« I thought that top eyelet was just there for show »: why skipping it is the real reason your toenails turn black
That unused eyelet at the top of your running shoe isn’t decorative—it’s a heel lock designed to prevent your foot sliding forward and your toenails turning black. Most runners never use it, which explains why black toenails are so common after long runs and hikes. The fix is surprisingly simple once you know the technique.