speed v time

Question
QUESTION: Hello

Which is more effective in burning fat and for cardio and aerobic benefit, just for comparison running at a faster pace for 20 mins or running at a slower pace for 30-40 mins.

Thank you.

Sincerely

Eddie Chan

ANSWER: This is a very interesting question. Lets start with cardio.
For a good cardio workout, the shorter, the faster, the better. Short endurance sprints (say, 400 meters to a mile) get your vo2 max to a threshold. Now most of us can't sprint for 1600 meters. But it's still a vo2 max run, but will also increase endurance. So for cardio, definitely the faster pace with the shorter time.

For burning fat, go with Long Slow Distance. The reason being: in the cardio workouts, if they're short, you're only using your small complex carb storage, and if it's a bit longer, you start using your glycogen storage in your liver(simple carb storage). So if you can run for long enough, the next thing your body burns is fat.

So really your cardio runs and your fat burning runs need to be separate to be the most effective. And of course you don't worry about your cardiovascular health unless you get to where you aren't overweight.

---------- FOLLOW-UP ----------

QUESTION: Hi Jared

Thanks for your answer. If i may ask further, at the moment I am doing tempo running ie I run at a slow pace for the first 10 min and then faster for the next 10 min and slow down again for around 10 mins and fast for next 10 min. The time duration is flexible, but what I am saying is that I incorporate slow and fast in my run. Is this OK? I am basically not a competitive runner, just running to burn fat/calories and for cardio/aerobic benefit.

Your reply is very much appreciated.

Eddie

Answer
If your goal is to slim down AND keep your cardiovascular system healthy, then you are definitely doing okay. Only in your tempo runs, I would recommend the ratio of slow running time to fast running time should be much less. You can't really run that second ten minutes fast...unless your first ten minutes is very slow. I think it would be better to do your ten minute easy pace, then a 3 minute faster pace.
So yes; unless you need serious, hardcore weight loss, keep at this. You're still loosing weight, and your cardiovascular system will want to thank you.