en Nutrition Nutrition پژوهشي Research <strong>Background and Objectives: </strong>One of the important factors in comparative athletes, especially swimmers, is respiratory function and respiration regulation during training and competition. The purpose of this study was to investigate the effect of 14 days of beta-alanine supplementation on first and second ventilatory threshold of the male swimmers.<br> <strong>Materials and Methods: </strong>Fourteen&nbsp;male swimmers were randomly divided into two groups, including supplementation (S) (age, 30.67 &plusmn; 6.34 years and BMI, 23.71 &plusmn; 2.28 kg/m²) and placebo (P) (age, 32.63 &plusmn; 10.26 years and BMI, 25.16 &plusmn; 2.51 kg/m²). The supplementation group took beta-alanine 2-3 g∙day^-1 in first week and 4-6 g∙day^-1 in second week whereas the control group took dextrose for two weeks instead but in same way. The respiratory indices of subjects were measured using cardio pulmonary exercise testing. Independent sample t test and paired-sample t test was used to compare the outcomes between and within groups respectively. The significance level was assumed as 95% for all cases (p<0.05).<br> <strong>Results: </strong>The results showed that &beta;-alanine supplementation increased first and second ventilatory threshold (VT₁ and VT₂respectively) in S group (p&le;0.05). However, there was no significant difference between groups for VT₂.<br> <strong>Conclusions: </strong>Two weeks of beta-alanine supplementation with a dose of 2-6 grams per day provides a sufficient stimulus to improve the competitive ability of swimmers.<br> &nbsp; Beta-alanine, Respiratory indexes, Swimmers performance, First ventilatory threshold, Second ventilatory threshold 17 22 http://nfsr.sbmu.ac.ir/browse.php?a_code=A-10-618-1&slc_lang=en&sid=1 Ali Arjmandpanah Eilaki a.arjmand1991@gmail.com 10031947532846003068 10031947532846003068 No University of Birjand Mohammad Esmaeil Afzalpour mafzalpour@birjand.ac.ir 10031947532846003069 10031947532846003069 No University of Birjand Reza Bagheri Bagheri@um.ac.ir 10031947532846003070 10031947532846003070 No Ferdowsi University of Mashhad Mohammad Mosaferi Ziaaldini mosaferi@um.ac.ir 10031947532846003071 10031947532846003071 Yes Ferdowsi University of Mashhad