As any gurrlll will tell ya -- certain times of the month (e.g. when we're bleeding down our legs) no matter what we eat/don't-eat, girls gain %^&*$weight. Then...yet at other times...we can eat E-V-E-R-Y-T-H-I-N-G in sight... bam... drop pounds... more energy... more shredding/shedding.
What's the issue...??
Human bodies do not obey the laws of matter and physics. Esp... girls... *wink* We break all the metabolism rules... and our hormones fluctuate.
Often like life... the more you give, the exponentially more . . . you get.
With more power propelling exercise and intense energy demands, the human body is the greatest machine to turn over and produce more outputs than inputs. Mitochondria, our tiny nuclear power-generating plants, are doubled...or even...QUINTUPLED in quantity and quality for future expected thermodynamics. (Conversely, they are degraded with 'hibernation signals' -- insulin, low thyroid, movement-deficiency, high carbs, high fructose, diminished daylight/Vitamin D deficiency, micronutrient/co-factor deficiencies.)
Frank Starling's Rule...of Heart/Muscles Biophysics:
Max Cardiac Output = Max Heart Rate X Max Stroke Volume
For us Paleo people, during functional exercise, how does the heart provide so much ATP, energy packets, with constant and high outputs? At high intensity efforts...like Tabata squats? 100 burpee-pullups? Oly-lifting like dead-lifts and power cleans 8 x3...?? Which then translate effortlessly (without practicing) to faster running, flying across hills, and jumping to never imagined heights...!? I n d e e d y . . . Olympic-lifting explodes vertical-leaping and bounding better than... Superman himself. Another one of our important muscles, the heart, works the same way. It is a muscular biological pump. How strong the heart can pump blood-volume and how efficiently oxygen is supplied are the factors that determine the max work and max volume delivered with every heartbeat. With the proper training, the heart muscle cells in fact grow BIGGER (yea)... THICKER (yea-aaahh) with mitochondria, the ATP-power-generators... MORE EQUIPPED with enzymes and co-factors to transfer energy -- fatty acids, lactate, glycogen/glucose -- and to take care of the 'end-products' of oxidation ( Coenzyme Q10 ). Our heart cells (cardiomyocytes) are one of nature's best examples of bio-engineering for structure, composition and mechanical genius. They beat for you every second...of your life. ~ 100,000 times per day.
In an untrained heart, the volume of mitochondria take up ~5% of the cell. However, in hearts of athletes, mitochondria reside in as much as 20-25% of the heart cell. That is five-times more massive...! Harness the power of your mitochondria... by optimizing your G-flux (flow of energy/chi).
Maximal cardiac output increases in response to exercise training. Intensity determines how fast this happens.
What is the preferred energy source of heart and skeletal muscle cells?
Well...it certainly aint Gu or sports drinks or energy bars. As we exercise and become more trained, the preferred source for mitochondria is fatty acids...both our temporarily stored fats in skeletal muscle and the band of saturated fat across the heart...
"Proper heart function relies on high efficiency of energy conversion. Mitochondrial oxygen-dependent processes transfer most of the chemical energy from metabolic substrates into ATP. Healthy myocardium uses mainly fatty acids as its major energy source, with little contribution of glucose." Metabolic and genetic regulation of cardiac energy substrate preference.de Jong JW et al. Comp Biochem Physiol A Mol Integr Physiol. 2007 Jan;146(1):26-39. Epub 2006 Oct 3. Review.
"Mitochondria in skeletal muscle tissue can undergo rapid and characteristic changes as a consequence of manipulations of muscle use (e.g. MOVEMENT...use it or lose it) and environmental conditions . . . Additionally, a shift of substrate metabolism toward a higher reliance on lipids is observed, structurally reflected as a doubling of the intramyocellular lipid content . . . Transcription factors AP-1 and PPARalpha/gamma and the protein kinase AMPK are signaling molecules that transduce the metabolic and mechanical factors sensed during endurance training into the complex transcriptional adaptations of mitochondrial proteins." Plasticity of skeletal muscle mitochondria: structure and function.Hoppeler H, Fluck M. Med Sci Sports Exerc. 2003 Jan;35(1):95-104.
G-Flux: Building the Ultimate Body (excerpt) by Dr John M Berardi (T-Nation.com)
"Well, G-Flux, otherwise known as energy flux (or energy turnover) is the relationship between energy intake and expenditure. It's the balance between the two. Put another way, it's the amount of calories you "turn over".
And as you'll learn in this article, having a high G-Flux is 100%, without a doubt, absolutely critical to building your ultimate body – which I'm assuming includes strong, functional, well-adapted muscle, low body fat, and great health."