Lactate, fructose and glucose oxidation profiles in sports drinks and the effect on exercise performance

Abstract

Exogenous carbohydrate oxidation was assessed in 6 male Category 1 and 2 cyclists who consumed CytoMax (C) or a leading sports drink (G) before and during continuous exercise (CE). C contained lactate-polymer, fructose, glucose and glucose polymer, while G contained fructose and glucose. Peak power output and VO2 on a cycle ergometer were 408+/-13 W and 67.4+/-3.2 mlO2 x kg(-1) x min(-1). Subjects performed 3 bouts of CE with C, and 2 with G at 62% VO2peak for 90 min, followed by high intensity (HI) exercise (86% VO(2)peak) to volitional fatigue. Subjects consumed 250 ml fluid immediately before (-2 min) and every 15 min of cycling. Drinks at -2 and 45 min contained 100 mg of [U-(13)C]-lactate, -glucose or -fructose. Blood, pulmonary gas samples and 13CO2 excretion were taken prior to fluid ingestion and at 5,10,15,30,45,60,75, and 90 min of CE, at the end of HI, and 15 min of recovery. HI after CE was 25% longer with C than G (6.5+/-0.8 vs. 5.2+/-1.0 min, P<0.05). 13CO2 from the -2 min lactate tracer was significantly elevated above rest at 5 min of exercise, and peaked at 15 min. 13CO2 from the -2 min glucose tracer peaked at 45 min for C and G. 13CO2 increased rapidly from the 45 min lactate dose, and by 60 min of exercise was 33% greater than glucose in C or G, and 36% greater than fructose in G. 13CO2 production following tracer fructose ingestion was greater than glucose in the first 45 minutes in C and G. Cumulative recoveries of tracer during exercise were: 92%+/-5.3% for lactate in C and 25+/-4.0% for glucose in C or G. Recoveries for fructose in C and G were 75+/-5.9% and 26+/-6.6%, respectively. Lactate was used more rapidly and to a greater extent than fructose or glucose. CytoMax significantly enhanced HI.

Figure 1. Time-course of VO₂ (L/min) while exercising at 62% for 90 minutes followed by exercise to exhaustion at 86% of VO₂max during three CytoMax (C) trials and two G trials.

The three C trials and two G trials were randomly ordered. Because no differences existed between trials, the data from the three C trials and two G trials were averaged. Data are means±SE. No difference existed between drinks. * significantly different from rest (p<0.01). † significantly different from steady state exercise (p<0.01). ‡ significantly different from VO₂ during HI (p<0.05).

Figure 2. Time-course of respiratory exchange ratio (RER = VCO₂/VO₂) while exercising at 62% for 90 minutes followed by exercise to exhaustion at 86% of VO₂max during three C trials and two G trials.

The three C trials and two G trials were randomly ordered. Because no differences existed between trials, the data from the three C trials and two G trials were averaged. Data are means±SE. No difference existed between drinks. * significantly different from rest (p<0.05). † significantly different from steady state exercise with the exception of minutes 5 and 10 (p<0.05). ‡ significantly different from HI (p<0.05).

Figure 3. Time-course of blood glucose concentration while exercising at 62% for 90 minutes followed by exercise to exhaustion at 86% of VO₂max during three C trials and two G trials.

The three C trials and two G trials were randomly ordered. Because no differences existed between trials, the data from the three C trials and two G trials were averaged. Data are means±SE. No difference existed between drinks. * significantly different from rest (p<0.05).

Figure 4. Time-course of blood lactate while exercising at 62% for 90 minutes followed by exercise to exhaustion at 86% of VO₂max during three C trials and two G trials.

The three C trials and two G trials were randomly ordered. Because no differences existed between trials, the data from the three C trials and two G trials were averaged. Data are means±SE. No difference existed between drinks. * significantly different from rest. For beverage G, only 5, 10, & 15 min time points significantly different from rest. For C, all time points indicated are different from rest. † significantly different from steady state exercise (p<0.05). ‡ significantly different from blood lactate during HI (p<0.05).

Figure 5. Time-course of CO₂ production (¹³CO₂ appearance in expired air) while exercising at 62% for 90 minutes followed by exercise to exhaustion at 86% of VO₂max during three C trials and two G trials.

The three C trials and two G trials were randomly ordered. * significantly different from G-glu (p<0.05). † significantly different from all other substrates (p<0.05). ‡ G-glucose significantly different from C-lac (p<0.05). Data are means. SE were omitted for the sake of clarity.

Figure 6. Time-course of the cumulative recovery of ¹³CO₂ in expired air while exercising at 62% for 90 minutes followed by exercise to exhaustion at 86% of VO₂max during three C trials and two G trials.

The three C trials and two G trials were randomly ordered. § cumulative recovery of lactate different from cumulative recovery from G-glu (p<0.05). ¥ cumulative recovery lactate different from cumulative recovery from glucose from both drinks (p<0.01). * cumulative recovery different from cumulative recovery from glucose from both drinks and fructose from G (p<0.01). † cumulative recovery different from cumulative recovery from glucose and fructose from both drinks (p<0.05). ‡ time point different from all other time points (p<0.01). Data are means±SE.

Figure 7. 2-hour cumulative recovery of lactate, fructose and glucose from C and glucose and fructose from G during 90 minutes of steady state exercise at 62% VO₂max followed by an 86% VO₂max effort until volitional fatigue.

Total recovery was calculated as the sum of the cumulative recovery. Data are means±SE. * significantly different from C-glu, G-glu, G-fru (p<0.01). † significantly different from C-fru (p<0.01).

Figure 8. Time to exhaustion at 86% of VO₂max after 90 minutes of cycling at 62% of VO₂max while drinking either C or G.

C is the mean±SE of three trials. G is the mean±SE of two trials. Five trials total were carried out in random order. Time to exhaustion while drinking C was significantly longer (6.5±0.8 min) than while drinking G (5.2±1.0, p = 0.05).