Should Your Muscles Burn and Doing a Second Set?

by Kacper

Hey Paul,

I've been using your book religiously now for almost 7 days and am definitely starting to see some results, although its hard to tell as I am currently traveling, and not able to commit to my ideal body building diet.

My main quesiton right now is this:

normally, with lifting weights, if you lift really "well" and burn your muscles out (as they say), the next day you really FEEL it, sometimes for days, that sore feeling. I have become accustomed to this being a sign that my training is working, muscle is being built/used etc.

However, when I do the isometric exercises, I don't really feel that soreness, at all, despite that I really push it to the MAX with the exercise. I do feel EXHAUSTED of course on an energy level, but not really any of that muscle soreness thing.

Is this typical? Am I suppose to feel the soreness to build muscle? Am I doing something wrong? Not putting enough intensity into it?

I got another isometric course and the guy recommends 2 sets, 1 like yours, 7-12 seconds at 100% intensity. the other set at 30%-505 intensity holding for up to 2-3 minutes. I did this a few times and did feel some soreness the next day, but still not as much as when I lifted weights.

Would really appreciate your thoughts on this... Still trying to undo years of confusion about lifting weights and gaining body mass.


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Dec 30, 2011
Part 4 of my answer NEW
by: Paul from

Ultimately it is the nature of the resistance, NOT the movement that exhausts the fibers. If you exhaust them doing a thousand reps over an hour great, you'll stimulate SO fiber. If you tense against a thousand lbs of tension for 12 seconds, ( as in isometrics) then you'll exhaust the SO and FIG fibers and tap into the FG fibers giving you bigger stronger muscles much faster. I personally would much prefer to spend 12 seconds once a week, over 5 hours a week, training. Not to mention that the 12 seconds will develop bigger stronger muscles than then the 5 hours ever could it also saves the joints, builds a better body, strengthens my heart and lungs, improves my immune system and gives me loads more free time. ;-)

Finally, doing another set, or extending the isometrics for longer than 12 seconds or so has a number of negative effects. First it creates similar compression damage to weight lifting - leading to feedback in the blood flow and can lead to increase in cardiac conditions, e.g. heart attacks. Secondly it dramatically can increase blood pressure, a very bad idea - and finally psychologically, you'll hold back the intensity of the contraction so you can last the 30 seconds plus you propose, meaning you WON'T tap into the FG fibers and achieve the right stimulation.

If there was a more effective way of doing it - I would have written it that way ;-)

Hope that helps,


Dec 30, 2011
Part 3 of my answer NEW
by: Paul from

Each fiber type as a different recovery period. Let's break it down - I go into huge detail on fiber types and recovery in Project Dragon but the basics are this -

- Slow Twitch (SO), which are used for repetition and endurance movements, like walking, holding up your head etc. They take little energy and exhaust slowly and recover quickly. In fact, assuming you haven't depleted all of them, they can recover within 90 seconds. They do not result in high muscular tension

- Intermediate Fibers - fibers that can become either Slow or Fast depending on the stimulus. An this group be subdivided further. If you do more endurance based activity eg marathon's they'll mostly become SO. If you spend your time lifting heavy weights explosively they'll mostly become Fast Twitch. These can take between 2-7 days to recover.

Fast Twitch - again there are more subsets to this but basically there's easy access Fast twitch and hard to access fast twitch. These are generally ticker fibers than SO. They are fast to activate, capable of generating huge muscle tension and strength, but last only seconds and can take a minimum of 7 days to several weeks to recover.

Now - in order to build muscle size and strength you need to stimulate your muscle fibers. Those that spend their time doing repetitive movements eg, multiple weight lifting reps and sets or distance and endurance based activity primarily stimulate the development of SO fibers. This takes a long time and is best done using positive and negative movements. The can of course train more frequently - but in doing so they develop thinner tissue, and cause joint wearing, not to mention develop issues with the heart and lungs (again all explained in detail in PD)

A moderate program 3 times a week will hit some of the FIG fibers, but not many. Again, same problems as before.

The strong thick fibers that create muscular strength, the FG fibers are only stimulated under the greatest muscular straining (highest intensity), when the SO and FIG fibers have fatigued - isometrics present the fastest safest way to stimulate these fibers. Greater intensity, means the FG fibers are called into play and as already discussed these only last for 7-12 seconds.

Dec 30, 2011
Part 2 of my answer NEW
by: Paul from

Q:"...the guy recommends 2 sets, 1 like yours, 7-12 seconds at 100% intensity. the other set at 30%-505 intensity holding for up to 2-3 minutes. I did this a few times and did feel some soreness the next day, but still not as much as when I lifted weights."

Different authors will recommend different times under isometric tension. Pete Sisco and John Little (who wrote art of expressing the human body on Lee's training methods) recommend as little as 5 seconds. Mueller and Hettinger recommend upwards of 10. Steve Justa advocates isometric holds for longer than three minutes, as does Matt Furey, and Shroeder. And Bruce Lee varied between 7 seconds and 8 hours. (Yes, he performed an 8 hour isometric hold).

The reason for this is intensity level and fiber stimulation. You can hold an isometric contraction with anything from 1% -100% intensity. Justa advised holds of 35% of max for long periods of time. (Similar to martial arts). Sisco and Little advocate a max contraction approx 90-100% for 5-7 seconds. I recommend a 7-12 second contraction because the majority of people starting these exercises cannot produce a full muscular contraction, even with the best of intentions and trying their hardest most will only produce an 80% contraction so a few additional seconds are recommended. Studies now show that as little as a 1/4 of a second in needed to stimulate growth and strength increases.

My second reason to recommend the 7-12 seconds is based on the energy pathways of the human body - our bodies were designed to exhaust Adenosine Triphosphate (ATP) stores in the muscle last for approximately 2 seconds and the resynthesis of ATP from Creatine/Phosphate (CP) will continue until CP stores are depleted, approximately 4 to 5 seconds. This gives us around 5 to 7 seconds of ATP production. Repeat, 5-7 seconds.

Thus, in order to stimulate your fast twitch fibers (those primarily associated with muscular size, strength and speed), anything after 7 seconds is unproductive. However as I mentioned above, many students when starting CANNOT engage the maximal number of fibers straight off the bat and require upwards of 5 seconds to build to that contraction. Hence my recommendation. Some muscles however have a higher concentration of slow twitch fibers and intermediate fibers and thus require longer tension times to fatigue the muscle fully.

You'll note in those exercises that the intensity of the exercise and the level at which you contract is reduced in consideration of the longer hold time.

The "burn" you is utterly subjective as we've looked at in your previous question and in no way an indication of muscular effort - it differs from person to person and has shown to produce no additional benefits, however it does lead to an increase of stress on the lymphatic system and thus comprises your immune system. Burn is unnecessary.

Now look at the physiology.....

Dec 30, 2011
Feeling the Burn, the nature of intensity and isometric hold times NEW
by: Paul from

Hi Kacper,

Glad you're already starting to see the results. These are two good questions and I'm going to post the questions and my answers in the Perfect Body members forum if that's ok. But I'll answer them directly here too.

First up...

Q:"Am I suppose to feel the soreness to build muscle? Am I doing something wrong? Not putting enough intensity into it?"

No, you're not doing anything wrong at all, you're just used to a bad workout is all. ;-) let me explain.

The soreness you previously experienced is called DOMS. And it has nothing to do with building muscle or how hard or intense you workout.
DOMS tells you nothing. Soreness of the muscles bares absolutely NO correlation to the work done.

Some people feel it, others don't. It is utterly unimportant. The legendary HIIT bodybuilder Mike Metzner NEVER experienced DOMS once in his entire training life.

If you stretch your arm past the point it's comfortable and tense your chest - you'll cause micro tears in the muscle and you'll feel the same type of muscular soreness but you won't be building any tissue. Push yourself each time, then go further, push past the feeling of battery acid the feet shaking and focus on contracting the muscles slowly and steadily. Don't worry about being sore or not. ;-)

On intensity, it's good that you're tired and exhausted after the isometric workout but it should be an energizing kind of exhaustion if that makes sense. When I'm doing my isometrics, I'm pumping sweat, shaking like a leaf and psyched afterwards. Every time I complete a workout it's like I've gone toe to toe with an un-scale-able mountain and climbed it, an incalculably long distance and run it and fought a life and death struggle against the best fighter in the world and beat him. It's the euphoria of victory over the self.


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