I had a muscle biopsy in my left shoulder and it didn't hurt at all. I could feel them tugging on it and sense when they were cutting it. It was sore for a couple of days. They gave me a prescription for pain pills but I didn't need any. I was undiagnosed at the time & they were trying to find out what I had. Went to a Movement Disorder Specialist & was diagnosed with Parkinson's Disease. Maybe the pain depends on where they take the biopsy and how they do it. EMG's I've had hurt more than the Muscle Biopsy.