Use of the force-velocity test to determine the optimal braking force for a sprint exercise on a friction-loaded cycle ergometer

A group of 15 untrained male subjects pedalled on a friction-loaded cycle ergometer as fast as possible for 5–7 s to reach the maximal velocity (V{immax}) against different braking forces (F _B). Power was averaged during a complete crank rotation by adding the power dissipated againstF _B to the power necessary to accelerate the flywheel. For each sprint, determinations were made of peak power output ( ) power output attained atV _max ( ) calculated as the product ofV _max andF _B and the work performed to reachV _max expressed in mean power output ( ). The relationships between these parameters andF _B were examined. A biopsy taken from the vastus lateralis muscle and tomodensitometric radiographs of both thighs were taken at rest to identify muscle metabolic and morphometric properties. The value was similar for allF _B. Therefore, the average of values was defined as corrected maximal power ( ). This value was 11 higher than the maximal power output uncorrected for the acceleration. Whereas the determination did not require high loads, the highest value ( ) was produced when loading was heavy, as evidenced by the -F _B parabolic relationship. For each subject, the braking force ( ) giving was defined as optimal. The , equal to 0.844 (SD 0.108) N · kg⁻¹ bodymass, was related to thigh muscle area (r = 0.78,P < 0.05). The maximal velocity ( ) reached against this force seemed to be related more to intrinsic fibre properties (% fast twitch b fibre area and adenylate kinase activity). Thus, from the determination, it is suggested that it should be possible to predict the conditions for optimal exercise on a cycle ergometer.     

The applicability of the rooting technique measuring salt resistance in populations ofFestuca rubra andJuncus species

Summary Indices of salt resistance, based on the measurement of the Mean Relative Growth Rate of the total plant biomass were shown to be more reliable and easily obtained than those based on the rooting technique. Adaptation to salinity stress (NaCl toxicity, osmotic stress) differs essentially from heavy metal stress (mainly ion-toxicity). Extension of the root system under saline conditions should therefore be regarded as a compensatory growth mechanism rather than the direct result of salt stimulation. The application of the rooting technique for optimum measurement of salt resistance is questioned. The index of salt resistance technique may be applied to all vascular plants, while unmodified application of the rooting technique is confined to certain groups of the Monocotyledonae.     

Effects of root temperature on uptake of nitrate and ammonium ions by barley grown in flowing-solution culture

Summary Barley plants (Hordeum vulgare L.) grown from seed for 28 days in flowing solution culture were subjected to different root temperatures (3, 5, 7, 9, 11, 13, 17, 25°C) for 14 days with a common air temperature of 25/15°C (day/night). Uptake of NH₄ and NO₃ ions was monitored separately and continuously from solutions maintained at 10 M NH₄NO₃ and pH 6.0. Effects of root temperature on unit absorption rate , flux and inflow were compared. After 5 days , and increased with temperature over the range 3–11°C for NH₄ ions and over the range 3–13°C for NO₃ ions, with little change for either ion above these temperatures. Q₁₀ temperature coefficients for NH₄ ions (3–13°C) were 1.9, 1.7 and 1.6 for , and respectively, the corresponding values for NO₃ ions being 5.0, 4.5 and 4.6. For both ions, , and changed with time as did their temperature dependence over the range 3–25°C, suggesting that rates of ontogenetic development and the extent of adaptation to temperature may have varied among treatments.     

Some results in graph theory and their application to abstract relational biology

It has been shown in earlier work that one approach to what Rashevsky has called “abstract biology” is through the study of the class of ( )-systems that can be formed in an arbitrary subcategory of the category of sets. The concept of the ( )-system, however, depends on the availability of mappings that contain other mappings in their range. It is shown that, by introducing an appropriate measure for this property, the problem of characterizing those categories suitable for a rich theory of ( )-systems reduces to a problem familiar from the general theory of graphs. Some new results in these directions are obtained, and it is then shown that any category with mappings that possess properties we might expect to hold in the physical world will also admit a rich theory of ( )-systems. In particular, it is shown that a sufficiently large family of mappings drawn at random from such a category will with overwhelming probability contain an ( )-system. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command, under Grant No. AF-AFOSR-9-63.     

Correlation between cell density,membrane fluidity,and the availability of transferrin receptors in friend erythroleukemic cells

Undifferentiated Friend erythroleukemic cells (FL cells) acquire membrane microviscosity ( ), in accord with the culture cell density. At low cell density poise, whereas at confluency it increases to poise. Concomitantly, the total number of available transferrin receptors per cell decreases by about 80% upon increase in cell density. Modulation of membrane microviscosity, by artificial alteration of the membrane cholesterol level, mediates similar modulations of the availability of the transferrin receptors. The correlation between the availability of the transferrin receptors and the membrane lipid fluidity may take part in the overt decrease in iron uptake by erythroid cells along the erythropoiesis pathway.     

An evolutionary analytical model of a complementary circular code simulating the protein coding genes, the 5′ and 3′ regions

The self-complementary subset ∪{AAA,TTT} with = {AAC, AAT, ACC, ATC, ATT, CAG, CTC, CTG, GAA, GAC, GAG, GAT, GCC, GGC, GGT, GTA, GTC, GTT, TAC, TTC} of 22 trinucleotides has a preferential occurrence in the frame 0 (reading frame established by the ATG start trinucleotide) of protein (coding) genes of both prokaryotes and eukaryotes. The subsets ∪{CCC} and ∪{GGG} of 21 trinucleotides have a preferential occurrence in the shifted frames 1 and 2 respectively (frame 0 shifted by one and two nucleotides respectively in the 5′-3′ direction). and are complementary to each other. The subset contains the subset which has the rarity property (6 × 10⁻⁸) to be a complementary maximal circular code with two permutated maximal circular codes and in the frames 1 and 2 respectively. is called a C³ code. A quantitative study of these three subsets in the three frames 0, 1, 2 of protein genes, and the 5′ and 3′ regions of eukaryotes, shows that their occurrence frequencies are constant functions of the trinucleotide positions in the sequences. The frequencies of in the frame 0 of protein genes are 49, 28.5 and 22.5% respectively. In contrast, the frequencies of in the 5′ and 3′ regions of eukaryotes, are independent of the frame. Indeed, the frequency of in the three frames of 5′ (respectively 3′) regions is equal to 35.5% (respectively 38%) and is greater than the frequencies and , both equal to 32.25% (respectively 31%) in the three frames. Several frequency asymmetries unexpectedly observed (e.g. the frequency difference between and in the frame 0), are related to a new property of the subset involving substitutions. An evolutionary analytical model at three parameters (p, q, t) based on an independent mixing of the 22 codons (trinucleotides in frame 0) of with equiprobability (1/22) followed by t ≈ 4 substitutions per codon according to the proportions p ≈ 0.1; q ≈ 0.1 and r = 1 − p − q ≈ 0.8 in the three codon sites respectively, retrieves the frequencies of observed in the three frames of protein genes and explains these asymmetries. Furthermore, the same model (0.1, 0.1, t) after t ≈ 22 substitutions per codon, retrieves the statistical properties observed in the three frames of the 5′ and 3′ regions. The complex behaviour of these analytical curves is totally unexpected and a priori difficult to imagine.     

Relationship between cardiac output and oxygen uptake at the onset of exercise

The purpose of the present study was to assess the relationship between the rapidity of increased gas exchange (i.e. oxygen uptake ) and increased cardiac output ( ) during the transient phase following the onset of exercise. Five healthy male subjects performed multiple rest-exercise or light exercise (25 W)-exercise transitions on an electrically braked ergometer at exercise intensities of 50, 75, or 100 W for 6 min, respectively. Each transition was performed at least eight times for each load in random order. The was obtained by a breath-by-breath method, and was measured by an impedance method during normal breathing, using an ensemble average. On transitions from rest to exercise, rapidly increased during phase I with time constants of 6.8–7.3 s. The also showed a similar rapid increment with time constants of 6.0–6.8 s with an apparent increase in stroke volume (SV). In this phase I, increased to about 29.7%–34.1% of the steady-state value and increased to about 58.3%–87.0%. Thereafter, some 20 s after the onset of exercise a mono-exponential increase to steady-state occurred both in and with time constants of 26.7–32.3 and 23.7–34.4 s, respectively. The insignificant difference between and time constants in phase I and the abrupt increase in both and SV at the onset of exercise from rest provided further evidence for a cardiodynamic contribution to following the onset of exercise from rest.     

Modelling the dynamics of West Nile Virus

In this work we formulate and analyze a mathematical model for the transmission of West Nile Virus (WNV) infection between vector (mosquito) and avian population. We find the Basic Reproductive Number in terms of measurable epidemiological and demographic parameters. is the threshold condition that determines the dynamics of WNV infection: if the disease fades out, and for the disease remains endemic. Using experimental and field data we estimate for several species of birds. Numerical simulations of the temporal course of the infected bird proportion show damped oscillations approaching the endemic value.     

Dynamics of cardiorespiratory function in Standardbred horses during different intensities of constant-load exercise

Summary Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake ( max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100% max, the oxygen consumption ( ) increased to mean values of approximately 130 ml/kg·min, which represents a 40-fold increase above resting . At the low and moderate work rates, showed no significant change from 30 s to 300 s of exercise. At the high work rate, the mean at 30 s was 80% of the value at 300 s. The HR showed no significant change over time at the moderate work rate but differing responses at the low and high work rates. At the low work rate, the mean HR decreased from 188 beats/min at 30 s to 172 beats/min at 300 s exercise, whereas at the high work rate the mean HR increased from 204 beats/min at 30 s to 221 beats/min at 300 s exercise. No changes in acid base status occurred during exercise at the low work rate. At the moderate work rate, a mild metabolic acidosis occurred which was nonprogressive with time, whereas the high work rate resulted in a progressive metabolic acidosis with a base deficit of 16 mmol/l by 300 s exercise. It is concluded that the kinetics of gas exchange during exercise are more rapid in the horse than in man, despite the relatively greater change in in the horse when going from rest to high intensity exercise.Symbols and abbreviations E minute ventilation - V _T tidal volume - oxygen uptake - carbon dioxide output - oxygen pulse - ventilatory equivalent for oxygen - ventilatory equivalent for carbon dioxide - R respiratory exchange ratio - HR heart rate - SBC standard bicarbonate - STPD standard temperature and pressure dry - BTPS body temperature and pressure saturated - arterial oxygen content - arteriovenous oxygen content difference - Rf respiratory frequency     

The\dot V_A /\dot Q resolution of inert gas dataresolution of inert gas data

The non-uniqueness of distributions satisfying inert gas retention data without error is studied. The ability of such data to resolve blood flows at particular values is discussed through the application of linear programming and Backus-Gilbert theory. It is shown that the resolution deteriorates away from the extremes of low and high .     

Respiratory responses of elite oarsmen, former oarsmen, and highly trained non-rowers during rowing, cycling and running

The position of the body and use of the respiratory muscles in the act of rowing may limit ventilation and thereby reduce maximal aerobic power relative to that achieved in cycling or running, in spite of the greater muscle mass involved in rowing. This hypothesis was investigated for three groups of male subjects: nine elite senior oarsmen, eight former senior oarsmen and eight highly trained athletes unskilled in rowing. The subjects performed graded exercise to maximal effort on a rowing ergometer, cycle ergometer and treadmill while respiratory minute volume and oxygen consumption were monitored continuously. The VE at a given during intense submaximal exercise (greater than 75% of maximal ) was not significantly lower in rowing compared with that in cycling and treadmill running for any group, which would suggest that submaximal rowing does not restrict ventilation. At maximal effort, and for rowing were less than those for the other types of exercise in all the groups, although the differences were not statistically significant in the elite oarsmen. These data are consistent with a ventilatory limitation to maximal performance in rowing that may have been partly overcome by training in the elite oarsmen. Alternatively, a lower maximal VE in rowing might have been an effect rather than a cause of a lower maximal if maximal was limited by the lower rate of muscle activation in rowing.     

The effect of fertilization on litter decomposition in clearfelled spruce stands

Summary The influence of NPK-fertilizer on decomposition of litter layers and deposited logging residues (brash) on a clearfelled Sitka spruce stand was followed during two years by zero-tension lysimetry and litterbags. Root development of second rotation planted trees on this peaty gley soil are restricted to the litter layers (LFH) and without fertilizer are dependent on its decomposition for release of nutrients. A comparison of fertilized and control plots showed few site differences and similar hydrological properties. Fertilizer addition (urea-N, rock-P and KCl) immediately raised leachate concentrations of NH₄−N, K and PO₄−P, the last remaining high over the period. NO₃−N increased dramatically in the second year leachates from the fertilized area. Within two years 45, 60 and 75% of added NPK respectively were recovered in leachates. Two-year-old litter in litterbags lost weight significantly more slowly after fertilization. The calculated values were 0.28 (control plot) and 0.15 (fertilized plot). Mean values were derived from individual regressions and allowed microsite variation to be assessed. The difference in is attributed to available C limitation although N concentration of needles increased on both plots, P concentration increased slowly on the control plot while K and Mg decreased on both. Ca concentrations doubled with fertilization and remained constant over two years. The rapid loss of fertilizer and slight response from planted trees indicate delayed application of fertilizers may be desirable.     

Linkage analysis using multiple DNA polymorphic markers in normal families and in families with fragile X syndrome

Summary Linkage data, using the polymorphic markers 52A (DXS51), F9, 4D-8(DXS98), and St14(DXS52), are presented from 14 fragile X pedigrees and from 7 normal pedigrees derived from the collection of the Centre d'Étude du Polymorphisme Humaine. A multipoint linkage analysis indicates that the most probable order of these four loci in normal families is DXS51-F9-DXS98-DXS52. Recombination frequencies ( ) corresponding to maximum LOD scores ( ) were obtained by two-point linkage analysis for a nuber of linkage groups, including: DXS51-F9 ( =5.94, =0.03), F9-DXS98 ( =0.51, =0.26), F9-DXS52 ( =0.84, =0.27), and DXS98-DXS52 ( =0.32, =0.20). A multipoint linkage analysis of these loci, including the fragile X locus, was also performed for the fragile X population and the data support the relative order (DSX51, F9, DXS98)-FRAXA-DXS52. Recombination frequencies and maximum LOD scores, which again were derived from two-point linkage analyses, were obtained for the linkage groups DXS51-F9 ( =9.96, =0) and F9-DXS52 ( =0.07, =0.45), as well as for the groups DXS51-FRAXA ( =2.42, =0.15), F9-FRAXA ( =1.30, =0.18), DXS98-FRAXA ( =0.05 =0.36), and DXS52-FRAXA ( =2.42 =0.15). The linkage data was further tested for the presence of genetic heterogeneity both within and between the fragile X and normal families for the intervals DXS51-F9, F9-DXS52, F9-FRAXA, and DXS52-FRAXA using a modification of the A test. Except for the interval F9-FRAXA (P<0.10) there was no evidence of genetic heterogeneity for each of the various linkage groups examined. The heterogeneity detected for the interval F9-FRAXA, however, was most likely due to one family (Fx-28) that displayed very tight linkage between these two loci.     

The nucleotide sequence ofBeneckea harveyi 5S rRNA

Summary The complete sequence of the 5S rRNA from the bioluminescent bacterium,Beneckea harveyi has been determined to be p U G C U U G G C G C C A U A G C G A U U-G G A C C C A C U G A (U) C U U C A U U C C-G A A C C A G A A G U G A A C G A A U U A-G G C C G A U G G U G U G U G G G G C U-C C C C A U G U A G A G U A G G A A U C G-C C A G G U (U)_OH.Two sites of sensitivity to ribonuclease T₂ cleavage were identified; at A₄₁ and either A₅₄ or A₅₅. Comparison with existing sequence information fromEscherichia coli andPhotobacterium phosphoreum clarifies the amount of diversity among the bioluminescent bacteria and provides further insight into their phylogenetic position. Sequence heterogeneities were encountered and the importance of these in interpreting 5S rRNA data is discussed.     

Estimation of surface charges in some biological membranes

Summary The resting membrane potential data existing in the literature for the giant axon of the squid, frog muscle and barnacle muscle have been analyzed from the standpoint of the theory of membrane potential due to Kobatake and co-workers. The average values derived for the effective charge density (where is a constant, , and represents the fraction of counterions that are free, and is the stoichiometric charge density in the membrane) present on the different biomembranes existing in their normal ionic environment are 0.3, 0.325 and 0.17 M for the squid axon, frog and barnacle muscles, respectively. On the assumption that the values of are 0.4 and 0.2 for nerve and muscle membranes, respectively, values of 0.75, 1.62 and 0.85 M have been derived for the stoichiometric charge density present in the respective biological membranes. These correspond to 1 negative charge per 222, 103 and 195 Å of the membrane area of the squid axon, frog and barnacle muscles, respectively.     

Ammonium-limited growth and uptake by Oscillatoria agardhii in chemostat cultures

Growth of Oscillatoria agardhil was studied in ammonium-limited chemostat cultures, at various dilution rates (=growth rates, μ). The uptake kinetics for ammonium of nitrogen (ammonium or nitrate)-limited chemostat cultures also was investigated. The kinetics of ammonium-limited growth could be adequately described by both the Monod and Droop equations, and were closely similar to the nitrate-limited growth kinetics of this species. The uptake kinetics for ammonium showed similarities as well as differences with the uptake kinetics for nitrate. The similarities were apparent in the uptake capacity values for ammonium and nitrate , which were identical, high and independent of μ. The differences were to be found in the half-saturation constants for ammonium uptake and nitrate uptake , the former being hardly influenced by μ. A consitutive, high affinity, system is likely to operate in the uptake and assimilation of ammonium by nitrogen-limited O. agardhii. The use of ammonium uptake parameters in studies of growth-limiting factors in nature can provide information as to whether a nitrogen-limitation prevails in natural habitats of this species.     

Are oxygen uptake kinetics at the onset of exercise speeded up by local metabolic status in active muscles?

To assess the rate-limiting factor of oxygen uptake ( ) kinetics at the onset of exercise, six healthy male sedentary subjects performed repeated one-legged constant-load cycle exercise. The one-legged constant-load exercise test consisted of two 5-min periods of pedalling at an exercise intensity of 50 W, with a 5-min rest between periods (these exercise periods, i.e. first and second exercises, were performed by the same leg). The exercise was then repeated using the other leg. In addition, two-legged incremental exercise was investigated to establish whether kinetics were affected by slower heart rate kinetics. The incremental exercise test consisted of two-legged pedalling first with the cycle unloaded as a warm-up for 5 min followed by 50-W exercise for 5 min. The exercise intensity was then increased to 100 W for 5 min. During exercise, gas exchange parameters were determined by the breath-by-breath method and cardiac output ( ) was determined continuously by an impedance technique with a computer-based automated system. To determine the kinetics of heart rate (HR), and , a best fit procedure was employed using least-squares criteria with a time delay, except during the initial increase. During the one-legged constant-load exercise test, kinetics were significantly accelerated by repeated exercise using the same leg. On the other hand, when the exercise was changed to the other leg, kinetics were significantly slower, although kinetics continued to be faster. During the incremental exercise test, although the HR response was slower at the transition from 50-W to 100-W exercise than at the transition from warm-up to 50-W exercise, there were no significant changes in kinetics. These findings suggest that kinetics may be affected by metabolic conditions in the muscle, but not by blood flow ( and/or HR) kinetics.     

Times to exhaustion at 100% of velocity at [(V)\dot]\textO\text2 \dot V{\text{O}}_{\text{2}} max and modelling of the time-limit / velocity relationship in elite long-distance runners

The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits _{max max} in 38 elite male long - distance runners _max = 71.4 ± 5.5 ml.kg^–1.min^–1 and _max = 21.8 ± 1.2 km.h^–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in _max. Tlim value was negatively correlated with _max (r = -0.362, p< 0.05) and _max (r = –0.347, p< 0.05) but positively with LT (%v _max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at _max in a homogeneous group of elite male long-distance runners was inversely related to _max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) .     

A model of oxygen uptake kinetics in response to exercise: Including a means of calculating oxygen demand/deficit/debt

We present a new model of the underlying dynamics of the oxygen uptake kinetics for various exercise intensities. This model is in the form of a set of nonlinear coupled vector fields for the and , the derivative of the exercise intensity with respect to time. We also present a new and novel means for calculating the oxygen demand, D(v, t), and hence also the oxygen deficit and debt, given the time series of the . This enables us to give better predictions for these values especially for when exercising at or close to maximal exercise intensities. Our model also allows us to predict the oxygen uptake time series given the time series for the exercise intensity as well as to investigate the oxygen uptake response to nonlinear exercise intensities. Neither of these features is possible using the currently used three-phase model. We also present a review of both the underlying physiology and the three-phase model. This includes for the first time a complete set of the analytical solutions of the three-phase model for the oxygen deficit and debt.     

Breathing pattern and growth: comparative aspects

Summary The resting oxygen consumption and breathing pattern of nine newborn and adult species (ranging in body size from mouse to human) have been compared on the basis of data collected from the literature. Minute ventilation is similarly linked to at both ages, the percent of extracted as O₂ about 2.2. Tidal volume/kg is an interspecies constant in newborns and adults, approximately 8 ml/kg. Breathing frequency decreases with the increase in size in a different way at the two ages: large species have newborns breathing at rates 2–3 times above the corresponding adults' values, while in the small species newborns and adults breathe at almost the same rate. Therefore the newborns of the smallest species have both and below the expected values, implying a greater inability to cope with the external demands than newborns of larger species. Several considerations indicate that in the smallest newborns the mechanical properties of the respiratory system could be a constraint to resting ventilations larger than observed. It is therefore possible that their low is the cause, and not the effect, of the relatively small .