The other day, I ran 10 kilometers.

A comma isn’t necessary for so short an opening statement.

I thought I’d adopted the Jeffing, the Run-Walk-Run method.

I read an article about Fartlek and realized what I did the other day resembled a Fartlek.

However, athe big difference is that Fartlek is the Run-Jog-Run training method, not Run-Walk-Run.

The important point is that infor a Fartlek you should not make a plan.

Or you decide based on your instinct.

its common to use the phrase “based on one’s instinct”

I adopted this core idea when I started running and then started walkjogging the other day.

Hopefully jogging otherwise it wouldn’t be a Fartlek?

I thought I would adopted the Jeffing, the Run-Walk-Run method.

Sometimes you may set a landmark, for example, start running at athe next pole.

Or you decide on your instinctrandomly.

I adopted this corebasic idea when I started running and started walking the other day.

It was really fun for me to do it this way.

I thought I adopted the Jeffing, the Run-Walk-Run methodwas "Jeffing," ,a method where you run, then walk, then run again, but I read an article about Fartlek and realized what I did the other day resembled Fartlek.

I adopted the Jeffing -> I was "Jeffing,": the -ing ending of "Jeffing" turns it into a gerund, as most words ending in -ing are gerunds (Gerunds are verbs ending with -ing; swimming, running, ending, etc). The current way the sentence is written is confusing because it doesn't consider this fact.

the Run-Walk-Run method -> a method where you run, then walk, then run again: Even though it's more concise and is acceptable, it's more natural to explain a method that is unknown to the reader in plain words rather than more complex/compound explanations. ***

***it's also acceptable to say "a Run-Walk-Run" method, as it's less specific because the reader doesn't know if this is the ONLY run-walk-run method, or just one of many.

Append the next sentence to this one.

I read an article about Fartlek and realized what I did the other day resembled Fartlek.

However, a big difference is that Fartlek is thea Run-Jog-Run training method, not Run-Walk-Run.

You should start running and start jogging at random.

Sometimes you may set a landmark, for example, to start running at athe next pole.

verb corrections and article corrections

Or you decide on your instinctther times you just choose on the fly.

"Sometimes" is used in the previous sentence to describe a portion of the decision's circumstances, so "other times" should be used in the next that describes the other portion of the decision's circumstances.

I adopted this core idea when I started running and started walking the other day, and it was really fun.

Append the next sentence to this one.

It was really fun for me to do it.