The authors have shown that Cr supplementation 17-AAG is effective in increasing myosin synthesis in vitro and in cultures of differentiating skeletal muscle myoblasts. They also reported that Cr supplementation selectively stimulates the contractile protein synthesis in vitro and might also play a role in muscle hypertrophy [17]. Because of the discrepancies in the literature, it is evident that the exact mechanisms by which Cr can induce muscle hypertrophy are not completely understood.

Here, we are interested in elucidating whether Cr supplementation can play a direct effect in promoting hypertrophy, even when the training workload is similar between supplemented and nonsupplemented muscles. We determined whether Cr-supplemented muscles exhibit greater hypertrophic gain when they are required to perform the same training intensity as the Cr-nonsupplemented muscle. Therefore, we hypothesized that Cr supplementation promotes an additional hypertrophic effect on skeletal muscle fiber cross-sectional area (CSA) independent of increased Sirolimus training intensity on Cr-supplemented muscle compared

with Cr-nonsupplemented muscles. We investigated the soleus muscle because it is highly recruited in our training model [19] and because it possesses lower TCr content and higher Cr transporter protein content when compared with glycolytic muscle, indicating an increased potential for greater Cr uptake [20] and [21]. Moreover, previous studies have shown an inverse relationship between the TCr content of skeletal muscle and the Cr uptake rate [22], suggesting that oxidative

muscle (eg, soleus), with lower Cr total content, exhibits a greater Cr uptake rate than glycolytic muscle (eg, extensor Galactosylceramidase digitorum longus [EDL] and gastrocnemius) [21]. An animal model was used to test the hypothesis that Cr supplementation promotes an additional hypertrophic effect on skeletal muscle fiber CSA independent of increased training intensity on Cr-supplemented muscle compared with Cr-nonsupplemented muscles. For this model, the progressive workloads throughout the training period were the same in the Cr-supplemented (TRCR) and Cr-nonsupplementation (TR) trained groups; the only difference between the groups was the Cr treatment. We tested this protocol to ensure it was an effective manner to investigate the additional hypertrophic effects of Cr supplementation on skeletal muscle independent of a higher training intensity on Cr-supplemented muscle compared with Cr-nonsupplemented muscles. After 5 weeks of training, the soleus muscle was dissected and subjected to morphometrical analysis of fiber CSA. The muscle weight (MW) was normalized by MW-to–body weight (BW) ratio and was used to validate the hypertrophy of the fibers. The animal model is an accurate method to isolate single muscles and perform analysis on whole muscle preparations, reflecting the total muscle response.