But muscle can’t turn into fat, just like mud can’t turn into gold. If you quit lifting, your muscles mass will decrease over time because there’s no training to stimulate your body to keep it. And your body-fat level will increase if you don’t start eating less (since you burn less). The obvious solution when you stop lifting is to also stop eating so much.

It’s important to remember that since everybody is different, these estimates are just that. How the numbers work out for each person will definitely vary. So many factors—like genetics, hormones, sleep, and diet—can change the rate at which our bodies burn calories. And some people may have a harder time than others when it comes losing fat or gaining muscle—again, there are so many factors at play and our body chemistries are all different. Strength training is important for many, many, many other reasons (more on that later), but if you’re looking to increase your metabolism, it’s important to have realistic expectations and know that strength training can make a difference, but probably won’t drastically affect how many calories you burn from one day to the next.
^ Haykowsky MJ, Liang Y, Pechter D, Jones LW, McAlister FA, Clark AM (June 2007). "A meta-analysis of the effect of exercise training on left ventricular remodeling in heart failure patients: the benefit depends on the type of training performed". Journal of the American College of Cardiology. 49 (24): 2329–36. doi:10.1016/j.jacc.2007.02.055. PMID 17572248.

One pilot study using 150mg/kg creatine monohydrate for a five day loading phase followed by maintenance (60mg/kg) for the remainder of the five weeks noted that supplementation was associated with fewer muscle symptoms and complaints alongside improved muscular function,[572] yet a later trial trying to replicate the obsevations using 150mg/kg daily for five weeks noted the opposite, that creatine supplementation exacerbated symptoms.[573] 

One of the biggest goals of bodybuilders is to increase their muscle size and strength. Bodybuilding supplements often contain many ingredients that help to encourage this. Branched-chain amino acids are a common ingredient that can significantly increase muscle growth. Other ingredients help to increase the levels of hormones, such as growth hormone and testosterone, that can also stimulate muscle growth.
The United States Army is about to undertake a dramatic and unprecedented overhaul to the way it tests, and promotes, military fitness. The man who headed the research into the new standards talks with us about how and why, as well as the future of Army nutrition and how the Army plans to circulate 80,000 kettlebells to bases around the globe. January 22, 2019 • 43 min read
That soreness you feel post-strength session may seem like a setback. Yet over time, you’ll come to acknowledge that it signifies you’re getting stronger. “You think, ‘I’ve done something worthwhile. My body is telling me I’ve had a workout.’ You look forward to the fatigue and interpret it in a positive way,” says John Spence, PhD, professor of physical education and recreation at the University of Alberta in Canada, who wrote a review on the effect of exercise on self-esteem. (Wondering how sore is too sore to work out? Here’s your answer.)
This ingredient also plays a major role in cell growth, recovery, and communication. Increasing the amount of creatine stored in your muscles can speed up the growth of new muscle and help prevent current muscles from being degraded during exercise. By reducing muscle breakdown, creatine can speed up the healing and recovery processes, as there will be less damage to repair.
There are several different available forms of creatine: creatine anhydrous which is creatine with the water molecule removed in order to increase the concentration of creatine to a greater amount than that found in CM. Creatine has been manufactured in salt form: creatine pyruvate, creatine citrate, creatine malate, creatine phosphate, magnesium creatine, creatine oroate, Kre Alkalyn (creatine with baking soda). Creatine can also be manufactured in an ester form. Creatine ethyl ester (hydrochloride) is an example of this, as is creatine gluconate which is creatine bound to glucose. Another form is creatine effervescent which is creatine citrate or CM with citric acid and bicarbonate. The citric acid and bicarbonate react to produce an effervescent effect. When mixed with water the creatine separates from its carrier leaving a neutrally charged creatine, allowing it to dissolve to a higher degree in water. Manufacturers claim that creatine effervescent has a longer and more stable life in solution. When di-creatine citrate effervescent was studied [59] for stability in solution it was found that the di-creatine citrate dissociates to citric acid and creatine in aqueous solutions which in turn forms CM and eventually crystallises out of the solution due to its low solubility. Some of the creatine may also convert to creatinine.
This concept of timing has been applied to everything from fat burners, protein supplements, carbohydrates, and various other supplements. In some cases, you can see a difference based on when you take a product. But more often, the timing is based more on anecdotal evidence than any hard science. Recently, this nutrient timing aspect has even been extended to creatine, a product that is so effective that it’s worth the investigation of determining if there’s an element that can give you even greater benefits.
It is suggested [16,37] that another mechanism for the effect of creatine could be enhanced muscle glycogen accumulation and GLUT4 expression, when creatine supplementation is combined with a glycogen depleting exercise. Whereas it has been observed [38] that creatine supplementation alone does not enhance muscle glycogen storage. Hickner et al [15] observed positive effects of creatine supplementation for enhancing initial and maintaining a higher level of muscle glycogen during 2 hours of cycling. In general, it is accepted that glycogen depleting exercises, such as high intensity or long duration exercise should combine high carbohydrate diets with creatine supplementation to achieve heightened muscle glycogen stores [39].

The structure of cyclocreatine is fairly flat (planar), which aids in passive diffusion across membranes. It has been used with success in an animal study, where mice suffered from a SLC6A8 (creatine transporter at the blood brain barrier) deficiency, which is not responsive to standard creatine supplementation.[97] This study failed to report increases in creatine stores in the brain, but noted a reduction of mental retardation associated with increased cyclocreatine and phosphorylated cyclocreatine storages.[97] As demonstrated by this animal study and previous ones, cyclocreatine is bioactive after oral ingestion[97][98] and may merely be a creatine mimetic, able to phosphorylate ADP via the creatine kinase system.[97]
The specific mechanism of intestinal uptake for creatine is not clear, although transporters have been identified in rat jujenum, and confirmed at the mRNA level in humans.[129][130] The observation that creatine can be absorbed against a concentration gradient to a max ratio of 8:1 (8 times more creatine in the intestinal cell post absorption, relative to the lumen) supports transporter-mediated uptake, and the dependence on sodium and chloride implicate SLC6A8 (Creatine Transporter 1) as the operative transporter.[102]

Don’t take sets to the point of failure—where you absolutely can’t perform another rep. You should never get to where you’re turning purple and screaming like you’re getting interviewed by “Mean” Gene Okerlund before WrestleMania. Most of the time, you want to end your sets two reps before total failure. Not sure when that is? The moment your form breaks down, or you’re pretty sure it’s going to break down, end the set.
Age-related muscle loss: Many different dosing regimens have been used; however, most use a short-term “loading dose” followed by a long-term maintenance dose. Loading doses are typically 20 grams daily for 4-7 days. Maintenance doses are typically 2-10 grams daily. Older adults seem to only experience benefits from creatine supplementation when it is combined with resistance training.

de Salles Painelli V, Alves VT, Ugrinowitsch C, et al. Creatine supplementation prevents acute strength loss induced by concurrent exercise. Eur J Appl Physiol 2014;114(8):1749-55.del Favero S, Roschel H, Artioli G, et al. Creatine but not betaine supplementation increases muscle phosphorylcreatine content and strength performance. Amino Acids 2012;42(6):2299-305. View abstract.

Even if your focus is on a particular body part, say getting flat abs or losing fat around the hips, it's important to work all your muscle groups. Spot reduction doesn't work, so doing crunches for your abs or leg lifts for your thighs isn't going to help you achieve your goal. What does work is building more lean muscle tissue and burning more calories.
If you decide to join a gym, know that you're not expected to know how all of the equipment works right off the bat—or what to do with it. Be sure to take advantage of the free orientation so you can learn how to properly use everything that's offered and set up a basic strength-training program. At the gym, machines are preferred for beginners, because they're quite safe: Most require little coordination and offer more stability than free weights while performing the movements. 
Taking high doses of creatine might harm the kidneys. Some medications can also harm the kidneys. Taking creatine with medications that can harm the kidneys might increase the chance of kidney damage.

Some of these medications that can harm the kidneys include cyclosporine (Neoral, Sandimmune); aminoglycosides including amikacin (Amikin), gentamicin (Garamycin, Gentak, others), and tobramycin (Nebcin, others); nonsteroidal anti-inflammatory drugs (NSAIDs) including ibuprofen (Advil, Motrin, Nuprin, others), indomethacin (Indocin), naproxen (Aleve, Anaprox, Naprelan, Naprosyn), piroxicam (Feldene); and numerous others.

Wilkinson, S. B., Tarnopolsky, M. A., MacDonald, M. J., MacDonald, J. R., Armstrong, D., & Phillips, S. M. (2007). Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. The American Journal of Clinical Nutrition, 85(4), 1031-1040.

Prohormones are precursors to hormones and are most typically sold to bodybuilders as a precursor to the natural hormone testosterone. This conversion requires naturally occurring enzymes in the body. Side effects are not uncommon, as prohormones can also convert further into DHT and estrogen. To deal with this, many supplements also have aromatase inhibitors and DHT blockers such as chrysin and 4-androstene-3,6,17-trione. To date most prohormone products have not been thoroughly studied, and the health effects of prolonged use are unknown. Although initially available over the counter, their purchase was made illegal without a prescription in the US in 2004, and they hold similar status in many other countries. They remain legal, however, in the United Kingdom and the wider European Union. Their use is prohibited by most sporting bodies.