The nation's retirement assets hit a record $16.4 trillion last year, representing an 11% rise versus 2005 and a 55% jump since 2002, according to a study published by the Investment Company Institute.
   The upswing was fueled by growth in employer-sponsored defined contribution plans and individual retirement plans, which combined comprised slightly more than half of the retirement assets. The other half was spread across annuities, government pension plans and private defined benefit plans.
   The study demonstrated the growing popularity of lifestyle and lifecycle funds. The former allocates assets based on investors' risk tolerance; the latter change the allocation mix to more conservative weightings as investors get closer to their retirement target date.
   According to ICI, a trade group for the mutual fund industry, these two fund groups combined increased 50% in 2006 after they grew 57% in 2005.