Save for a final blast of winter cruelty, spring should be settling in for good across most of the country any time now. And that means goodbye treadmill until next winter.

It also brings that double-edged sword of rising temperatures. Those of us who use the words "only" and "10K" in the same sentence — back-to-back and in that order — like it when the weather warms up, but there is a limit.

The hotter it gets, the harder it is to perform. Throw in high humidity and you're bagged before you get out the door.

A study published in the latest issue of Medicine & Science in Sports & Exercise backs that up. Researchers looked at the impact of weather on the performance of athletes at several marathons, including Boston, New York and Vancouver. In the case of Boston, they looked at results over the past 36 years.

They found that when the heat was on, performance suffered — especially for slower runners. The longer you're on your feet in the heat, the more you're affected.

That's pretty much a no-brainer. Take Boston in 2004. The temperature at race time was around 30 degrees. The winner — Timothy Cherigat of Kenya — finished in two hours 10 minutes and 37 seconds. Two years later, another Kenyan — Robert K. Cheruiyot — set a course record of two hours seven minutes and 14 seconds in ideal conditions, with the temperature hovering around 15 degrees.

The performance disparities get even greater when you look further down the field. In 2006, a finishing time of three hours and 15 minutes would have meant finishing among the top 3,000 runners. In the heat of 2004, recording that same time would have placed you 826th.

I staggered across the line in four hours, nine minutes and 58 seconds in 2004, in 7,406th place. Out of the 17,500 runners who started the race, more than 1,000 needed medical attention because of the heat.

It was a similar story this year in Los Angeles. The temperature hit 27 degrees. Fred Mogaka — yes, from Kenya — won the race in a time of two hours 17 minutes and 14 seconds. Last year, Benson Cherono — from guess where — crossed the line in two hours eight minutes and 40 seconds — with the temperature in the upper teens. Again, ideal conditions.

Didn't do too badly myself in the heat and smog of LA this year. Must've been a very dry heat.