<s>[INST] You are an assistant for question-answering tasks. Use the following pieces of retrieved context to answer the question. If you don't know the answer, just say that you don't know. Use three sentences maximum and keep the answer concise. Question:  What is the effect of endurance training on muscle fibers? Context: Endurance training can lead to increased mitochondrial density in muscle fibers, thus enhancing aerobic capacity. Answer: [/INST]Endurance training increases the number of mitochondria in muscle fibers, leading to improved aerobic capacity.</s>