Paradoxical Effects of High Dose GPLC Supplementation

GPLC is certainly among the more promising carnitines marketed for their ergogenic effects in professional, as well as recreational athletes. Now, a very recent study by Jacobs & Goldstein, which was published in the Journal of the International Society of Sports Nutrition (Jacobs. 2010), indicates that inappropriate dosing may in fact decrease athletic performance.

Of the 45 resistance trained men who participated in the study one group received either 4.5 grams GPLC or 4.5 grams cellulose (PL) 90 minutes before performing two testing sessions; one with, one without GPLC supplementation. The exercise protocol itself consisted of five 10-second Wingate cycle sprints separated by 1-minute active recovery periods. This first test was then followed by a supplementation period where subjects were randomly assigned to receive 1.5 g, 3.0 g, or 4.5 g GPLC per day for a 28 day with another third test following the four weeks of GPLC supplementation using the same testing protocol. The results are quite intriguing:

[...] results indicated that sprint bouts three, four and five produced 2 - 5% lower values of [peak power] PP and 3 - 7% lower values of [mean power] MP with GPLC at 3.0 or 4.5g per day as compared to baseline values. Conversely, 1.5g GPLC produced 3 - 6% higher values of PP and 2 -5% higher values of MP compared with PL baseline values. Values of [percentage decrement of performance] DEC were significantly greater (15-20%) greater across the five sprint bouts with 3.0g or 4.5g GPLC, but the 1.5g GPLC supplementation produced DEC values -5%, -3%, +4%, +5%, and +2% different from the baseline PL values. The 1.5 g group displayed a statistically significant 24% reduction in net lactate accumulation per unit power output (p<0.05).

The graphical presentation renders it even more obvious that in the case of GPLC, as so often, more is not always more:

Figure 1: Mean power in exercise test after 4 week supplementation of 1.5g; 3.0g; 4.5g of PLCAR

So, GPLC is clearly ergogenic, but only if taken in very modest doses. So, if you are going to buy a GPLC containing supplement, you better watch your overall intake in order not to compromise your exercise performance by "carnitine poisoning" ;-)