Wall Street has lost momentum since the start of August, triggered by a series of bank downgrades, fears of higher rates for a longer-than-expected period and China slowdown. The Federal Reserve Chair Jerome Powell, in the Jackson Hole symposium on Friday, warned that the central bank is prepared to raise interest rates further and keep borrowing costs high until inflation comes in the target range of 2%. Mid-cap investing can be a strong option in volatile stock markets, offering a unique balance between growth and stability, diversification benefits and potential for undervalued opportunities.