Amplification efficiencies and R2 values of standard curves of potential reference genes and target genes for reverse transcription-quantitative PCR (RT-qPCR) experiments in skeletal muscle of growing mice. Standard curves were constructed from six cDNA dilutions of a pool of samples of 2-, 4- and 9-week-old normal animals. Amplification efficiencies of each pair of primers were calculated from the slope of the curves, obtained by linear regression, according to the equation E% = (10(−1/slope) − 1) × 100%.