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Why is my back pain temporarily alleviated after I run 20 minutes on the elliptical?

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My question states my question.
asked Feb 14, 2011 by anonymous
edited Feb 28, 2011 by k2climbit

4 Answers

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First lets address the reasons why you may be having back pain. Sometimes low back pain can actually result from inactivity. Our bodies are designed to move. Our lymph and circulatory system are very dependent upon muscular contractions and although these two systems can function even if someone is paralyzed or in a coma, movement accelerates the efficiency of these body systems.
 
The reason why its often hard to exercise for the first time in a while as well as the reason why we are able to gain strength relatively fast when we first begin exercise are both a result of the nervous system. A muscular contraction is ultimately the result of the firing of whats called a motor unit. This is a group of myelnated nerve endings that innervate a muscle specifically for the function of contraction. When we don't exercise, we lose the efficiency of these motor units. We don't necessary lose the amount of motor units but we definitely decrease the efficiency of the nervous system to promote a proper muscular contraction. This means that both neurological depolarization of the nerve as well as cross-bridge formation within the muscle spindle is not working as well as it could if exercise is not a priority in our lives. The first few days, weeks and months of exercising is predominately a re-education of the nervous system than it is a hypertrophying of musculature. This is particularly true with strength training and power lifting especially.
 
Lower back pain is commonly a product of instability in the abdominal wall. When people refer to core stability, what they are speaking of is really about 20 different muscles that wrap around your waist like a band or thick belt, providing stabilty and power for movement. Some of these muscles include multifidus, quadratus lumborum, internal and external obliques the erector spinae group transverse abdominus and rectus abdominus. Other muscles which are not so well known which aid significantly in core stability and make up the floor of the abdomnal cavity are the levator ani, coccygeus and perineum to name a few. These muscles are primarily used to contain pelvic viscera but are also actively used during squats when the legs are wider than shoulder width and the thighs go at or below parallel to the ground while executing the squat. Powerlifters rely on these small muscles to generate large amounts of power throughout their lifts. When these bands of musculature are weak, the low back muscles have an increased stress placed them. There is a corresponding loss of motor unit efficiency going to these muscles due to their under-use and therefore cannot meet the demand that is being asked of them. This decrease in motor unit efficiency results in loss of strength and because of the disuse, there is loss of mitochondria within the muscle as well.
 
Mitochondria are required for the generation of ATP and is used for areobic metabolism in the body. When you lack mitochondria in your cells you not only reduce the bodies capacity to make sufficient ATP but you also lose the ability to remove lactate build up efficiently because you are not producing high enough quantities of NAD and NADH in the cell. Lactate build up is what causes the burning sensation in your muscles from high intensity activity. The more “in shape” you become the more efficient the cells recycling of NAD and NADH becomes, therefore the burning sensation is reduced or takes a longer into your workout to feel. There has also been studies to verify that there is a direct correlation between lack of exercising the multifidus muscle in the low back and and increase low back injury. The multifidus will literally increase the proportion of adipose to muscle when it isn’t being used. In elderly populations the multifidus is almost entirely adipose. But with youth on our side, even with not exercising, a large part of it is still muscle. But even a little loss of this musculature can result in an increased incidence of low back pain.
answered Feb 28, 2011 by k2climbit (320 points)
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Another, less subtle reason for pain in the low back is structural dysfunction. Im sure you've heard of the old biology adage “form equals function”? A structural dysfunction can result for a number of reasons. It could be do to repetative improper ergonomics, body habitus, nutritional deficiency such as insufficient manganese to promote ligimentous strength, previous injury causing subtle distortion which the average eye could not pick up or it could be the result of any or all of the previous reasons I listed above.
 
Now that we've addressed reasons for low back pain, lets discuss why using an elliptical machine can reduce your symptoms within minutes.
 
The first reason is obvious and is probably what your friends at the gym can tell you but regardless it's still true. You cause an increase in blood-flow to the muscles being worked and thus raise both your core and peripheral body temperatures. This raise in body temperature helps to increase the efficiency of enzymatic reactions in your body as well as the removal of waste products from your cells. More importantly however, you are activating the nervous system. When you have structural imbalances or musculature weakness you lose the muscles contracting capabilities. This results in a loss of local and global range of motion. The receptors in the joints called mechnoreceptors relay information to the brain that there is localized reduction in the potential for movement within the joint. This results in a and a subsequent increase in nocepetive (unconcious pain impulses) input to the thalamus. In other words, when you lose range of motion you increase the amount of unconscious pain input to the brain. At a certain point however, if there is enough nocepeption to the brain, pain becomes a part of our awareness.
 
Here's a crash course in neurology. As I stated before, noceception is the fancy word for unconscious pain signals. It is a normal function of the body. There is constant communication going on between your brain and all parts of the rest of your body. Your brain registers where your body is in space through a continuous sequence of neural input to the cerebellum and thalamus called proprioception. (Proprioception is more or less, the word for bodily awareness in space whereas mechanorecpetion is used for where a joint is in space.) Every joint in your body has these mechanoreceptors. They tell your cerebellum “hey my arm is flexed at 16 degrees and my knee is extended 22 degrees, go and check with my thalamus to make sure im doing this correctly. If your free of neurological pathology, the thalamus says, “yea cerebellum your cool, keep doin what your doing”. An increased stimulation of mechanoreptors decreases the amount of nociceptive input that is going to the thalamus.
 
A muscular contraction begins with the voluntary desire to move via the cortex. There are lots of reasons to move but for the sake of simplicity lets say it's because you want to run on the eliptical. When you initiate movement, the first two muscles you need to contract to start running on the eliptical are probably the illiopsoas and anterior tibials.. From the highly developed volitional center in the cortex a neural impulse is sent to signal the pryamidal fibers in the corticospinal tract located in the most primitive part of the brain, the medulla. 90% the pryamidal fibers dessucate or cross-over to the opposite side of the medulla and go down to the spinal cord. The signal moves down your spinal cord and out the appropriate nerve root level that will eventually branch to that specific muscle. The impulse continues along this pathway until it reaches the motor units located in the muscle spindle. (there’s also a simultaneous stretching of the golgi tendon organ of the antagonistic muscle at this time but that's for another day). The joints that are required for this motion are fitted with receptors that tell your cerebellum (which relays the info to your thalamus) where it is in space so you can keep your balance.
answered Feb 28, 2011 by k2climbit (320 points)
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Lets get into the anatomy of pain a little. Nociceptive neurons travel in the peripheral nervous system and are only lightly myelenated. The cell bodies of these nerves reside in the dorsal root ganglion within the spinal cord just before the nerve root extends out. Normal sensory neurons such as those for light touch or pressure are heavily myelenated and conduct quickly but nociceptive neurons conduct more slowly due to the relative lack of myelenation. There are 3 divisions of nociceptive neurons. The first is mechanosensitive meaning it responds to pressure and touch. The second is mechanothermal meaning it responds to heat in addition to pressure and touch and the third is known as a polymodal nociceptor. This is the slowest conducting nociceptor and responds to a variety of stimuli. Also, this stimulus can only reach as far as the thalamus in the brain because it does not register specific pain, but rather dull diffuse pain. In other words, if this nociceptor is activated you would not be able to point and tell someone where exactly the pain is but rather you'd use your whole hand and say “it just hurts all around here”. The somatosensory system in the cortex is activated with sharp pain and is relayed through heavily myelenated delta A fibers rather than the slow, unmyelenated C-fibers of nociception.
 
When you experience pain that is dull and diffuse such as low back pain, the polymodal nociceptors are active. The pain is also a result of the release of pain stimulating chemical irritants such as prostaglandins, histamins and bradykinin. This are immune cells that invade an area in response to inflammation. Also Substance P is another chemical irritant that is released during inflammatory processes and adds to the feeling of pain. All of these substances cause action potentials in the nociceptor neurons and create the sensation of pain. Analgeics work through influencing these chemicals to eliminate the depolarization of the specific noceceptive neurons that are causing the perception of pain. Once these chemicals cause an action potential in the nociceptive neuron, the nerve depolarizes up through the spinal cord and into the dorsal root (cell bodies). It is there that they synapse on neurons within the dorsal horn within the gray matter of the cord at one or two segments above or below their actual segment of entry. Because of this non-specific course of entry, it, again, creates the perception of diffuse, non specific pain in the area of injury. The nerve continues upward toward the medulla and thalamus via the spinothalamic tract in the antherior lateral horn in the cords white matter.
 
Part of the modulation of pain occurs through inhibitory descending pathways from the thalamus and hypothalamus. Thalamic neurons descend to the midbrain and there they synapse on ascending pathways in the medualla and spinal cord and actually inhibit incoming nerve signals. This descending inhibition results in production of endorphins, GABA, edynorphins, enkephalins and anandamides.
 
Exercise promotes the release of all of these, especially GABA and anandamides. People always say that endorphins are released when you exercise but it's still up for debate as to what impact they actually have on the body during exercise. They are not actually able to cross the blood brain barrier and thus shouldn't have a direct affect on the brain. Anandamides however, do cross the blood-brain barrier and current research has shown that they may be whats really responsible for the opiate-like affects of exercise.
 
The processing of pain, however, is infinitely more complicated than what I described and has many different factors in determining the degree to which we perceive it aside from the severity of the injury. Age, gender, fatigue, and past experiences (memory and limbic system) all influence pain perception.
answered Feb 28, 2011 by k2climbit (320 points)
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Cross crawl. Cross crawl is something that is often overlooked in exercise and development. It can be most easily noticed during a normal gait pattern. If a person is free from debilitating muscular or neurologic disease and the nervous system is communicating effectively with the body, one will exhibit a normal gait pattern. The right arm flexes while the left leg flexes and vice versa. This is important in maintaining a healthy nervous system and especially important for infant development. The baby first learns to crawl in this same pattern thereby helping to myelenate the corpus collosum adding efficiency to the communication of both hemispheres of the brain. Remember the first time you were taught how to do jumping jacks and it took you a few minutes to get the pattern right and maybe you'd mess it up the first couple try’s? Well that’s because traditional jumping jacks go against the normal muscle patter of abductor to opposite abductor or flexor to opposite flexor. The proper way to do a jump jack is to have the hands together when you have the feet together rather than the opposite.
 
When you go on the elliptical machine, assuming you are using the the moving arm handles as well, you are influencing the hemispheres of the brain to communicate better. You are helping to eliminate neurological switching or a sub-clinical pathology that can result in a myriad of neurological disruptions manifesting in dysponetic musculature.
 
The proper functioning of cerebral hemispheres may have a subtle but profound impact on promoting healthy bodily functions from the endocrine, cardiovascular and neurological systems. Brain hemisphere balance influences brain wave synchronization. Brain wave synchronization has a positive impact on heart-rate variability. Heart-rate variability is a term used to describe fluctuations of the heart-beat. The more variability within the heart-rate, the better, in general. Babies, for instance show consistently high heart-rate variability on ECG. The older we get, the more stressful life becomes and our nervous systems lose balance. This negatively influences heart-rate variability and autonomic regulation. Both acute and chronic stress as well as illness can make the nervous system sympathetic dominant thereby losing parasympathetic tone. This indicates that someone is not relaxed and regular involuntary bodily functions like digestion, cognition, cellular metabolism are reduced. This is why chronic stress can result in bowel disturbances, insomnia, lack of appetite, adrenal fatigue, lowered immune system and accelerated aging. Exercise however, although very much a sympathetic dominant activity, allows for an increase in HRV over time. HRV has been shown to been shown to be significantly increased in patients with fibromyalgia, the ambiguous term for idiopathic origin of diffuse global pain.
 
In summary exercising stimulates mechanoreceptors which inhibit the perception of pain processing in the brain. Exercise also excites descending inbitory pathways in the brain causing the release of endogenous opiate compounds like endorphins and anandamides and pain inhibiting compounds like GABA. Exercise also increases the efficiency of the nervous system, allowing it to fire appropriately which creates a more efficient sequence of muscular contractions. In other words, the cross-bridges are more effectively used. Cellular metabolism becomes more efficient also, especially through weeks and months of consistent training. With continued aerobic training, you increase the amount of mitochondria in a muscle. Also the cross-crawl gain pattern positively impacts HRV promoting healing, stress alleviating chemicals through brain-wave synchronization.
 
All of the above reasons are strong contributors as to why you will have a decrease in low back pain after only 20 minutes of exercise.
answered Feb 28, 2011 by k2climbit (320 points)
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