Prolonged selective breeding of Hsd:ICR mice for high levels of voluntary wheel running has favored an unusual phenotype (mini-muscle [MM]), apparently caused by a single Mendelian recessive allele, in which hindlimb muscle mass is reduced by almost 50%. We recently described the creation and phenotypic characterization of a population suitable for mapping the genomic location of the MM gene. Specifically, we crossed females from a high-runner line fixed for the MM allele with male C57BL/6J. F1 males were then backcrossed to the MM parent females. Backcross (BC) mice exhibited a 50:50 ratio of normal to MM phenotypes. Here, we report on linkage mapping of MM in this BC population to a 2.6335-Mb interval on MMU11. This region harbors approximately 100 expressed or predicted genes, many of which have known roles in muscle development and/or function. Identification of the genetic variation that underlies MM could potentially be very important in understanding both normal muscle function and disregulation of muscle physiology leading to disease.