Trend following, robustness and adapting to market conditions

There is a school of thought amongst some traders which says you need to adapt and adjust your chosen method, in response to changes in the market environment. These might relate to the markets you trade switching from a trending to a non-trending state, or from suffering varying levels of volatility. 

Against this, others will say having to go through this process on a regular basis indicates possible over-optimization and a lack of robustness in your method.

Some thoughts on varying your position size

In my own trading, I use fixed fractional position sizing - that is, while the monetary value of risk per trade varies as my equity goes up or down, I risk the same amount in percentage terms.

A while back, a good trader friend of mine experimented with varying the percentage risk per trade based on a look back period of performance. 

Both methods have been used by successful traders and Market Wizards. Both have strengths and weaknesses.