Eccentric contraction question

Training Q&A [Moderated]
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Hi Drs,

I have a question regarding eccentric muscle contractions:

If e.g. a bicep muscle is capable of producing 5 units of Force, it will be able to curl a dumbbell the weight of which means a gravitational Force of <5.

I’ve read that we are stronger in the eccentric phase than we are in the concentric phase, and that this has to do with titin. The role that titin plays in the eccentric phase of a contraction results in the bicep being able to produce more force than it is in the concentric phase.

Before coming across this wisdom, I simply reasoned that we are “stronger” in the eccentric phase (IE we are able to lower a heavier weight (safely) than we are able to lift up) because, if we produce 5 units of Force on a dumbbell that is being pulled by 6 units of gravitational Force, it would still “fall” in a more or less controlled manner.

So my question is; is the bicep actually capable of producing MORE force in the lengthening phase than in the shortening phase? Like 5 Units in the shortening, and 7 Units in the lengthening phase (random numbers). Or is it just the classical mechanic reality that we can lower a heavier dumbbell than we can lift because as long as it doesn’t fall too fast, we can still sort of control the fall?

The reason I’m asking is because I honestly don’t get it. I first thought that Yeah obviously we are “stronger” in the lengthening phase because we can reduce the gravity on the weight sufficiently so that it doesn’t snap our elbow and just fall to the floor, but then I realized that Wait a minute, they are actually saying that my bicep is producing MORE force in the lowering phase.

So, yes, just trying to clear this up as I’m still unsure. Which is it?

Thank you!

2

RW,

I think we can employ the Socratic method here and see if we can encourage some knowledge gainzZz.

A few questions back at you:

  1. How do we define the force a muscle can produce? In other words, is there only one “force” value it can produce or does it change by contraction type?
  2. How could you determine experimentally if muscles can produce more force eccentrically than concentrically over the same ROM? Are there any experiments that do this?
  3. Can we really reduce gravity?

-Jordan

3
  1. How do we define the force a muscle can produce? In other words, is there only one “force” value it can produce or does it change by contraction type?

I’m not sure I understand what you’re getting at. The principle of specificity would suggest that No, there is not only one “force” value it can produce, as contraction type, as well as joint angles, velocity, etc, all come into play. That was sort of my question, though. Sure, we can (safely) squat down from an upright position with a heavier weight than we can stand up to an upright position from a squatted position with. But I’m wondering if the muscles involved, say the bicep in a bicep curl, is capable of producing more force in the “negative” phase than in the shortening phase, given the same ROM and everything else. My understanding is that that is the case, because of the role that titin plays in eccentric contractions (I won’t pretend to understand how this works exactly)… But again, I’m not sure what you mean.

  1. How could you determine experimentally if muscles can produce more force eccentrically than concentrically over the same ROM? Are there any experiments that do this?

Well, say I can curl a 30kg dumbbell (1RM), the force produced by the bicep would be (slightly above) = 30*g =~ 295N. Then I do a “negative curl” with let’s say an 80lb dumbbell. It would be relatively simple, at least in theory, to measure the force produced by the bicep, by looking at the time it takes for the weight to move through that range of motion and comparing it to the time it would take for it to fall without my bicep pulling on it.

  1. Can we really reduce gravity?

I meant making the net force on the weight ( -F(gravity) + F(bicep) ) smaller. The harder we pull on the falling weight, the slower it falls. No, we can’t reduce gravity.

My question is simply if the bicep actually can generate more force in an eccentric contraction than in a concentric contraction, all else being equal. As I said, I saw something about titin doing some cool stuff to enable this. Comparing a person’s 1RM squat to their 1RM eccentric squat seems like a very subjective measurement of “strength”. I mean, what counts as a 1RM eccentric squat? “Safely” lowering the weight? A toddler would get into a squatted stance from an upright stance if 1000lbs was placed on their back, but I don’t think it would count as an eccentric 1RM squat.

I’m guessing that my question is nonsensical and thus unanswerable… not sure what the missing pieces in my worldview are that make it so.

4

I realized that my follow-up might’ve been as unclear as my op. So, a clarification:

  1. How do we define the force a muscle can produce? In other words, is there only one “force” value it can produce or does it change by contraction type?

That is, as I said, sort of my question. My understanding of strength being specific, is, wrt contraction type for instance, that the muscle does indeed produce different amounts of force depending on the contraction type (as well as joint angles, movement velocity, etc). As I tried to say, of course we are able to lower heavier weights than we are able to move up; in order to lift something up, the force we produce must overcome the gravitational force on the weight. While in order to just lower a weight (“safely”), we only need to reduce the magnitude of the net force sufficiently to not let the weight come crashing down, by combatting the -F(g) with our F(bicep)… that’s what I meant by “reducing gravity”, btw.

So my question is whether the Newtonian reality of the situation explains the entirety of why we are “stronger” in the eccentric than in the concentric phase, OR, do our muscles produce different amounts of force depending on the specific circumstances (contraction type, joint angles, etc)? My understanding, especially now after having tried to read some more stuff, is that we indeed produce more or less force depending on contraction type, IE different processes are actually occurring in the body depending on the circumstances, such as titin doing some stuff during a negative rep that it doesn’t do during a concentric rep.

So, yeah, that’s my question. I guess it could also be extended to more than contraction type: do the specific circumstances of a movement (contraction type, joint angles, etc) actually make different things happen in the body so that different amounts of force are produced depending on them… or is it just about leverage or whatever, while the muscle works in exactly the same way otherwise? My understanding is that the former is true; different things are happening in the muscle depending on the specific circumstances. Chris Beardsley said:

“During muscle lengthening, titin attaches itself to the acting and myosin myofilaments once a muscle fiber is activated. Once attached, it then resists lengthening like a giant spring uncoiling. Titin does not play the same role when the muscle is shortening, so our ability to produce force is enhanced during eccentric contractions.”

I mean, it seems as if the answer to my question is an obvious Yes, different things occur physiologically depending on the circumstances, like contraction type… I’m just looking for experts’ confirmation as I don’t feel confident taking my own word for it. I’m a total noob at this.