Journal Title (Medline/Pubmed accepted abbreviation): Int J Sport Nutr Exerc Metab
Page numbers: 311-317
doi (if applicable):
Summary of background and research design:
Background: Metabolic acidosis may contribute to fatigue during long, high-intensity exercise sessions. Increasing the buffering capacity of the blood (increase pH and bicarbonate [HCO3–] levels) through sodium bicarbonate intake has shown to improve intensive exercise tolerance. Oral lactate consumption also increases blood buffering capacity to a similar extent as sodium bicarbonate; however, the limitations of the existing study information have left the exercise performance effects of lactate intake in question.
Hypothesis/Purpose: Evaluate the effects of low-dose calcium lactate on blood buffering capacity and exercise performance during high-intensity cycling.
Subjects: Eleven competitive cyclists with ≥ 1 year of experience and regularly training (mean age, 22 ± 2 yr; weight, 77.1 ± 6.7 kg; height, 175.5 ± 11.7 cm; maximal oxygen uptake [VO2max], 60.5 ± 6.6 mL/kg/min) participated in this study.
Experimental design: Cross-sectional
Treatments and protocol: Each cyclist completed 3 interval performance tests (IPT) separated by ≥ 48 hours and all within 14 days under 1 of 3 conditions: water alone, calcium lactate in water (120 mg/kg body mass), and placebo (aspartame) in water. Fluid was consumed 70 minutes before a 10-minute warm-up (start at 50 W below maximal power output [MPO], determined previously), increased 10 W/minute for 5 minutes, plateaued for 5 minutes, and 25% MPO for 1 minute. The IPT consisted of four 1-minute work intervals at 100% MPO, with 1-minute recovery periods at 25% MPO, and a fifth work period to exhaustion (volitional, or if cadence dropped below 50 rpm for 8 sec). Blood samples for lactate, pH, and HCO3– were collected before fluid intake (baseline) and warm-up, the last 30 seconds of warm-up, and immediately following exhaustion. Levels of perceived illness and stomach ache were determined at the same time points. Time to exhaustion and total work were assessed in the final cycling interval.
Summary of research findings:
- Before warm-up, HCO3– levels in the lactate group were significantly higher than at baseline (P = .04), the placebo group (P < .01), and water group (P = .03).
- HCO3– levels in the placebo and water groups did not significantly change from baseline and were not different from each other.
- HCO3– levels remained significantly higher in the lactate group in the last 30 seconds of warm-up compared with the placebo and water groups (P < .01 and P = .03, respectively).
- HCO3– levels in the placebo and water groups were not different from each other.
- At exhaustion, HCO3– levels had decreased in all groups with no significant differences between groups.
- Blood pH were decreased and lactate levels were increased at exhaustion compared with all the other time points in every group (P < .01 for all pH groups and P < .05 for all lactate groups), but was not different between groups at any time point in the study.
- Lactate levels increased in the lactate group after intake (from 1.00 mmol/L to 1.50 mmol/L before warm-up; P = .07).
- Time to exhaustion was significantly longer in the lactate group compared with the placebo and water groups (P = .02 for both).
- There was no order effect on IPT performance.
- Perceived illness and stomach ache scores were low for all treatments and had little change throughout the study.
Interpretation of findings/Key practice applications:
Substantial metabolic and performance effects from lactate consumption were observed in this study. Timing of lactate ingestion may be an important factor for enhancing exercise performance as peak changes in HCO3– levels have been observed at 80 to 100 minutes after ingestion. Additionally, agents that improve the buffering capacity of the blood may provide performance benefits in intensive interval exercises over those in a single intensive exercise session. Notably, blood pH did not change in this study as the result of the supplementation, whereas previous studies showed a concomitant increase in blood pH and HCO3– levels after lactate consumption. Previous studies used higher lactate doses and different formulations. The increase in HCO3– levels observed in this study could have the buffering capacity to aid muscle contraction, but it is unclear whether HCO3– levels need to increase enough to raise blood pH to optimize muscle performance. Also, the effects on blood from using sodium verus calcium bound to lactate are unknown. A limitation of this study is the use of time to exhaustion and its poor reliability. The results were presented as percentage of improvement to reduce intersubject variance, but time-trial formats may be a more reliable performance measure.