Positive results were seen after four weeks of supplementation, the researchers reported in their study, published in the Journal of the International Society of Sports Nutrition on Wednesday.
The supplementation and exercise period was on the longer end for studies on the popular pre-workout ingredients.
“Presently, there are studies which have evaluated the effectiveness of L-citrulline or citrulline malate after periods of 7 and 16 days,” they wrote.
“There appear to be no studies involving longer-term (e.g., 8–12 weeks) periods of supplementation.”
Funding for the study came from a grant from Baylor University, with which many of the authors are affiliated, as well as ingredient manufacturer Kyowa Hakko, which also supplied the test ingredients—its commercialized glutathione marketed under the brand name Setria.
Positive link to increased strength after four weeks
The researchers also reported that supplementation was “positively associated with muscle strength.”
They deduced this by equating the participants’ training volume—total weight lifted during the resistance training protocols, which included a variety of presses, rows, and curls—and expressed it relative to body mass.
Though there were no significant differences between groups in terms of volume, they did find a significant relationship between lean mass and strength at week eight for the bench press exercise.
For lean mass and leg press strength, are relationship was observed only at week four.
“More specifically, we observed that, only for the glutathione plus L-citrulline group, the increase in muscle strength was significantly correlated to the increase in lean mass,” compared to the placebo and ‘L-citrulline only’ group.
Not much difference after week eight
Across the board, however, there were no significant differences in body mass, fat mass, and total body water observed after week eight.
“However, the data suggest that [glutathione plus L-citrulline] increased lean mass over placebo after four weeks, and that a similar increasing tendency compared to placebo existed after eight weeks,” they wrote.
They weren’t able to provide a specific explanation to the response, but postulated that this may have occurred because the group was eating less at week eight than at baseline, or with effort exerted during the resistance training sessions, “perhaps related to over-reaching and fatigue.”
More long-term resistance training studies are still needed to generate a better understanding of its mechanisms of action, they added.
Study details
Seventy-five resistance-trained males between 18 and 35 completed the study, randomly assigned in a double-blinded manner to either a glutathione plus L-citrulline group, L-citrulline malate group, or placebo group. There were 25 participants in each group.
Only participants who were non-smokers, considered low risk for cardiovascular disease, and had not consumed any nutritional supplements three months prior to the study were eligible.
Supplements, delivered in capsule form, were ingested one hour prior to exercise. On non-exercise days, participants took their supplement in the morning with breakfast.
For the glutathione and L-citrulline group, capsules contained 200 mg of glutathione and 2 g of L-citrulline per day. The other capsules contained either 2 g of L-citrulline malate or 2.52 g of cellulose placebo per day.
Source: Journal of the International Society of Sports Nutrition
Published online, https://doi.org/10.1186/s12970-018-0235-x
“Eight weeks of resistance training in conjunction with glutathione and L-Citrulline supplementation increases lean mass and has no adverse effects on blood clinical safety markers in resistance-trained males”
Authors: Paul Hwang, Flor E. Morales Marroquín, Josh Gann, Tom Andre, Sarah McKinley-Barnard, Caelin Kim, Masahiko Morita and Darryn S. Willoughby