Mini-Medical School #6 December 2, 2017
by Stephanie Taylor M.D., PhD.
Fitness historically referred to the ability to complete a task. What we now mean by “fitness” has no formal definition and it is highly context dependent. A concrete fitness goal could be to achieve a specific percent body fat (26-31% body fat is normal for women, and 18-22% for men), or the ability to hike to the top of Garland Park.
One hundred years ago, fitness meant being able to haul wood and carry water and walk to the town when the horse was lame. Our century has a very different definition of activities of daily living. Given our 2st century environment, today’s fitness would be defined as the ability to sit in front of a computer or television for hours!
A recent article in the cardiology journal “Circulation” reported that most adults spend 6-8 hours a day in sedentary activities, and adults over 60 years of age averaged 9 sedentary hours a day. Sitting time increases risk of metabolic syndrome, diabetes, cardiovascular disease and all-cause mortality. Just two hours of extra TV time increases diabetes risk 14%. Fortunately, just 2 hours standing or walking decreases diabetes risk 12%. There is a similar increase in cardiovascular disease from prolonged sitting. All-cause mortality also increases with the degree of sedentary behavior, with the most sedentary (70% of the time) showing a 6 times increased death rate.
The physiology underlying increased morbidity and mortality involves many endocrine glands as well as muscles, fat and inflammatory and endothelial cells. One of the most important and well researched risks is the reduction in insulin sensitivity with sedentary behavior. Glucose from meals is intended to go to the cells for immediately available energy. If there is local resistance to the transfer of glucose into the cells, the level of glucose in the blood increases. If blood glucose goes past a certain threshold, it initiates a cascade of negative events specifically, increased inflammation, oxidative stress, endothelial dysfunction and an increase in sympathetic tone.
How do you get folks to increase their activity when there are so many attractive distractions? There is research support for two interventions: changes in the workplace environment, and use of smart phone apps that remind users to take a walk break. It is ironic indeed that the very technology that caused the problem is being used to solve the problem! Even regular short breaks for a walk reduce risk.
Bones and Muscles
Astronauts can lose as much as 5% of their bone density per month. An extended deployment in space may return them with a bone density close to osteoporosis. This can be mitigated by exercising as much as 2 hours a day while they are weightless. Bones respond to muscle pull even in low gravity environments. Muscle pull and gravity are the two main forces that maintain bone density.
Muscle pull on the bone stimulates bone to remodel. This constant remodeling is essential for good quality bone. There are two types of cells in bone-osteoblasts and osteoclasts. The former build bone and the latter dissolve bone. Usually they are in balance, but if the osteoblasts decrease activity, bone loss ensues. Physical activity is essential for good bone quality, but if there is a loss of bone structure, then it is essential to modify the exercises to prevent micro fractures. Exercises that involve flexion (forward lean) and rotation of the spine are particularly dangerous. You will have to say good bye to your crunches, toe touches, and toe touches with twist. Similar benefits can be obtained by modifying these exercises to maintain an upright posture. It is essential to work with an instructor who is trained to adapt exercises to individuals with low bone mass.
The beneficial effect of gravity can be optimized by maintaining an upright posture. Slumping compresses the anterior aspect of the vertebral bone, and can cause micro-fractures. Slumping and lateral rotation also increase pressure on the intervertebral disc and can even cause it to slip, possibly causing a nerve compression. Slumping also reduces the area for your lungs to expand, and for your bowls to digest. Tai Chi Chuan, some Yoga and the Bones for Life program apply the beneficial effect of posture on bone density.
The Turtle Wins
Whatever you decide to do for exercise, pick something that you enjoy and start out slowly. One ligament tear will put you back six months. Be very mindful of your feet if you are fast walking or hiking. See an excellent podiatrist if you have any foot pain. Chronic foot problems decrease your activity level and always result in the accumulation of a few unwanted pounds.
If you choose to start weight training, start with light weights and more repetitions. A good rule of thumb is to use a weight that fatigues you by about the 15th repetition.
Make it social. You will be more consistent if you are gathering with friends. If you enjoy your private time, you can exercise with an audio book. Just be sure it is a page-turner!
Martin, Margaret. Exercise for Better Bones. Yoga for Better Bones. www.melioguide.com
Switzer, Katherine. Running and Walking for Women over 40: the road to sanity and vanity
Tai Chi ClassesOnline: https://www.onlinetaichilessons.com/