Performance issues with clen also vary. Some studies show reduced exercise (cardiovascular) performance with clen (9), while some show that clen can alleviate exercise induced asthma (10)!Clearly, this compound will have different effects on different people, and I suspect that a lot of it is sports specific. Many bodybuilders claim that clen makes it difficult for them to do cardio, yet I can play a full game of rugby on it. You need to figure out how it affects you, and tailor your dose personally.