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.

Photocatalytic production of methane and hydrogen through reduction of carbon dioxide with water using titania pellets

This paper presents an experimental study on employing a pellet form of catalyst in photo-reduction of carbon dioxide with water. Water was first absorbed into titania pellets. Highly purified carbon dioxide gas was then discharged into a reactor containing the wet pellets, which were then illuminated continuously for 65 hours using UVC lamps. Analysing the products accumulated in the reactor confirmed that methane and hydrogen were produced through photo-reduction of carbon dioxide with water. No other hydrocarbons were detected. Increasing the temperature in the reactor has showed little change on the amount of methane produced.

Photosynthesis of hydrogen and methane as key components for clean energy system

While researchers are trying to solve the world's energy woes, hydrogen is becoming the key component in sustainable energy systems. Hydrogen could be produced through photocatalytic water-splitting technology. It has also been found that hydrogen and methane could be produced through photocatalytic reduction of carbon dioxide with water. In this exploratory study, instead of coating catalysts on a substrate, pellet form of catalyst, which has better adsorption capacity, was used in the photo-reduction of carbon dioxide with water. In the experiment, some water was first absorbed into titanium dioxide pellets. Highly purified carbon dioxide gas was then discharged into a reactor containing these wet pellets, which were then illuminated continuously using UVC lamps. Gaseous samples accumulated in the reactor were extracted at different intervals to analyze the product yields. The results confirmed that methane and hydrogen were photosynthesized using pellet form of TiO₂ catalysts. Hydrogen was formed at a rate as high as 0.16 micromoles per hour (μmol h⁻¹). The maximum formation rate of CH₄ was achieved at 0.25 μmol h⁻¹ after 24 h of irradiation. CO was also detected.

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.

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.

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).

Chronic intermittent hypoxia and incremental cycling exercise independently depress muscle in vitro maximal Na+-K+-ATPase activity in well-trained athletes

Athletes commonly attempt to enhance performance by training in normoxia but sleeping in hypoxia [live high and train low (LHTL)]. However, chronic hypoxia reduces muscle Na⁺-K⁺-ATPase content, whereas fatiguing contractions reduce Na⁺-K⁺-ATPase activity, which each may impair performance. We examined whether LHTL and intense exercise would decrease muscle Na⁺-K⁺-ATPase activity and whether these effects would be additive and sufficient to impair performance or plasma K⁺ regulation. Thirteen subjects were randomly assigned to two fitness-matched groups, LHTL (n = 6) or control (Con, n = 7). LHTL slept at simulated moderate altitude (3,000 m, inspired O₂ fraction = 15.48%) for 23 nights and lived and trained by day under normoxic conditions in Canberra (altitude ~600 m). Con lived, trained, and slept in normoxia. A standardized incremental exercise test was conducted before and after LHTL. A vastus lateralis muscle biopsy was taken at rest and after exercise, before and after LHTL or Con, and analyzed for maximal Na⁺-K⁺-ATPase activity [K⁺-stimulated 3-O-methylfluorescein phosphatase (3-O-MFPase)] and Na⁺-K⁺-ATPase content ([³H]ouabain binding sites). 3-O-MFPase activity was decreased by –2.9 ± 2.6% in LHTL (P < 0.05) and was depressed immediately after exercise (P < 0.05) similarly in Con and LHTL (–13.0 ± 3.2 and –11.8 ± 1.5%, respectively). Plasma K⁺ concentration during exercise was unchanged by LHTL; [3H]ouabain binding was unchanged with LHTL or exercise. Peak oxygen consumption was reduced in LHTL (P < 0.05) but not in Con, whereas exercise work was unchanged in either group. Thus LHTL had a minor effect on, and incremental exercise reduced, Na⁺-K⁺-ATPase activity. However, the small LHTL-induced depression of 3-O-MFPase activity was insufficient to adversely affect either K⁺ regulation or total work performed.