I have treadmill its says it should be plugged into Single outlet surge protector why a single and not a multiple that you just sole plug the treadmill into and what is the best surge protector to buy and from where thanks

Let me ask a couple of questions first. What's on the nameplate in terms of volts, watts, amps, VA and/or HP and it may help form an answer.

Hi well lets it's a proform treadmill says must be 1449 ul rated min 450 joules 120 volts ac and 15 amps voltage rating 400 volts or less

That's the suggested rating of the suppressor, not the treadmill, so I can't comment directly on why not a multiple strip except that a direct plug in has a lower resistance to ground.

As for a recommendation, look at the 1st 3 items on this page:

Tripp Lite Isobar Surge Suppressors

Note the equipment warranty.

I have used their suppressors and have exercised their warranty at work.