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Bending the Aging Curve

Using Exercise to Keep Us Young and Fit

On occasion two books by unrelated authors and publishers that complement each other superbly come out at the same time. Now is one of those times. Almost simultaneously with the release of Dr. Walter Bortz’s Next Medicine (Oxford, 2011) explaining why prevention must be brought front and center in our health care system (link to commentary below), Human Kinetics published Bending the Aging Curve (2011) by Joseph F. Signorile, PhD. Signorile is a highly regarded professor of exercise physiology at the University of Miami and co-author (with Arthur Agatston, MD) of The South Beach Diet Super Charged (Rodale, 2008). Dr. Signorile makes the case for interval training in both books, but goes far beyond that in his new book. He provides a complete exercise guide for making us younger, stronger, fitter, and healthier.

Signorile uses a metaphor that Bortz would love. He recalls the advertising slogan of the Castrol oil company that you could spend a few dollars to change your oil now or you could spend a few thousand dollars later to change your engine. It’s the corporate version of an ounce of prevention or a pound of cure. “Some where along the way we have lost sight of this simple concept in our health care system,” Signorile writes. “Rather than using simple tools such as exercise and diet to help reduce the negative effects of aging, we allow physical declines to occur and then address them with prescription drugs, assistive devices, and rehabilitation. In other words, the industrial nations of the world spend billions of dollars trying to change the engine when instead they could spend much less to change the oil.”

Signorile’s book, aimed at fitness professionals, shows “how to get the most fitness bang for your exercise buck.” The writing style is clear and conversational; you don’t have to be a fitness pro to understand and use the material Signorile presents. You’ll like what he says and how he says it.

Bending the Aging Curve includes many tables and graphs, but the one that sums up the message best is a graph showing the neuromuscular aging curves for the untrained person, for the person who starts exercising at about 40, and finally the trajectory of men and women who have been exercising their entire life. The differences are stunning. The capacity of exercise to bend the aging curve is awesome.

The loss of neuromuscular function for untrained individuals begins in earnest at about 40 and drops more and more rapidly with each passing decade; the decline is exponential. The person who begins exercising at 40 shows a relatively flat curve until about 60, and then begins a slow decline. The lifelong exerciser, however, soars above the others at every decade of life. The regular exerciser will have a curve that begins at a much higher level than the other two—and stays there. The inevitable decline that does occur leaves the 75-year-old lifelong exerciser at a level equivalent to an untrained person at 20. At 90, the lifelong trainer is at a level equivalent to an untrained person 30 years younger 

If that doesn’t make you want to exercise, nothing will.  

Professor Signorile covers body composition, testing, flexibility, bone density, muscular strength and endurance, cardiovascular fitness, periodization, and functional training for the activities of daily living. (I told you it’s a complete exercise guide.) We can’t cover all that here, but we can relate a few of the salient points.

Let’s start with a look are the aging curves of slow twitch and fast twitch muscle fibers, which fare quite differently for people who exercise and those who don’t, especially after the age of 50.

Dismal Decline of Fast Fibers

It’s no secret that muscle size and strength drop rapidly after the age of 50. When we understand the physiology of muscle fibers, however, it becomes apparent that the big drop isn’t inevitable; it can be countered or reversed. Let’s take a look at aging muscle fibers and the nerves that activate them.

The loss of muscle size that occurs as we age is called sarcopenia, taken from Greek meaning “abnormal reduction” or “deficiency.” Sarcopenia occurs for two reasons. First, individual muscle cells (fibers) shrink and eventually die. Because muscle fibers are bundled together, when individual fibers shrink, the whole bundle loses size. In addition, every muscle fiber has a nerve, called a motor nerve, which innervates it. For efficiency, motor units branch out and control many muscle fibers (100 to 10,000). The motor nerve and the fibers it controls are called a motor unit.

“As we age, our motor nerves and their associated muscle fibers die off at an ever increasing rate,” Signorile explains. “A small percentage of these fibers are rescued by neighboring motor units, but the number of living fibers still drops exponentially…The bottom line is that as we age we not only have smaller but also fewer muscle fibers.”

Fiber type also plays a major role in muscle size. Slow-twitch fibers are small, and fast-twitch fibers are large. The slow-twitch fibers are the endurance fibers, which predominate in marathon runners and other endurance athletes. Like the Energizer Bunny, they don’t give out, they keep on contracting. They don’t generate much force, however. Fast-twitch fibers are the strength fibers, which rule the roost in sprinters, weight lifters, and other strength athletes. They are strong, but fatigue rapidly. Most of us are born with a roughly equal balance of slow/small and fast/large fibers.

“As we age, the motor units that we lose are mainly the fast-twitch variety,” Signorile writes. “The slow-twitch fibers show practically no change.” This phenomenon is due, in part, to the rescue process mentioned earlier. “During the rescue process, slow-twitch motor units rescue fast-twitch fibers and change them into slow-twitch fibers. So the cost of rescuing a few fibers is that the aging muscle shows a predominance of slow-twitch fibers.”

A picture is worth a thousand words. Right? Signorile uses another graph to show the pattern of change in fast and slow twitch muscle fibers as we age. This one, however, can be described in a few words. The curve of the slow-twitch fibers over time is no curve at all; it’s flat, showing essentially the same number of slow fibers at 60 and 90. On the other hand, the fast-fiber curve drops rapidly from 60 to 90.

In short, the loss of muscle size with age is virtually all due to shrinkage and death of fast-twitch fibers. Translated to the activities of everyday life, this means the untrained person becomes slower and weaker with age. Independence suffers over time.

It’s a dismal picture, but all is not lost. Far from it. We can keep our fast-twitch fibers alive and well with resistance training. Signorile is a big booster of resistance training. His chapter on the subject is the longest in book, 76 pages. Again, we can only cover a few of the most important points here. (Interval training also comes to the rescue. We’ll talk about that in the next section.)

Resistance Training to the Rescue

How many people are affected by sarcopenia? “A lot,” says Signorile. “It has been estimated that from the age of 60 to 80 the prevalence of sarcopenia [2 standard deviations below the mean muscle mass of healthy young adults] in the general population progresses from 15% to 32% for men and 23% to 36% for women. After the age of 80 these values increase to 51% for women and 55% for men.”

It’s a big problem. 

Reduced physical activity is the main culprit. Resistance training is the best antidote. “Resistance training has been shown to positively affect neurological, hormonal, and mechanical factors associated with muscle maintenance and growth,” Signorile writes. “You could fill up a small warehouse with articles touting the benefits of resistance exercise in reducing sarcopenia and its impact on independence, falls, and mobility." 

The bottom line is that resistance training can have a positive effect on all aspects of the neuromuscular and biochemical decline that accompanies aging.

Front and center is the effect on the fast-twitch muscle fibers, the type 2 fibers, which are most dramatically affected by the aging process. Resistance training increases the size of the type 2 fibers and the ability of the motor nerves to recruit those fibers. Resistance training also increases the ability of the fast fibers to repair themselves, thus reaching higher levels of hypertrophy.

On the biochemical side, resistance training increases levels of testosterone and growth hormone. What’s more, it increases blood glucose utilization and ATP production and recycling.

(There are many more benefits. I cherry picked a few of the most transparent.)

 Signorile explains how resistance training can be used to target different needs—muscular strength, endurance, power, hypertrophy, and maximal strength—by changing the nature of the training. He discusses sets, reps, intensity, and rest periods for specific goals in considerable detail. (Frankly, I would prefer that less time be devoted to these variables and more on the many options available that do the job quite well. The key, as I see it, is finding a training routine that the individual enjoys and wants to continue over the long term. The biggest job facing fitness professionals is not finding the best combination of sets and reps--it is motivating clients to keep training. As we’ve already seen, regular trainers reap the greatest benefits over a lifetime.)

Now, let’s talk cardiovascular fitness and intervals.

Intensity’s the Name of the Game

The most common measure of cardiovascular capacity is maximal oxygen uptake, or VO2max.  VO2max is a measure of the maximal rate at which your body can use oxygen, or simply your aerobic power. As in the case of neuromuscular function, an exponential drop in maximal aerobic power occurs with age. Men and women decline at essentially the same rate, with men having marginally higher VO2max throughout life. 

Again, it doesn’t have to be that way.  

“Researchers who examine training protocols to increase aerobic capacity consistently report that high-intensity exercise produces greater improvement in VO2max than low- or moderate-intensity exercise produce,” Dr. Signorile writes. If improving aerobic power is the goal, “intensity is the name of the game.”

Interval training is the most effective and efficient form of high-intensity cardio training—for old and young alike. “If increasing aerobic capacity, reducing high blood pressure, or weight loss (especially around the waistline) is the goal, then interval training is one of the most effective tools you possess to reach that goal,” Signorile states.

Dr. Signorile offers the following study as evidence of the superiority of interval training for older individuals.

“One study compared moderate-intensity continuous training (70% peak HR) with aerobic interval training (95% peak HR) performed three times per week for 12 weeks,” Signorile writes. “The subjects were 27 postinfarction heart failure patients and the average age was 75.7 years. VO2 peak increased more than three times as much with the interval training than it did with the moderate continuous training.” (Emphasis mine) What’s more, only interval training improved “the filling and emptying capacity of the heart” and the ability of the arteries to accommodate increased blood flow.

What’s the most efficient work/rest ratio to improve the cardiovascular system? Signorile says, “The winner is…the old 2:1 standby composed of 20 seconds of work and 10 seconds of recovery.” (Sound familiar? It’s the original Tabata protocol reported here in 1997.)

That, however, doesn’t mean that Dr. Signorile recommends only one ratio. He wisely suggests a varied approach to interval training. “This is not to say that a work-recovery duty cycle of 20 seconds to 10 seconds is the panacea of cardiovascular training. In fact, the best idea is to use a diverse mix of work-recovery cycles…”

In addition to work-recovery ratio, other variables are the length of the work cycle, intensity, and number of work-recovery cycles. The options are almost limitless. Dr. Signorile lists several things to keep in mind. “Short work cycles (10 to 20s) allow the highest intensity, while short recovery periods (20 to 40s) limit recovery between reps. Moderately short work cycles (30s) allow for fairly high intensity, and somewhat longer recovery periods (60s) allow more complete recovery. Longer work cycles (60s) require the most difficult mix of work and recovery (60 to 120s), perhaps too difficult to be feasible for non-athletes. Finally, very long work (2 to 5 min) and recovery (4 to 10 min) cycles are impractical, and make it more beneficial to simply do steady state exercise.  

My suggestion is to make intervals as hard as you can tolerate without killing motivation—hard but not too hard.

*  *  *

As in the case of resistance training, variation is the key to long term success in cardio training. Change keeps you motivated and gives your body and your mind an opportunity to adapt and grow stronger and fitter.

Signorile provides details on a wide range of aerobic and resistance training options, including volume resistance training and steady state aerobic training. If you want chapter and verse on strength and cardiovascular training and design—and much more—Dr. Signorile’s Bending the Aging Curve (Human Kinetics, 2011) is the book for you. (We do not sell this book.)

Train regularly—resistance and cardio. Flatten your aging curve. Do it now—and don’t stop.

(For details on Dr. Walter Bortz’s book Next Medicine, see my commentary.

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