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Physiology of Fatigue: What are we fighting when we try to push through a challenging workout?

Why are workouts so hard?

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We are fighting a lot when we push ourselves through workouts that are challenging. There are times we may be fighting a bad attitude, discouragement, lack of confidence, drive or our own personalities, but we are, at times, also fighting a very complex regulatory system designed to protect us from severe self-induced damage.

Fatigue and Temperature

Fatigue can be defined as reaching a point where the body seeks to slow down or stop. Exhaustion is that point where a person (or animal) is unable to continue. The most important factor driving suppression of motor activity is believed to be brain temperature. In an untrained person, exhaustion may occur when core body temperature reaches 100 to 102F(~38 to 39C) while a highly trained person may not reach exhaustion until body temperature has reached 104F (~40C).

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Interestingly, it’s not only humans who are stopped at these temperatures. Internal temperatures of ~104 oF will stop other animals whether sprinters (Cheetahs) or the generally more placid and possibly endurance-oriented (Goats) (Taylor and Rowntree 1973). And yes, I’m sure you’re wondering: temperatures were measured rectally, and the animals ran on a treadmill while wearing masks so oxygen and carbon dioxide levels could be assessed. The research team also cranked the heat up. Cheetahs ran for shorter periods when the room was hot. The authors of this paper concluded that the duration of a Cheetah’s sprint is limited by core temperature, which is influenced by air temperature. Keep this in mind when you are working out in the summer with no air-conditioning. There are other factors that are also thought to play roles in regulation of intense physical output. Working muscles send feedback to the brain, and in most of us, they are not yelling “Go! Go! Go!” At first they are saying things like “we need more oxygen over here” and “pump the heart faster.” Unfortunately you maximum output can only go on for as long as you have the necessary materials to keep the system running. Your maximum obtainable heart rate will matter. That may be one you cannot make “just do it.” although you can improve your ability to pump blood with training.

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Blood concentrations of important factors or metabolites, and depletion of working materials, are also monitored by the brain. Changes in concentrations and availability of neurotransmitters, endorphins, cytokines, along with a build-up of ammonia in the brain, occur during continued intense exercise. Cerebral energy use increases requiring more oxygen, while blood flow will decrease by about 20% due to constriction of brain arterioles. Low oxygen, loss of neurotransmitters, and accumulation of waste products can cause a problem that is truly “all in your head” but a real problem none the less. An increased need for oxygen and fuel in the brain may be part of what causes someone to want to slow down or stop.

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Practice improves physiology and performance.

Increasing oxygen intake may improve performance not necessarily by providing muscles with additional oxygen, but in providing the brain with what it needs to keep the system running. Depletion of brain glycogen and excessive use of lactate as an alternative brain fuel may also signal fatigue. This may happen faster in untrained athletes. Physical training is, after all, about much more than simple strength and endurance. It includes getting all systems, including subtler aspects of physiology like the ability to dissipate heat, produce lactate, carry oxygen and oxygenate the brain, to work as efficiently as possible. We can reach our limits, but our brains rarely stupid enough to allow us to go beyond them and recklessly run our bodies off the edge of a cliff. The brain also likes to know what’s going on and practice (going through the motions) and rehearsal are important to performance. Rehearsing movements before a WOD may be as important as traditional warming up. It preps your system for what it is about to do and lets it know what is coming. Even imagining movements may help improve strength output and performance (Jeukendrup et al. 1996).

CrossFit training, rational mental toughness.

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We can improve performance intelligently rather than fight what we imagine to be a lack of mental toughness, or allow ourselves be discouraged. We can keep cool and well-hydrated. We can be patient enough to recognize that our physiological and biochemical systems are becoming more efficient as we train, even if our speed or strength has plateaued, and not give up on long-term goals. Finally, encouragement and cheers can help people achieve their maximal level of oxygen consumption (Nybo & Secher 2004) and maximum performance. This may be especially true if they are new to Crossfit and have type A personalities. New Crossfitters may be putting superhuman efforts into their workouts and should be congratulated and admired for these as much as our seasoned champions.

Taylor CR, & Rowntree VJ (1973). Temperature regulation and heat balance in running cheetahs: a strategy for sprinters? The American journal of physiology, 224 (4), 848-51 PMID: 4698801

JEUKENDRUP, A., SARIS, W., BROUNS, F., & KESTER, A. (1996). A new validated endurance performance test Medicine & Science in Sports & Exercise, 28 (2), 266-270 DOI: 10.1097/00005768-199602000-00017

Nybo, L., & Secher, N. (2004). Cerebral perturbations provoked by prolonged exercise Progress in Neurobiology, 72 (4), 223-261 DOI: 10.1016/j.pneurobio.2004.03.005

Taylor CR, & Rowntree VJ (1973). Temperature regulation and heat balance in running cheetahs: a strategy for sprinters? The American journal of physiology, 224 (4), 848-51 PMID: 4698801 Nybo, L., & Secher, N. (2004). Cerebral perturbations provoked by prolonged exercise Progress in Neurobiology, 72 (4), 223-261 DOI: 10.1016/j.pneurobio.2004.03.005ResearchBlogging.org

Does Low Estrogen Make Women Unresponsive to Anti-Depressants?

Depression may be caused by poor Serotonin handling

Depression stinks.  It hurts.  And it hurts others too.   Taking care of yourself, and your moods, is important.  A positive outlook and sense of optimism can carry you a long way.  And it will help you bring along those you care about.  Its easy to get frustrated with someone who is depressed.  “why don’t they snap out of it?”  This article reports on some very interesting research on depression and female hormones.  It is especially interesting for women whose hormones are shifting.  (in peri-menopause or menopause.)

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First, a little background:

  • Serotonin is a neurotransmitter
  • Serotonin allows neurons to communicate with each other.  And sometimes help produce emotions.
  • Depression in some people may be caused by too little serotonin
  • Selective Serotonin Re-Uptake Inhibitors (SSRIs)  work by keeping serotonin active and keeping nerves functioning well.
  • Prozac, Zoloft, and Citalopram are examples of SSRIs.

There are differences in Serotonin Receptors

Neurotransmitters are chemical messengers.  They travel from one neuron to another by docking at a receptor.  The receptor is a molecule that is designed especially for its transmitter.  Serotonin needs a serotonin receptor if it is going to work.   The shape of the receptor is very important.  But not every person has the same receptor shape.  There are some people whose receptors don’t seem to fit as well.  And they are more likely to suffer from depression.  And anxiety.

Estrogen and Progesterone may be needed for SSRIs to be effective

Estrogen and progesterone influence the serotonin system including serotonin receptors.  One of the genes responsible for the serotonin receptor is called 5HTT.  So far it looks like you can have either a “short”  version or a “long” version.  The short version (s-5HTT) looks like the problem version.  Monkeys have similar systems.  Like Crossfit women.  Researchers used monkeys to see how important estrogen and progesterone are the response to SSRIs.   Monkeys with the shorter gene for the serotonin receptors did not have as strong a response to SSRIs.  Monkeys with low estrogen and low progesterone were the least responsive.  Crossfit women too?

Take away for CrossFit Women and all Women.

If you are post-menopausal or hovering around that neighborhood you may not respond well to SSRIs.  Especially if you have the short version of the serotonin receptor gene.   This is one reason why hormone replacement therapy might make some women less depressed.

 

Michopoulos V, Berga SL, & Wilson ME (2011). Estradiol and progesterone modify the effects of the serotonin reuptake transporter polymorphism on serotonergic responsivity to citalopram. Experimental and clinical psychopharmacology, 19 (6), 401-8 PMID: 21843009

Putting a positive view on physical challenges ramps up natural opiods.

CrossFit and mental toughness. Its a cultural thing. If you do CrossFit you are supposed to be stronger than the pain you are feeling. Sometimes this gets a little nutty. You should stop or slow down if you are going to hurt yourself. You should go lighter on weights sometimes. For some of us, that some times may be all the time. It is dangerous to sacrifice form for heroics. That can be hard to keep in mind when pushing yourself is fun. And rewarding.  And you are addicted.

Fitness and getting the right attitude..

New research indicates that a positive mental attitude towards pain can make you feel awesome.  Or at least awesomer than you would feel with a negative attitude.  The paper, “Pain as a reward: Changing the meaning of pain from negative to positive co-activates opioid and cannabinoid systems” was published this month.  You can see the reference at the bottom of this post.  Two groups of people were either told “this is going to hurt.”  Or: this will make your muscles stronger.  The people who thought the pain would make them stronger were able to endure more pain.  That may surprise few readers.  Here is what is surprising and very interesting:The ability to tolerate pain could be blocked by blocking the chemicals that produce the runner’s high.

Its more than attitude: implications for CrossFit Athletes.

The research mentioned above is especially interesting because the researchers were able to turn off the increased ability to withstand pain by blocking the opiods and cannabinoids.   Part of the “runner’s high” is caused by natural opiods and cannabinoids that are produced in the brain.  These can be addictive.  And lead to people getting addicted to their workouts.  Maybe it is attitude that makes some people love working out.  And makes other people feel that working out just sucks.  Being able to train harder will make you better at CrossFit WOD s.  And knowing that you will get better at your workouts will make you better able to handle them.  Just don’t try it with an opiod blocker.

 

Benedetti F, Thoen W, Blanchard C, Vighetti S, & Arduino C (2013). Pain as a reward: Changing the meaning of pain from negative to positive co-activates opioid and cannabinoid systems. Pain, 154 (3), 361-7 PMID: 23265686

CrossFit Games Competition: Recovery between WODs

CrossFit Games Competition and New Research.

There have been several new papers out on recovery from repeated sets of resistance exercise.  These may be important for people headed to the CrossFit Games Regional Competitions.  For those who don’t know, the CrossFit Games regional competitions last for several days and involve multiple WODs per day.  (note: WOD stands for WorkOut of the Day and is the term used for CrossFit workouts.)The same is true for the big CrossFit Games.  In CrossFit every “rep” counts.  Recovery between WODs and recovery between days may determine who moves from regional competition to The CrossFit Games 2013.  This is very different from the CrossFit Open Competition where CrossFit Games competitors may have up to a week before the next WOD.

Ice Between CrossFit WODs

Apply ice to stressed muscles between WODs when possible.  A lot of people will apply ice if they have injured themselves during a competition.  Or if they feel pain.  Applying ice to uninjured muscles during rests may also let an athlete do more sets.  A study published last May (2012) examined the effects of icing on trained rock climbers.  Those who iced their arms and shoulders were able to more pull-ups on the second and third sets than those who rested without ice.  Some things to note: The pull-ups were open hand, which is important to rock climbers.   Closed hand holds are pretty uncommon on rock.

 

Should muscles be iced after the CrossFit Open WODs?

Maybe.  If you find that you are still in pain three days after a WOD you may benefit from applying ice the next go around.  Its uncertain how this works.  It might work by slowing production of enzymes that are involved in producing molecules that cause pain and inflammation.  The pain, tenderness and inflammation  show up about 24 hours after an intense workout is known as delayed onset muscle soreness.  Cold slows down enzyme rates and may slow the onset of pain.  Or may reduce its intensity.

Bacon NT, Wingo JE, Richardson MT, Ryan GA, Pangallo TC, & Bishop PA (2012). Effect of two recovery methods on repeated closed-handed and open-handed weight-assisted pull-ups. Journal of strength and conditioning research / National Strength & Conditioning Association, 26 (5), 1348-52 PMID: 22516908