The Invesco S&P MidCap Momentum ETF (XMMO) is designed to track the S&P Midcap 400 Momentum Index. It commits at least 90% of its total assets to the component securities of this index. The underlying index itself consists of 80 stocks selected from the S&P Midcap 400 Index. These are chosen based on their superior "momentum scores," which quantify each security's upward price movement relative to other eligible companies within the S&P Midcap 400. Both the ETF and its benchmark index are rebalanced and reconstituted twice a year.