We have previously found alterations in expression of native myosin isoforms during adaptations to 30 d of stretch-induced hypertrophy in the quail anterior latissimus dorsi muscle (ALD). However, myosin heavy and light chain expression have not been studied during adaptations to stretch. In the current study, expression of myosin heavy and light chains and native myosin isoforms were characterized after placing a weight on one wing of Japanese quail for 0, 7, 14, or 21 d (N = 8 birds.d-1). ALD muscle mass was significantly greater at days 14 (67.0 +/- 4.4%) and 21 (70.2 +/- 4.0%) of stretch compared to day 7 (53.6 +/- 2.9%) of stretch. Native slow myosin-2 (SM2) expression increased from 43.1 +/- 17% in control muscles to 55 +/- 1.2% in stretch muscles, relative to the total myosin pool. The increase in native SM2 expression (approximately 12%) was observed at all three time points of stretch. In contrast, native slow myosin-1 (SM1) expression significantly decreased from 34.1% +/- 1.7% in the control muscles to 24.6 +/- 1.2% in the stretch muscles, relative to the total myosin pool. There was an increased expression of slowly heavy chain-two (SHC2) concurrent with a downregulation of the slow heavy chain-1 (shc1). There was no change in the relative percentages of either slow or fast myosin light chains in overloaded muscles at any of the time points following stretch. These results demonstrate that changes in myosin heavy chain expression, but not myosin light chain expression accompany stretch-induced hypertrophy in the quail ALD.