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We examined associations among myostatin (MSTN) 2379 A > G and 163 G > A and follistatin (FST) −5003 A > T and −833 G > T single nucleotide polymorphisms (SNP) on the muscle size and the strength response to resistance training (RT).Subjects (n = 645, age = 24.1 ± 0.2 yr, body mass index [BMI] = 24.2 ± 0.2 kg·m−2) self-disclosed themselves as Caucasian (78.9%), African American (3.6%), Asian (8.4%), Hispanic (5.0%), or Other (4.2%). They were genotyped for MSTN 2379 A > G (n = 645), MSTN 163 G > A (n = 639), FST −5003 A > T (n = 580), and FST −833 G > T (n = 603). We assessed dynamic (one repetition maximum [1RM]) and isometric (maximum voluntary contraction [MVC]) muscle strength and size (cross-sectional area [CSA]) of the elbow flexors before and after 12 wk of unilateral upper-arm RT. Repeated-measures ANCOVA tested associations among genetic variants and muscle phenotypes with age and BMI as covariates.Baseline MVC was greater among African Americans who were carriers of the MSTN G2379 allele (AG/GG, n = 15) than the A2379A homozygotes (n = 8; 64.2 ± 6.8 vs 49.8 ± 8.7 kg). African Americans who were carriers of the FST T−5003 allele (n = 12) had greater baseline 1RM (11.9 ± 0.7 vs 8.8 ± 0.5 kg) and CSA (24.4 ± 1.3 vs 19.1 ± 1.2 cm2) than African Americans with the A-5003A genotype (n = 14; P < 0.05). No MSTN or FST genotype and muscle phenotype associations were found among the other ethnic groups (P ≥ 0.05).MSTN 2379 A > G and FST −5003 A > T were associated with baseline muscle strength and size among African Americans only. These ethnic-specific associations are hypothesis generating and should be confirmed in a larger sample of African Americans.