I purchased the Skins Bio A400 after being on the skins website and reading into the compression technology and theory behind it all, after being on the website i searched for reviews on the product but there are not many about. The top arrived promptly within 2 days of placing order, the first thing i noticed was the packaging very well put together and gave a full description of the what was inside. I am 6ft 2in 86kg with a 42in chest so using the skins size guide on the website i ordered LARGE, as i found that on some websites selling this top the size guides they were using was a generic guide for all products and i know that sizing for skins is slightly different. So before buying check the skins web page for size then order using that as your guide. The large fits perfectly, yes its still very tight but that is its design. I run most days and i am in the gym as well, i do know a little about what they say this product does, how it helps get oxygen into the muscles to allow you to work harder for longer and how it will help recovery times and in all honesty i have not felt a difference in either and i have given the top a fair crack at the whip i have not worn it for just one training session then based my review on it, i have worn it for a full weeks training cycle. I reckon it works like a placebo because it makes you look like the advertising pictures making you feel like superman and if you look good you feel good and when out for a run that can have a powerful effect, i agree with what the other review says that if you do have body fat even a small amount this top will make you look like a whale and you would feel more comfortable wearing a t-shirt over the top. all in all a great training top great quality can not see it ever falling apart thats why it got 4 stars from me.