthesis in Plants of Four Tropical Species Growing under Elevated CO&lt;sub&gt;2&lt;/sub&gt;

We studied the responses of leaf gas exchange and growth to an increase in atmospheric CO2 concentration in four tropical deciduous species differing in carbon fixation metabolism: Alternanthera crucis, C3-C4; Ipomoea carnea, C3; Jatropha gossypifolia, C3; and Talinum triangulare, inducible-CAM. In the first stage, plants were grown in one open-top chamber at a CO2 concentration of 560±40 μmol mol-1 (EC), one ambient CO2 concentration chamber (AC), and one unenclosed plot (U). In the second stage, plants were grown in five EC chambers (CO2 concentration = 680±30 μmol mol-1), five AC chambers, and five unenclosed plots. During the first weeks under EC in the first stage, plants of all the species had a very marked increase in their maximal net photosynthetic rates (Pmax) of 3.5 times on average; this stimulatory effect was maintained for 11-15 weeks, rates dampening afterward to values still higher than controls for 37 weeks. After a suspension of CO2 enrichment for 6 weeks, an increase in Pmax of EC plants over the controls was found in plants of all the species until week 82 of the experiment. Stomatal conductance (g) showed no response to EC. Carboxylation efficiency decreased in all the species under EC

THE EFFECTS OF CONCURRENT AEROBIC AND ANAEROBIC TRAINING VERSUS SEQUENCED TRAINING ON 80 S CYCLING

789 The purpose of this study was to investigate the influence of concurrent versus sequenced aerobic and anaerobic training on supramaximal performance. Twenty-four male and female well trained cyclists (VO2max = 4.2 ± 0.7 L.min−1; mean ± SD) participated in a 19-week training study. A 5 week baseline period was performed to ensure a stable level of fitness. Following the baseline phase, subjects were randomly assigned to one of two groups: either concurrent aerobic and anaerobic training for 12 weeks; or sequenced aerobic training for 6 weeks followed by anaerobic training for 6 weeks. Subjects trained five days per week for a total of 60 sessions of training. After the first 6-week block of training and at the end of the training period, subjects were assessed with physiological (VO2max, lactate equilibrium, maximal anaerobic cycling test [MACT]) tests and an 80 s power test. Although both groups improved significantly in the 80 s test, there was no significant difference between groups. However, the way in which each group progressed towards their final performance in the 80 s power test was different. The concurrent training group improved significantly from the pre test (451 ± 76 W) to the mid test (471 ± 81 W) and then again to the post test (489 ± 90 W). These improvements were associated with an increase in maximal power (Pmax) measured by the MACT (Pre 697 ± 145 W, Mid 770 ± 169 W, Post 795 ± 175) but no changes in aerobic function measured by either VO2max or power output at lactate equilibrium (Pre 205 ± 41 W, Mid 205 ± 45 W, Post 207 ± 40 W). The sequenced group did not improve significantly between pre (444 ± 75 W) and mid (454 ± 68 W) 80 s tests despite a significant improvement in lactate equilibrium (Pre 206 ± 34 W, Mid 213 ± 35 W) and Pmax (Pre 726 ± 119 W, Mid 742 ± 121 W), but showed a larger significant improvement in the post test (486 ± 66 W) associated with a significant increase in Pmax (Post 796 ± 132 W). In conclusion, the order in which the training sessions were performed in this study was not as important as the total training volume performed.

Stress of Corrugated Fiberboard Made by Compression under Uniform Bending of Moment Axis in Machine Direction (On Single Wall Fiberboard with Symmetrical Thickness Strength)

We investigated stress generation in a semichemical corrugated medium (SM) by compressional forces under uniform bending with the bending moment axis of the machine direction (MD) in single-wall corrugated fiberboard (SWCF), and attempted to derive an elastic expression for its generation stress σ sp. Using this expression, the analysis of σ sp was carried out. Values of the lateral force W sx and fixed moment M s0 per unit length at the joint between kraftliner (KL) and SM are determined, and relationships between those values and the shape of SWCF are considered. The following results are obtained from the expression. The maximum value σ pmax of σ sp is found at the joint on the outer surface of SM. W sx, M s0 and σ pmax increase markedly with the increase of wavelength L and decrease markedly with the increase of wave height h for SM.

Quantifying the short-term temperature effect on light-saturated photosynthesis of intertidal microphytobenthos

A mathematical expression is proposed to describe the relationship between the photosynthetic capacity (Pmax) of natural assemblages of motile benthic diatoms and temperature. Experiments were performed in 2 different seasons to document the response of Pmax to a rapid increase in temperature (3*C h-1). In both cases, there was a progressive increase in Pmax up to an optimum temperature (Topt), beyond which Pmax declined rapidly. Topt did not change from September to December 1995, but the maximum photosynthetic capacity (PMAX, i.e. Pmax at Topt) was twice as high in September as in December.

Specificity of leg power changes to velocities used in bicycle endurance training.

Increases in leg power production resulting from 8 wk of bicycle endurance training (30 min/day, 5 times/wk) were studied using an isokinetic dynamometer. In addition, biopsies of vastus lateralis were analyzed to characterize muscle ultrastructural changes. Performance increased on the dynamometer specifically near the estimated average knee angular velocity used during the bicycle training (200 degrees/s). Power measurements were made during the first 5 contractions (maximal power: Pmax) and last 5 contractions (final power: Pend) of 25 and 50 consecutive contractions (at 60 and 240 degrees/s, respectively). Pmax and Pend increased only at 240 degrees/s but not at 60 degrees/s. These increases in Pmax (86 W) and Pend (78 W) resulted primarily from longer torque maintenance but also from increased peak torque during each contraction and were close to the increase in mechanical power output maintained on the bicycle (Pb; 78 W) during the training sessions. The specificity of these changes to the angular velocities used in the bicycle training indicates a neural basis to these adaptations. We suggest that these neural adaptations, coupled with the observed enhancement of muscle mitochondrial and capillary density (+41 and +15%, respectively) underlie the increased ability to maintain power production on a bicycle after endurance training.

Maximal static pressures and lung volumes in young female swimmers

The postulate that lung volumes are increased in swimmers because of a training effect that increases maximal static pressures (Pmax) thus augmenting the ability to inflate and deflate the lung was examined by comparing 38 competitively trained female swimmers to 59 controls between 7 and 13 years of age. Maximal static pressures on inspiration and expiration were generated near residual volume (RV), at functional residual capacity (FRC) and near total lung capacity (TLC). Lung volumes were measured by body plethysmography. The expected increase in lung volumes was present in the swimmers and was most marked in the oldest subjects. However, training did not have the anticipated effect on Pmax. In the younger swimmers training was associated with an increase in Pmax, but in the older swimmers Pmax was actually decreased in comparison to controls. These findings suggest that training may directly enhance lung growth, since the changes in lung volume cannot be accounted for by increases in respiratory muscle strength.