Strontium was tested to see if it could do the job of calcium in helping human sperm work well. The researchers looked at how well sperm wanted to open up their heads when they interacted with human follicular fluid. Sperm left overnight in strontium couldn't do this well, but once put back in calcium, they did better. However, the amount of protein tags, and the fertility of sperm were the same in both cases. Sperm in strontium or calcium could attach to the outer layer of an egg the same way. So, strontium can help sperm get ready for fertilization and stick to eggs, but it can't help them react to certain fluids as well as calcium can.