Relationships between pretraining muscle molecular and cellular measures and percent strength gain after 12 weeks of high-intensity progressive resistance training of the thigh muscles for older adults (N = 7, Age 69 ± 6 yrs). (A). Pearson correlation between the number of macrophages and IGF1 mRNA. The number of macrophages staining positive for CD163 by immunohistochemistry were counted per myofiber. IGF1 mRNA was measured using quantitative real-time reverse transcriptase polymerase chain reaction. (B). Pearson correlation between the number of muscle macrophages and strength gain for knee extension. One outlier was excluded from these analyses due to having macrophage levels that were fourfold higher than the group average.