Studies that use a dosage range typical of creatine supplementation (in the range of 5g a day following an acute loading period) note increases to total body water of 6.2% (3.74lbs) over 9 weeks and[608] 1.1kg over 42 days.[609] Interestingly, some studies comparing creatine paired with training against training itself fail to find a significant difference in percentage of water gained (which is inherently to activity) with standard oral doses of creatine[609][607][610] (although low dose creatine supplementation of 0.03g/kg or 2.3g daily doesn’t appear to increase water retention[611]) despite more overall water weight being gained, due to an equal gain of dry mass in muscles. One study has quantified the percentage increase in mass of muscle cells to be 55% water, suggesting the two groups are fairly equal.[609]
It is known that intracellular energy depletion (assessed by a depletion of ATP) stimulates AMPK activity in order to normalize the AMP:ATP ratio,[333][334] and when activated AMPK (active in states of low cellular energy[335] and colocalizes with creatine kinase in muscle tissue[336]) appears to inhibit creatine kinase via phosphorylation (preserving phosphocreatine stores but attenuating the rate that creatine buffers ATP). While phosphocreatine technically inhibits AMPK, this does not occur in the presence of creatine at a 2:1 ratio.[334] It seems that if the ratio of phosphocreatine:creatine increases (indicative of excess cellular energy status) that AMPK activity is then attenuated, since when a cell is in a high energy status, there is less AMP to directly activate AMPK.[334][336][337] 

The general sentiment among nutrition experts is that creatine monohydrate is, for most people, the best bet. It’s the cheapest form and more importantly, it’s the most well-researched. Hundreds of studies have been performed on creatine monohydrate and there’s no evidence of ill effects, whereas many of the more novel forms of creatine have one or sometimes no studies supporting them.
Creatine is an energy substrate: a small peptide serving as a reservoir for high-energy phosphate groups that can regenerate ATP, the main currency of cellular energy. An increase in creatine intake (through food or supplementation) increases cellular energy stores, promoting the regeneration of ATP in the short term. Stores are limited, however, and glucose or fatty acids are responsible for ATP replenishment over longer durations.
Competitive and professional bodybuilders, however, can often build up to two to three pounds of muscle per month during dedicated bulking periods. "But they are living and breathing muscle growth. They aren't just in and out of the gym like most people," Simpson says, noting that under extreme conditions, hyperplasia, or the growth in the number of muscle cells in a given muscle tissue, may actually occur, further adding to muscle growth results.
The muscle endurance objective is pursued when you want your muscles to be able to perform the same motions over an extended period of time or in other words when you want your muscles to be strong and not become tired rapidly. You'll want to use at least 4 sets from which at least 16 repetitions are performed. The muscle endurance objective is often used for muscles in your lower body, such as those located in your legs or your buttocks.
In addition to the HIIT sessions, it’s always a good idea to go for a 30–60-minute walk as many days per week as you can. I recommend getting a minimum of 10,000 steps every day. Use a phone app to track them. If you’re into jogging, swimming, hiking, or some other form of long-duration, fairly low-intensity cardio, that is fine to do as well, and as often as you like.
Research shows that starting as early as age 30, the body begins to slowly lose muscle mass, with women losing up to 15 percent of their total-body muscle per decade by age 50. Apart from declines in strength, that declining muscle mass comes with a declining metabolism, Emilia Ravski, D.O., a sports medicine specialist with Hoag Orthopedic Institute in California, tells SELF. This decline in metabolic rate is actually one driving factor of the weight that women generally tend to put on after we naturally hit our peak muscle levels in our 20s, research from Tufts University suggests.
Creatine helps create essential adenosine triphosphate (ATP). This is the energy source of muscle contractions. By upping your levels, you can increase the amount of energy available to your muscles, boosting your performance. Because your muscle strength and size increases when you add weight and reps, improving your performance can be a game changer in terms of increasing your muscle mass. If you’re able to lift longer and harder, your muscles will grow. Creatine is certainly a winner among muscle building supplements.

I HATE that the resistance training community can be so tribal. I have been preaching to bodybuilders for years about the benefits of powerlifting, or Olympic lifting or kettlebells or even Crossfit style conditioning and many have been receptive. Learn from each other and achieve levels of fitness you simply could not have otherwise. Don’t brush off bodybuilding wisdom…it could be the missing factor in your program.
One case study exists of a man with focal segmental glomerulosclerosis who experienced an accelerated rate of GFR decline during supplementation (5g thrice daily for loading, then a 2g maintenance for seven weeks) which was partially reversed upon supplement cessation. This was deemed strong circumstantial evidence, and the brand of supplement was not named.[616] Elsewhere, interstitial nephritis associated with creatine supplementation has been reported in a man, although symptoms arose four weeks after supplementation started with no evidence to support correlation.[617] Some studies involving athletes and various dietary supplements have attempted to draw a correlation with creatine and cases of rhabdomyolysis.[618][619][620][621] Finally, one study in a diabetic person ingesting both metformin and creatine resulting in metabolic acidosis has attempted to place causation on creatine, but it did not establish causation or circumstantial evidence.[622]