Journal Title (Medline/Pubmed accepted abbreviation): J Int Soc Sports Nutr
Page numbers: 1-8
doi (if applicable): N/A
Summary of Background and Research Design
Background: Success in endurance sports is related to an ability to continue with relatively high efforts for extended periods of time. While numerous factors underlie exercise capacity, a primary consideration is that of energy demand vs energy supply. It has been demonstrated that acute glycine propionyl-l-carnitine (GPLC) supplementation produces enhanced anaerobic work capacity with reduced lactate production in resistance-trained males. However, it is not known what effects chronic GPLC supplementation has on anaerobic performance or lactate clearance.
Hypothesis/purpose of study: To examine the long-term effects of different dosages of GPLC supplementation on repeated, high-intensity, stationary cycle sprint performance
Subjects:Forty-five, male, resistance-trained individuals participated in the study, of which 38 completed all analyses (baseline characteristics range between doses: age 23.6 to 25.5 yr, weight 84.2 to 89.6 kg, height 173.5 to 179.0 cm). Subjects were between 18 and 35 years of age and had reported participation in at least 2 weekly resistance training sessions over the 6-month period immediately before the start of the study.
Experimental design: Double-blind, randomized independent groups
Treatments and protocol:All subjects were asked to complete 3 testing sessions. The first 2 testing sessions were performed 1 week apart with the third session scheduled after 28 days of GPLC supplementation. The first 2 tests were performed over 90 minutes following oral ingestion of either 4.5 g GPLC or 4.5 g cellulose (PL), in randomized order. Subjects were matched by body mass and then randomly assigned to 1 of 3 study groups. Each group received 28 days of GPLC supplementation in 1 of 3 dosages (1.5 g/d, 3.0 g/d, or 4.5 g/d). During the 1 month supplementation period, subjects were directed to continue with their own individual training and nutritional programs. On testing day 28, subjects were provided with the same dosing as they had taken during the 28-day supplementation period. The testing protocol included 5 high-intensity stationary cycle sprints, each sprint was 10 seconds in duration with a 1-minute active recovery period. Power output variables included peak power (PP), which was determined as the power output established during the first 5 seconds of each 10-second sprint; and mean power (MP), which was the power output measured during the full 10 seconds of each sprint. The third power output variable was a power decrement (DEC), which was calculated as the difference in power output between the first 5 seconds and the second 5 seconds of each sprint, as expressed as a percentage of the first 5-second period. Heart rate, blood lactate levels, and thigh girth of the dominant leg were also measured.
Summary of research findings:
- There were no significant effects of condition or significant interaction effects for PP or MP, despite the changes in PP and MP reported as follows
- Compared with baseline, GPLC 3.0 g or 4.5 g per day resulted in sprint bouts 3, 4, and 5 with
- 2% to 5% lower values of PP
- 3% to 7% lower values of M
- Conversely, 1.5 g GPLC per day compared with baseline values produced
- 3% to 6% higher values of PP
- 2% to 5% higher values of MP
- There was a significant group x condition interaction (P < 0.05) for DEC
- DEC values were significantly greater (15% to 20%) across the 5 sprint bouts with 3.0 g or 4.5 g GPLC.
- DEC values with 1.5 g GPLC supplementation were –5%, –3%, +4%, +5%, and +2% different from the baseline.
- The 1.5-g group displayed a statistically significant 24% reduction in net lactate accumulation per unit power output (P < .05).
- There were no significant effects of GPLC in any dosage or interactions in regard to thigh circumferential measurements.
Interpretation of findings/Key practice applications:
The study findings suggest that increasing daily intake of GPLC has somewhat inconsistent influences on repeated high intensity cycle sprint performance. The current findings suggest that long-term GPLC supplementation at higher dosages (3.0 and 4.5 g/day) did not result in greater values of power output but rather lower mean values of PP and MP. In contrast, the lower intake group (1.5 g/day) achieved mean values of PP and MP greater than baseline across the 5 sprints, with values that are similar to those previously reported with acute intake of 4.5 g GPLC. Unfortunately, the results of this study are not sufficient to definitively explain the apparent decline in sprint performance with higher GPLC intake.
The authors noted several limitations of their study, including a modest sample size that restricted the statistical analyses and some variability within groups that could be attributed to differing levels of compliance with taking the study supplement. Regardless of these potential limitations, these subjects did not display the same main effects for enhancement of power output with reduced lactate accumulation as had been observed in previous studies with acute supplementation. A further point of note is that the serum lactate results were inconsistent. For example, from the 4- to 14-min postexercise period, lactate clearance was improved from baseline to 4 weeks in both the 1.5-g and 4.5-g dosage groups. However, this was not the case for the 3.0-g dose. There are some potentially interesting findings in this paper, but the inconsistent dose effects, and possible ergolytic effects in some cases, indicate that more research is required for GPLC to be considered an ergogenic aid.
NOTE: It appears on Figures 1, 2, and 3 of the article that the authors intended to report percentage change on the vertical axis. However, for that to be the case, all of the decimal values on each of these vertical scales should be multiplied by 100 to be converted to a percentage.