Monday, January 20, 2014

Is Exercise Really So Great?

     Now that the holidays are over, if you're one of those resolution-makers who's vowed to start exercising again, don't be surprised if you get sick.
     Gym memberships are at their peak in January, paralleling a rise in respiratory illnesses.  Despite new insurance deductibles, which ought to be a deterrent to doctor visits, January remains one of the sickest months of the year.  No one has ever properly correlated illness with freezing temperatures, so Grandma's admonishment, "Bundle up, or you'll catch your death of cold," isn't validated by research.  December's visiting relatives and the viruses they distribute account for a percentage of sore throats, bronchitis and colds in January, but not all.  I wonder if vigorous exercise could be a cause of illness, rather than the preventive it's touted to be.
     When you exert yourself at the gym, especially doing muscle work, your body perceives it as injury and gets to work repairing torn muscle filaments.  The reparative process recruits an army of satellite cells, the oldest known stem cells, with large nuclei and very few intracellular organelles, located adjacent to muscle cells, capable of differentiating into and fusing with muscle cells.  Satellite cells receive marching orders via chemicals secreted by your body in response to exercise.
     Exercise triggers release of many inflammatory substances--cytokines and growth factors--as well as an increase in the sub-contents of muscle cells, like mRNA, ribosomes, Golgi apparatus and mitochondria.  In short, when muscles are damaged, inflammation results.  Inflammatory chemicals rush to the site of injury, as they ought to, but they get there via blood and lymphatics, which are your body's public transport systems making local stops along the way to drop off their chemical passengers everywhere, including nasal and bronchial membranes, the gastrointestinal tract, and the meninges, which enfold the brain and spinal cord like Saran wrap.
     Sometimes exercise hurts in places you didn't stress at all, causing headaches, distant joint pain, neck stiffness, gouty arthritis, and stomach upset.  Overexertion has been linked to more frequent respiratory illnesses, perhaps because it stimulates the body to manufacture and deposit inflammatory chemicals all over, especially in highly sensitive membranes like the respiratory and gastrointestinal tracts, increasing susceptibility to ubiquitous viruses.
     Inflammation is the scapegoat in medicine these days for cancer, coronary disease, aging, dementia, and almost any problem you can name.  The cytokines and growth factors which were designed to repair tissues sometimes do their job too well, creating nodes of panic in anatomical locations that become the setting for worse problems.  Inflammatory cells that help pave over damage to the endothelial lining of coronary arteries can leave scars on top of which cholesterol and protein debris get fixated, strangling the flow of blood and causing heart attacks.  A similar process may take place in joints, tendons and organs, triggering arthritis, tendonitis and organ inflammation.  Inflammation in one body part may ignite inflammation in other parts.
     Arthritis patients often say, "The pain started in my knee, but it traveled to my back and neck."  The idea of arthritis "traveling' used to seem unscientific to me, so I'd nod quizzically when I heard this.  But so many patients described their pains in the same way that I began to understand:  inflammatory cells from one body part can travel to distant sites and ignite inflammation in other parts.
     Here's the sequence.  1) vigorous exercise causes muscle fiber damage;  2) cytokines and other inflammatory factors are produced in response to this damage;  3) these inflammatory factors hitch a ride via blood or lymphatic circulation to the rest of the body;  4) susceptible body structures, like the joints, coronary arteries, lungs, or oropharynx receive messages from these inflammatory factors and go on red alert, producing more chemicals of alarm, more cytokines;  5) the body parts affected by distant inflammation may have something to do with a person's genetic make-up or previous medical conditions--if you're prone to neck pain, headaches, asthma or a bum knee, those areas will be the first to pick up inflammatory signals and start hurting.
     Like all doctors, I had many patients from a previous generation that never exercised.  Many people in their seventies and eighties grew up with the idea that the only ones who used their muscles were manual laborers, therefore they weren't going to join that group.  In many countries today, the leisure class really is at leisure, leaving exercise to those lower-class workers who have to make a living with their muscles.   Among the many older folks who never exercised, I saw few people who truly suffered ill-health, as long as they lived lives of moderation and weren't completely sedentary.  If we were to interview the centenarians of this country, I doubt if many of them would be found to have exercised in a formal way--lifting weights, running marathons--for any part of their lives.  There is even some evidence that regular bouts of vigorous exercise taxes the heart, making cardiac rhythm problems more likely.
     It's an unpopular idea in medicine nowadays, but my recommendation is that people get whatever physical exercise is needed to support their lives, and no more:  carry groceries, mow the lawn, wash the car, pull weeds, take walks, hang out clothes, plant flowers, clean the gutters, sweep the driveway-- and forget about joining a gym, training for triathlons, biking across America, and impressing people with your biceps.  

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