“Ab-solute Facts:” Abdominal Myths Dismissed By Brent Brookbush NSCA & IFPACPT, ACSM H/FI, NASM CPT/IFS/SFS Research facilities all over the world work diligently to bring us up-to-date information about our bodies, exercise, and health/fitness. So, why does the American popular media feel a need to ignore or somehow taint this information? The individuals, who write and edit popular books and magazines, appear on talk shows, and bring us the latest break through via infomercial, are intelligent people. Why do they refuse to research credible sources and bring you, the reader, one step closer to the truth? The harsh reality is, many books and magazines are endorsed or owned by product manufacturers. Research in magazines, books, talk shows, or even the news, is often paid for by the product’s manufacturer. (How’s that for unbiased market research.) So much of the information pumped out by our popular media is a scam, ads in disguise and trumped-up press releases, that its hard to sift through all the misinformation and find a fact in this sea of fiction. The truth is not always easy to hear, and even harder to “sell” to the public. However, hard truth is hardly hopeless. Every myth that you get conned into is a step in the wrong direction, and we all know the shortest path between any two points is a straight line. It is about time that the American public and fitness professionals alike stood up and made the media back up their “B.S.”. We need to force the media to lead us down the path of fastest possible, not fastest profitable. Abdominal, waist line, midsection, and “how to get a six-pack” information might be the most shrouded in myth. There is no lack of creativity or energy in promoting any one of hundreds of products that supposedly improve your midsection, but why is it that only a handful of individuals sport that sexy six pack?
“Ab-solute Facts & Myths Dismissed” Fact: The majority of individuals do not have a visible six pack because the muscle is covered by belly fat. Fact: No amount of abdominal exercise is going to specifically target that stubborn belly fat Fact: The primary focus for those looking to get a sexy waist line should be on total body fat reduction. Fact: Everyone is born with the six-pack muscle, known as your rectus abdominis or “abs” for short. Fact: Your abs do not attach to your legs, so your abs cannot raise, lower, or twist your legs in any way. Myth: You can target your upper or lower abs. Myth: Electric stimulation will get you the abs you always wanted.
Myth: You should train your abs every day. Fact: In five separate studies using electromyography to compare several abdominal exercises, the standard crunch was found to create significantly larger EMG activity.
Fact: In three separate studies doing crunches on a stability ball created more EMG activity than the standard crunch.
Myth: We should all have six-packs.
The majority of individuals do not have a visible six pack because the muscle is covered by belly fat. Everyone has a six-pack, however, most of us are just a little “over insulated“. No matter how tight, toned, strong, or big those muscles get, as long as they are covered by fat you will never see them. Think of it like this: If you put a pillow over a tennis ball can you see it? No, of course not, but you know that it is there. If you press on the pillow you can feel the tennis ball, you feel its size, and general firmness, but it is definitely not visible. If you replaced the tennis ball with a softball, could you see it then? The size of the ball increased, and softballs are definitely harder than tennis balls, but until you get rid of the pillow you cannot see the softball either. One of the larger problems with articles, books, videos, and devices dedicated to helping you get tight, toned abs, is no amount of abdominal exercise is going to specifically target that stubborn belly fat. Regardless of which muscle you work, a muscle does not satisfy its energy needs during physical exertion by burning only the fat lying directly over it. In fact, our primary fuel source for resistance and strength training is sugar (via anaerobic glycolysis), and body fat is later burned to offset the energy deficit that strength training created. Unfortunately, your subcutaneous fat stores (those lying just under your skin) are used in what is presumed to be a genetically predetermined pattern. After all, if this so called “spot reduction” was a reality than telemarketers would have the thinnest faces on the planet. The primary focus for those looking to get a sexy waist line should be on total body fat reduction. Body fat will only be reduced when less calories are consumed than burned. The following paragraphs were pulled from my article “The Truth About Weight Loss“: Fat loss does not have to be complicated, in fact, it is as simple as, “be more active and reduce your caloric intake“. If more calories are burned than ingested than weight loss will occur (1,6,12), and if you consume excess calories they will be stored as fat (6). We derive this principle from a fundamental law of physics, “the first law of thermodynamics“, which states: energy cannot be created or destroyed, only transferred or changed from one form to another. With this in mind if excess calories are consumed, they cannot be destroyed, so they must be transferred, and if not immediately needed for energy or metabolic functions they will be stored as fat, hence weight gain. This means no matter what you eat, whether it be carbohydrates, fat, or protein, if energy input, is greater than energy output you will gain weight. The opposite is also true. If more energy is spent than ingested, energy cannot be created, so your body will likely pull from your body fat stores to compensate for the caloric deficit, hence weight loss. With this in mind, whether a person restricts carbohydrates, fats, or protein, as long as total calories ingested are less than that burned, the result will be a loss in weight. All macronutrients (carbs, fat, and protein) are extremely important, and have there individual functions within
the body. A restriction of one macronutrient may be hazardous to your long term health. To say that weight loss (other than that lost due to fluctuations in hydration.) happens irregardless of a caloric deficit would be trying to break the laws of physics. All diets, supplements, prescription drugs, and fad exercise equipment work because they create a caloric deficit in one way or another that inevitably leads to weight loss. The real question then becomes, what is the safest and most effective way to do this, and what methods have the highest success rate for long term results? Please feel free to read the rest of this article at Hobokencafe.com in the fitness section. Lets talk anatomy for a second. Everyone is born with the six-pack muscle, known as your rectus abdominis or “abs” for short. This muscle starts at the front part of your pelvic bone (originates at pubic crest and pubic symphysis), and ends at the lower portion of your breast bone and ribs (inserts into your sternum, xyphoid process, and the costal cartilage of ribs 5,6,7). When this muscle contracts it pulls your ribs and the front part of your pelvis closer together, and in doing so it bends your spine forward. A perfect example of this movement is the crunch. Your abs also play an important role in stabilizing and protecting your spine, however, there are several other muscles involved in what is commonly referred to as “core stabilization”. Keep in mind, your abs do not attach to your legs, so your abs cannot raise, lower, or twist your legs in any way. Many so called abdominal exercises involve leg lifts, bicycle kicks, or require you to bend at the hip, such as a sit-up. The prime mover in all of these actions are muscles in your legs known as your hip flexors (Iliacus, Psoas Major, Psoas Minor, Rectus Femoris, Tensor Fascia Latae). Many of your major “hip flexor” muscles are not visible because they lie below other larger muscles in your legs. If vanity is the motivating factor behind your ab work, then why would you do exercises that work your hip flexors, muscles you cannot see. More importantly, research shows over development of your hip flexor musculature may contribute to low back pain. Remember, that when your abs contract they simply bring your rib cage and hips closer together, and in doing so flex your spine forward. One of the largest myths in the fitness industry is whether or not you can work your upper and lower abs separately. Allow me to destroy this myth right now. All muscles contract from origin to insertion. That is to say, your abs, when activated will always contract across the whole length of the muscle from pelvis to rib cage. The muscle must contract across its full length to generate force. You would never think of working your upper bicep or upper glutes, so why your upper abs. Could you pull on one end of a piece of rope with out creating tension on the other. Suppose this rope was tied to an object you needed to pull, could you pull that object before there was tension across the entire length of the rope? You certainly could not pull on your end of the rope, and expect the object to move if there was still slack in the line. Several studies comparing upper and lower abdominal exercises and the activity of your upper an lower abs via electromyography, show that an increase in upper rectus abdominis activity does not occur with out an increase in lower abdominal activity.(7,17,19,21) They must work together, they are the same muscle. Getting far more technical, (if you are tired of anatomy, kinesiology, physiology, and other big words skip this paragraph) there are two nerve innervations for your rectus abdominis. Nerve innervations are like power chords, they transmit a signal from your brain and tell a muscle to “turn-on” or contract. One intersects the lower rectus abdominis and one intersects the upper rectus abdominis, however, put simply theses two chords seem to be attached to the same switch. When either your upper or lower abs gets the “command” to fire, the other is forced to fire as discussed earlier with the rope example. There is a chance that the nerve to your upper abs, and the nerve to your lower abs may be able to send separate levels of stimuli. Studies using electromyography to record electrical stimulation in a muscle prove the largest amount of stimulation is elicited during a concentric contraction, that is when a muscle shortens against resistance, it takes slightly less stimulation to isometricly contract, or simply hold a position against resistance, and the least amount of stimulation to eccentrically contract, or let down slowly against resistance. With this in mind if the upper abs just held there position (isometric contraction) and the lower abs shortened against them (concentric contraction), we would have a gross shortening of your abdominal muscles and therefore movement of your pelvis, spine, and ribcage, and a larger amount of stimulation in your
lower abs than upper abs. However, keep in mind that both the upper and lower abs are still active, there is just more “stimulus” in the lower abs. The real problem with this theory is there is almost no practical application. In a single study the reverse crunch did create a larger amount of stimulation in the lower abs than the upper abs, however the difference was not statistically significant, providing shaky evidence at best.(7) I have yet to see a another study comparing exercises via electromyography that showed a particular exercise creating more stimulus in the lower abs, than the upper. So, although it is great in theory, stay away form so called lower abdominal exercises such as lying leg lifts, hanging leg raises, and the roman chair leg raises, generally these require an isometric contraction from your rectus Abdominis as it tries to hold your pelvic bone in place, and studies show concentric contractions, or exercises that require your abdominal wall to shorten create more stimulation. There is a fundamental flaw with moving your legs to work your abs. Your abs in no way attach to your legs so how would they move them? If you want to work your abs, you have to forcefully bring your ribs closer to your pelvic bone causing spinal flexion, against resistance. Even if the resistance is gravity pushing against your own bodyweight, such as a crunch. Speaking of electrical stimulation we have a number of devices marketed to us that will use an electric current to work our abs while we sit behind our desks, watch TV, or even sleep. I wish this worked, I would likely skip many a work-out in favor of “plugging in“. But, as with so many other things, “if sounds to good to be true, it probably is“. This method is not effective because the level of electrical stimulation required to create growth or an increase in strength would be unbearably painful for most, and a device that could deliver that level of stimulation would not be commercially available. Note, the amount of calories burned during this type of stimulation is unlikely to create a caloric deficit, and a subsequent reduction in body fat. In one study electric stimulation was found to be an effective means of increasing strength and size of the targeted muscle in novice exercisers.(15) However, the equipment they used was stronger than anything you could possibly purchase via infomercial, in fact, the current was so strong that candidates had to be tested for tolerance before the study could commence. The stimulation was equal to 80% of an individuals maximum voluntary effort (maximum voluntary isometric contraction). This would be painful to say the least. In a study using a common over the counter electrical muscle stimulation device (Bodyshapers model BM1012BI) subjects were tested for strength gains, body fat, girth measurements and physical appearance over eight weeks. This study even included a questionnaire in which the subjects assessed their muscle strength, muscle tone, and muscle firmness at various points during the study. There was no significant change in any of the tested parameters.(13) In a study measuring oxygen consumption (an indirect method of determining calories burned) during electrical muscle stimulation with a commercially available product, no significant increase in oxygen consumption was found.(10) In fact, this study, which used the Abtronic and Feminique devices, found that the total caloric burn would be approximately equivalent to 36 calories per day if the device was worn 24 hours per day. This is equal to about a half a slice of bread. If you wore this abdominal stimulator 24 hours a day, 7 days a week, it would take about 3 months to burn a pound of fat. That is in no way a suggestion. The long term health effects could be devastating. Note that the Bodyshaper, Abtronic, and Femineque electronic muscle stimulation devices were not capable of producing more than a 30% maximum voluntary isometric contraction. Studies have shown that a stimulus of at least 60% is required for growth or an increase in strength. Training frequency can be a very confusing topic in regards to abdominal exercise, and rightfully so. Your abs and the other muscles of your midsection or “core” serve two very important functions. They work to mobilize or flex your spine, and perhaps most importantly stabilize your ribs, spine, and pelvic bone during movement.(5,6) You constantly work your abs during any movement in order to protect your spine and the delicate spinal chord it protects. During all movement stabilization is essential. Stabilization often requires your abs to contract and hold a relatively static length over long periods of time to control and dissipate external forces. In this case movement can be made more efficient by increasing endurance and coordination of the muscles in your midsection. Generally, these are exercises that require static positions to be held for as long as possible, or exercises in which the goal is better balance and coordination. With these exercises increased endurance and better form are your best markers of improvement. This may include activities like the bridge, side bridge, plank, quadruped, “super-mans” or cobra. Many of these exercises increase intensity by adding balls, or disks to create instability. Those exercises that require increased stabilization or work on muscular endurance may be done fairly often, perhaps even most days of the week.
If the goal is vanity, i.e. an increase in size and strength of your 6-pack muscles, than we need to focus on exercises that isolate your rectus abdominis, take your abs through a complete range of motion, and create temporary muscular fatigue in 15 reps or less. Crunches, reverse crunches, oblique crunches, and cable chops are extremely effective at creating gains in strength and muscle size. These exercises should not be attempted more than every 48 hours to allow for recovery. The largest increases in strength will likely occur if these activities are performed every forth day. In a study that tested force output after short term training abstinence the largest increases in force production were found on day four.(20) Keep in mind your abs do not attach to your legs, so your abs cannot raise, lower, or twist your legs in any way, such exercises are ineffective and potentially dangerous. If your goal is to “tone up” than the largest improvements will likely come with a reduction in body fat. In this case I usually instruct my clients to stop destroying there abs, a relatively small muscle, and work larger muscle such as your chest, back, and legs, that will likely burn more calories, and create a larger caloric deficit. What is the best abdominal exercise? Luckily there is no shortage of research done by state-of-the-art strength and conditioning facilities at universities and research centers all over the world comparing many popular exercise devices. Many having no other motivation than sifting through the misinformation to find the most effective ways to increase performance. In five separate studies using electromyography to compare several abdominal exercises the standard crunch was found to create significantly larger EMG activity (measure of electrical stimulation in a muscle) than the AbDoer Pro, Perfect Abs, Perfect Abs Roller, Abs Roller Plus, Ab Sculptor, Ab-Trainer, Ab Works, Ab Scissor, Ab Swing, 6SecondAbs, Torso Track, Torso Track 2, leg lowering exercises, stability ball roll outs, reverse curl-ups, sit-ups, and crunches in which the feet were hooked.(7,9,18,19,21) The crunch also allowed for a larger range of motion of the spine than did rocking or pivot type devices such as the Ab Trainer, Abs Health Rider, Abs T45 and Ab Shaper.(16) This would allow for a more complete contraction, larger EMG activity, and possibly better results over time. (providing there is no spinal injury) The Ab-One was the only device to create a larger level of stimulation than a crunch.(18) However, this device was designed to apply direct pressure to your abs as your doing a crunch, and is thought to create a larger level of stimulation only as a means of protection, as your abdominal wall tries to protect your internal organs. I don’t know about you, but I would prefer not to crush my midsection while I crunch. In three separate studies doing crunches on a stability ball created more EMG activity than the standard crunch(2,7,8) Your body must recruit more fibers with in your trunk musculature to stabilize your spine in an unstable environment. In fact, this goes beyond just abdominal exercises. Several studies have shown increased activity of global musculature during relatively unstable exercise. During unilateral activities (one arm, or one leg at a time) there was an increase in trunk activity, in a study testing leg strength under stable and unstable conditions the unstable environment increased EMG activity of the opposing musculature, and just adding a stability ball to traditional exercise increased EMG activity of the trunk musculature.(2,3,8) This is great news for many who are bored with the standard floor crunch, however, there needs to be a level of progression. Try this: First, ensure that you are always performing exercise with proper posture, good form, and in a slow controlled fashion. Draw your belly button to your spine at the beginning of each exercise and hold that “Drawing-In maneuver” through out the duration of the exercise to initiate activity of your deep core stabilization musculature. Change should be made every couple weeks as you have time to practice. You can safely progress when you can perform 3 sets of 15 with good form. 1. Crunches: Arms across your chest Arms back with elbows bent cradling your head with your finger-tips just behind your ears. (do not interlace your fingers and pull forcefully on your head)
Arms straight up above your chest holding a weighted medicine ball Arms straight back behind you 2. Add Oblique Crunches (Shoulder to opposite knee) Arms across your chest Arms back with elbows bent cradling your head with your finger-tips just behind your ears (do not interlace your fingers and pull forcefully on your head) Arms straight out above your chest holding a weighted medicine ball Arms straight back behind you 3. Add Reverse Crunches (lying flat on your back with knees bent and feet suspended try slowly lifting your tail bone off the floor) 4. Replace crunches with crunches on a stability ball and follow the same progression. 5. Replace Oblique Crunches with Oblique crunches on a ball and follow the same progression 6. Add Standing Cable Chops We can also ensure more abdominal activity during our strength training. The body works as a system, and organizes movement via muscle synergies, or grouping of muscles working together.(6) Improving the coordination of these groupings, including your midsection, will help improve your performance in the gym which could ultimately lead to larger gains. Try this simple strategy to improve upper body strength, stability, coordination, and increase abdominal activity. First, ensure that you are always performing exercise with proper posture, good form, a slow controlled tempo, and the “drawing in maneuver�. Then try performing any cable, dumbbell, or band exercise with this simple strategy. Change should be made every couple weeks as you have time to practice the new activity. Both arms at the same time Alternating arms (Note: you perform a rep with the left arm and then the right, but there is still weight in both hands) One arm at a time ( Note: you only have weight in one hand, ensure that you do not twist at the trunk) Finally perform the exercise w/ contrary motion. (Note: This is similar to alternating however as one arm goes down the other is going up at the same time, this is performed with no break at the top or bottom of the repetition, the only time your limbs stop moving is at the end of a set.) I assure you that when you return to two hands you will be stronger than when you started and have a stronger midsection to boot.
Many individuals are prescribed abdominal activity for low back pain. In this case it is important to find exercises that decrease chances of excessive stress on the low back musculature, and reduce the activity of the hip flexor musculature. Tight and/or over-developed hip-flexors could be a contributing factor to low back pain.(14) Studies show, lumbar support devices such as weight belts and cradles only increase low back muscle activity.(4,14) Crunches with hooked feet, ball roll outs, leg lifts, hanging leg raises, and sit-ups would all be contraindicated because of increased likely hood of low back strain and hip flexor recruitment. For the reduction of low back pain, stabilization exercises may be more appropriate with simple floor crunches for strengthening. The fact that everyone should have a tight toned six-pack may be the biggest part of this myth. We look upon these individuals in magazines (fitness models) and think, “if only I could be that healthy, and look like that when I take my shirt off“, however, it is not necessarily healthy to be that lean, nor do most of these models keep that low body fat all the time. Fat plays an important role in temperature regulation and cushioning joints.(11) Excessive fat loss may lead to depression, infertility, impaired temperature regulation, or even death.(11) A healthy body fat percentage for a man is around 15 percent, and women, should be close to 23 percent, but I have never known an individual with a 6 pack who had more than half that. How many individuals do you know personally, who have a clearly visible “six-pack“? I’m a fitness professional and I only know a handful. I mean, “Why have a 6-pack when you can have a keg?“. (Ha Ha Ha) Don’t get me wrong, decreasing your body fat is important, studies show a link between abdominal girth and cardiovascular disease (11), but there is a huge difference between a smaller waist line and a six-pack. Maybe the myths are less harmful than the goal itself. If such a small percentage of the population has a six pack, maybe it is our vanity that condemns us. Many of the individuals who I cross paths with-in the gym, I will never see again. I try to help, but so many are frustrated with there lack of progress, or overwhelmed by all the routines they have tried that have promised unrealistic results. Many of these routines coming from our popular media sources. So many promising a result that the routine cannot physiologically deliver. With every failure, motivation is thwarted. Eventually, many reach a point in which the goal is not worth the price. But, never forget the real goal is health, not vanity, and a little persistence goes a long way towards a better life. References 1. Thomas R. Baechle, Roger W. Earle. Essentials of Strength Training and Conditioning, 2nd Edition Copyright 2000 by the National Strength and Conditioning Association. 2. David G. Behm, Kenneth Anderson, and Robert S. Curnew. Muscle Force and Activation Under Stable and Unstable Conditions. J Strength Cond. Res. 16(3), 416-422. 2002 3. David G. Behm, Allison M. Leonard, Warren B. Young, W. Andrew C. Bonsey, and Scott N MacKinnon. Trunk Muscle Electromyographic Activity With Unstable and Unilateral Exercise. J. Strength Cond. Res. 19(1), 193-201. 2005 4 Jeffrey A. Bauer, Andrew Fry, and Cory Carter, The Use of Lumbar-Supporting Weight Belts While Performing Squats: Erector Spinae Electromyographic Activity. J. Strength Cond. Res. 13(4), 384-388 1999 5. Paul Chek The Inner Unit: A New Frontier in Abdominal Training. IAAF Technical Quarterly: New Studies in Athletics 4/99. http://www.coachr.org/innerunit.htm 6. Michael A. Clark, Rodney J. Corn, NASM OPT: Optimum Performance Training for the Fitness Professional, First Edition Copyright 2001 National Academy of Sports Medicine 7. Kathryn M. Clark, Laurence E. Holt, and Joy Sinyard. Electromyographic Comparison of the Upper and Lower Rectus Abdominis During Abdominal Activities. J. Strength Cond. Research. 17(3), 475-483. 2003
8. Ludmila M. Cosio-Lima, Katy L Reynolds, Christa Winter, Vincent Paolone, and Margaret T. Jones. Effects of Physioball and Conventional Floor Exercises on Early Phase Adaptations in Back and Abdominal Core Stability and Balance in Women. J. Strength Cond. Res. 17(4), 721-725. 2003 9. Susan J. Hall, Jurip Lee and Terry M. Wood. Evaluation of Selected Sit-up Variations for the Individual with Low Back Pain. J. of Applied Sports Sci. Research, Volume 4, Number 2, 1990 10. Tina L. Hayter, Jeff S. Coombers, Wade L. Knez, and Tania L. Brancato. Effects of Electrical Muscle Stimulation on Oxygen Consumption. J. Strength Cond. Res. 19(1), 98-101 11. Edward T. Howley, PhD and B. Don Franks, PhD: Health Fitness Instructor’s Handbook/ Third Edition, Pg. 16, Human Kinetics: Copyright 1997 by Edward T. Howley, PhD and B. Don Franks, PhD 12. John M. Jackic, Kristine Clark, Ellen Coleman, Joseph E. Donnely, John Foreyt, Edward Melenson, Jeff Volek, and Stella L. Volpe, Appropriate Intervention Strategies for Weight Loss and Prevention of Weight Regain for Adults. Medicine & Science in Sports & Exercise 0195-9131/01/3312-2145 Copyright 2001 by the American College of Sports Medicine 13. John P. Porcari, Karen Palmer McClean, Carl Foster, Thomas Kernozek, Ben Crenshaw, and Chad Swanson. Effects of Electrical Muscle Stimulation on Body Composition, Muscle Strength, and Physical Appearance. J. Strength Cond. Res. 16(2), 165-172. 2002 14. Mike Ross, Susan J. Hall, Nick Briet, and Sam Britten. Effect of a Lumbar Support Device on Muscle Activity During Abdominal Exercises. J. Strength Cond. Res. 7(4), 219-223, 1993 15. Christine L. Ruther, Catherine L. Golden, Robert T. Harris, and Gary A. Dudley. Hypertrophy, Resistance Training and the Nature of Skeletal Muscle Activation. J. Strength Cond. Res. 9(3), 155-159. 1995 16. William A. Sands and Jeni R. McNeal. A Kinematic Comparison of Four Abdominal Training Devices and a Traditional Abdominal Crunch. J. Strength Cond. Res. 16(1), 135-141, 2002 17. Roberto Simao, Paulo de Tarso Veras Farinatti, Marcos Doederlein Polito, Alex Souto Major, and Steven J. Fleck. Influence of Exercise Order on the Number of Repetitions Performed and Perceived Exertion During Resistance Exercises. J. Strength Cond. Res. 19(1), 152-156. 2005 18. Eric Sternlicht, Stuart G. Rugg, Matt D. Bernstein, and Scott D. Armstrong. Electromyographical Analysis and Comparison of Selected Abdominal Training Devices With a Traditional Crunch. J. Strength Cond. Res. 19(1), 157-162 19. Eric Sternlicht and Stuart Rugg. Electromyographic Analysis of Abdominal Muscle Activity Using Portable Abdominal Exercise Devices and a Traditional Crunch. J. Strength Cond. Res. 17(3), 463-468. 2003 20. Lawrence W. Weiss, Larry E. Wood, Andrew C. Fry, Richard B. Kreider, George E. Relyea, Daryl B. Bullen, and Pamela D. Grindstaff. Strength/Power Augmentation Subsequent to Short-Term Training Abstinence. J. Strength Cond. Res. 18(4), 765-770. 2004 21. William C. Whiting, Stuart Rugg, Andre Coleman, and William J. Vincent. Muscle Activity during Sit-ups Using Abdominal Exercise Devices. J. Strength Cond. Res. 13(4), 339-345. 1999