Amino acids supplementation is effective not only to improve sport performance but also preservation of athletes' physical conditions. Many studies which investigated effects of amino acids supplementation usually adopt high dose of amino acids, whereas effects of lower dose of amino acids intake are still unclear. Pre-exercise intake of lower amounts of peptide form of amino acids, which can be more rapidly and efficiently absorbed than amino acids itself, may have positive effects on athletes' conditioning especially during in-season.
PURPOSE: To investigate the effects of pre-exercise supplementation with lower dose of soy peptide on serum creatine kinase (CK) level and psychological fatigue in soccer players through in-season. METHOD: Sixteen Japanese collegiate soccer players volunteered to participate in this study which was carried out in double-blind manner. The subjects were divided into two groups of soy peptide (SP) group (N=8, age; 19.1 ± 0.6 yrs, height; 174.3 ± 4.8 cm, weight; 65.6 ± 3.5 kg), and placebo (Pl) group (N=8, age; 19.6 ± 1.4 yrs, height; 172.3 ± 6.3 cm, weight; 66.8 ± 5.9 kg). SP group was instructed to take 4,000 mg/day of soy peptide supplement one hour prior to matches or training sessions for 8 weeks, while Pl group was administrated placebo which was mainly composed of isocaloric dextrin powders. To assess physical and psychological aspects of the players' condition, serum CK level and profile of mood states (POMS) were utilized as conditioning parameters. These parameters were measured before and during the intervention period.
RESULTS: Serum CK level of SP group was significantly lower than that of Pl group at the 5th week (194 ± 115 vs. 355 ± 143 U/L, p<0.05), and statistically lower trends were also observed at the 1st (248 ± 108 vs. 426 ± 235 U/L, p=0.07) and 8th week (220 ± 134 vs. 506 ± 411 U/L, p=0.08). There were no significant differences in fatigue scores of POMS.
CONCLUSION: Pre-exercise supplementation with 4,000 mg/day of soy peptide can suppress elevations of serum CK level, but did not affect on subjective fatigue level in soccer players through 8 weeks of in-season.