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Put another way if the muscle is given everything it needs to contract and do work will it ever get tired or have a reduction in energy efficiency?

As far as I understand muscles depend upon a blood supply delivering oxygen and nutrients (e.g. glucose and calcium) to effectively contract at its best level of performance. With the ability to work under anaerobic conditions if need be but producing lactic acid as a by-product which reduces the muscles ability to contract and therefore producing fatigue.

I also know that muscles are dependent upon temperature to work efficiently like the rest of the body. So, if the muscles temperature was able to be regulated well enough to maintain efficiency and aerobic conditions are met could fatigue be negated?

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I think you need to clarify something. I was going to answer, but then I realized there's a difference between constantly working and operating under stress. Your heart is an example of a muscle that never quits, so it is one example of an answer to your question. However, if you mean when muscles are stressed beyond their normal operating parameters, as the heart rarely is for extended periods of time, then that's a different answer. –  MCM Apr 14 '13 at 13:55
    
ATP is also needed.. –  WYSIWYG Apr 15 '13 at 5:03
    
thanks for the input. Yeah I was meaning constantly working and/ or under stress in terms of endurance training or activity, I was curious about the limits to how long and far the skeletal muscles can be exposed to. I should have specified the skeletal muscles in regards to the muscles that allow us to run and walk. –  MICHAEL TAYLOR Apr 15 '13 at 9:35
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2 Answers 2

It seems that you are asking about activity significantly above basal metabolic rate. If aerobic conditions are maintained (and with appropriate training), muscles can operate more or less continuously for very long durations, days to weeks. In non-humans:

  • Godwits have been recorded flying over 7000 miles (>11000 km) without stopping for 9 days
  • Arctic terms migrate 44000 miles (>70000 km), albeit with stopovers
  • Humpback whales migrate 5000 miles (8000 km). Their muscles are probably operating close to continuously.
  • Many (most?) species of sharks swim continuously.

There are probably other examples as well (feel free to add). For humans, usually the limit to endurance is sleep. Two forms of racing push human endurance, but the longer races almost always require at least minimal sleep:

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thanks, I never thought about it from this point of view with examples of animal performance. In regards to the performance of muscles over such long endurance events do you know if they reduce in their energy efficiency, of converting glucose (ATP) muscular contraction, as time passes. I have read in multiple sources the energy efficiency is around 25% for muscles but could find no stats on their performance over time and increase in operating temperature. –  MICHAEL TAYLOR Apr 15 '13 at 9:41
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If the muscle is provided with adequate food and oxygen, the muscle can theoretically work indefinitely. However, microtearing when a muscle is stressed more than usual can over time damage the muscle. This is the mechanism by which you get larger, stronger muscles. Without rest, it's theoretically possible to simply destroy the muscle faster than it can be repaired.

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