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Jonathan Watkins, Simon Platt, Erik Andersson and Kerry McGawley

Purpose:

The aim of the current study was to investigate pacing strategies and the distribution of physiological resources in best vs worst performances during a series of 4-min self-paced running time trials (RunTTs).

Methods:

Five male and 5 female recreational runners (age 32 ± 7 y) completed a submaximal ramp test and 5 RunTTs on a motor-driven treadmill fitted with a speed-controlling laser system. The supramaximal oxygen-uptake (V̇O2) demand was estimated by linear extrapolation from the submaximal relationship between V̇O2 and speed, enabling computation of the accumulated oxygen deficit.

Results:

There were no significant differences between the 5 RunTTs for any of the performance, physiological, or subjective responses (P > .05). The trial-to-trial variability in pacing (ie, separate quarters) was typically low, with an average within-athlete coefficient of variation of 3.3%, being highest at the start and end of the 4 min. Total distance covered and distance covered over the first and last 2 min for best and worst performances were 1137 ± 94 and 1090 ± 89 (P < .001), 565 ± 53 and 526 ± 40 m (P = .002), and 572 ± 47 and 565 ± 54 m (P = .346), respectively.

Conclusions:

Negative pacing strategies were evident during both the best and the worst performances of the RunTT. Best performances were characterized by more aggressive pacing over the first 2 min compared with worst performances. In addition, the relatively low trial-to-trial variability in running speed suggests that pacing strategies are similar during a series of 4-min self-paced running time trials.

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Victoria L. Bowden and Robert G. McMurray

The purpose of this study was to determine if there is a difference between the way in which aerobically trained and untrained women metabolize fats and carbohydrates at rest in response to either a high-fat or high-carbohydrate meal. Subjects, 6 per group, were fed a high CHO meal (2068 kJ, 76% CHO. 23% fat, 5% protein) and a high fat meal (2093 kJ, 21% CHO, 72% fat, 8% protein) in counterbalanced order. Resting metabolic rate (RMR) was measured every half-hour for 5 hours. RMR was similar between groups. Training status had no overall effect on postprandial metabolic rate or total energy expenditure. The high fat meal resulted in no significant differences in RMR or respiratory exchange ratio (RER) between groups. However, after ingesting a high CHO meal, trained subjects had a peak in metabolism at minute 60, not evident in the untrained subjects. In addition, postprandial RER from minutes 120-300 were lower and fat use was greater after the high CHO meal for the trained subjects. These results suggest that aerobically trained women have an accelerated CHO uptake and overall lower CHO oxidation following the ingestion of a high CHO meal.

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Amanda Claassen, Estelle V. Lambert, Andrew N. Bosch, Ian M. Rodger, Alan St. Clair Gibson and Timothy D. Noakes

The impact of altered blood glucose concentrations on exercise metabolism and performance after a low carbohydrate (CHO) diet was investigated. In random order, 1 wk apart, 9 trained men underwent euglycemic (CI) or placebo (PI) clamps, while performing up to 150 min of cycling at 70% VO2max, after 48 h on a low CHO diet. The range in improvement in endurance capacity with glucose infusion was large (28 ± 26%, P < 0.05). Fifty-six percent of subjects in CI failed to complete 150 min of exercise despite maintenance of euglycemia, while only 2 subjects in PI completed 150 min of exercise, despite being hypoglycemic. Total CHO oxidation remained similar between trials. Despite longer exercise times in CI, similar amounts of muscle glycogen were used to PI. Maintenance of euglycemia in the CHO-depleted state might have an ergogenic effect, however, the effect is highly variable between individuals and independent of changes in CHO oxidation.

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Philippe Hellard, Robin Pla, Ferran A. Rodríguez, David Simbana and David B. Pyne

Purpose: To compare the dynamics of maximal oxygen uptake (V˙O2), blood lactate ([La]b), total energy expenditure (E tot), and contributions of the aerobic (E aer), alactic anaerobic (E an,al), and lactic anaerobic (E an,lac) metabolic energy pathways over 4 consecutive 25-m laps (L0–25, L25–50, etc) of a 100-m maximal freestyle swim. Methods: Elite swimmers comprising 26 juniors (age = 16 [1] y) and 23 seniors (age = 24 [5] y) performed 100 m at maximal speed and then 3 trials (25, 50, and 75 m) at the same pace as that of the 100 m. [La]b was collected, and V˙O2 was measured 20 s postexercise. Results: The estimated energetic contributions for the 100-m trial are presented as mean (SD): E aer, 51% (8%); E an,al, 18% (2%); E an,lac, 31% (9%). V˙O2 increased from L0–25 to L25–50 (mean = 3.5 L·min−1; 90% confidence interval [CI], 3.4–3.7 L·min−1 to mean = 4.2 L·min−1; 90% CI, 4.0–4.3 L·min−1) and then stabilized in the 2nd 50 m (mean = 4.1 L·min−1; 90% CI, 3.9–4.3 L·min−1 to mean = 4.2 L·min−1; 90% CI, 4.0–4.4 L·min−1). E tot (juniors, 138 [18] kJ; seniors, 168 [26] kJ), E an,al (juniors, 27 [3] kJ; seniors, 30 [3] kJ), and E an,lac (juniors, 38 [12] kJ; seniors, 62 [24] kJ) were 11–58% higher in seniors. Faster swimmers (n = 26) had higher V˙O2(4.6L·min1, 90% CI 4.4–4.8 L·min−1 vs 3.9 L·min−1, 90% CI 3.6–4.2 L·min−1), and E aer power was associated with fast performances (P < .001). Conclusion: Faster swimmers were characterized by higher V˙O2 and less time to reach the highest V˙O2 at ∼50 m of the 100-m swim. Anaerobic qualities become more important with age.

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Gordon I. Smith, Asker E. Jeukendrup and Derek Ball

At rest, administration of the short-chain fatty acid acetate suppresses fat oxidation without affecting carbohydrate utilization. The combined effect of increased acetate availability and exercise on substrate utilization is, however, unclear. With local ethics approval, we studied the effect of ingesting either sodium acetate (NaAc) or sodium bicarbonate (NaHCO3) at a dose of 4 mmol·kg-1 body mass 90 min before completing 120 min of exercise at 50% VO2peak. Six healthy young men completed the trials after an overnight fast and ingested the sodium salts in randomized order. As expected NaAc ingestion decreased resting fat oxidation (mean ± SD; 0.09 ± 0.02 vs. 0.07 ± 0.02 g·min-1 pre- and post-ingestion respectively, p < .05) with no effect upon carbohydrate utilization. In contrast, NaHCO3 ingestion had no effect on substrate utilization at rest. In response to exercise, fat and CHO oxidation increased in both trials, but fat oxidation was lower (0.16 ± 0.10 vs. 0.29 ± 0.11 g·min-1, p < .05) and carbohydrate oxidation higher (1.67 ± 0.35 vs. 1.44 ± 0.22 g·min-1, p < .05) in the NaAc trial compared with the NaHCO3 trial during the first 15 min of exercise. Over the final 75 min of exercise an increase in fat oxidation and decrease in carbohydrate oxidation was observed only in the NaAc trial. These results demonstrate that increasing plasma acetate concentration suppresses fat oxidation both at rest and at the onset of moderate-intensity exercise.

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L.P. Kilduff, E. Georgiades, N. James, R.H. Minnion, M. Mitchell, D. Kingsmore, M. Hadjicharalambous and Y.P. Pitsiladis

The effects of creatine (Cr) supplementation on cardiovascular, metabolic, and thermoregulatory responses, and on the capacity of trained humans to perform prolonged exercise in the heat was examined. Endurance-trained males (n = 21) performed 2 constant-load exercise tests to exhaustion at 63 ± 5 % VO2max in the heat (ambient temperature: 30.3 ± 0.5 °C) before and after 7 d of Cr (20 g · d–1 ’ Cr + 140 g • d–1 glucose polymer) or placebo. Cr increased intraccl-lular water and reduced thermoregulatory and cardiovascular responses (e.g., heart rate, rectal temperature, sweat rate) but did not significantly increase time to exhaustion (47.0 ± 4.7 min vs. 49.7 ± 7.5 min, P = 0.095). Time to exhaustion was increased significantly in subjects whose estimated intramuscular Cr levels were substantially increased (“responders”: 47.3 ± 4.9 min vs. 51.7 ± 7.4 min, P = 0.031). Cr-induced hyperhydration can result in a more efficient thermoregulatory response during prolonged exercise in the heat.

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Weronika N. Abramowicz and Stuart D.R. Galloway

Twelve healthy active subjects (6 male, 6 female) performed 60 min of exercise (60% VO2max) on 3 occasions after supplementing with L-Carnitine L-tartrate (LCLT) or placebo. Each subject received a chronic dose, an acute dose, and placebo in a randomized, double-blind crossover design. Dietary intake and exercise were replicated for 2 d prior to each trial. In males there was a significant difference in rate of carbohydrate (CHO) oxidation between placebo and chronic trials (P = 0.02) but not placebo and acute trials (P = 0.70), and total CHO oxidation was greater following chronic supplementation vs. placebo (mean ± standard deviation) of 93.8 (17.3) g/hr and 78.2 (23.3) g/h, respectively). In females, no difference in rate of, or total, CHO oxidation was observed between trials. No effects on fat oxidation or hematological responses were noted in either gender group. Under these experimental conditions, chronic LCLT supplementation increased CHO oxidation in males during exercise but this was not observed in females

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Beatriz Bachero-Mena, Miguel Sánchez-Moreno, Fernando Pareja-Blanco and Borja Sañudo

widespread use of resisted sprint training, to our knowledge, no previous research has examined the acute effects of this training method on metabolic response, muscle damage, and impairments in athletic performance. Despite the scientific attention received by sled towing, there still exists controversy

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Rachel B. Parks, Hector F. Angus, Douglas S. King and Rick L. Sharp

increasingly being used in sports nutrition products to moderate the metabolic response ( Bjorck et al., 1994 ; Roberts et al., 2011 ). Slowly absorbed and incompletely digested starches, termed “resistant” starches, are rarely used because a relatively large fraction of carbohydrate escapes small intestine

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Campbell Menzies, Michael Wood, Joel Thomas, Aaron Hengist, Jean-Philippe Walhin, Robbie Jones, Kostas Tsintzas, Javier T. Gonzalez and James A. Betts

-2018-0098 Claassen , A. , Lambert , E.V. , Bosch , A.N. , Rodger , l.M. , St. Clair Gibson , A. , & Noakes , T.D. ( 2005 ). Variability in exercise capacity and metabolic response during endurance exercise after a low carbohydrate diet . International Journal of Sport Nutrition and