Investors are bracing for what could shape up to be a very volatile trading session as the Russell 2000 and 1000 indexes get scrambled on Friday.

An estimated $3.8 trillion in assets track the Russell indices; 43 names will head from the Russell 1000 into the Russell 2000; 31 companies will go the other way. Just within the 2000, there will be 186 additions and 107 deletions. There will also be 10 additions to the 1000. Between $1.5 billion and $1.8 billion are expected to flow into both the energy and tech sectors, while financials should see outflows of more than $2.6 billion.

John Eade, President of Argus Research, expects the Russell rebalancing to take on greater significance amid the rise of passive investing.

Meanwhile, health insurance stocks responded positively to the Senate's health care bill, unveiled Thursday, with Aetna (AET) , UnitedHealth (UNH) and Cigna (CIG) gaining steam. 

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