Most 401k’s should have a SP 500 Index fund or something close, and a guaranteed fund, which is mostly bonds. You can always move into bonds during uncertain periods, and into the SP 500 or equivalent fund during good periods.
Unfortunately, alot of 401k’s are not allowing people to move around alot like this nowadays, so if you make allocation changes, be prepared to sit in your new allocation for awhile, and also be questioned for being a market timer.
They (PPT) are again trying to rig the market to go up by stopping people from timing things. However, it is what it is so be aware of it going in.