Figure 4. Analysis of muscle quality in vitamin D sufficient and insufficient mice. To assess impacts of vitamin D insufficiency on muscle biology, tissues were harvested following 12 months of sufficient (STD) or insufficient (LOW) supplementation. Quadriceps muscle was then analyzed with NADH staining (A) allowing for quantification of the cross-sectional area (CSA) of light stain fibers that corresponds to fast twitch fibers, n=5, 4 respectively (B). Gastrocnemius muscle was analyzed by differential centrifugation to determine myofibrillar, sarcoplasmic, and mitochondrial protein content, n=6 (C). Atrogin-1 expression was also determined in gastrocnemius muscle with western blotting and relative expression (atrogin / tubulin) was quantified using ImageJ software, n=6 (D). Mitochondrial biomass (E) and activity (F) in soleus muscle, n=6, were determined by quantitative PCR and biochemical assays, respectively. Statistical significance indicated by “*” p < 0.05 and “ns” indicating non‑significance.