Lipitor is a brand name for the drug atorvastatin, which is a type of medication known as a statin. Statins are commonly used to lower cholesterol levels in the blood, which can help prevent heart disease and stroke. However, there is some evidence to suggest that statins may also affect muscle endurance.

One study published in the Journal of Clinical Lipidology found that patients taking atorvastatin experienced a decrease in muscle endurance compared to those taking a placebo [2]. The study involved 42 healthy adults who were randomly assigned to receive either atorvastatin or a placebo for six months. Participants underwent a muscle endurance test at the beginning and end of the study, which involved performing repeated knee extensions until they could no longer continue. The researchers found that those taking atorvastatin had a significantly shorter time to exhaustion compared to those taking a placebo.

Another study published in the Journal of Clinical Medicine Research found that atorvastatin was associated with a decrease in muscle strength and endurance in patients with metabolic syndrome [3]. The study involved 38 patients with metabolic syndrome who were treated with atorvastatin for six months. Participants underwent a muscle strength and endurance test at the beginning and end of the study, which involved performing leg press exercises until they could no longer continue. The researchers found that those taking atorvastatin had a significant decrease in muscle strength and endurance compared to baseline.

It is important to note that these studies were relatively small and focused on specific patient populations, so the findings may not be generalizable to all individuals taking atorvastatin. Additionally, the studies did not examine the long-term effects of atorvastatin on muscle endurance.

In conclusion, there is some evidence to suggest that atorvastatin may affect muscle endurance, based on the findings of two small studies. However, more research is needed to fully understand the effects of atorvastatin on muscle endurance and to determine if these effects are clinically significant.

Sources:
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3463373/
[3] https://pubmed.ncbi.nlm.nih.gov/28807461/