It is well documented that acute carbohydrate (CHO) supplementation can enhance exercise performance across a range of exercise intensities and durations. Yet, less is known about CHO supplementation during maximal sprint interval exercise (SIE) - the performance of exercise at an ‘all-out’ or ‘supramaximal’ effort, separated by periods of active or passive recovery.
Only a few studies have investigated the effects of CHO ingestion on repeated maximal SIE performance and associated physiological responses. These previous studies have reported a beneficial effect of acute CHO ingestion on repeated sprint performance versus placebo, versus CHO and caffeine combined, and versus CHO mouth rinse conditions.
However, possibly the most frequently used SIE protocol for anaerobic/aerobic training involves several consecutive 30 second maximal efforts, separated by ≥ 3 min of passive recovery and no studies have investigated the role of CHO supplementation with interval durations of 30 seconds.
The purpose of the present investigation was to assess the effects of acute CHO supplementation during repeated, longer duration, maximal sprint interval exercise, on indices of cycling performance and associated physiological responses.
Ulster Uni researchers therefore carried out a study on 15 active young adults which compared the influence of carbohydrate consumption versus a placebo during interval durations of 30 seconds.
The study report, published in Nutrients, concludes that CHO ingestion has no impact on performance or physiological responses.
"These findings question the potential ergogenic value of CHO for repeated maximal sprint performance for SIE of longer durations than previously observed in literature. This study also provides novel insights with specific reference to performance during intervals of longer duration, which until now, have not been reported. Thus, the results of the study are important to consider when fuelling for training and performance."
The randomised, double-blind, placebo controlled, crossover study using a sample of fifteen physically active (moderate intensity physical activity at least 2–3 times per week) males and females, aged 20-24.
They were randomised into two conditions: carbohydrate supplementation and placebo. Participants each visited the laboratory on two occasions to perform a bout of SIE (4 × 30 s maximal sprints on WattBike). Ten minutes prior to and during the bout of SIE, participants consumed either a carbohydrate solution or a placebo. Participants were asked to maintain an identical nutritional intake 24 h before each visit to the lab, with participants’ last food intake (breakfast) about three hours prior to exercise.
Pre-exercise blood lactate and heart rate were taken at rest, following completion of the warm-up and approximately one minute prior to SIE. Participants then performed four bouts of SIE, consisting of repeated maximal effort for 30 seconds at a standardised air resistance of level 6, followed by 3.5 minutes of passive recovery following each interval.
The primary outcomes of interest in this study were peak and mean power output during each sprint. Power output was measured (100 Hz) continuously during each sprint.
Relative peak power output (RPPO) and relative mean power output (RMPO) were calculated by dividing the absolute power outputs by body mass.Physiological responses, including oxygen uptake, respiratory exchange ratio (RER), blood lactate concentrations, heart rate, and ratings of perceived exertion (RPE) were secondary outcomes of this study.
At first glance, the results of the current investigation appear to contrast with previous studies, which have concluded that CHO supplementation improves SIE performance. However, the current study's authors argue there are aspects of the previous studies which can be critiqued.
The report states: "Lee et al. found that ingestion of an 0.8 g/kg−1 solution had a significant performance effect on peak and mean power output, and total work versus placebo, in young, female athletes. However, on further examination, this performance effect was only evident during one of the sets (set 6), out of the total of 10 sets completed, with negligible effects observed throughout the rest of the bouts.
"Another study by Pomportes et al. also reported a beneficial impact of acute CHO ingestion (7% CHO solution) on peak power output and perceived tiredness (a surrogate index of fatigue). However, it is worth noting that these conclusions were based on inferences made using magnitude based inferences (MBI), with ‘most likely positive’ and ‘likely positive’ effects of CHO supplementation reported for peak power and tiredness, respectively.
"The MBI approach has recently received substantial scrutiny for failing to adequately control type 1 error rates (i.e., false positives), particularly for effects characterised as ‘likely’. Furthermore, the study of Pomportes et al. also reported (alongside MBI) no significant effect on either variable when assessed using a repeated measures ANOVA. Finally, Krings et al. also investigated the influence of acute CHO ingestion (300 mL of a 10% CHO solution) on repeated maximal sprint interval performance.
"The results of this study reported significantly greater mean power output and total work, and significantly lower fatigue index, in the CHO ingestion condition, compared with a CHO mouth rinse condition.
"Critically, however, there were no differences in performance variables, compared with either an ingested or mouth rinse placebo condition, thus, inferring that other factors aside from the ingested CHO may have been associated with the performance differences between the conditions."
The authors note that there were a number of limitations in their own study.
They did not quantify/analyse/prescribe nutritional intake in the 24-h period prior to each trial, which could have meant that glycogen stores and blood glucose levels may have been different upon commencing exercise.
Objective measures of participant training/fitness status were not conducted, which could affect responses and recovery to SIE and they did not perform any mechanistic/biochemical measurements.
McMahon. G., and Thornbury. A.