Senior Distance Running Essentials Series

Chapter 7: Our Control Systems (May 2024)

Greetings and welcome to Chapter #7 of Senior Distance Running Essentials.  

Here we look at the nervous, endocrine, and immune systems.  These three control systems all rely on feedback mechanisms with the nervous and endocrine systems leading our body’s efforts to maintain homeostasis.  If any of these systems are out of whack, so are we!  And to run hard and then recover, there is an even higher level of function asked of these systems.  

Nervous System

The nervous system with its 45 miles of nerves starts with the brain, then branches out, and serves as the master controller of our body.

Central nervous system to peripheral nerves

As shown here, the central nervous system includes the brain and the spinal chord.  From and to the spinal chord are peripheral nerves.  

For movement, the motor nerves of the peripheral nervous system convey instructions from the brain to our muscles.  The gun goes off, our brain signals it’s time to go, and a bunch of things happen to allow us to get us off the line and then stay with the pack.  

Action potential

So, down the wire goes this instruction to move, which leads to something called an action potential, shown below.  

The upward movement is called depolarization, which is caused by sodium ions flowing into the cell and the downward movement is repolarization, caused by potassium ions flowing out of the cell.  You might recall sports drinks like Gatorade containing sodium and potassium being touted to improve endurance and recovery.  These may help if you have deficiencies in those electrolytes. But the largest short-term boost from these drinks is probably the sugar in them. 

Cyclical pattern of depolarization and repolarization

In any event, it is this cyclical pattern of depolarization and repolarization that allows for a continued delivery of signal to our running muscles.  For a cell to depolarize, or “fire,” a threshold stimulus must be met.  This is called the all-or-none phenomenon.  Once the threshold is met, the next criteria is the rate of firing.  A boxing analogy might be landing a single punch compared to delivering a fast combination of punches. The first punch will be felt but with a combination, it’s probably lights out.  For muscle cells, it’s lights on!  An increased rate of firing elicits a stronger response. 

Synapses and Neurotransmitters

Signals from the brain arrives at muscles as a result of signals flowing through a chain of nerve cells. 

The gap between individual cells is called a synapse. And for a signal from the brain to jump that gap quickly, a neurotransmitteris required. In effect, neurotransmitters serve as messengers of these signals. They are molecules secreted at the ends of nerve cells where gaps are located.  So, for muscle movement to happen quickly, we need both the signal coming from the brain and neurotransmitters to speed up this signal moving along a string of nerve cells until it reaches its destination: activated muscle cells.  

Effects of aging

Aging generally results in a decline in the number of nerve cells, fewer synapses in the cells that remain, and impulses conducting slower through the body.  The combined effect is a slowing of both mental and physical reactions. 

What we can do

In addition to regular sound sleep, including activities in our training that involve high levels of neural stimulation, such as striders, hills, intervals, and strength training, give us the best chance of retaining our neural networks.    

Endocrine System

Now we look at the endocrine system.  While the nervous system relies on electrical impulses to activate movement in the body, the endocrine system acts via hormonal secretions from the body’s nine endocrine glands, which empty their secretions of over 50 hormones into the blood stream. 

Life without hormones, even if possible, would be pretty dull.  Hormones are chemical messengers that travel through the blood.  Along with regulating metabolic activity in our bodies, they often shape, directly or indirectly, our reactions to physical activity.  When we’re excited at the beginning of a race, our adrenals secrete adrenalin.  At the same time, secretions of insulin and glucagon by the pancreas help regulate our blood sugar level as the race proceeds. If our blood sugar is low during the day we might feel drowsy, light-headed, or irritable.  But if that happens during a race, we bonk! 

Growth and recovery

While some hormones are secreted in response to immediate needs, much of their work in athletes relates to growth and recovery.  For example, growth hormone, secreted by the pituitary gland during exercise works to metabolize fat so it can be used as fuel when we are running aerobically.  During recovery, growth hormone enhances the formation of bone and muscle cells, facilitating replacement of those cells lost during intense exercise.  

Neural/hormonal interactions

There are interrelationships between neural stimulation and hormone secretion, especially during exercise.  An example is nerve fibers stimulating the release of epinephrine from our adrenals giving us the needed push to pick up the speed or crest that steep hill!  While neural stimulation generally results in immediate muscle and tissue response, hormonal effects can last for hours or even weeks.  In this way, it is well designed to stimulate growth and recovery, processes that take time to unfold.

Hormone receptors

A key element of the endocrine system is hormone receptors.  Hormones need a way to get through cell membranes that are otherwise designed to selectively keep things out. A combination of hormones can alter the permeability of cell membranes, speed up or slow down the effect of enzymes on cellular activity, and stimulate cell division and growth.

A ‘metabolic key” 

It might be useful to think of hormones as having a metabolic key to enter cells they are targeting.  Hormones are specific – they are on the prowl for those cells that have receptor sites for them. Appropriately these are called target cells. If they encounter unreceptive cells, they move on.  This is called sensitivity.  

Gender differences

Women and men have different concentrations of certain hormones.  These differences are mostly found in steroidal hormones, such as testosterone and estrogen.  Higher levels of testosterone may allow for greater strength and muscle growth in men. The decline in testosterone is gradual but can be maintained best by including high-intensity aerobic activity and strength-training.  This pertains as well to senior women, though baseline levels of testosterone are typically much lower.  

Post-menstrual effects

Post menstrual women with reduced estrogen often experience less collagen production, affecting skin color and tone. Reduced estrogen may also result in bone calcium loss, which can lead to osteoporosis and fractures.  Senior women may find hormone replacement therapy (HRT) a suitable option.  But there are tradeoffs, and a long-term NIH study was halted due to increased risks observed in subjects taking HRT.  Professional medical advice is encouraged.  

To summarize, as we age, the rate of production and secretion of various hormones decline as does the sensitivity of target cell receptors.  What to do?  We know that strength training is beneficial for all seniors, and for both men and women senior athletes it is imperative.  We also know that all of our bodily systems respond well to regular physical stress as we age.  Running checks that box!  In addition to diet, the importance of sleep is well documented in Matthew Walker’s 2017 book, Why We Sleep, a must read for people of all ages.  Walker suggests melatonin supplementation may have a comparative advantage for seniors over younger people due to the greater gap in production as we age. 

Immune System

We’ll finish up with the immune system.  It essentially controls things coming from outside our body, whereas the nervous and endocrine systems control the internal environment.  The immune system is a functionalsystem, not an organ or gland, per se, that organizes our multi-faceted defense against anything unwanted by the body.   

A tag team

The immune system functions as a tag team, starting at the surface with our skin.  Substances that penetrate the skin are attacked by specialized cells, often accompanied by inflammation.  Inflammation gets a bad rap – we take Ibuprofen or pack on ice to reduce it.  Yet, it prevents the spread of bad stuff to nearby tissues, helps to dispose intruders, and begins the repair process.  

Innate Defenses

The first actors of defense are called innate defenses, which, In general, often take care of things before they do us any serious harm. They include macrophages, which literally means “big eaters.”  Their diet is a broad range of pathogens that if allowed to remain and/or multiply can make us sick.  

Natural Killer Cells

Natural Killer Cells are another member of this team.  They roam throughout the body and generally take out specific types of cells.  They keep their powder dry, so to speak, until they encounter their desired culprits.  

Inflammation and fever

In comparison, inflammation and its close relative fever are also innate defenses, but are called upon as a general response to injury.  

Adaptive Immune System

If innate defenses do not solve the incursion, an adaptive system takes over, which is slower moving and attacks specific pathogens or unwanted substances.  It is called into action by the presence of antigens, which are specific foreign substances.  Meaning, the adaptive system needs to be activated.  It is something like a muscle, in that once it has been activated, it tends to have “memory” and is able to hold off further attacks. You may have heard of B cells and T cells, the foot soldiers of the adaptive immune system.

Increased Awareness due to Covid-19

The Covid-19 virus has raised the profile of adaptive immunity.  The coronavirus is an antigen, which the body’s defenses seek to destroy.  The vaccines produced intend to boost the body’s natural ability to fight the virus.  While there are detractors, the evidence strongly suggests the downside risk of vaccines is small and the upside benefit significant.  As has been commonly reported, older people are more susceptible to Covid-19 due to reduced immune function, which is why they were given priority in vaccination.

Combined effect

The innate and adaptive immune systems work together and cumulatively rather than separately.  As to aging, it is known the number of T cells and B cells, critical to adaptive defenses, decline with age.  Yet, it has been shown in animal studies that regular exercise benefits an older cohort to a greater degree than younger ones. Meaning weakened defense systems in older subjects are more apt to regain lost function.  Presumably, this result pertains to humans as well.  If it does, this is good news for us seniors!  Of course, we are most interested in retaining immune function rather than regaining it!

Delayed effects from strenuous exercise

We have probably all felt a bit weak and tired, maybe with some sniffles, the days after an exhaustive event.  A 2018 study by Campbell and Turner indicated that while strenuous exercise may negatively impact the immune system after a vigorous effort, in the long-term an athlete’s immunity is enhanced by such exertion.   Bottom line, Exercise is Medicine, and let’s keep taking a full dose!    

This concludes our consideration of the control systems.  The brevity hardly reflects the importance of these three systems, not only in our performance as senior runners but also for optimal health in daily living.

Our next chapter is on nutrition, a huge topic, which I look forward to exploring with you.

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