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Listen to Your Body

The best way to achieve a high level of fitness without injuring yourself is to listen to your body. Don't depend on heart rate monitors, fitness trackers or other gadgets. The most sophisticated fitness tracker and injury-avoider is your brain. Training to achieve a high level of fitness requires intense exercise and most exercise injuries are caused by continuing to exercise intensely when your body tells you to take the day off.

A fascinating study from Boston University showed how rats' brains automatically record both time and distance. The researchers had rats run on treadmills with brain implants to measure brain function during exercise (Neuron, November, 2015). The treadmills forced the rats to run in the same place so they were not distracted by different visual effects. Their brains generated electrical impulses that fired off regularly at repeatable specific distances and times. Some repeatable electrical brain waves were recorded every eight seconds. Some were recorded every 400 centimeters. We can assume that the human brain functions in a similar way.

You Don't Need Electronic Devices to Track Exercise
You can buy sophisticated gadgets to monitor your:
• heart rate,
• variability of heart rate,
• blood lactic acid, carbon dioxide, sugar and oxygen levels,
• speed or cadence,
• number of steps, breaths or arm motions that you take,
• stride length, and so forth.
However, these devices cannot tell you whether you are exercising intensely enough to gain your maximum improvement in ability to take in and use oxygen or to damage your muscles enough for maximum strength gain. Only your brain can tell you whether you are at your maximum, if you need to take off because you are about to injure yourself, or when you need to slow down because you are exhausted.  Fitness gadgets can help to motivate you and can be fun to use, but do not count on them to tell you how intensely you should exercise or when you are at the edge of an injury.

A report from Deakin University in Australia reviewed 56 studies that compared the way that electronic devices and your brain tell you when to slow down or stop exercising (Br J Sports Med, September 29, 2015). Half of these studies showed that the brain and sophisticated machines were equally effective in telling you that you are training too intensely and need to reduce your training. The other half of the studies showed that 85 percent of the time, the brain was a better gauge of over-training than sophisticated machines.

Your Brain Talks to You
Your brain can tell you when you are tired, short of breath and your muscles hurt. All you have to do is to ask, "How do I feel?" Researchers can measure signs of fatigue such as lactate levels, VO2max, heart rate, heart-rate variability, rapid morning heart rate, recovery heart rate, hormone levels (cortisol, testosterone, etc.), red cell counts (hemoglobin, hematocrit, red cell indices), immunity (white blood cells, interleukins, inflammation), muscle damage (creatine kinase, oxidative stress), blood pressure, and much more. But in the real world for athletes and regular exercisers, all you need to do is listen to your body.

For example, the test called VO2max measures the major limiting factor to how fast you can move over distance: the maximum amount of oxygen you can take in and use over time. However, you do not need to monitor VO2max with a machine; you can increase VO2max just by becoming short of breath in your training. To make muscles stronger, you have to exercise intensely enough to damage muscles so that when they heal, they will become stronger.

Stress and Recover
Almost all competitive athletes use the training principal of "stress and recover":
• On one day they take an intense workout to damage their muscles.
• On the next day they feel sore and go less intensely to allow their muscles to heal.
• Then when their muscles feel fresh again, they take their next very intense workout.

Running causes tremendous muscle damage, so runners usually run very fast only two or three times a week, long once a week and have three or four slower recovery days, even if they are working out twice a day. Competitive swimmers are different. The water seems to protect their muscles so they usually try to take one hard and one easy workout every day. Pedaling causes less muscle damage than running, so bicycle racers do some fast riding on most days, and have to learn when to slow down.

Rules to Prevent Injuries
1. When you are training properly, your muscles will feel sore when you get up almost every morning. If you warm up for a workout and your muscles don't recover and feel fresh after 10 minutes, take the day off or go very slow. It doesn't matter what workout you have planned for that day.
2. If you are training and you feel a soreness or pain in one area that worsens as you continue to exercise, take the day off. You are headed for an injury. Wear-and-tear injuries are usually not symmetrical. One side of your body will feel far more uncomfortable than the other. Wear-and-tear injuries don't just happen, they give you plenty of warning.
3. Stop your intense workouts immediately when your legs start to feel heavy or hurt.
4. You recover faster from workouts by eating food and drinking fluids immediately after you finish a workout and getting off your feet as much as possible. You recover faster by lying instead of sitting and sitting instead of standing.

What Does This 80-Year-Old Bicycle Rider Do for Training?
I spent my entire competitive running career injured because I thought that the runner who does the most miles is the best. Of course, that is ridiculous. It took me 60 years to learn when to take off and I have not been injured in the last six years. That means that I hope that I have finally learned when to take days off.

Remember, I am no longer a runner. Running causes so much muscle damage that runners must go much slower three or four days a week. Bicycle riding is done in a smooth rotary motion with no road shock, so cyclists can test their legs every day. Diana and I ride very fast in a tandem bicycle group of couples in their 40s to 80s. We usually ride about 30 miles on Tuesday, Thursday and Saturday. After these hard rides, my legs are always sore when I get up the next day. I take a very slow 10-minute warm up. If my legs still feel tired or stiff or I have localized pain after the warm up, I take the day off. If my legs recover during the warm up, I then do a series of standing 50-pedal-stroke intervals fast enough to make me short of breath each time, followed by a slow recovery of however long it takes to get my breath back and for my muscles to feel fresh again. I do not time recoveries, since starting an interval before full recovery would slow down my next interval. As soon as my legs start to feel heavy, I stop the interval workout and start my slow and short cool down.
See Rests Between Intervals Should Not Be Too Short
Interval Workout Rest Periods

I am riding about 125 miles a week (30-mile fast group ride three times a week plus about 12 miles of warm up and intervals three times a week). My 30 mile rides are close to as fast as I can go, depending on how I feel. Of course I go slower on some days. I do 21 to 24 fifty-pedal-stroke intervals on my average interval workout, which takes about 40 minutes. I always stop my interval workout when my legs start to feel heavy. I am usually forced to take off or go very slow at least one day and perhaps two days a week.

Caution: People who have narrowed arteries leading to the heart can suffer heart attacks when they exercise intensely. All vigorous exercisers must learn when to back off of training because not allowing enough time to recover from hard exercise can damage your heart muscle as well as your skeletal muscles. Check with your doctor before beginning an exercise program or making a sudden change in the intensity of your existing program.

Checked  4/26/18

December 27th, 2015
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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