Comparison of a sports-hydration drink containing high amylose starch with usual hydration practice in Australian rules footballers during intense summer training

In elite high-performance AFL footballers undertaking intensive pre-season training at the peak of an Australian summer, dual-action SpORS hydration drink with an RS preload on the evening before resulted in body weights that were significantly heavier at all three assessment points (pre-training, post training and post recovery) and a consistently lower hematocrit, compared with the Control period when following their usual hydration practices. These results reflect better hydration before training and at the completion of training as well as 30–60 min after commencement of the post-training recovery period.

ORSs containing HAMS have been established to improve outcomes in severe diarrhea in adults and children where the mechanism is high fluid and electrolyte loss even in the face of fever and vomiting, and where dehydration is often present before hydration is commenced [12, 14, 15]. This study is the first to demonstrate the benefit of including HAMS in the sports setting. The mechanisms of fluid and electrolyte losses relate to sweating and transpiration in the sports context and the nature of the electrolyte loss is different from that in the medical setting, hence the adjustment in the electrolyte composition to match that of existing sports drinks. Despite this difference in the pathogenesis of fluid losses, and the pragmatic nature of this effectiveness study, the SpORS Intervention was successful. In the sports setting, dehydration due to vomiting or pathophysiological disturbances causing diarrhea are unlikely; thus it is possible to intervene prior to commencing dehydrating physical exertion both to optimize hydration at commencement as well as to prevent dehydration during exertion.

There are many types of resistant starch [20]. Acetylated HAMS (HAMSA) was selected for this study because it is readily fermented to SCFA by the colonic microflora [13, 21], and the presence of the additional acetate covalently bonded to the HAMS provided an added immediate boost to the rehydration once the HAMSA reaches the colon. It was also chosen because of its proven medical benefits, tolerability in humans and a long history of safe use in foods and its corresponding approved regulatory status as GRAS (generally regarded as safe) by the US Food and Drug Administration. No other RS meets these criteria.

Our primary markers of hydration, namely body weight and hematocrit, were significantly better in the Intervention than the Control periods at the pretraining assessment, consistent with better hydration due to the ingestion of RS the evening before. The presumed mechanism is active fermentation in the colon overnight with increased SCFA production, as previously demonstrated in healthy subjects [16], resulting in better fluid absorption in the colon. This also ensures presence of RS in the colon at the time of exertion and consumption of water (in any form).

The benefit of SpORS on body weight and hematocrit relative to control was maintained during exercise and recovery. Players were instructed to drink as much as they could during this period and given the circumstances of the training, their actual fluid consumption was not able to be determined with precision. During the Control arm, they followed their own usual personal practice which was highly variable in volume, mostly comprising water or Gatorade but also comprised of other personally preferred drinks. It should be noted though that they were asked not to consume these during the second half of exercise or during recovery in the Intervention periods and instead only consume SpORS and water.

While it was not possible to measure total body water content, total body weight is an indirect measure of this. The improvement in hematocrit, the most direct measure of hydration used here, was apparent at all times assessed. Importantly, this was true at the end of the recovery period at which time, blood flow would have been rediverted away from muscles and back to visceral organs, a shift that seems likely to enhance fluid absorption from the gut.

Subjective measures did not reveal any benefits for thirst, refreshment or fatigue, which might be expected under such circumstances but bloating and discomfort were scored higher in the Intervention period. This is an anticipated effect of RS [13, 20, 22] and indicates good compliance with the SpORS Intervention. Players did not find this to be unacceptable, except several who could not tolerate the full 100 g preload. A number of studies reporting these symptoms in subjects consuming RS indicate that after a short period of regular consumption, these symptoms settle [22]. Further studies with repeated use, exploring tolerability of different preload doses and different timing of those doses, are now indicated to determine if symptoms do settle and if there are alternatives to consumption the night before. The decision to ask players to consume it the night before was based on the known oral-cecal transit time of around 6–8 h for solid foods.

The strengths of this study centered around the crossover design, the two intervention and control periods, the short timeframe of the study and its execution in extremely hot weather. No period effects that indicated the effect of treatment were different for the first or second period were observed.

The main weakness was that this was a single blinded study with players being aware of the study arm they were in on each day; it is possible that this could have influenced the amount of fluid they decided to consume. However, the measures reported were objective and not subject to recording bias as the recorders were blinded to the study arm which applied to each participant. The exact intensity of the training on each day was unable to be regulated, however our measures of exercise time and intensity indicated that there were no major differences for the two study conditions (see Table 3). Furthermore, a sensitivity analysis adjusting for intensity of effort made no difference to the results (see Methods).

In the context of undertaking the study in the real-world environment of training, it was not possible to rigidly apply time periods that corresponded to the precise minute, to ensure that exertion was identical between participants. Similarly, it could not determine exactly how much fluid and/or RS had been consumed. However, this reflects the “real” context of training and competition and differences were demonstrated despite this. These constraints also meant that analyses were limited to the measures undertaken in the study and more sophisticated measures of body water content were not practical. Urine collection was problematic in this study and urine specific gravity has been shown to be unreliable over short periods as applied here and does not give an accurate perspective at a given point in time, whereas hematocrit does. [23]. While there was a significant difference across the three timepoints, the actual difference was very small and likely to be of no physiological significance. Based on our observations, undertaking further studies of the SpORS strategy in highly controlled exercise environments with standardized workloads, tightly controlled timing of measurement and efforts to assess fatigue and consequences for performance are now indicated.

The physiological changes associated with dehydration affect player performance [47, 24, 25]. The level of hydration when commencing exercise is also important as relative rate of oxygen uptake, heart rate and rate of perceived exertion were increased if dehydrated when commencing exercise [26]. Dehydration also leads to 13% slower time-trial performance and accelerated muscle glycogen use in cyclists [6], impaired cognitive ability [27], degraded aerobic performance, high-intensity endurance and sports-specific skills [28]. Recovery kinetics of physical performance is also compromised [29].

It is not possible at this point to know exactly what the benefits of this dual-action rehydration strategy are to performance. However, based on what is known about the adverse effects of dehydration on performance, and the benefits to better hydration, it is reasonable to predict that performance benefit will follow. The weight at point A in the Control arm (88.59 kg) is effectively the baseline weight prior to training and without any RS intervention. If this weight is used to calculate the change from baseline to the final weight (point C) in each arm, we obtain a complete estimate of benefit of the rehydration strategy to weight. As can be seen from Tables 2, 0.80 kg was lost in Control arm compared to 0.12 kg in the Intervention arm, a difference of 0.68 kg corresponding to an 85% lower reduction in weight. As a percentage of mean body weight the Control arm lost 0.92% (0.80/87.22) compared with 0.13% (0.12/87.22) in the Intervention arm. Given that fluid deficits of 1.65% and above lead to physical and cognitive impairment, this weight benefit may have a positive impact on athlete performance.