Hi Marnie and everyone!
Just your friendly neighborhood nurse here, putting in her two-cents worth!
All the replies to Marcia's post are good and true...to some extent.
I subscribe to Muscle Media, which, IMHO, is one of the most reputable sources for the lay person (non-medical professional)to get research-based info on the effects of exercise and nutrition. To, perhaps, lay to rest some of the mysteries of long-slow aerobic work versus high intensity bursts of cardio, I am going to quote from an article written in the October 2001 issue on "Guerilla Cardio".
"BUILDING A BETTER FAT-BURNING PROGRAM"
"Recently, Dr. Izumi Tabata, PhD., and colleagues from the National Institute of Health and Nurtrition in Tokyo, Japan, set out in search of 'the ideal' aerobics training protocol--one that would most efficiently increase fat burning and cardiovascular fitness. Such a plan, the researchers believed, should be:
"HIGH INTENSITY: For years, we've been told that low-effort aerobics is the best method for burning fat. New research tells another story. While studies show high-intensity aerobics may burn a little less fat than its low-intensity counterpart DURING the time actually spent exercising, the total expenditure of calories (and fat) is up to 50 PER CENT GREATER with intense cardio. You see, most of the fat you burn with high-intensity cardio occurs AFTER exercising, not during the workout itself. Research presented in the journal 'Medicine and Science In Sport and Exercise' shows that when you work out using high-intensity intervals, the total amount of calories your body burns is elevated up to 142 PER CENT MORE than low-effort aerobics within the hour after your workout. And it doesn't stop there. Research published in the journal 'Metabolism' shows this potent post-exercise 'burn' may persist for up to 48 hours after exercising.
FITNESS PROMOTING: The more fit you become, the more likely you are to use fat as fuel for any given activity. Peak fitness is generally defined as having both a high aerobic AND anerobic capacity. Your maximum oxygen capacity, or VO2 peak, is generally considered the best measure of aerobic fitness. As exercise intensity increases beyond your VO2 peak, your body shifts to anaerobic (without oxygen) energy production. In the face of this oxygen debt, lactic acid levels build up in tissues, making your muscles feel sore. Your ability to continue exercising at this point is called anaerobic capacity. Notice that athletes in sports where a high level of both aerobic and anaerobic fitness are necessary (wrestling, basketball, boxing, speed skating, etc) are some of the leanest, most muscular individuals around. Unfortunately, with most of the cardio programs offered up today, its a case of either/or. You either maximally stress your aerobic system (like most slow-go cardio programs) OR maximally stress your anaerobic system (like most high-intensity cardio programs with long rest periods). So clearly, a cardio program that maximally improves BOTH aerobic and anaerobic capacity would be a Godsend.
BRIEF: Too much aerobics burns muscle! And muscle not only helps you look leaner and stronger, it also makes your body more metabolically active. The ideal cardio program would be just long enough to "spark" your metabolism for that important post-exercise fat "burn" but not so long that it begins to eat away at your hard-earned muscle!"
The article goes on to produce comparative study results that support short bursts of VERY VERY intense exercise (working at 170 per cent of VO2 max)in eight sets of 20 seconds each with a 10 second rest between. Granted, that's only 4 minutes of exercise total, but the results were amazing. This type of program is one used during training of the Japanese speed skating team...the guys who took away a LOT of speed skating medals at the 1998 Nagano Olympics.
What I took away from the article is this: I can (and do) exercise for approximately 45 minutes each cardio session. Whether Im doing a Cathe tape or working on the elliptical in the gym, I incorporate "intervals" into my program. I do the warmup, then, every three to four minutes, I'll jump higher, kick higher, etc (or pedal faster at a high resisitance if on the elliptical) for 30 seconds to 1 minute...inotherwords, until I find I'm breathing so hard I CAN'T pass the "talk test" (which is an indicator of anaerobic effort). Personally, this means my heart rate is in the high 170 range. After that effort, I bring my movements down to where I can breathe easier, but not so far down that I get comfortable. This is the "active recovery" we've all read about so much. Then, after another two to three minutes, I do it again. (And again and again.....you get the picture)
Granted, my approach isn't as intensly intense as the example given in Muscle Media, but I have noticed faster improvements in my ability to perform during exercise than any other approach I've used before. Also, I stay very warm (and continue to sweat) for a solid hour (or more) post-exercise. I've also seen greater gains in what I can lift during weight training than ever before....much more so now, with an interval program, than when I was just doing long long aerobics and keeping my heart rate lower.
So, take from this what you will. Anyone can "make" a Cathe tape an "interval" exercise. Modify to bring the intensity down, add more enthusiasm during intervals when you want the intensity to "smoke"! Believe me, it works. Since I started this intense intensity program (January) I have gone down two whole pants sizes. I do not weigh myself, because it is too easy to get caught up in the weight yo-yo experience. I LOOK at my body and SEE the changes, and my clothes tell the real story. Plus, I've found I am more energetic and less prone to over-use and over-training fatigue and depression than when I was exercising longer. And, my desire to exercise is higher. I don't know if its because I'm releasing endorphins faster and at a higher rate, but I actually get cranky if I take more than one day off from exercise.
Hope this helps...or maybe, it'll just stir more questions and controversy! <VBG>
For those die-hards (like me) who want their research in black and white, the article I just quoted from was derived from research published in the following journal articles:
"Effect of Intensity on Excess Post-exercise O2 Consumption" from the journal "METABOLISM"
"The Effects of Intensity of Exercise and Excess Post-Exercise Oxygen Consumption and Energy Expenditure in Moderately Trained Men and Women" from the EUROPEAN JOURNAL OF APPLIED PHTSIOLOGY
"Effects of Moderate-Intensity Endurance and High-Intensity Intermittant Training On Anaerobic Capacity and VO2 Max" from the journal MEDICINE and SCIENCE in SPORTS EXERCISE.
Also from that same journal, "Metabolic Profile of High-Intensity Intermittant Exercises".