To burn fat without losing muscle there are two options when it comes to cardio and they’re at extreme opposite ends of the spectrum.
You can either do very high intensity cardio (sprint).
Or you can very low intensity cardio (walk).
It’s the midrange stuff that presents a problem for most people.
When you hop on a machine and go at it with moderate-high intensity for 30-40 minutes you will get all of the negative effects associated with cardio (increased cortisol, muscle loss, overuse injuries, decreased power output- meaning you’ll be less explosive, etc.).
Why I Hate “Interval Training”
Many people know that traditional cardio sucks so they recommend intervals.
I personally hate intervals.
On a bike, stair climber, ski machine thingy and whatever else they stock Bally’s and Gold’s with these days…
Especially the rowing machine. Thirty minutes of repeated spinal flexion sounds fun but I think I’ll pass.
According to typical interval training prescriptions you’re supposed to push as hard as you can for 30 seconds followed by a lower intensity period of 90 seconds, or something along those lines.
No matter what anyone says that will also sap your power production because the lactic acid buildup is massive.
Lactic acid is the arch enemy of fast twitch muscle fibers.
Sprint to Lose Fat & Keep Your Muscle
A better option for intervals would be to rage against the machines and get outside and sprint.
But who do you know personally that can sprint for thirty seconds straight? That would be over 200 yards! Talk about an injury waiting to happen.
Yet that’s what interval training enthusiasts regularly advise their normal 40 year old office worker client to do.
To sprint for 30 seconds, followed by a 90 second rest period, over and over for 10-20 minutes straight is nearly impossible for most non-Olympians. And risky as hell.
If you want to sprint like a sprinter.
Not a nitwit.
Start Slowly
Start with short distances and slowly work your way up over time. Take adequate rest periods and slowly decrease them as you get in better shape.
If you’re an average dude it will take you in the neighborhood of 6-7 seconds to run a 40 yard sprint. And that would be a very far distance for your first time sprinting.
I’d recommend sticking with 20’s your first few weeks.
So instead of the silly recommendation of sprinting for 30 seconds straight I advise you to sprint for two or three seconds straight.
HUGE difference. 
It’s funny that intelligent strength coaches who work with high level football players rarely let their athletes sprint at balls out intensity, 40 yards or more during the off season (because the risk of injury is too high), yet fitness trainers recommend that the average lay person head right out to the track and start running 100’s from day one.
People have got to be more responsible than that. It’ll take months to work up to that distance.
Assuming you are sprinting proper distances and taking care to be safe the next question is how long should you rest?
The truthful, nonspecific answer is… as long as you need to.
Keep track of it and try to improve over time. Everyone’s different.
That’s why when people ask me about specific guidelines for hill sprints I tell them I don’t know. I don’t know what kind of shape you are in and what hills you have available to you. Because you’re really limited by the hills you have.
If I told you that you should be sprinting for 15 seconds yet you could make it up the only hill in your neighborhood in eight seconds would you not sprint up the hill?
Don’t Over-Complicate It
You can’t always be a slave to exact prescriptions; sometimes you need to just man up and do work… son.
Your sets, reps, intervals, whatever, are based on your hill and your fitness level.
Now, eventually you may work your way up to being able to sprint your hill for 30 seconds, followed by a 90 second break and repeat that for 20 minutes straight.
So I guess you could say you’re doing intervals at that point. But who cares?
I call them hill sprints. Like Walter Payton did. If you’re sprinting on a football field or a track just say you’re sprinting.
Don’t actually say to anyone that you’re “doing intervals.” That’s so 2004 and so not cool.
If you had absolutely no other option, for whatever reason, than to do intervals on a bike I’d keep the sprints very short and the rest periods as long as necessary, removing almost all tension from the bike while cruising.
You really want to avoid that extreme lactic acid buildup if you want to maintain your power.
A Better Way to Do Interval Training
The best way to come close to traditional interval prescriptions is achieved by performing a variety of exercises such as swings, burpees, med ball slams, battling ropes, mountain climbers, etc. in a circuit.
Mixing it up prevents the massive accumulation of lactic acid in any one area and is far more beneficial than be locked into the versa climber for twenty minutes.
For athletic purposes I prefer to keep the intervals or work times/set duration lower than 30 seconds. Ten to twenty seconds would be a better idea for power athletes.
This type of “interval training” is often associated with the training of combat athletes.
Low Intensity Cardio
As far as the low intensity stuff goes you can walk with a sled, a light weighted vest, walk up hill, walk through the woods or trails or just walk the streets like Omar from The Wire.
Be sure to whistle The Farmer and the Dell to let the suckas know you’re coming.
The best time to do it is first thing in the morning on an empty stomach.
Try to keep your heart rate at around 65% of max for 30 minutes.
The nice thing about this is there is no negative effect at all. No cortisol, no muscle loss, nothing. And you start your day with some nice fresh air which is great for your health and your mind.
This should be done three times per week, minimum. This will help keep you lean while you’re in the process of trying to gain size and will also help you recover more efficiently.
The old days of bulking and cutting are dead.
A smarter approach is to include some high and low intensity cardio methods year round, skip the traditional cardio machines and never let yourself become an out of shape fat ass.
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