Principal component analysis (PCA) biplots.

<p>Biplots show the correlation vectors representing the projection (in 2 dimensions) of loading for each of the variables (for 27 participants) included in the particular PCA. Vectors project onto the 3 axes (dimensions) of the principal components (PCs) 1 (x-axis), 2 (y-axis), and 3 (z-axis, positive is upward, perpendicular to the page). A. PCA-1, on the full dataset (N = 23 variables). B. PCA-2, Supraspinatus variables only (N = 16). C. PCA-3, variables of interest from previous comparisons, including “muscle” as a variable (N = 15 variables). Variables that loaded onto PC3 (as shown in Tables <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0162494#pone.0162494.t001" target="_blank">1</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0162494#pone.0162494.t003" target="_blank">3</a>) are indicated with an asterisk (*) to emphasize that the correlation vector projects upward, perpendicular to PC1 and PC2 axes. Variable labels on the vectors are abbreviated as follows: C (control muscle), SS (Supraspinatus muscle), BMI (body mass index), Sx-to-Surg (weeks from symptom onset to surgery), diam (fiber diameter), SS:C diam (ratio of fiber diameter in SS/C), SC-base (baseline SC activation in explant cultures), SC-ISDN (SC activation in explants cultured with ISDN), dystr (expression of dystrophin protein relative to β-actin), mmp9 (level of matrix metalloproteinase 9 protein relative to β-actin), logRed (log-transformation of average maximum Sirius Red staining), γ:ε (γ:ε ratio of AchR subunits), γ (expression of the γ-subunit of AchR protein relative to β-actin), and BvD (vascular density).