A big clue is digestion. He does occasional cleanses. (“There’s no planes that week,” he said. “And no judgment at home.”) The slightest change in a muscle, just a stripe in a striation, is noticed. And while Heath does most workouts alone, he has a trainer, Hany Rambod, who is based in California. They see each other about once a month. In between, Heath sends photos and receives workout and dietary advice in return. 

One study in elite swimmers subject to sprints (varying in length from 25-100m) failed to find benefit with creatine supplementation, although there was also a failure on leg extension strength, suggesting nonresponse.[399] This has been noted twice elsewhere with a similar protocol,[400][401] while one study in elite swimmers subject to single 50m or 100m sprints found benefit with supplementation[402] and one found benefit with six repeated 50m sprints by 2%, yet not ten repeated 25m sprints with elite male swimmers (females failed to find benefit).[403] Another study also noted benefits in elite swimmers on a sprinting protocol.[156] Overall, the evidence is quite limited and suggests either a mild, or more likely, no increase for elite swimmers, although one study confirming an increase in body and water weight[401] failed to find a decrement in performance.
Still, it's important to realize that for everyone, at a certain point, building muscle becomes more difficult. "We all have an endpoint to our genetic potential," Matheny says. "Someone who is starting strength training for the first time can build muscle with a lower percentage of their 1RM [the maximum amount of weight they can lift one time] than a more tenured athlete. The longer you train and the closer you to get to your natural potential, the more specific you need to get with your training and nutrition to keep making progress. And that week-by-week progress will likely be much smaller than it once was."
Over time, we naturally lose muscle mass in a process called sarcopenia. On average, men lose about 30% of their muscle mass during their lives. Usually, this begins in your 30s and progresses slowly as you age. But, don’t despair. You can rebuild and maintain muscle mass even as you age. Often, diet and exercise are enough. But, sometimes, if the above hormones play a role, your doctor may recommend medications and additional treatments (4).
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.
Change things up. After six or more weeks of consistent strength training, which is about the amount of time it takes to start seeing improvement in your body, you can change your routine to make it more difficult. Lifting the same weights for the same exercises every week will keep your body in the same place. You can modify weights or repetitions, choose different exercises, or change the order in which you do them. You only have to make one change at a time to make a difference, although more is often better. 

While muscle growth is critical for bodybuilding, getting rid of extra fat is a necessity to improve your total physique. These supplements can help to increase your metabolism, forcing your body to burn away more of its fat stores. They can also slow down the digestion process to prevent excess fat and carbohydrates from entering the body and being stored.

In humans, studies that investigate links between serotonin and creatine supplementation find that 21 trained males, given creatine via 22.8g creatine monohydrate (20g creatine equivalent) with 35g glucose, relative to a placebo of 160g glucose, was found to reduce the perception of fatigue in hot endurance training, possibly secondary to serotonergic modulation, specifically attentuating the increase of serotonin seen with exercise (normally seen to hinder exercise capacity in the heat[233]) while possibly increasing dopaminergic activity (conversely seen to benefit activity in the heat[234]).[155]

Muscle imbalances are quite common among strength athletes and are arguably the most common cause of their injuries. Many times this is due to a “weak link” in the kinetic chain of muscles that activate during their activity. Identifying the “weak” muscle and being able to feel, isolate and contract that “weak” muscle makes correctional exercise and rehab much easier. Bodybuilding training, with its focus on “feel” rather than movement, helps to train and develop the mind to muscle connection. This comes in handy when you need to train a muscle imbalance with correctional exercise and, in the case of injury, for rehab.

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]