After eight consecutive weeks of gains, it is time to consider when strength becomes exhaustion in the stock market.

Overbought Eventually Means Overbought
SPDR S&P 500 (NYSE: SPY) closed up 0.11% in a holiday-shortened trading week. This was the eighth time in a row SPY posted a weekly gain. It was also the smallest weekly gain in the winning streak and the second week in a row the rate of change has declined.

The concept of overbought is a challenging one, and traders have spent countless hours trying to understand it. Many indicators, such as stochastics and Relative Strength Index (RSI), are used to define an overbought market, but they all share a common flaw. At the beginning of a very strong up move, markets become overbought and stay overbought.

The chart below demonstrates the challenge of defining when a market is overbought. SPY is shown with the stochastics indicator. The monthly chart is used to decrease the sensitivity of the indicator, but similar patterns can be seen on weekly and daily charts.

Stochastics became overbought in 2003 and remained overbought until the end of 2007. Bollinger Bands(r) confirm that SPY was overbought throughout that time as prices stayed close to the upper Band throughout the advance.