Q&A Muscle Fatigue, Inroad, and Intensity

Question: Is there a difference between inroad and fatigue? Some HIT trainers seem to use them interchangeably. What does inroad have to do with exercise intensity?

Answer: Fatigue and inroad are related concepts, but not the same thing. Fatigue is the reduction a muscle’s ability to produce force. Inroad is a measure of fatigue, usually expressed as the percent difference between your starting and momentary strength.  For example, if your strength at the start of an exercise is one hundred units of force and fatigue reduces it to eighty units of force your inroad would be twenty percent.

Inroad is also a measure of the average intensity of an exercise when compared with total exercise time. The higher your intensity of effort during an exercise, the greater your rate of inroad will be. You have to work harder to achieve an inroad of twenty percent within sixty seconds than an inroad of only ten percent, or to achieve an inroad of twenty percent within sixty seconds than within ninety seconds.

Intensity = Inroad / Time

For example, the deadlift is much harder when performed continuously, without setting the weight down between repetitions. When done this way momentary muscular failure will be achieved more quickly than if you rest between repetitions (and some studies suggest this will stimulate greater increases in strength and size).  In either case, if the exercise is performed to failure you will have reached maximum intensity, but if you get there faster your average intensity during the exercise was higher.

You could compare the difference in the average intensity between the two approaches by comparing the time to failure using the same approximate percentage of your one repetition maximum (for the sake of example we will ignore all of the practical problems with doing this accurately). For example, if you achieve a twenty percent inroad within forty seconds your average intensity would be twice as high as if you achieved the same inroad in eighty seconds (.5 percent inroad per second versus .25 percent). This would only be true for a single individual though; because different people with different percentages of slow, intermediate, and fast twitch muscle fiber types fatigue at different rates with the same percentage of 1RM.

Inroad is not directly proportional to exercise effectiveness, however. While some fatigue is necessary too much fatigue can be counterproductive and achieving momentary muscular failure appears to be far more important if your goal is to build bigger, stronger muscles. Studies comparing the effects of training with lighter loads and higher repetitions (higher inroad) with heavier loads and lower repetitions (lower inroad) have shown no significant differences in muscular strength and size increases, on average. If there was a direct relationship between inroad and growth stimulation we would expect to see greater increases in muscular strength and size with lighter weights and longer sets, but this is not what happens.

Instead, there appears to be a broad range of inroad that is effective, however like most things what is optimal would vary between individuals and having either too little or too much for an individual will compromise results. This is why people who have a fast fatigue response/higher percentage of fast twitch fibers tend not to respond as well to longer set durations and people who have a slow fatigue response/higher percentage of slow twitch fibers tend not to respond as well to shorter set durations.

 

References:

Gie?sing J, Fisher J, Steele J, Rothe F, Raubold K, Eichmann B. The effects of low-volume resistance training with and without advanced techniques in trained subjects. J Sports Med Phys Fitness. 2016;56(3):249-58.

Morton RW, Oikawa SY, Wavell CG, et al. Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. J Appl Physiol. 2016;121(1):129-38.

Join the discussion or ask questions about this post in the HIT List forum

Like it? Share it!

Comments on this entry are closed.

  • Matt Jul 26, 2017 @ 18:21

    Hi Drew,

    Thanks for all this great information! How would this TUL be calculated for bodyweight-only exercise (say, Project Kratos)?
    Thanks for all you do!

    • Drew Baye Jul 27, 2017 @ 8:34

      You’re welcome!

      Finding the optimal TUL for bodyweight exercises without performing a fatigue response test with weights requires some experimentation. If you have difficulty exceeding a particular TUL on an exercise but are able to match that TUL at a higher level in the progression system it is an indication you may need to reduce your TUL range for that exercise. If your TUL consistently drops significantly after going up a level on a particular exercise you may need to wait until you achieve a higher TUL before progressing, and may be an indication you need to increase your TUL range for that exercise.

  • Mike Jul 27, 2017 @ 7:22

    Drew, thanks for all the knowledge you are sharing, I think you are the best!

    • Drew Baye Jul 27, 2017 @ 8:27

      You’re welcome! I hope the article is helpful.

  • ops30 Jul 27, 2017 @ 11:43

    Drew,

    You are the best exercise writer in the world. The way you concisely break down this stuff makes it so easy to grasp and apply.

    I look forward to the books you have planned for the future. Thank you!

    • Drew Baye Jul 27, 2017 @ 22:58

      Thank you and you’re welcome!

  • Steven Neid Aug 7, 2017 @ 9:32

    Quick question Drew…
    Why do chest press AND shoulder press in the same (Big 5) workout?…aren’t they working the same muscle groups (pecs, delts, tric) with only slightly variances on emphasis between the chest and shoulders? Wouldn’t doing chest press on Monday and Shoulder Press on Thursday’s workout be more efficient? Same for Rows and pulldowns too?
    As always, Drew…
    Thank you for your time!
    Steve

    • Drew Baye Aug 7, 2017 @ 10:33

      No, because while there is some overlap there is a significant difference in the relative effect on the different muscles involved and a benefit to working them as frequently as recovery ability allows.

  • João Aug 7, 2017 @ 17:30

    Hi Drew, how you’re doing?

    I have an off topic question, and I apologize for posting it here. I wasn’t able to find your contact anywhere, so here it goes:

    I was alternating between a weight training in the gym and a bodyweight session. By that time I noticed a more rapid recover following the bodyweight session in comparison to the weight training session. Both were highly intense (measured with RPE post-workout), both were comprised of 7 exercises (Pull/push in vertical/horizontal, leg exercise, trunk extension, calf raise, in the same order) and had more or less the same recovery between exercises (I was timing at 60 seconds). Did you noticed the same thing with yourself or with your clients?

    Currently, I’m doing two sessions inspired by your book Project Kratos (which is very good, by the way) and really enjoying them, because it allows me to exercise a bit more frequently (once every three to four days, as opposed to once every five to seven days when I did weight training) and because it is very fun to find such a challenge in simple bodyweight exercises.

    All the best, and thank you!

    • Drew Baye Aug 12, 2017 @ 11:15

      This is usually the case in the beginning when people are still learning to perform the exercises as efficiently as possible, but as you get better at the exercises and your intensity increases you may find you need more recovery.

  • Randy jung Aug 10, 2017 @ 8:12

    What is the best and simplest way to
    Determine whether you tend to have more fast or slow twitch fibres and therefore optimize for higher or lower load training as stated in your last paragraph?

    • Drew Baye Aug 12, 2017 @ 10:43

      The simplest way to determine this is with a fatigue response test, but these should not be attempted until someone is proficient in the performance of the exercise. I cover this in detail in High Intensity Workouts

  • Eric in Santa Fe Aug 15, 2017 @ 11:30

    In studying this material, I have had the most trouble trying to figure out exactly what the different authors mean by the word “intensity.” This is a new one, and you might want to reconsider it. You have intensity being rate of inroad, and has units 1/time. You also point out that inroad isn’t all the useful, since working a lighter weight — 40% of 1RM — to momentary muscle failure has 3 times the inroad of working a heavier weight — 80% of 1RM — to MMF, but doesn’t produce any better results. If that’s the case, it is hard to care about rate of inroad. Working with 100% of 1RM would maximize rate of inroad, but is probably not optimal for training.
    Another meaning of “intensity” is working to a percentage of MMF. The people who stop 1 rep short are working at a lower intensity than those achieve MMF or those who use techniques such a drop sets or negatives to achieve more than 100% of (positive) MMF. I like this definition, because it is simple to understand and apply, but I’m never sure if it matches what the different HIT authors intend.

    • Drew Baye Aug 20, 2017 @ 10:21

      The best definition of intensity is the relative effort; how hard you are working at any moment relative to how hard you are capable of working. The higher your average intensity of effort the greater the rate of inroad.

      While simple, percentage of 1RM is not a good definition of intensity because there are other factors that can influence how difficult an exercise is with the percent of your 1RM. I explained this in What Is Intensity?

      Also, be careful with drop sets and negatives. The more skilled a trainee becomes the less useful these are in most circumstances, and they can be counterproductive if done incorrectly or too frequently.

  • Ahmed Sep 20, 2017 @ 23:56

    Does one find out if one is fast-twitch or slow-twitch by experimenting?

    For example, I can go heavy and do few reps. Logically, if I go light I should do more reps. But let’s say my reps are only slightly higher despite reducing weight considerably. Does this mean I am fast-twitch predominant?

    • Drew Baye Oct 1, 2017 @ 14:38

      This is one of the indicators of a faster fatigue response. I explain how to determine the appropriate repetition range or TUL for different muscle groups in High Intensity Workouts.

  • Eric Ramos Nov 14, 2017 @ 0:38

    I need to finally do this and test my fatigue response. I assumed that due to the the research you stated here, high load vs low load, that it didn’t matter what what TUL I did as long as I reached fatigue.

    Pulling exercises I tend to do alright 1 or 2x a week. Pressing exercises I have a harder time. I recently discovered that most should be able to get stronger, with strength as a goal, on even 1x a week. I thought this an exaggeration of HIT authors but after closer examination it seems I’m the outlier. I do not. Not on 2x or 3x a week either. Because at first I thought perhaps the 1x a week was not providing enough stimulus.

    So the only thing that makes sense to me at this point is to test my Optimal rep range like in your book and see if I’ve been completely training in the wrong range.

    Thanks for the article

    • Drew Baye Nov 14, 2017 @ 8:58

      A variety of repetition ranges and TULs can be effective, but what is optimal will vary between individuals.

      • Eric Ramos Nov 16, 2017 @ 15:35

        Thanks, I tested a few movements the squat, dead, and Row. I got 11 or 12 reps on each. I was curious on my press and chin but I was fried by then.

        I’ll have to give working out in these higher rep ranges for a bit. I usually do 5-8.