I heard you only burn fat for the first 45 minutes?

[RBtrucking4]

I was told that during cardio you only burn fat for the first 45 minutes of your workout then your body starts using other forms of energy can this be true?

 

[mbcrump]

I believe that beyond 45-55 minutes of cardio will usually yield a diminishing rate of return for the time spent. Its still burning fat, just not enough for your time (you would be better doing 45 in morning, then 45 in the evening compared to all at once). Lets see what the pros on here say, I'm still learning myself.

 

[calitrainman]

It really depends on the intensity of the cardio you're doing. If it's high intensity stuff.....mostly carbs will be burned because your body demands a lot of energy immediately. Also, carbs are more readily converted to glucose and used for energy than fat. If it's a low/moderate intensity, a higher percentage of energy will be from fat (high intensity = 85-95% MHR, low/moderate intensity = 25% - 60% MHR)

 

[cyrex]

I was told that during cardio you only burn fat for the first 45 minutes of your workout then your body starts using other forms of energy can this be true?

I'd say that if you want to burn fat the most efficiently stop around 30 min. After you stop, you have fat burning momentum build up and you continue to burn up fat after you stop for a while.

 

[Lifterforlife]

That depends.....on low calories, longer duration/intensity cardio can very well lead to overtraining, thus CNS taxing and muscle wasting.

I believe unless you are an endurance trainee, this would lean somewhere towards fact for most. How many long distance runners do you see that are muscular?

In the end, the body will use whatever substrate is available to it. It is easier to use glycogen up(think of hitting the wall??), than to mobilize FFA's for any intense exercise. I.E...HIIT type cardio. In fact, it cannot do so.

 

[superman40229]

I believe and have had great results walking on a treadmill at around 4.0mph
but my time does not start untill I hit my fat burning heart rate this might be 5 or 10 minutes depending on warm up . Then i walk for 45 min.

 

[cityhick]

I get my heart rate to about 145 with a incline and then go flat at about 4mph. for about 20 min. Everyone is different