OzFACE: the Australian savanna free air CO2 enrichment facility and its relevance to carbon-cycling issues in a tropical savanna

A free air CO2 enrichment (FACE) facility has recently been constructed in a tropical savanna in north-eastern Queensland, Australia. The system has a novel and cost-effective design and uses an industrial source of pure CO2 piped directly to the site. We describe the design details of this facility and assess the likely contribution it will make towards advancing our understanding of the direct impacts of rising atmospheric CO2 on savannas. These include addressing uncertainties about future shifts in the tree–grass balance and associated changes in carbon stocks, responses of C4 grasses in dry tropical environments, potential sequestration of soil carbon, and the modifications of CO2 responses by moisture and nutrient interactions. Tropical regions have been poorly represented in climate change research, and the work at the OzFACE facility will complement existing and ongoing FACE studies at temperate latitudes.

Adrenaline increases skeletal muscle glycogenolysis, pyruvate dehydrogenase activation and carbohydrate oxidation during moderate exercise in humans

# 1.
To evaluate the role of adrenaline in regulating carbohydrate metabolism during moderate exercise, 10 moderately trained men completed two 20 min exercise bouts at 58 ± 2 % peak pulmonary oxygen uptake (̇V_o2,peak). On one occasion saline was infused (CON), and on the other adrenaline was infused intravenously for 5 min prior to and throughout exercise (ADR). Glucose kinetics were measured by a primed, continuous infusion of 6,6-[2H]glucose and muscle samples were obtained prior to and at 1 and 20 min of exercise.

# 2.
The infusion of adrenaline elevated (P < 0.01) plasma adrenaline concentrations at rest (pre-infusion, 0.28 ± 0.09; post-infusion, 1.70 ± 0.45 nmol l−1; means ±s.e.m.) and this effect was maintained throughout exercise. Total carbohydrate oxidation increased by 18 % and this effect was due to greater skeletal muscle glycogenolysis (P < 0.05) and pyruvate dehydrogenase (PDH) activation (P < 0.05, treatment effect). Glucose rate of appearance was not different between trials, but the infusion of adrenaline decreased (P < 0.05, treatment effect) skeletal muscle glucose uptake in ADR.

# 3.
During exercise muscle glucose 6-phosphate (G-6-P) (P = 0.055, treatment effect) and lactate (P < 0.05) were elevated in ADR compared with CON and no changes were observed for pyruvate, creatine, phosphocreatine, ATP and the calculated free concentrations of ADP and AMP.

# 4.
The data demonstrate that elevated plasma adrenaline levels during moderate exercise in untrained men increase skeletal muscle glycogen breakdown and PDH activation, which results in greater carbohydrate oxidation. The greater muscle glycogenolysis appears to be due to increased glycogen phosphorylase transformation whilst the increased PDH activity cannot be readily explained. Finally, the decreased glucose uptake observed during exercise in ADR is likely to be due to the increased intracellular G-6-P and a subsequent decrease in glucose phosphorylation.

Reliability of performance in repeated sprint cycling tests

We have estimated the reliability of performance in a commonly employed exercise test consisting of repeated sprints on a cycle ergometer. Eight recreationally active young men completed a practice trial and three more trials at 3- to 6-day intervals. Each trial consisted of two bouts of 30-s maximal-effort cycling on an electromagnetically braked cycle ergometer; the bouts were separated by 4 min of rest. The typical (standard) errors of measurement for peak and mean power between trials 2 to 4 were 2.5 and 1.7% respectively for the first bout and 1.9 and 1.8% for the second bout. These errors are substantially less than those in previous reliability studies of single 30-s sprint tests, probably because of differences in quality of ergometer. The typical errors for the difference between bouts (i.e., fatigue) for peak power and mean power were 3.0 and 2.5%, respectively. Typical errors for the average of the two bouts were 1.6 and 1.2% for peak and mean power respectively, which are small enough to give adequate precision for moderate treatment effects in studies with modest sample sizes.

Cycling at 120 when compared to 80 rev/min increases the accumulated oxygen deficit but does not affect the precision of its calculation

The aim of the present study was to determine the influence of pedal rate on the precision and quantification of the accumulated oxygen deficit (AOD). Eight trained male triathletes completed a lactate threshold test, VO2 peak test, 10 x 3 min submaximal exercise bouts and a high-intensity exercise bout, all performed at 80 and 120 rev/min. For both pedal rates the intensities for the sub-maximal and high-intensity tests were relative to the lactate threshold and VO2 peak work rates. The VO2-power regressions were calculated using 5 intensities from above the lactate threshold combined with a y intercept value with VO2 measured after 3 min of exercise. For the 120 compared to the 80 rev/min tests, the lactate threshold work rate (255±13 versus 276±47 Watts) (p<0.01) and VO2 peak work rate (352±17 versus 382±20, Watts) (p<0.05) were lower at 120 rev/m. Conversely, the VO2 peak and the VO2 measured during the exhaustive exercise were the same for both pedal rates (p>0.05). Using linear regression modelling the slope of the VO2-power regression (0.0112 versus 0.010 L/Watt) (p<0.01), the estimated total energy demand (ETED) (5.13±0.75 versus 4.89±0.88 L/min) and the AOD (4.27±0.94 versus 3.66±1.25 L) (p<0.05) were greater at 120 rev/m. However, the 95% confidence interval for the ETED and the standard error of the predicted value were the same for both pedal rates (p>0.05). Our results demonstrate that pedal rate effects the size but not the precision of the calculated AOD and should therefore be considered when developing an AOD protocol.

Healthy revolutions: promoting cycling among women

Issue addressed: Australian women's participation in cycling for transport and recreation is approximately half that of men. These gender differences do not occur in several western European countries. Research is required to investigate the individual, social and environmental determinants of Australian women's participation in cycling for transport and recreation.

Discussion: Few studies have systematically investigated women's perceptions and experiences of cycling and little is known about what motivates and sustains their involvement. Preliminary indications are that, for women, there may be an interest in and capacity to participate in cycling that is not being translated into practice. Safety concerns appear to be a significant deterrent to women cycling. Safety factors have a differential impact on women as they are generally more risk averse than men. Quantitative risk assessments suggest that the risk of injury associated with cycling is small and that the health benefits outweigh the health costs. Cycling promotion campaigns may achieve greater success with women if they enable women to experience cycling in an environment that both is, and is perceived to be, safe and supportive.

Conclusions: Research is needed to determine what strategies are likely to be most effective in promoting cycling among Australian women, as a basis for developing programs, policies and facilities to support women's participation in cycling.

Perceptions about the local neighborhood and walking and cycling among children

Background. This study examined associations between perceptions of the local neighborhood and walking and cycling among children. Methods. Children aged 5–6 years (n = 291) and 10–12 years (n = 919) were recruited from 19 Australian primary schools. Parents reported their child's usual walking or cycling to local destinations and their perceptions of their neighborhood. Ten- to twelve-year-olds were asked their perceptions of traffic, strangers, road safety and sporting venues, and their perceptions of their parent's views on these issues. Results. Five- to six-year-old boys whose parents believed there was heavy traffic in their area were 2.8 times more likely (95%CI = 1.1–6.8), and 5- to 6-year-old girls whose parents owned more than one car were 70% less likely (95%CI = 0.1–0.8), and whose parents believed that public transport was limited in their area were 60% less likely (95%CI = 0.2–0.9) than other children to walk or cycle at least three times per week. Parental belief that there were no lights or crossings was associated with walking or cycling among 10- to 12-year-old boys (OR = 0.4, 95%CI = 0.2–0.7). Among older girls, parent's belief that their child needed to cross several roads to reach play areas (OR = 0.4, 95%CI = 0.2–0.8) and that there is limited public transport in their area (OR = 0.7, 95%CI = 0.4–0.97), and child's belief that there were no parks or sports grounds near home (OR = 0.5, 95%CI = 0.3–0.8) were associated with a lower likelihood of walking or cycling. Conclusion. Perceptions of the local neighborhood may influence children's physical activity.

How do perceptions of local neighborhood relate to adolescents` walking and cycling?

Purpose. To examine how perceptions of the local neighborhood relate to adolescents' walking and cycling. Design. Exploratory cross-sectional study. Setting. Birth cohort from the Nepean Hospital, Sydney, Australia. Subjects. Three hundred forty-seven adolescents (79.1 % response rate; 49.6% boys; mean age - 13.0 ± 0.2 years) and their parents. Measures. Self-report and parental-report questionnaires. Results. Multiple linear regressions, adjusted for level of maternal education, revealed that boys who reported having many peers to hang out with locally, cycled for recreation (β = 0.242, p = .006) or for transport (β = 0.141, p = . 046) more often, and walked for transport for longer (β = 0.129, p = .024) on weekdays. For girls this variable was related to cycling for recreation on weekends (β = 0.164, p = .006) and walking to school (β = 0.118, p = .002). Adolescents who waved/talked to neighbors walked for transport more often (boys, β = 0.149, p = .037; girls, β = 0.119, p = .012). Girls who perceived local roads to be safe spent more time walking for transport on weekdays (β = 0.183, p = .007) and for exercise on weekends (β = 0.184, p = . 034). Parents' perception of heavy traffic was negatively associated with boys' walking for transport (β = -0.138, p = .037) and many aspects of girls' walking and cycling. Conclusion. Social interaction and road safety may be important predictors of adolescents' walking and cycling in their neighborhood. Limitations are the use of self-report and cross-sectional data. Longitudinal studies may clarify these relations.

Associations among individual, social, and environmental barriers and children's walking or cycling to school

Purpose. To examine associations among individual, social, and environmental barriers and children's walking or cycling to school.

Design. Exploratory cross-sectional study.

Setting. All eight capital cities in Australia.

Subjects. Parents (N = 720) of school-aged children (4-13 years; 27% response rate 49% parents of boys,).

Measures. Multivariate-adjusted odds ratios (OR) and 95% confidence intervals (CI) for parental reporting of barriers to their children's walking or cycling to school, based on a computer-assisted telephone interview.

Results. Forty-one percent of children walked or cycled to school at least once per week. Multivariable analyses found inverse associations with individual ("child prefers to be driven" [OR = 0.4, 95% CI = 0.3-0.6], "no time in the mornings" [OR 0.5, 95% CI = 0.3-0.8]); social ("worry child will take risk" [OR = 0.6, 95% CI = 0.3-0.9], "no other children to walk with" [OR = 0.7, 95% CI = 0.4-0.99], "no adults to walk with" [OR = 0.6, 95% CI = 0.4-0.9]); and environmental barriers ("too far to walk" [OR = 0.1, 95% CI = 0.0- 0.1], "no direct route" [OR = 0.4, 95% CI = 0.2-0. 7]) and positive associations with "concern child may he injured in a road accident" (OR = 1.9, 95% CI = 1.1-3.1) and active commuting.

Conclusion. Working with parents, schools, and local authorities to improve pedestrian, skills and environments may help to overcome barriers.

No effect of mild heat stress on the regulation of carbohydrate metabolism at the onset of exercise

To investigate the influence of heat stress on the regulation of skeletal muscle carbohydrate metabolism, six active, but not specifically trained, men performed 5 min of cycling at a power output eliciting 70% maximal O(2) uptake in either 20 degrees C (Con) or 40 degrees C (Heat) after 20 min of passive exposure to either environmental condition. Although muscle temperature (T(mu)) was similar at rest when comparing trials, 20 min of passive exposure and 5 min of exercise increased (P < 0.05) T(mu) in Heat compared with Con (37.5 +/- 0.1 vs. 36.9 +/- 0.1 degrees C at 5 min for Heat and Con, respectively). Rectal temperature and plasma epinephrine were not different at rest, preexercise, or 5 min of exercise between trials. Although intramuscular glycogen phosphorylase and pyruvate dehydrogenase activity increased (P < 0.05) at the onset of exercise, there were no differences in the activities of these regulatory enzymes when comparing Heat with Con. Accordingly, glycogen use in the first 5 min of exercise was not different when comparing Heat with Con. Similarly, no differences in intramuscular concentrations of glucose 6-phosphate, lactate, pyruvate, acetyl-CoA, creatine, phosphocreatine, or ATP were observed at any time point when comparing Heat with Con. These results demonstrate that, whereas mild heat stress results in a small difference in contracting T(mu), it does not alter the activities of the key regulatory enzymes for carbohydrate metabolism or glycogen use at the onset of exercise, when plasma epinephrine levels are unaltered.

Effect of carbohydrate ingestion on metabolism during running and cycling

The effects of carbohydrate or water ingestion on metabolism were investigated in seven male subjects during two running and two cycling trials lasting 60 min at individual lactate threshold using indirect calorimetry, U-¹⁴C-labeled tracer-derived measures of the rates of oxidation of plasma glucose, and direct determination of mixed muscle glycogen content from the vastus lateralis before and after exercise. Subjects ingested 8 ml/kg body mass of either a 6.4% carbohydrate-electrolyte solution (CHO) or water 10 min before exercise and an additional 2 ml/kg body mass of the same fluid after 20 and 40 min of exercise. Plasma glucose oxidation was greater with CHO than with water during both running (65 ± 20 vs. 42 ± 16 g/h; P < 0.01) and cycling (57 ± 16 vs. 35 ± 12 g/h; P < 0.01). Accordingly, the contribution from plasma glucose oxidation to total carbohydrate oxidation was greater during both running (33 ± 4 vs. 23 ± 3%; P < 0.01) and cycling (36 ± 5 vs. 22 ± 3%; P < 0.01) with CHO ingestion. However, muscle glycogen utilization was not reduced by the ingestion of CHO compared with water during either running (112 ± 32 vs. 141 ± 34 mmol/kg dry mass) or cycling (227 ± 36 vs. 216 ± 39 mmol/kg dry mass). We conclude that, compared with water, 1) the ingestion of carbohydrate during running and cycling enhanced the contribution of plasma glucose oxidation to total carbohydrate oxidation but 2) did not attenuate mixed muscle glycogen utilization during 1 h of continuous submaximal exercise at individual lactate threshold.

Live high: train low increases muscle buffer capacity and submaximal cycling efficiency

This study investigated whether hypoxic exposure increased muscle buffer capacity (βm) and mechanical efficiency during exercise in male athletes. A control (CON, n=7) and a live high:train low group (LHTL, n=6) trained at near sea level (600 m), with the LHTL group sleeping for 23 nights in simulated moderate altitude (3000 m). Whole body oxygen consumption (V˙O₂) was measured under normoxia before, during and after 23 nights of sleeping in hypoxia, during cycle ergometry comprising 4×4-min submaximal stages, 2-min at 5.6 ± 0.4 W kg^–1, and 2-min 'all-out' to determine total work and V˙O_2peak. A vastus lateralis muscle biopsy was taken at rest and after a standardized 2-min 5.6 ± 0.4 W kg^–1 bout, before and after LHTL, and analysed for βm and metabolites. After LHTL, βm was increased (18%, P < 0.05). Although work was maintained, V˙O_2peak fell after LHTL (7%, P < 0.05). Submaximal V˙O₂ was reduced (4.4%, P < 0.05) and efficiency improved (0.8%, P < 0.05) after LHTL probably because of a shift in fuel utilization. This is the first study to show that hypoxic exposure, per se, increases muscle buffer capacity. Further, reduced V˙O₂ during normoxic exercise after LHTL suggests that improved exercise efficiency is a fundamental adaptation to LHTL.

Effect of sodium bicarbonate on muscle metabolism during intense endurance cycling

Introduction: Sodium bicarbonate (NaHCO₃) ingestion has been shown to increase both muscle glycogenolysis and glycolysis during brief submaximal exercise. These changes may be detrimental to performance during more prolonged, exhaustive exercise. This study examined the effect of NaHCO₃ ingestion on muscle metabolism and performance during intense endurance exercise of ~60 min in seven endurance-trained men. Methods: Subjects ingested 0.3 g·kg^-1 body mass of either NaHCO₃ or CaCO₃ (CON) 2 h before performing 30 min of cycling exercise at 77 ± 1% [latin capital V with dot above]O_2peak followed by completion of 469 ± 21 kJ as quickly as possible (~30 min, ~80% [latin capital V with dot above]O_2peak). Results: Immediately before, and throughout exercise, arterialized-venous plasma HCO₃- concentrations were higher (P < 0.05) whereas plasma and muscle H⁺ concentrations were lower (P < 0.05) in NaHCO₃ compared with CON. Blood lactate concentrations were higher (P < 0.05) during exercise in NaHCO₃, but there was no difference between trials in muscle glycogen utilization or muscle lactate content during exercise. Reductions in PCr and ATP and increases in muscle Cr during exercise were also unaffected by NaHCO₃ ingestion. Accordingly, exercise performance time was not different between treatments. Conclusion: NaHCO₃ ingestion resulted in a small muscle alkalosis but had no effect on muscle metabolism or intense endurance exercise performance in well-trained men.

Pyruvate dehydrogenase activation and kinase expression in human skeletal muscle during fasting

Fasting forces adaptive changes in whole body and skeletal muscle metabolism that increase fat oxidation and decrease the oxidation of carbohydrate. We tested the hypothesis that 40 h of fasting would decrease pyruvate dehydrogenase (PDH) activity and increase PDH kinase (PDK) isoform mRNA expression in human skeletal muscle. The putative transcriptional activators of PDK isozymes, peroxisome proliferator-activated receptor-α (PPAR-α) protein, and forkhead homolog in rhabdomyosarcoma (FKHR) mRNA were also measured. Eleven healthy adults fasted after a standard meal (25% fat, 60% carbohydrate, 15% protein) with blood and skeletal muscle samples taken at 3, 15, and 40 h postprandial. Fasting increased plasma free fatty acid, glycerol, and β-hydroxybutyrate concentrations and decreased glucose and insulin concentrations. PDH activity decreased from 0.88 ± 0.11 mmol acetyl-CoA · min^-1 · kg wet muscle wt^-1 at 3 h to 0.62 ± 0.10 (P = not significant) and 0.39 ± 0.06 (P < 0.05) mmol · min^-1 · kg wet mass^-1 after 15 and 40 h of fasting. Although all four PDK isoforms were expressed in human skeletal muscle, PDK^-2 and -4 mRNA were the most abundant. PDK^-1 and ^-3 mRNA abundance was ~1 and 15% of the PDK^-2 and 4^- levels, respectively. The 40-h fast had no effect on PDK^-1, ^-2, and ^-3 mRNA expression. PDK-4 mRNA was significantly increased ~3-fold after 15 h and ~14-fold after 40 h of fasting. Skeletal muscle PPAR-α protein and FKHR mRNA abundance were unaffected by the fast. The results suggest that decreased PDH activation after 40 h of fasting may have been a function of the large increase in PDK-4 mRNA expression and possible subsequent increase in PDK protein and activity. The changes in PDK-4 expression and PDH activity did not coincide with increases in the transcriptional activators PPAR-α and FKHR.

Carbohydrate-electrolyte feedings and 1h time trial cycling performance

The effects of a commercial sports drink on performance in high-intensity cycling was investigated. Nine well-trained subjects were asked to complete a set amount of work as fast as possible (time trial) following 24 h of dietary (subjects were provided with food, energy 57.4 ± 2.4 kcal/kg and carbohydrate 9.1 ± 0.4 g/kg) and exercise control. During exercise, subjects were provided with 14 mL/kg of either 6% carbohydrate-electrolyte (CHO-E) solution or carbohydrate-free placebo (P).

Effects of aerobic training on pyruvate dehydrogenase and pyruvate dehydrogenase kinase in human skeletal muscle

This study examined the effects of short- and long-term aerobic training on the stable up-regulation of pyruvate dehydrogenase (PDH) and PDH kinase (PDK) in human skeletal muscle. We hypothesized that 8 weeks, but not 1 week, of aerobic training would increase total PDH (PDHt) and PDK activities compared to pretraining, and this would be detectable at the level of gene transcription (mRNA) and/or gene translation (protein). Resting muscle biopsies were taken before and after 1 and 8 weeks of aerobic cycle exercise training. PDHt and PDK activities, and their respective protein and mRNA expression, did not differ after 1 week of aerobic training. PDHt activity increased 31% after 8 weeks and this may be partially due to a 1.3-fold increase in PDH-E₁α protein expression. PDK activity approximately doubled after 8 weeks of aerobic training and this was attributed to a 1.3-fold increase in PDK2 isoform protein expression. Similar to 1 week, no changes were observed at the mRNA level after 8 weeks of training. These findings  suggest that aerobically trained human skeletal muscle has an increased maximal capacity to utilize carbohydrates, evident by increased PDHt, but increased metabolic control sensitivity to pyruvate through increased contribution of PDK2 to total PDK activity.