Feigenbaum : Yeah. Just briefly on the protein kidney thing, that’s super interesting to me. I’m actually writing a piece for the Starting Strength website called, “The Problem with Protein and Kidneys,” so it’s not a very sexy title but it’s pretty thorough. There’s actually not evidence to suggest that people eating a higher protein diet have negative changes in their kidney function. There tend to be adaptive changes in how the kidneys filtering and processing basically the blood, that’s effectively what the kidney’s doing, they just keep filtering the blood all throughout the day. It just tends to be an adaptive change. Once you have more protein it just does it a little differently and adapts accordingly. Your body is able to adapt to different things. That’s going to be an interesting article.
The structure of cyclocreatine is fairly flat (planar), which aids in passive diffusion across membranes. It has been used with success in an animal study, where mice suffered from a SLC6A8 (creatine transporter at the blood brain barrier) deficiency, which is not responsive to standard creatine supplementation.  This study failed to report increases in creatine stores in the brain, but noted a reduction of mental retardation associated with increased cyclocreatine and phosphorylated cyclocreatine storages.  As demonstrated by this animal study and previous ones, cyclocreatine is bioactive after oral ingestion   and may merely be a creatine mimetic, able to phosphorylate ADP via the creatine kinase system. 
Alan: In the research I’ve collaborated on thus far, I unfortunately can’t report anything spectacular. In fact, it’s some of the most anticlimactic/unsexy results in the literature (LOL). However, in the most recent RCT of ours that’s in publication (PMID: 28070459), we did report individual data, and one of the subjects showed approximately an 18 mm gain in biceps thickness ( inches), measured via ultrasound, over an 10-week period. The rest of the subjects – all of whom were resistance-trained – stayed pretty much the same, which was not surprising since they were in hypocaloric conditions. It’s interesting to imagine what type of response this high responder would have if conditions were optimized for muscle growth, and/or supplementation was implemented. On the poor responder side, one of the subjects experienced a huge drop in quadriceps thickness (25 mm; about 1 inch) during this study. Interindividual response variability is just the nature of the beast, and a very poignant example of this is work by Ahtiainen et al (PMID: 26767377), who demonstrated vast heterogeneity in subjects’ responses to resistance training. Their study is openly accessible, have a look at this figure showing the full range of differences in strength & size gains (and losses): https:///pmc/articles/PMC5005877/figure/Fig4/. High responders gained 4-5 times the muscle mass of average responders. Of course there are the unfortunate subjects (2% of the subjects were classified as low responders) who included those who experienced losses in size and strength as a result of resistance training (and in my speculation, other factors as well).