One of the key findings from this study was that the ingestion of a CPE beverage maintained total distance, average speed and power output in ST2 when compared to PL. At a prescribed exercise intensity, total distance covered significantly decreased by 9.12% from 20.18 ± 0.28 km in ST1 to 18.34 ± 0.36 km in ST2 when participants consumed a fruit concentrate PL. In contrast, there was no significant difference between ST1 and ST2 for total distance covered when participants consumed a CPE beverage. Whilst there were no differences found between conditions for ST1 or ST2, the significant reduction in work output for the PL group does support previous research indicating that CHO ingestion is likely to be more beneficial for longer duration [15, 16] or subsequent high intensity exercise bouts .
Additionally, as there has been previous interest in the effect of CHO beverages in the latter stages of exercise, the decrement in exercise maintenance with the ingestion of PL was also observed in the last 15 minutes of ST2. When participants undertook ST2 during the PL condition, average speed significantly reduced from 27.05 ± 0.39 km.hr-1 in ST1 to 24.75 ± 0.49 km.hr-1 in ST2. This was replicated with a significant reduction in average power output in the final 15 minutes of ST2 of 16.0 W in the PL condition. As the degree of statistical significance was greater at 45 minutes compared with 30 minutes, it can be inferred that the level of fatigue was exacerbated in the last 15 minutes without ingestion of CPE.
The maintenance of submaximal work output observed with CPE indicates the beneficial effects of such beverages on single day repeated training sessions. It is probable that such replication of work output is explained by the maintenance of plasma glucose, especially in ST2. Interestingly, the ingestion of CPE resulted in a greater mean blood glucose in the first exercise bout compared with PL (5.06 ± 0.13 mmol.L-1 and 4.53 ± 0.08 mmol.L-1 respectively), but this did not impact on short term work output in ST1. The maintenance of a higher mean blood glucose was further apparent with CPE in ST2 (4.77 ± 0.08 mmol.L-1 compared with 4.18 ± 0.06 mmol.L-1 for PL), which potentially contributed to overall and end stage work output.
The ingestion of a PL beverage clearly resulted in increased levels of fatigue, demonstrated by significant reductions in power output and total distance covered during ST2 relative to ST1. Concomitant reductions in VCO2, RER and CHOTOT suggest that depletion of endogenous energy stores may be the major mechanism contributing to short term fatigue, particularly in a glycogen-fasted state. With increased utilisation of endogenous carbohydrate, there will be a decreased reliance on glycolytic flux and hence reduced lactic acid production, as demonstrated in the PL condition. With a reduced demand to buffer hydrogen ion production, this likely explains the significantly lowered VCO2 levels observed in ST2 for PL. Whilst mean CHOTOT was observed to decrease in ST2 with CPE (from 2.615 ± 0.216 g.min-1 in ST1 to 2.159 ± 0.132 g.min-1 in ST1), the reduction was not significant, and indicates a relative maintenance of CHOTOT throughout the repeated submaximal exercise. The absolute reduction between submaximal bouts for CHOTOT in the CPE trial could be explained by low carbohydrate ingestion rates used in the study.
Whilst CHOTOT was not assessed during the recovery period, the inclusion of a double bolus of the test beverage at 0 and 60 minutes of recovery resulted in significant differences in mean blood glucose between conditions at 30 minutes (6.30 ± 0.30 mmol.L-1 for CPE and 3.87 ± 0.12 mmol.L-1 for PL) and 60 minutes (5.47 ± 0.27 mmol.L-1 for CPE and 3.82 ± 0.12 mmol.L-1 for PL) of the recovery period. The inclusion of a standard protein bar at 60 minutes into the recovery period was employed to minimise any absolute risk of hypoglycaemia in the PL condition, and to replicate strategies often employed by athletes in daily practice. In the CPE condition a total of 123.1 g of CHO was therefore ingested prior to the start of ST2 in comparison to 17.7 g ingested with the PL condition. Prior to the start of ST2, this would have equated to a total CHO ingestion rate of 0.59 g.min-1 for the CPE condition. This is considerably below the 1.0-1.2 g.min-1 suggested saturation range of intestinal glucose transporters [16, 18], yet still infers an ergogenic benefit.
There has been much, and often controversial interest, in the potential performance ergogenic effects of CHO beverages both for shorter duration exercise sessions, as well as repeated bouts. It is widely known that in the absence of sufficient CHO, absolute work output will gradually decline with exercise duration and intensity, based on both liver and muscle glycogen depletion rates, and associated mechanisms of intracellular fatigue. In this study, the use of a CPE beverage did not confer performance advantages in PT1 compared to PL, with average power outputs being comparable (134.21 ± 4.79 W for PL and 136.82 ± 3.80 W for CPE). Interestingly, in PT1, mean distance when consuming CPE was 0.91 km greater than PL, which comprised a 4.2% overall improvement comparable to other studies .
The lack of statistical significance between conditions for PT1 however do conflict with other studies both for cycling  and running tests . In the latter study, the ingestion of a 6.4% CHO-E solution 30 minutes before and at 15 minute intervals during a 1-hr treadmill run, significantly improved performance by 2.7%. Both studies proposed that the inclusion of carbohydrate prior to exercise resulted in higher CHOTOT which conveyed the performance increments in the latter stages of exercise. In the current study, carbohydrate ingestion preceded PT1, but not under resting conditions. The lack of difference in CHOTOT between conditions for ST1 suggests that ingestion rates were not of sufficient magnitude to elicit short term performance gains. In the previous study , participants ingested a total of 67.1 g of CHO prior to completion of a time trial (effectively an ingestion rate of 0.75 g.min-1). In the current study, participants ingested a total of 35.4 g CHO prior to completion of PT1 (an effective ingestion rate of 0.39 g.min-1). It is therefore possible that higher ingestion rates either pre exercise and/or during PT1 may have resulted in significant short term gains.
However, when repeated bouts of exercise are undertaken, the beneficial effects of CPE ingestion appear to be more pronounced. Total distance covered in PT2 was 17.1% greater with the ingestion of CPE compared to PL. The demanding nature of the trials was observed, with a significant 10.3% reduction in total distance covered between trials for the CPE condition (22.55 ± 0.34 km for PT1 compared to 20.23 ± 0.65 km in PT2), potentially explained by the relatively low total CHO ingestion rates employed.
Average power output during (and in the final 15 minutes) of PT2 were significantly reduced in PL, demonstrating the contrasting benefits of CPE. Whilst the type and quantity of CHO has been shown to enhance exogenous CHO oxidation rates [3, 7, 18], late stage performance enhancement may still occur with more conservative ingestion rates. By the start of PT2, during the CPE trial, participants had consumed a total of 158.5 g CHO or 37.3 g.hr-1. Comparable ingestion rates have been shown to enhance late stage exercise performance elsewhere  despite being below known optimal delivery rates of 1-1.2 g.min-1 or 60-70 g.hr-1.
It is most likely that any ergogenic or recovery effects from the CPE beverage are explained by the combination of the maltodextrin and dextrose formulation. It has been demonstrated that the inclusion of multiple carbohydrates will result in higher exogenous carbohydrate oxidation (CHOEXO) rates . The combined uptake of total sugars from the sodium dependent glucose transporter (SGLT1) and GLUT5 intestinal transport mechanisms provides potential for maximal exogenous oxidation rates . Whilst the oxidation rates of both dextrose and maltodextrin are similar, the inclusion of maltodextrin reduces beverage osmolarity, hence increasing the potential for carbohydrate delivery to the intestinal lumen, as well as fluid uptake.
Furthermore, the inclusion of sodium to the test beverage is known to enhance carbohydrate bioavailability . Despite relatively low CHO ingestion rates employed in the current study, an enhancement in both CHO delivery and CHOEXO would still have a resultant sparing or even suppressing effect on endogenous CHO utilisation , as well as maintaining the CHOTOT observed between performance bouts. As CHOEXO rates have typically been shown to plateau after 90 minutes of steady state exercise, this in part explains the ergogenic potential observed in PT2 with CPE.
Alternatively, as CHO ingestion rates were below optimal delivery levels, it is possible that the co-ingestion of protein may have provided additional ergogenic value through increased caloric content. Whilst it has been suggested the addition of approximately 2% protein to a CHO beverage has minimal effect on subsequent performance, or glycogen resynthesis [26, 27], other studies have demonstrated a positive effect of co-ingestion of protein on endurance performance [8, 9, 28, 29] and short term recovery . When carbohydrate-protein beverages have been administered during acute recovery (in comparison to an iso-energetic carbohydrate beverage), there is supporting evidence that the addition of protein positively enhances repeated same day time to exhaustion trials [31, 32]. The most likely explanation for this is the higher caloric content of the beverages employed, in comparison to lower dose carbohydrate only beverages . In the current study, as the protein intake for CPE was only 0.6% or 2.84 g per 40 g serve, any enhancement of acute recovery through insulin-mediated pathways would most likely be explained via the inclusion of a standard protein bar between exercise trials.
In terms of short term recovery post trials, the only significant observations from this study were reductions in mean quadriceps soreness, mean vastus lateralis soreness and mean distal vastus lateralis soreness by day 3. This was expected considering subjects had a 7 day rest period between trials, hence explaining the gradual reduction in perceived soreness for both conditions. As no differences were found between conditions for post exercise muscle soreness or DALDA responses, the inclusion of early protein feeding (mainly in the form of a protein meal bar) may have assisted recovery in both conditions, as demonstrated elsewhere . It has been suggested that the inclusion of protein to a carbohydrate beverage during early recovery, particularly in higher dosages than the present study, may facilitate intracellular rps6 and mTor signalling pathways leading to enhanced protein resynthesis and hence recovery [34–36]. However, beneficial effects of such beverages on acute glycogen resynthesis is most likely accounted for by underlying carbohydrate dosage and content .