Luke Moseley

The reliability of cycling efficiency

PURPOSE The aim of this experiment was to establish the reproducibility of gross efficiency (GE), delta efficiency (DE), and economy (EC) during a graded cycle ergometer test in seventeen male subjects. METHODS All subjects performed three identical exercise tests at a constant pedal cadence of 80 rpm on an electrically braked cycle ergometer. Energy expenditure was estimated from measures of oxygen uptake (VO(2)) and carbon dioxide production (VCO(2)) by using stoichiometric equations. RESULTS The subjects characteristics were age 24 +/- 6 yr, body mass 74.6 +/- 6.9 kg, body fat 13.9 +/- 2.2%, and VO(2max) 61.9 +/- 2.4 mL x kg(-1) x min(-1) (all means +/- SD). Average GE, DE, and EC for the three tests were 19.8 +/- 0.6%, 25.8 +/- 1.5%, and 5.0 +/- 0.1 kJ x L(-1), respectively. The coefficients of variation (confidence limits) were GE 4.2 (3.2-6.4)%, DE 6.7 (5.0-10.0)%, and EC 3.3 (2.4-4.9)%. GE was significantly lower at 95 W and 130 W when compared with 165 W, 200 W, 235 W, 270 W, and 305 W. GE at 165 W was significantly lower (P < 0.05) that GE at 235 W. A weak correlation (r = 0.491; P < 0.05) was found between peak oxygen uptake (VO(2peak)) and GE, whereas no correlations were found between VO(2max) and DE or EC. CONCLUSION We conclude that a graded exercise test with 3-min stages and 35-W increments is a method by which reproducible measurements of both GE and EC can be obtained, whereas measurements of DE seemed slightly more variable.

Nutritional considerations in triathlon

AbstractTriathlon combines three disciplines (swimming, cycling and running) and competitions last between 1 hour 50 minutes (Olympic distance) and 14 hours (Ironman distance). Independent of the distance, dehydration and carbohydrate (CHO) depletion are the most likely causes of fatigue in triathlon, whereas gastrointestinal (GI) problems, hyperthermia and hyponatraemia are potentially health threatening, especially in longer events. Although glycogen supercompensation may be beneficial for triathlon performance (even Olympic distance), this does not necessarily have to be achieved by the traditional supercompensation protocol. More recently, studies have revealed ways to increase muscle glycogen concentrations to very high levels with minimal modifications in diet and training.During competition, cycling provides the best opportunity to ingest fluids. The optimum CHO concentration seems to be in the range of 5–8% and triathletes should aim to achieve a CHO intake of 60–70 g/hour. Triathletes should attempt to limit body mass losses to 1% of body mass. In all cases, a drink should contain sodium (30–50 mmol/L) for optimal absorption and prevention of hyponatraemia.Post-exercise rehydration is best achieved by consuming beverages that have a high sodium content (>60 mmol/L) in a volume equivalent to 150% of body mass loss. GI problems occur frequently, especially in long-distance triathlon. Problems seem related to the intake of highly concentrated carbohydrate solutions, or hyperosmotic drinks, and the intake of fibre, fat and protein. Endotoxaemia has been suggested as an explanation for some of the GI problems, but this has not been confirmed by recent research. Although mild endotoxaemia may occur after an Ironman-distance triathlon, this does not seem to be related to the incidence of GI problems. Hyponatraemia has occasionally been reported, especially among slow competitors in triathlons and probably arises due to loss of sodium in sweat coupled with very high intakes (8–10L) of water or other low-sodium drinks.

OXIDATION OF COMBINED INGESTION OF GLUCOSE AND FRUCTOSE DURING EXERCISE

The purpose of the present study was to examine whether combined ingestion of a large amount of fructose and glucose during cycling exercise would lead to exogenous carbohydrate oxidation rates >1 g/min. Eight trained cyclists (maximal O(2) consumption: 62 +/- 3 ml x kg(-1) x min(-1)) performed four exercise trials in random order. Each trial consisted of 120 min of cycling at 50% maximum power output (63 +/- 2% maximal O(2) consumption), while subjects received a solution providing either 1.2 g/min of glucose (Med-Glu), 1.8 g/min of glucose (High-Glu), 0.6 g/min of fructose + 1.2 g/min of glucose (Fruc+Glu), or water. The ingested fructose was labeled with [U-(13)C]fructose, and the ingested glucose was labeled with [U-(14)C]glucose. Peak exogenous carbohydrate oxidation rates were approximately 55% higher (P < 0.001) in Fruc+Glu (1.26 +/- 0.07 g/min) compared with Med-Glu and High-Glu (0.80 +/- 0.04 and 0.83 +/- 0.05 g/min, respectively). Furthermore, the average exogenous carbohydrate oxidation rates over the 60- to 120-min exercise period were higher (P < 0.001) in Fruc+Glu compared with Med-Glu and High-Glu (1.16 +/- 0.06, 0.75 +/- 0.04, and 0.75 +/- 0.04 g/min, respectively). There was a trend toward a lower endogenous carbohydrate oxidation in Fruc+Glu compared with the other two carbohydrate trials, but this failed to reach statistical significance (P = 0.075). The present results demonstrate that, when fructose and glucose are ingested simultaneously at high rates during cycling exercise, exogenous carbohydrate oxidation rates can reach peak values of approximately 1.3 g/min.

HYPOGLYCEMIA FOLLOWING PRE-EXERCISE CARBOHYDRATE INGESTION IS NOT ACCOMPANIED BY HIGHER INSULIN SENSITIVITY.

Pre-exercise carbohydrate feeding may result in rebound hypoglycemia in some but not all athletes. The aim of the present study was to examine whether insulin sensitivity in athletes who develop rebound hypoglycemia is higher compared with those who do not show rebound hypoglycemia. Twenty trained athletes (VO(2max) of 61.8 +/- 1.4 ml.kg(-1).min(-1)) performed an exercise trial on a cycle ergometer. Forty-five minutes before the start of exercise, subjects consumed 500 ml of a beverage containing 75 g of glucose. The exercise trial consisted of 20 min of submaximal exercise at 74 +/- 1% VO(2max) immediately followed by a time trial. Based upon the plasma glucose nadir reached during submaximal exercise, subjects were assigned to a Hypo group (<3.5 mmol/L) and a Non-hypo group (> or =3.5 mmol/L). An oral glucose tolerance test was performed to obtain an index of insulin sensitivity (ISI). The plasma glucose nadir during submaximal exercise was significantly lower (p <.01) in the Hypo-group (n = 10) compared with the Non-hypo group (n = 10) (2.7 +/- 0.1 vs. 4.1 +/- 0.2 mmol/L, respectively). No difference was found in ISI between the Hypo and the Non-hypo group (3.7+/-0.4 vs. 3.8 +/- 0.5, respectively). The present results suggest that insulin sensitivity does not play an important role in the occurrence of rebound hypoglycemia.