Carbohydrate intake before and during high intensity exercise with reduced muscle glycogen availability affects the speed of muscle reoxygenation and performance.

Muscle glycogen state and carbohydrate (CHO) supplementation before and during exercise may impact responses to high-intensity interval training (HIIT). This study determined cardiorespiratory, substrate metabolism, muscle oxygenation, and performance when completing HIIT with or without CHO supplementation in a muscle glycogen depleted state. On two occasions, in a cross-over design, eight male cyclists performed a glycogen depletion protocol prior to HIIT during which either a 6% CHO drink (60 g.hr-1) or placebo (%CHO, PLA) was consumed. HIIT consisted of 5 × 2 min at 80% peak power output (PPO), 3 × 10-min bouts of steady-state (SS) cycling (50, 55, 60% PPO), and a time-to-exhaustion (TTE) test. There was no difference in SS [Formula: see text], HR, substrate oxidation and gross efficiency (GE %) between CHO and PLA conditions. A faster rate of muscle reoxygenation (%. s-1) existed in PLA after the 1st (Δ - 0.23 ± 0.22, d = 0.58, P < 0.05) and 3rd HIIT intervals (Δ - 0.34 ± 0.25, d = 1.02, P < 0.05). TTE was greater in CHO (7.1 ± 5.4 min) than PLA (2.5 ± 2.3 min, d = 0.98, P < 0.05). CHO consumption before and during exercise under reduced muscle glycogen conditions did not suppress fat oxidation, suggesting a strong regulatory role of muscle glycogen on substrate metabolism. However, CHO ingestion provided a performance benefit under intense exercise conditions commenced with reduced muscle glycogen. More research is needed to understand the significance of altered muscle oxygenation patterns during exercise.

The effect of acute manipulation of carbohydrate availability on high intensity running performance, running economy, critical speed, and substrate metabolism in trained Male runners.

Completing selected training sessions with reduced glycogen availability is associated with greater signalling and improved muscle oxidative capacity, although it may impact the overall quality of the session. We examined the effects of low carbohydrate availability on high intensity exercise performance, running economy, critical speed, and substrate metabolism. On two occasions, nine male runners (V̇O2peak 60.3 ± 3.3 mL.kg-1.min-1) completed a glycogen depletion protocol involving 90-min at 75%vV̇O2peak followed by 10 × 1-min at 110% vV̇O2peak. This was followed either by high (HIGH) or low (LOW) carbohydrate intake (>6 g.kg-1.day-1 and <50 g.day-1, respectively) until completion of a performance protocol on day 2 consisting of a series of time-trials (TT) (50m to 3000m) and physiological assessments. There were no differences between LOW and HIGH for any TT distance (mean TT performance times for LOW and HIGH were: 3000m TT 651.7 ± 52.8s and 646.4 ± 52.5s, 1500 m TT 304.0 ± 20.2s and 304.2 ± 22.1s, 400 m TT 67.64 ± 4.2s and 67.3 ± 3.8s, 50 m TT 7.27 ± 0.44s and 7.25 ± 0.45s, respectively, P > 0.05), though some athletes performed better in LOW (n = 5). While fat oxidation in LOW was significantly greater than HIGH (Δ0.32 ± 0.14 g.min-1; P < 0.001 at 14 km.h-1 and Δ0.34 ± 0.12 g.min-1 at 16 km.h-1; P < 0.01), running economy did not differ between trials (P > 0.05). Acute manipulation of carbohydrate availability showed immediate effects on substrate metabolism evidenced by greater fat oxidation without changes in RE. Acute low carbohydrate availability did not affect high intensity running performance across a range of distances.Highlights Acute manipulation of muscle glycogen availability using an exercise and dietary manipulation protocol did not affect subsequent high intensity running performance across a range of running distances.Reduced muscle glycogen resulted in a marked increase in fat oxidation in low glycogen condition but no changes in running economy or critical speed.Individual factors should be considered when prescribing high intensity sessions with restricted carbohydrate availability.

A three-minute all-out test performed in a remote setting does not provide a valid estimate of the maximum metabolic steady state.

PURPOSE: The three-minute all-out test (3MT), when performed on a laboratory ergometer in a linear mode, can be used to estimate the heavy-severe-intensity transition, or maximum metabolic steady state (MMSS), using the end-test power output. As the 3MT only requires accurate measurement of power output and time, it is possible the 3MT could be used in remote settings using personal equipment without supervision for quantification of MMSS. METHODS: The aim of the present investigation was to determine the reliability and validity of remotely performed 3MTs (3MTR) for estimation of MMSS. Accordingly, 53 trained cyclists and triathletes were recruited to perform one familiarisation and two experimental 3MTR trials to determine its reliability. A sub-group (N = 10) was recruited to perform three-to-five 30 min laboratory-based constant-work rate trials following completion of one familiarisation and two experimental 3MTR trials. Expired gases were collected throughout constant-work rate trials and blood lactate concentration was measured at 10 and 30 min to determine the highest power output at which steady-state [Formula: see text] (MMSS-[Formula: see text]) and blood lactate (MMSS-[La-]) were achieved. RESULTS: The 3MTR end-test power (EPremote) was reliable (coefficient of variation, 4.5% [95% confidence limits, 3.7, 5.5%]), but overestimated MMSS (EPremote, 283 ± 51 W; MMSS-[Formula: see text], 241 ± 46 W, P = 0.0003; MMSS-[La-], 237 ± 47 W, P = 0.0003). This may have been due to failure to deplete the finite work capacity above MMSS during the 3MTR. CONCLUSION: These results suggest that the 3MTR should not be used to estimate MMSS in endurance-trained cyclists.

Cardiorespiratory parameters of exercise capacity in a healthy Lithuanian population: the pilot study.

INTRODUCTION: The normative values of exercise capacity used for the interpretation of exercise testing results are influenced by a variety of internal and external factors specific to certain populations. Therefore, in clinical practice it is recommended that population-specific reference values be employed. Cardiorespiratory fitness norms have not yet been established for a healthy Lithuanian population over a wide age span. The purpose of the present study was to determine the main cardiorespiratory fitness parameters for healthy adults living in Lithuania and to compare these parameters with the reference values established for different foreign populations. METHODS: This was a cross-sectional, community-based study involving 168 healthy adults aged from 20 to 60 years who were randomly selected from the general population. All subjects performed a progressive incremental exercise test on the cycle ergometer. The main cardiorespiratory fitness parameters analysed were peak oxygen consumption (VO2peak), ventilatory anaerobic threshold, and peak heart rate (HRpeak). RESULTS: The average estimated VO2peak was 35.02 ± 7.37 mL.kg(-1).min(-1) for men and 28.27 ± 6.33 mL.kg(-1).min(-1) for women. According to the results presented by other authors, this parameter is approximately 9-22% lower compared to other populations in all age groups, with the exception of the 20-29 year old group who alone satisfied fair aerobic fitness criteria. The average age-related decline in VO2peak was 0.016 L.min(-1) per year for men and 0.011 L.min(-1) per year for women. However, age itself explained only 12-14% of the variance. After VO2peak was adjusted relative to body mass, the difference in the decline between men and women remained insignificant: VO2peak decrease was 0.34 mL.kg(-1).min(-1) per year for men (coefficient of determination R(2) 0.250) and 0.32 mL.kg(-1).min(-1) per year for women (R(2) 0.330). A decline in peak heart rate of approximately 9 beats per minute was observed in each following age decade, which was well explained by the advancing age (R(2) 0.512 for men and R(2) 0.484 for women). CONCLUSIONS: Cardiorespiratory fitness parameters estimated for healthy adults living in Lithuania appeared to be lower compared to different foreign populations, despite the relatively similar general trends in the age-related decline in exercise capacity. Exercise testing laboratories and rehabilitation clinics in Lithuania may use these results in clinical practice when evaluating patients' exercise capacity, or as a promotional tool for physical activity in the general public.