95 out side with index of 107 or 20 with a feels like of 7.

Just run baby

20 with a wind chill of 7 ANY DAY OF THE WEEK. I cannot take 100-degree heat. Cold alone is no obstacle to a quality workout.

For practice, aside from a long run, I'd choose the heat. It's harder, I like sun and I can just jump in the lake after. For a race or long run, I would take the cold.

So to answer your question, heat.

95 heat index 107

Heat baby Heat

I won't even consider racing this winter after doing so last winter and being miserable. I raced a bunch of times last summer at temps from 85°-95° and it really didn't slow me down too much. On training runs though, I couldn't go much over 8 or 9 miles without getting dehydrated.

The heat definitely. I hate the cold

Cold. I thought everyone was gonna say the cold, guess not

20, "feels like 7" is pretty abstract. Who is the one doing the feeling? A man from Wisconsin or some kid from Florida?

Anyhow 20 isn't that cold and 20 with a wind chill of 7 still isn't that cold.

I think that heat wouldn't hit you too hard on such a short workout although that 10 mile run could be a bitch.

20 rf of 7. I do well in the heat when I'm thin, and cold is riskier for injuries. That's not too bad for 400s with tights, though. It'd have to be below zero before the wind chill for me to pick the heat.

10 miles in the cold with appropriate winter gear.

12 x 1/4 in the heat because I can sip fluids the whole time.

10 miles with a heat index of 107 can be life threatening, especially if you are stubborn like me and refuse to run with a fanny pack!

The question should be amended for the cold: instead, 0 degrees F with a wind chill of -20 degrees F.

Whatever I went with I would be dreaming of the other one when I was doing the workout!

I would say heat. That is insanely hot though. That is feel like you're going to pass the F out after 25 minutes running hot if you're in the sun.

Nothing makes me as miserable as being too cold though.

The cold. The cold isn't going to debilitate me. It is just going to suck.

I was planning on doing a 6 mile tempo at 5:20 this summer in late July, in Central Florida. It was 96 with a heat index of 107 actually. I got 3 miles with splits at 5:45, 5:50, 6:00 and had to quit (ran 9:11 and 4:14 that spring and low 15's for cross this year so that's how bad it was). I've grown up in heat and and trained for like 3 years in heat so I'm as acclaimated as you can get.

So from a Florida kid: cold alllll the way.

You'd never complete the workout in the heat.

Cold is the choice all the way and I'm one who's attempted both.

Heat for intervals and cold for a long run. Plus, the "feels like" almost always implies a wind, which screws with intervals even further. I'll take the heat in almost every situation, except on a long run it's just a nuisance to hydrate through heat for that long when you can just trudge along in the cold with your layers on. If, however, I were doing a long run where I really cared about pace, I think I'd take a heat index instead of a wind.

I'm in florida... so I hate the cold. The only problem with the heat in the summer is it is impossible to run longer than 12 miles unless you are out at 5am or you run at 9pm. Also... you run much slower in extreme heat and humidity. it drains you big time. I have been out running late afternoon where the heat and sun just stop you dead in your tracks.... In 90 mins you can lose 10+ lbs of fluids (starting at 160) which is borderline dangerous.

Definitely the cold. That's only a bit below average winter temperatures here.

Now, -40 windchill would be another story. That is ffffffffucκin cold.

word. when you get an icebeard in 2 minutes you know its cold.

I'm hoping it stays in the teens or 20s this week! that would be nice.

another thing about the heat - it isn't going to snow and ruin any attempts at running fast like the cold will