Supplemental Creatine Modified With Polyethylene Glycol Effectively Loads Skeletal Muscle With Lower Doses

ABSTRACT: Fry, AC, Parra, ME, and Cabarkapa, D. Supplemental creatine modified with polyethylene glycol effectively loads skeletal muscle with lower doses. J Strength Cond Res 35(5): 1256-1261, 2021-The purpose of this study was to compare the efficacy of skeletal muscle uptake of creatine monohydrate (Cr H2O) with that of creatine bound to polyethylene glycol (Cr PEG). Healthy men (X ± SE; age = 23.5 ± 1.0 years) were divided into control (Con, n = 9, 20 g·d-1 of Cr H2O) and experimental (Exp, n = 8, 10 g·d-1 of Cr PEG) groups. Blood samples and muscle biopsies were used to determine acute gastrointestinal absorption over 5 hours and muscle cellular uptake over 5 days. Both groups exhibited significantly (p < 0.05) elevated concentrations of muscle-free Cr (M·gdw-1; Con, pre = 23.0 ± 4.2, post = 39.2 ± 2.7; Exp pre = 22.1 ± 2.9, post = 33.6 ± 3.2), total Cr (M·gdw-1, Con pre = 94.7 ± 5.4, post = 114.8 ± 7.4; Exp pre = 92.6 ± 5.4, post = 106.6 ± 8.4), which were also elevated when these values were normalized for adenosine triphosphate using molar ratios. Circulatory uptake of Cr was significantly different between the groups, with blood concentrations (mg·dL-1) for the Con group peaking at 2 hours post-ingestion (25.99 ± 2.96), whereas the concentrations for the Exp group were lower and were still rising at 5 hours (4.05 ± 0.87). The integrated area under the curve for the 5-hour postingestion period was 7-fold greater for the Con group. Although total Cr ingested over the 5 days supplementation period was less for the Cr PEG group, skeletal muscle uptake of Cr PEG was similar to Cr H2O. Based on circulating Cr concentrations, it seems that Cr PEG is cleared more slowly from the gastrointestinal tract. Thus, lower dosages of Cr may be ingested while maintaining optimal loading kinetics.