Why we consume energy while holding something statically?

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Discussion Overview

The discussion centers around the phenomenon of energy consumption in muscles while holding a static weight, exploring the biological and physical principles behind why living organisms expend energy even without visible movement. The scope includes conceptual and technical explanations related to muscle physiology and energy expenditure.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that energy is consumed by muscles even when holding a weight statically, questioning why this occurs when non-living objects do not require energy to support weight.
  • One participant explains that muscle fibers are not truly static, as they alternate between contraction and relaxation, which consumes energy.
  • Another participant mentions that keeping muscles stretched also consumes chemical energy, even without external movement.
  • A participant contrasts the energy dynamics of living muscles with non-living objects, stating that a table does not transfer energy when supporting a weight due to the lack of internal motion.
  • Some participants express uncertainty about the references supporting the claims regarding muscle energy consumption, with requests for further evidence.
  • It is noted that the human body continues to expend energy even at rest, producing heat, which suggests a baseline level of energy consumption.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding and uncertainty regarding the mechanisms of energy consumption in muscles. While some concepts are acknowledged, there is no consensus on specific references or detailed explanations supporting these claims.

Contextual Notes

Participants mention the need for references to substantiate claims about muscle behavior and energy consumption, indicating a potential gap in available literature or clarity on the topic.

Curiosity 1
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Hello.

When we are lifting up weight using arm, there is work done by us (we give energy for the weight to move upward and so we feel tired), and by law of conservation of energy, we can write mgΔh= mΔ(v^2)/2.

However, when we are holding the weight statically (arm does not move at all), we also feel tired some time later. It seems like we are still consuming energy even when we do not have any work done on the weight and our muscle does not move at all. Why? How a contracted muscle that is static consumes energy? Non-living things that support weight does not need energy but living things does! Why?

Your answer will be appreciated. Thanks!
 
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Curiosity 1 said:
Why? How a contracted muscle that is static consumes energy?

At the cellular level your muscles actually aren't static. The muscle fibers alternate between fully contracted and fully relaxed, which consumes energy even when your overall muscle is "static".
 
Curiosity 1 said:
mgΔh= mΔ(v^2)/2.

Thanks for sharing knowledge!
I should've written E_used= mgΔh+mΔ(v^2)/2.
 
Otoh, a table transfers no energy, internally or externally when it supports a brick. That's because there is no motion within it - apart from thermal motion and that will be in equilibrium with its surroundings
 
Drakkith said:
At the cellular level your muscles actually aren't static. The muscle fibers alternate between fully contracted and fully relaxed, which consumes energy even when your overall muscle is "static".
I've heard that before, but I'm not sure if I've ever seen a good reference - do you have one?

In either case, it is worth noting that our bodies are so inefficient that even when in a dead sleep, we still put out about the same heat (about 70-80 watts) as when at rest and awake. Our muscles don't need to be vibrating to consume energy.
 
russ_watters said:
I've heard that before, but I'm not sure if I've ever seen a good reference - do you have one?

I can't seem to find one that directly says that, but I swear I've seen one before, and everything I've read leads me to understand that this is the way it works. I'll let you know if I find a good reference.
 
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Figure 8 in that reference is interesting.
 

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