[General] I used to run

I used to run for 5 kilometers daily.

Can we avoid "for" in the above sentence?

You should avoid it. It is incorrect.

You should omit it. "Avoid" is the wrong word.

Picky, picky. :roll:

Do you consider the following wrong?
'for
6 used to talk about distance:
We walked for miles.'── quoted from http://www.ldoceonline.com/dictionary/for_1

It is wrong in that sentence.

Do you mean 'for' should be omitted in that sentence?

Mike, you can't be serious. "We walked for miles" is bad usage?

(That expression has, in fact, been around for a while.)

suniljain said:

I used to run for 5 kilometers daily.

Can we avoid "for" in the above sentence?

Click to expand...

You can say "I used to run five kilometers a day." Small numbers are usually written out.

Is it uncommon, unnatural or ungrammatical to use 'for' in the OP's sentence?

It is unnatural in the original sentence.

I used to run five kilometres every day. :tick:
I used to run for five kilometres every day. :cross:

We ran for miles. :tick:

In colloquial BrE, "for" can be omitted from that usage too.

A: What did you do with your mum yesterday?
B: We went for a walk. My legs really ache - we walked miles!

Matthew Wai said:

Is it uncommon, unnatural or ungrammatical to use 'for' in the OP's sentence?

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It's not ungrammatical, but I'd say it's uncommon and unnatural. Oddly, it would be completely normal to say "I run for miles" or "for miles and miles every day."

emsr2d2 said:

<snip>
We ran for miles. :tick:

In colloquial BrE, "for" can be omitted from that usage too.

A: What did you do with your mum yesterday?
B: We went for a walk. My legs really ache - we walked miles!

Click to expand...

In AmE, that dialog would be
A: What did you do with your mom yesterday?
B: We went for a walk. My legs really ache - we walked ​for miles!

That was not the sentence under discussion. Do you think "for" is needed in "I used to run for 5 kilometers daily"? You can't be serious. Ah! I see what happened. Matthew changed the sentence.

You say you run a certain distance or run a race/marathon.

But you run for 30 minutes, run for miles, run for hours or run for keeping fit.

tedmc said:

You say you run a certain distance or run a race/marathon. :tick:

But you run for 30 minutes :tick:, run for miles :tick:, run for hours :tick: or run for keeping fit. :cross:

Click to expand...

See above. You run to keep fit.

Ems
While I agree that "run to keep fit" is the common way of saying it,
is "run for keeping fit" wrong?

You run for a purpose.
The purpose is keeping fit(gerund).
So, you run for keeping fit.