Oxygen uptake during swimming in a hypobaric hypoxic environment

The purpose of this study was to determine oxygen uptake (VO2) at various water flow rates and maximal oxygen uptake (VO2max) during swimming in a hypobaric hypoxic environment. Seven trained swimmers swam in normal [N; 751 mmHg (100.1 kPa)] and hypobaric hypoxic [H; 601 mmHg (80.27 kPa)] environments in a chamber where atmospheric pressure could be regulated. Water flow rate started at 0.80 m.s-1 and was increased by 0.05 m.s-1 every 2 min up to 1.00 m.s-1 and then by 0.05 m.s-1 every minute until exhaustion. At submaximal water flow rates, carbon dioxide production (VCO2), pulmonary ventilation (VE) and tidal volume (VT) were significantly greater in H than in N. There were no significant differences in the response of submaximal VO2, heart rate (fc) or respiratory frequency (fR) between N and H. Maximal VE, fR, VT, fc, blood lactate concentration and water flow rate were not significantly different between N and H. However, VO2max under H [3.65 (SD 0.11) l.min-1] was significantly lower by 12.0% (SD 3.4)% than that in N [4.15 (SD 0.18) l.min-1]. This decrease agrees well with previous investigations that have studied centrally limited exercise, such as running and cycling, under similar levels of hypoxia.     

Transient oxygen uptake response to exercise characterizes functional capacity of the cardiocirculatory system in patients with chronic heart failure: a random stimulus approach

The transient response of oxygen uptake (V˙O₂) to submaximal exercise, known to be abnormal in patients with cardiovascular disorders, can be useful in assessing the functional status of the cardiocirculatory system, however, a method for evaluating it accurately has not yet been established. As an alternative approach to the conventional test at constant exercise intensity, we applied a random stimulus technique that has been shown to provide relatively noise immune responses of system being investigated. In 27 patients with heart failure and 24 age-matched control subjects, we imposed cycle exercise at 50 W intermittently according to a pseudo-random binary (exercise-rest) sequence, while measuring breath-by-breath V˙O₂. After determining the transfer function relating exercise intensity (W˙) to V˙O₂ and attenuating the high frequency ranges (>6 exercise-rest cycles · min⁻¹), we computed the high resolution band-limited (0–6 cycles · min⁻¹) V˙O₂ response (0–120 s) to a hypothetical step exercise. The V˙O₂ response showed a longer time constant in the patients than in the control subjects [47 (SD 37) and 31 (SD 8) s, respectively, P < 0.05]. Furthermore, the amplitude of the V˙O₂ response after the initial response was shown to be significantly smaller in the patients than in the control subjects [176 (SD 50) and 267 (SD 54) ml · min⁻¹ at 120 s]. The average amplitude over 120 s correlated well with peak V˙O₂ (r = 0.73) and ΔV˙O₂/ΔW˙ (r = 0.70), both of which are well-established indexes of exercise tolerance. The data indicated that our band-limited V˙O₂ step response using random exercise was more markedly attenuated and delayed in the patients with heart failure than in the normal controls and that it could be useful in quantifying the overall functional status of the cardiocirculatory system. Accepted: 6 January 1998     

Oxygen uptake during running as related to body mass in circumpubertal boys: a longitudinal study

To investigate the effect of endurance training on physiological characteristics during circumpubertal growth, eight young runners (mean starting age 12 years) were studied every 6 months for 8 years. Four other boys served as untrained controls. Oxygen uptake (VO2) and blood lactate concentrations were measured during submaximal and maximal treadmill running. The data were aligned with each individual's age of peak height velocity. The maximal oxygen uptake (VO2max; ml.kg-1.min-1) decreased with growth in the untrained group but remained almost constant in the training group. The oxygen cost of running at 15 km.h-1 (VO2 15, ml.kg-1.min-1) was persistently lower in the trained group but decreased similarly with age in both groups. The development of VO2max and VO2 15 (l.min-1) was related to each individual's increase in body mass so that power functions were obtained. The mean body mass scaling factor was 0.78 (SEM 0.07) and 1.01 (SEM 0.04) for VO2max and 0.75 (SEM 0.09) and 0.75 (SEM 0.02) for VO2 15 in the untrained and trained groups, respectively. Therefore, expressed as ml.kg-0.75.min-1, VO2 15 was unchanged in both groups and VO2max increased only in the trained group. The running velocity corresponding to 4 mmol.l-1 of blood lactate (nu la4) increased only in the trained group. Blood lactate concentration at exhaustion remained constant in both groups over the years studied. In conclusion, recent and the present findings would suggest that changes in the oxygen cost of running and VO2max (ml.kg-1.min-1) during growth may mainly be due to an overestimation of the body mass dependency of VO2 during running.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of the time of day on physical performance in patients with coronary artery disease

The exercise training workload for cardiac patients is determined from the peak heart rate achieved safely during a stress test. Circadian rhythms may play a key role in changing physiological responses to the stress test. Therefore, the purpose of this study was to evaluate the influence of the time of day on cardiopulmonary and metabolic responses in highly trained men with coronary artery disease. A group of 15 patients with coronary artery disease [53.5 (SD 6) years] performed two sessions of graded tests to exhaustion: one session was performed at 10 a.m. and the second at 5 p.m. in randomized order. Treadmill velocity was kept constant at a speed of 4.8 km · h^–1 starting with an elevation of 0% which was increased thereafter by 2.5% every 3 min. At rest the results revealed that only oxygen uptake was significantly lower (P < 0.05) in the morning compared to that observed in the evening [2.9 (SD 0.4) compared to 3.5 (SD 0.5) ml O₂ · kg^–1 · min^–1, respectively]. During exercise, differences due to time of day were found in the variables of maximal oxygen uptake which were significantly higher (P < 0.05) in the evening than in the morning [34.2 (SD 2.6) and 40.8 (SD 2.5) ml O₂ · kg^–1 · min^–1, respectively]. These data indicated that in these well-trained coronary artery disease patients there was a significant time of day effect associated with metabolic responses following stress-testing.     

Validation of a physical activity questionnaire in the elderly

The purpose of this study was to validate a physical activity (PA) questionnaire, Questionnaire d'Activité Physique Saint-Etienne (QAPSE), in an homogenous population of elderly subjects and to estimate its potential for application in routine PA assessments in that age group. A group of 65 (31 men and 34 women) community dwelling, healthy people aged 65–84 years volunteered to participate in a validation substudy comparing maximal oxygen uptake ( ) and anthropometric data. correlated positively with mean habitual daily energy expenditure (MHDEE) (r=0.56,P<0.0001), greater than 3MET (metabolic equivalent) daily energy expenditure (DEE) activity (r=0.371,P=0.002), leisure activity (r=0.368,P=0.003), sports activity (r=0.461,P<0.0001), basic daily activity (r=0.325,P=0.008) and moving DEE activity (r=0.273,P=0.028) in both sexes, with MHDEE (r=0.366,P=0.043) and moving DEE activity (r=0.388,P=0.031) in the men and with MHDEE (r=0.624;P<0.001), greater than 3MET DEE activity (r=0.513,P=0.002), leisure activity (r=0.388,P=0.024) and sports activity (r=0.683,P<0.001) in the women. The MHDEE was positively correlated with body mass (r=0.464) and with fat free mass (r=0.639) and negatively correlated with percentage body fat (r=−0.501). In a reproducibility substudy (n=44) a paired Student'st-test, based on mean differences between the two administrations of the questionnaire did not reach statistical significance for any of the QAPSE activity scores studied. Test-retest correlation coefficients ranged from 0.648 for moving score to 0.967 for MHDEE with correlation coefficientP values being less than 0.001 for all of the QAPSE activity scores. We concluded that QAPSE demonstrated excellent repeatability and good validity in relation to physical fitness and anthropometric data in the population of these healthy elderly volunteers.     

The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man

This study examined the effects of dietary manipulation upon the respiratory exchange ratio (R = VCO2/VO2) as a predictor of maximum oxygen uptake (VO2max). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45 +/- 5% carbohydrate (CHO] for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3 +/- 2% CHO), and again after three days of a high CHO diet (61 +/- 5% CHO). Respiratory gases were continuously monitored during each test using an on-line system. No significant changes in mean exercise oxygen uptake (VO2), VO2max or maximum functional heart rate (FHRmax) were found between tests. Mean exercise carbon dioxide output (VCO2) and R were significantly lower than normal after the low CHO diet (both p less than 0.001) and significantly higher than normal after the high CHO diet (both p less than 0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p less than 0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p less than 0.05) over the final 5 min of exercise, after the high CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhancing phosphorus and zinc acquisition efficiency in rice: a critical review of root traits and their potential utility in rice breeding

Background

Rice is the world''s most important cereal crop and phosphorus (P) and zinc (Zn) deficiency are major constraints to its production. Where fertilizer is applied to overcome these nutritional constraints it comes at substantial cost to farmers and the efficiency of fertilizer use is low. Breeding crops that are efficient at acquiring P and Zn from native soil reserves or fertilizer sources has been advocated as a cost-effective solution, but would benefit from knowledge of genes and mechanisms that confer enhanced uptake of these nutrients by roots.

Scope

This review discusses root traits that have been linked to P and Zn uptake in rice, including traits that increase mobilization of P/Zn from soils, increase the volume of soil explored by roots or root surface area to recapture solubilized nutrients, enhance the rate of P/Zn uptake across the root membrane, and whole-plant traits that affect root growth and nutrient capture. In particular, this review focuses on the potential for these traits to be exploited through breeding programmes to produce nutrient-efficient crop cultivars.

Conclusions

Few root traits have so far been used successfully in plant breeding for enhanced P and Zn uptake in rice or any other crop. Insufficient genotypic variation for traits or the failure to enhance nutrient uptake under realistic field conditions are likely reasons for the limited success. More emphasis is needed on field studies in mapping populations or association panels to identify those traits and underlying genes that are able to enhance nutrient acquisition beyond the level already present in most cultivars.     

The use of different models for the estimation of residual feed intake (RFI) as a measure of feed efficiency in meat sheep

The concept of residual feed intake (RFI), in determining differences among animals in converting feed into body tissue, was first raised in 1963. Feed efficiency is typically calculated as a function of liveweight gain (LWG) and feed intake (FI). Historically two versions of the same model were proposed, one where FI was adjusted for liveweight (LW) and LWG, and the other where LWG was adjusted for FI and LW. Variation in LWG or FI could then be partitioned into two parts; that which is expected and can be attributed to differences in FI or LWG; and that which is the residual portion, which is the deviation from the expected value based on regression, and therefore not accounted for by differences in FI or LWG. Based on this definition, it is the residual portion which is the measure of efficiency. Both within a livestock industry and between different livestock industries there is no set model for calculating RFI. This paper evaluated four models used to calculate RFI and one model used to calculate residual LWG (RLWG) at a standard level of nutrition. They were the main model currently in use in the Australian beef cattle industry (RFI_B), the original models proposed in 1963 (RFI₁₉₆₃; RLWG₁₉₆₃); a French model which included ultrasound measures of muscle and fat depth (RFI_F) and the use of the Australian feeding standards to calculate predicted intake and thus RFI (RFI_SCA). Using feed intake, liveweight and body composition data generated from the same group of sheep (n = 52) at two ages (6 mo, 13 mo), the relative merits of each model were evaluated and compared to the other models, to determine the most appropriate model to calculate RFI for sheep. For all the models except that used to calculate RLWG, over half of the variation in FI could be explained by the model. The amount of variation in FI accounted for depended on the parameters included and the dataset, with less variation in FI explained by the specific models in the older animals. The RFI_F model, which included measures of body composition, accounted for the greatest proportion of the variation in FI and as such suggests that the inclusion of body composition parameters is likely to more accurately reflect true biological efficiency.     

Elevated CO2 enhances photosynthetic efficiency,ion uptake and antioxidant activity of Gynura bicolor DC. grown in a porous‐tube nutrient delivery system under simulated microgravity

It is well known that plants can grow under space conditions, however, perturbations of many biological phenomena have been highlighted due to the effect of altered gravity and its possible interaction with other factors (e.g., CO₂, ion radiation, etc. Our aim was to test whether elevated CO₂ could provide ‘protection’ to Gynura bicolor against the damaging effects of simulated microgravity (SM) on photosynthesis, ion uptake and antioxidant activity. As compared to G. bicolor grown in ambient CO₂ with no SM (ACO₂), growth and yield of the plants increased under elevated ambient CO₂ with no SM (ECO₂) and decreased under ACO₂+SM, whereas there was no significant effect on ECO₂+SM. Reductions in the content of Chl a, carotenoids and Chl a+b were 17.9%, 20.7% and 17.9% under ACO₂+SM, respectively, but under ECO₂ there was a significant effect on all photosynthetic pigments except Chl b, compared to ACO₂. Photosynthesis was improved under ECO₂ with SM and such an improvement was associated with improved water use efficiency and instantaneous carboxylation efficiency. Furthermore, SM caused a reduction in ion absorption rate, except for Ca²⁺, while ECO₂ increased the uptake rate. Finally, the activity of SOD, POD and the content of MDA and H₂O₂ were enhanced under SM treatments and were highest in ACO₂+SM. In contrast, T‐AOC activity and GSH content significantly declined in ACO₂+SM compared to other treatments. These results suggest that ACO₂ is not sufficient to counteract SM impact, but the increase is usually caused by improvement in CO₂ nutrition in ECO₂+SM in comparison with ACO₂+SM.