Exercise provides a wide variety of health benefits, including improved cognition, mental health, blood-pressure, insulin sensitivity, body-composition, body weight, sleep, bone health, cardiorespiratory fitness, and physical function.^[7] Moreover, regular exercise is associated with a reduced risk of all-cause mortality and an assortment of diseases (e.g., type-2-diabetes, cardiovascular-disease, certain cancers, dementia).^[7] Similarly, higher levels of muscle mass are associated with improved health outcomes, such as a reduced risk of falls and all-cause mortality.^[8]

Resistance exercise is the most effective type of exercise for muscle gain.^[5][9] Performing sets to muscular failure (i.e., the point at which another repetition cannot be completed while maintaining proper form) is just as effective as ending sets a few repetitions away from muscular failure when moderate to heavy loads (60–90% of one-repetition maximum) are used,^[10] but sets should be performed to muscular failure when light loads (30–40% of one-repetition maximum) are used.^[11] Training frequency doesn’t seem to meaningfully affect muscle gain as long as the amount of volume performed is the same,^[12] but a high training frequency (e.g., training a muscle group three times per week) may be particularly advantageous when performing a high-volume training program.^[13][14]

Muscles require ATP (the energy currency of cells) to contract and produce movement.^[27] Depending on the type, intensity, and duration of exercise, the body will make ATP primarily from one of three energy systems: the creatine-phosphate system (fastest), glycolysis, and fat oxidation (slowest). All three energy systems are always working, but some will work more than others under certain conditions. Through greater activity and training, the efficiency and effectiveness of each of these systems can be increased.

Delayed onset muscle soreness (DOMS) is common after exercise, particularly when starting a program or increasing intensity or frequency of exercise. It is caused by the stress put on muscles and connective tissue when exercising. Contrary to popular belief, it is not caused by lactic acid buildup in the muscles (lactic acid is gone from muscles within 1–2 hours after exercise). Cooling^[28], especially cold water immersion, appears to be effective for mitigating DOMS, although the previously mentioned potential to blunt adaptation and delay recovery should be noted. Compression garments^[29][30] mitigate decrements in muscle strength and DOMS without overtly impacting measures of muscle damage. Supplements including caffeine,^[31] omega-3 fats,^[31] tyrosine,^[31] whey protein,^[32] and BCAAs^[33] are potential candidates and often operate through different mechanisms of action. Sodium bicarbonate (baking soda) and magnesium have been studied for DOMS, with some positive results ^[34].

There are a variety of herbal interventions^[35] that could potentially ameliorate DOMS, but the reader is cautioned about the rigor of specific studies and interactions with other supplements and pharmaceuticals. Moreover, there's some evidence in favor of an anti-DOMS effect of massage.^[36] One thing to keep in mind, though, is that both "massage" and "antioxidants" are catchall terms for groups of different interventions. Accordingly, we should be wary of unwarranted generalizations of the results of individual studies on specific antioxidants and/or massage techniques to "antioxidants" or "massage therapy" in general.

What is soreness?

Soreness in the muscle during and immediately following exercise manifests as mild pain and stiffness that makes it hard to continue exercising. Muscle soreness usually goes away relatively quickly.

Prolonged muscle soreness is called 'Delayed Onset Muscle Soreness', or DOMS for short. It is more delayed in its resolution and can sometimes last for days. This is the soreness that somebody would feel after a hard run or leg session and be unable to easily walk up stairs the next day.

What causes soreness?

There are various things that contribute towards DOMS.^[37] Including:

• Neutrophil accumulation
• Substance P
• Aseptic Inflammation
• Interstital Edema
• Creatine Kinase

Lactic Acid is commonly thought to induce muscle failure or soreness, but has not been shown to be the causative factor. It is highly correlated though^[38], as lactic acid is produced when the muscle is sore; however its more of a fuel source than a soreness causing agent.^[39][40][41]

How can I get rid of soreness?

There are various mechanisms of reducing DOMS.^[42]

Non-steroidal Anti-inflammatory agents (NSAIDs) like Aspirin (Acetylsalicyclic acid) or Ibuprofen (Advil) can reduce future DOMS when taken at around the time of exercise.^[43][44]

Some light exercise, or moving the affected joints and muscles, can also alleviate DOMS.^[44][45] This may be due to merely moving the affected muscles, as 'whole-body vibration therapy' has recently been suggested to do similar.^[46][47]

Cryotherapy, or ice water submerging, has beneficial anecdotes by various athletes but has not been shown to be of much benefit in randomized controlled trials.^[48][49] That being said, cryotherapy may hold some potential in cases of muscular trauma such as hamstring tears or intense muscular strains.^[50][51][52] Cryotherapy's effectiveness may be closely tied in to the degree of muscular damage, and serve as a bridge between such anecdotes in high level athletes and a lack of results in novice trainees in intervention studies.^[53]

Athletic massage after exercise may also be effective in controlling DOMS^[54], possibly via reducing how many neutrophils get to the site to induce soreness.^[37]

Proper pre-workout nutrition can also play a role in preventing DOMS, as BCAA supplementation has been shown to be beneficial^[55] (and can be consumed through whey protein or protein-containing foods)

Stretching (static) before or after exercise is not significantly effective in reducing DOMS from exercise.^[56]

Six-packs; a function of both low body fat and high muscular density

The role of low body fat

The display of abs is more of a function of low bodyfat than anything else. You cannot reduce the fat around your belly without reducing overall fat.^[61][62] Attempts should be made to reduce body fat in general, and fat located on the core will generally be lost in proportion to the rest of the body.

At very low body fat levels, a six-pack will almost always be visible. However, without adequate muscle density on the core this six-pack will look somewhat emaciated and reminiscent of skin covering chicken wire.

The role of muscular density

Like any skeletal muscle, the muscles that comprise the abs (rectus abdominus, serratus anterior, obliques, etc.) respond to stimuli and damage and grow in response to said stimuli; given adequate nutrition and repair is given.

The larger the core muscularity, the more likely it is to see the outlines of the highly sought after 'six-pack'. However, until body fat is lost any six-pack at higher body fat levels will appear blurry or otherwise soft.

Sort of, kind of, maybe; not really.

What weight lifting will do

Weight lifting can increase muscle mass, primarily through becoming damaged (via weight lifting) and then sending out signals to the body to turn ingested proteins into new muscle tissue as a repair mechanism. Carbohydrates and fats are used as energy to fuel this process.

Weight lifting can also decrease fat mass, by using up body fat stores to fuel both this muscle building process and also using fat stores directly as fuel for the exercise that is needed to damage the muscle.

What weight lifting will not do

The technical, literal, direct conversion of fat into muscle.

Fat is comprised of triglycerides, which are molecules shaped like a capital E comprising a backbone and three chains of fatty acids (shown below). These chains are made up of carbon, hydrogen, and oxygen almost exclusively.

Muscle mass is made up of muscle tissue, glycogen, water, and some intra-muscular fat.^[98][99] The muscle tissue (the only tissue able to contract) is made up of chains of amino acids, which can be quite various in their structure. These chains contain nitrogen, and nitrogen is almost exclusively stored in the body as muscle (with some amino acids floating around).

It is impossible for fat to directly turn into muscle, since fat lacks the nitrogen and no mechanism exists in the body to reconstruct fat into amino acids. No evidence has surfaced implying that amino acids can be made in the body from anything other than other amino acids, a process known as transamination.^[100][101]

The vast majority of muscle built is from dietary nitrogen intake; dietary protein is the only significant source of nitrogen in the human diet.^[102][103]

So although lifting weights can both build muscle and induce fat loss, these should be viewed as two separate results and not one being the result of another.

It is generally accepted that exercise can improve blood glucose control and enhance insulin sensitivity. Several physiological processes may be responsible for these improvements, including the following:

• Adaptations in muscle insulin signaling^[17]
• Glucose transporter type four (GLUT-4)^[18] protein expression, content, and action
• Enhanced intramyocellular oxidative enzyme capacity^[19]
• Increased muscle capillary density.^[20]

However, it is not entirely clear whether exercising in the fasted state may be better than exercising in the fed state. Based on the available scientific evidence, it seems that being physically active and losing weight (through a hypocaloric diet) are the most important factors^[21] for improving glycemic control and insulin sensitivity, while performing exercise in a fasted vs. fed state plays a minor role at most. However, the research comparing the effects of fed vs. fasted exercise on glycemic control and insulin sensitivity is still in its infancy, so it’s probably best to wait until there is more research before drawing definitive conclusions.

Picture yourself eating the following calories and macros, every single day, for months on end. But with little-to-no junk food included!

• 4,000 calories
• 300 grams of protein
• 500 grams of carbs

Many heavyweight bodybuilding pros eat like that. Some eat more than that.

Of course, what applies to a mass monster using pharmaceutical assistance doesn’t quite apply to non-enhanced bodybuilders. And there’s no one bodybuilding diet that all high level competitors eat.

But these diets do have several commonalities. So are bodybuilding diets healthy? Let’s see what the evidence says.

Are very-high protein diets healthy?

Top bodybuilders always eat a ton of protein, which is the most satiating macronutrient by far.^[84] So in that way, pro diets can be quite beneficial. More protein and less junk food is a big factor in eating healthy.

Is too much protein unhealthy though? Well, trials thus far haven’t shown detriments to liver, kidney, and bone health in people without pre-existing conditions. Nor have extremely high protein intakes shown detriments for blood lipids or glucose levels.^[85]

How about longevity? Well, nobody knows for sure. Some studies suggest that restriction of certain amino acids (methionine and BCAAs) could help with longevity.^[86] But these studies are all in cells or mice, since you can’t really do a long term trial on humans because of cost and ethical concerns. Confounders also abound, since high protein usually means high calories. High protein levels in older folks can stave off sarcopenia (age-related muscle loss) as well.^[87]

One option is mixing up your diet, with periods of high protein interspersed with periods of either lower protein or some form of fasting. That may mitigate longevity concerns,^[88] although it won’t be optimal for maximal muscle gain.

Very high protein intake has not been shown to have detriments for the liver, kidneys, and bones. There is a potential concern for longevity, however it's difficult to directly study because long-term trials are not possible, and many confounders exist.

Is it unhealthy to eat a lot of protein during each meal? Is protein wasted?

In a word, no. The outdated maxim that you can only absorb 30 grams of protein per meal is simply not true.

Not to mention that most knowledgeable bodybuilders spread their protein intake in several meals throughout the day in order to absolutely maximize muscle mass (even if the marginal gains after three to four meals are fairly small).^[89]

Eating a lot of protein in one meal (over 30-40 grams) is perfectly fine for most people, and not unhealthy. The protein doesn’t go to waste.

Are the non-protein foods eaten by bodybuilders healthy?

What’s the most direct reason for the increase in obesity-related chronic disease worldwide? Overeating junky food. And what do bodybuilders aim to do? Stay away from eating junky food, otherwise known as food that will not help them either gain muscle or lose fat or lift weights better.

It’s not the 1980s anymore. So not every bodybuilder sustains themselves on mainly chicken, broccoli, and brown rice. But “cheat days” are few and far between for top competitive bodybuilders.

In 2019, a highly controlled metabolic ward study showed that including too much ultraprocessed food in your diet substantially increases food intake and weight gain.^[90] You could probably guess that already, but it does heavily contribute to the low fat levels of bodybuilders: they just don’t eat ultraprocessed foods very often.

And they typically eat a decent helping of veggies and other fiber-rich foods, which are also satiating.^[91][92] So in that way, pro-style diets can be quite beneficial.

Aside from protein, bodybuilders often to stick to several fairly healthy staples such as rice and spinach, or potatoes and broccoli. They also burn off a lot of calories, so starch consumption doesn’t lead to fat gain. Fried foods are rare, as are processed foods, and the overall healthfulness of their staple foods is quite high.

Is rigorous calorie-counting healthy?

Some of the bodybuilding ethos has trickled down over the years, and helped non-bodybuilders lose weight and attain a healthier body composition. Prime among these has been calorie counting: competitive bodybuilders were some of the first people to actively count calories on a regular basis. This might sound obsessive to some, but if you count your calories regularly (sometimes under the label of IIFYM or “If It Fits Your Macros”), it’s much harder to stray into binging territory.

But is calorie counting useful for non-bodybuilders? The evidence is mixed, but studies are scarce and often not of high quality.

Calorie counting definitely works to regulate energy balance and hence weight gain. However, many of the main impediments to health diets are typically psychological, so calorie counting can work until it doesn’t, and you go off the rails.

Numerous editorials and reviews poo-poo calorie counting,^[93][94] and one study even concludes that people dislike calorie-counting apps,^[94] while another associates it with eating disorders.^[95]

Associations and editorials are good to discuss, except that many people have relied on calorie counting apps for adherence to a healthy diet, and massive weight loss and health improvements. This hasn’t been captured by large scale studies yet. So if you like it, stick to it!

Bodybuilders started counting calories before virtually anyone else. If a strict calorie-counting approach helps you, then by all means go for it. You don't have to answer to anyone else’s preferences.

Are repeated bulking and cutting cycles healthy?

First, a note: bulking and cutting is typically followed by a delicate peaking routine, meant to shed water from under the skin yet keep muscles looking full. It can be dangerous to manipulate water and electrolyte intake to prepare for a contest. Even for seasoned competitors, it may cause organ damage or other long-term consequences.^[96]

Second, note the difference between “smart” bulking and “dirty” bulking. Some bodybuilders gain an inordinate amount of weight during bulking cycles, stuffing their faces with too much unhealthy food. But these bodybuilders will invariably lose their competitions, unless they take the right combination of anabolics or have incredible genetics.

Repeated bulking and cutting cycles haven’t been studied in depth for health effects. Presumably, gut health (due to disturbances in gut flora from wild swings in diet) and cardiometabolic health (exacerbated by stresses from heavy exercise during wild swings in diet) may be at risk from dirty bulks and severe cuts. But we await studies specifically looking at this.

Bulking and cutting aren't inherently unhealthy. But repeated bulking and cutting cycles over long periods could theoretically have detrimental effects, especially to gut and cardiometabolic health.

Is it healthy to take a boatload of supplements?

At any one moment, chances of side effects from taking tons of supplements (like 15-20 different supplements each day, or even more) may be low. But compounded over time, the health risk gets higher. Unfortunately, this is a highly understudied area that leaves more questions than answers.

Supplement side effects lead to an estimated 23,000 emergency room visits in the US per year,^[97] and that’s not accounting for possible chronic health effects that occur in the long run, which may not get connected to the specific supplement(s) at fault.

The more supplements you take, the greater the chance is for interactions, especially for supplements that influence hormones and basic metabolic processes. Taking several nutrient supplements along with a protein powder and creatine isn’t likely to be as risky as taking several less-studied supplements, of course.

There haven't been any randomized trials comparing very high supplement use against low supplement use. So nobody knows the impact of prolonged intakes of specific supplement combinations. It's likely, however, that the marginal benefits of taking tons of supplements (like 15-20 different supplements each day, or even more) don't outweigh the risks for most people. How can you even know which supplement is having which effect?

Overall, bodybuilding diets include several health-promoting characteristics. After all, obviously unhealthy diets (such as a diet of chips and soda) would go against the goal of obtaining maximum musculature and minimum fat. Pro bodybuilders need to stay relatively healthy to push maximum reps and weights in the gym.

But the long-term effects of a hardcore bodybuilding diet are unknown, especially with regards to repeated extreme bulking and cutting cycles. Potential risks may be greater for those using higher levels of anabolics.

Supplements are probably not absolutely necessary, although there is a lack of direct research to look to when guiding this decision. One study^[15] found that supplementation with BCAA enhanced exercise capacity and lipid oxidation during endurance exercise after muscle glycogen depletion. However, an extremely important point to remember is that the only way to substantially deplete muscle glycogen is through exercise. That means whatever muscle glycogen you have when you go to sleep at night is mostly all still there in the morning when you’re at the gym, so your muscles may have a full tank of gas for the workout. Perhaps surprising to some, one study^[16] showed that resting muscle glycogen levels were at the same level after an overnight fast and an 84-hour fast! It has also been shown that BCAA intake affects protein metabolism in muscle after but not during exercise.

Supplementing with these amino acids does not appear to have meaningful ergogenic benefits for trained athletes. However, supplementation may provide long-term benefits with respect to muscle growth^[22] and preservation,^[23] which may lead to accumulated performance benefits in the long term.

Some people are creatine nonresponders, meaning that the creatine that they ingest largely fails to reach their muscles. Alternate forms of creatine, such as creatine ethyl-ester, have been marketed to nonresponders, but they lack scientific support. Currently, the best way to lessen creatine nonresponse is to take 5 grams twice per day, each time with protein and carbs, and preferably close to a time of muscle contraction (i.e., before or after your workout). It was once thought that caffeine inhibits the absorption of creatine, although more recent research fails to support this hypothesis ^[24]. Still, if you are not getting the response that you want from creatine, try taking it several hours after your last ingestion of caffeine. Note that even if supplemental creatine fails to enter your muscles, it can still benefit you in other ways, such as by improving your body’s methylation status (methylation is a way for your cells to help manage gene expression).

Caffeine is a popular, well-studied, and effective ergogenic aid. However, the vast majority of the available trials have been conducted in men, and most of the interventions that have been conducted in women tested the ergogenic properties of caffeine during the follicular phase of the menstrual cycle, which possibly minimized the potential effects of hormonal variations on a given study’s performance outcomes (speed, strength, etc).

The menstrual cycle

Adapted from Draper et al. Sci Rep. 2018.^[25]

Only one study has looked at the relationship between menstrual cycle phase and caffeine’s ergogenic effect, and it found that caffeine yielded similar effects regardless of the participants’ menstrual phase.^[26]

Supplementation with creatine has been found to improve physical performance (mainly power output) in athletes competing at the elite level in a host of different sports, including soccer,^[57] volleyball,^[58] wrestling,^[59], and swimming.^[60] That said, the beneficial effects of supplemental creatine appear to be less noticeable in elite athletes than in novice athletes.

Glutamine is the most abundant amino acid in your body. Your body can synthesize it, so it is not an essential amino acid (EAA), but your requirements may at time outpace your rate of synthesis, making glutamine conditionally essential. Historically, however, glutamine has been considered conditionally essential only in the critically hurt or sick — burn victims and other people in whom physical stress is exceptionally high and catabolism (body-tissue breakdown) rampant.^[63]

It is only recently that glutamine studies have started exploring the lesser stress and catabolism caused by strenuous exercise. Some of these studies examined the effect of glutamine on body composition, others on muscle recovery, and yet others on the immune system.

Body composition

The benefits of glutamine in the critically hurt or sick have led some researchers to propose that it might be a useful supplement for athletes engaged in heavy exercise, which is also catabolic in nature.^[64] These researchers tested their hypothesis through a double-blind RCT involving 6 resistance-trained men who consumed glutamine or glycine (0.3 grams per kilogram of body weight) one hour before a weightlifting session.^[65] Glutamine did not benefit performance.

Another group of researchers tested glutamine (0.9 g/kg) against placebo in 31 resistance-trained men and women during a 6-week resistance-training program.^[66] Even such a high daily dose of glutamine did not affect strength or lean-body mass (LBM) more than did placebo (strength and LBM increased in both groups).

Of course, neither study exposed its participants to the high levels of stress experienced by, for instance, burn victims. An RCT involving 18 collegiate male wrestlers aimed to address this issue by comparing placebo with glutamine (0.35 g/kg) during an intensive 12-day cut.^[67] Both groups lost 2 kg, with no significant differences between groups with regard to changes in LBM or fat mass.

A 2018 meta-analysis of 5 studies also found no benefit from glutamine on body composition.^[68] Although glutamine does play a part in muscle synthesis (it is an independent activator of mTOR^[69]), what we obtain through foods seems to suffice; supplementation doesn’t appear to confer additional benefits.

Glutamine supplementation has no effect on lean mass or fat mass, even during aggressive dieting.

Muscle recovery

So glutamine supplementation has no effect on body composition; but might it facilitate recovery from resistance-training sessions?

To help answer that question, researchers gave placebo or glutamine (0.3 g/kg) to 15 recreationally active men right after a muscle-damaging exercise (100 drop-jumps) and for the next four days. They reported that, compared to placebo, glutamine significantly reduced muscle soreness and improved strength recovery.^[70]

However, a study of 17 untrained young men reported that taking glutamine (0.1 g/kg) thrice a week for 4 weeks had no effect on muscle soreness, range of motion, or EMG activity up to 48 hours after a muscle-damaging exercise (eccentric leg extensions at 75% of 1-RM).^[71] Importantly, this latter study involved untrained men and used a smaller dose, a different dosing schedule, and a different exercise protocol — all factors that could explain the discrepancy between the two studies.

A contraction is isometric when the muscle’s length does not change, and isotonic otherwise. An isotonic contraction is called concentric when the muscle shortens under load (as when you lift a dumbbell) and eccentric when it lengthens under load (as when you control the dumbbell on its way down). Your one-repetition maximum (1-RM) is the heaviest weight you can lift (concentric contraction) for a given exercise.

Most recently, a study of 23 resistance-trained men investigated the effects of taking glutamine with leucine.^[72] The men were randomized into three groups and took either leucine (0.087 g/kg), leucine with glutamine (0.087 g/kg + 0.3 g/kg), or a placebo 30 minutes before and after a muscle-damaging exercise (100 drop-jumps), and again before and after recovery tests conducted 24, 48, and 72 hours afterward. Leucine led to better strength recovery at 72 hours only. Leucine with glutamine led to better strength recovery at 24, 48, and 72 hours. Muscle soreness, however, didn’t differ between groups.

Note that these three studies were conducted in men only. Another study recruited 8 men and 8 women, all recreationally active, and gave them placebo or glutamine (0.3 g/kg) one hour before and after a muscle-damaging exercise (80 eccentric contractions at 125% of 1-RM), and again before recovery tests conducted 24, 48, and 72 hours afterward.^[73] Strength recovery was modestly improved in men but not in women, although both sexes experienced significant reductions in muscle soreness.

In recreationally active men, glutamine supplementation around exercise appears to improve strength recovery and might reduce muscle soreness. Only one study lasted more than 72 hours, though, which precludes drawing conclusions about the effects of chronic supplementation. Likewise, only one study included women, which precludes drawing conclusions about the effects of supplementation in women.

Illness

Glutamine is a major fuel for cells of the immune system.^[74] Plasma glutamine levels are reduced after prolonged endurance exercise, and this reduction correlates with an increased risk of infection.^[75]

An early study of endurance athletes (marathoners and ultra-marathoners) reported that taking 5 grams of glutamine right after an athletic event and 2 hours later significantly reduced the occurrence of infections over the following week.^[76] Specifically, 19% of the glutamine group reported illness, compared to half of the placebo group.

No other trial has studied the effects of glutamine on infection as an outcome in athletes, but other trials have looked at various aspects of the immune system,^[68] such as white-blood-cell function^[77][78] and salivary IgA concentrations,^[79] and none has found a relationship between an exercise-induced decrease in plasma glutamine levels and changes to the immune system.^[80]

Glutamine’s benefits may be mediated by its effects on the intestinal barrier, as more recent evidence has begun to suggest. Prolonged endurance exercise is known to cause leaky gut — a condition in which heat stress and reduced blood flow to the gastrointestinal tract cause intestinal cell damage that loosens tight junctions between cells, allowing for the absorption of things that are not supposed to pass through the intestinal barrier.^[81]

In a recent study, glutamine (0.25, 0.5, and 0.9 g/kg) showed a dose-dependent reduction in exercise-induced intestinal permeability.^[82] In an earlier study, the reduction in intestinal permeability from glutamine supplementation had correlated with reductions in serum endotoxin and in inflammatory markers.^[83]

Glutamine is an important source of energy for intestinal cells and the immune system. Supplementation may reduce exercise-induced dysfunctions of the intestinal tract and might decrease the risk of falling sick from prolonged endurance exercise.

In Summary

There is no evidence that supplemental glutamine helps build muscle or improve body composition.

There is evidence that supplemental glutamine improves strength-training recovery. It may also help maintain the integrity of the gastrointestinal tract during prolonged endurance exercise and thus decrease the risk of getting sick afterward.

So if your goal is to build muscle, don’t waste your money on glutamine. Other supplements are more likely to help, notably creatine, and of course you should ensure you get enough protein.

Exercise performance tends to be better in the late afternoon/early evening (1–8 p.m.) than the morning (8–10 a.m.),^[104] particularly for short-duration maximal exercise (e.g., a 30-second Wingate test or tests of jump height, repeated sprint ability, or maximal voluntary contraction).^{[105][106][104]} Currently, there is limited evidence to suggest that a specific time of day is best for endurance exercise performance.^[104]

The main mechanism that underlies this finding is core body temperature, which reaches a peak in the evening hours.^[107][108] An increase in core body temperature may improve exercise performance by enhancing metabolic reactions, increasing the extensibility of connective tissue, reducing muscle viscosity, and increasing the conduction velocity of action potentials.^[109] Moreover, using cold water immersion to decrease core body temperature before evening exercise has been shown to decrease muscular strength and repeated sprint ability.^{[110][111][112]}

While exercise performance may be better in the evening than the morning at baseline, consistently training in the morning can offset this natural diurnal variation in performance. Indeed, long-term resistance exercise interventions that have participants train in the morning or evening report similar increases in strength and hypertrophy.^[106] This suggests that training at a consistent time each day is more important than the time of day training takes place. Therefore, an individual interested in maximizing exercise adaptations should choose a time of day that suits their preferences and will facilitate long-term training adherence.

Besides consistently training in the morning, there are acute strategies that can diminish the natural diurnal variation in exercise performance, including exercising in a warm and humid environment,^[113][114] performing an extended warm-up (e.g., 12 minutes of cycling at 50% of VO₂max interspersed with brief accelerations of 5 seconds),^{[115][116][117]} ingesting caffeine,^[118][119] and listening to music.^[120][121]

While there is a general consensus that exercising in the morning or afternoon benefits sleep, it’s often recommended to avoid exercising, especially at a high intensity, in the evening in fear of it negatively affecting sleep.

However, according to a meta-analysis published in 2021, an acute bout of high-intensity exercise performed 2–4 hours before bedtime does not disrupt sleep.^[122] In fact, performing high-intensity exercise 2 hours before bedtime tends to increase total sleep time (+16 minutes) and decrease the time it takes to fall asleep (−5 minutes). However, longer duration high-intensity exercise (>30–60 minutes) may decrease rapid-eye movement sleep to a small extent (−3%).

In a 7-week study in elite youth soccer players, an evening high-intensity exercise session did not affect sleep quality and slightly increased sleepiness at bedtime, compared to nights where no exercise was performed.^[123]

In sum, high-intensity evening exercise does not appear to negatively affect sleep. Careful consideration should be given to pre-workout supplements when exercising in the evening, as products containing caffeine can negatively affect sleep.

The evidence is mixed, but the preponderance of the evidence suggests that it’s unlikely that creatine will increase your testosterone levels.

Three randomized controlled trials conducted in healthy young men reported that supplementing with creatine for 1–3 weeks produced small increases in the levels of testosterone or dihydrotestosterone (DHT; a highly active androgen converted from testosterone).^{[124][125][126]} One of the 3 trials looked at the effect of creatine loading (25 grams/day for 1 week) followed by a maintenance phase (5 grams/day for 2 weeks) on testosterone and DHT in 20 young, healthy rugby players. Although no effect on testosterone was found, creatine increased the levels of DHT by 12 nanograms of DHT per deciliter of blood (ng/dL).^[124] The other 2 trials found that supplementation with creatine for 1 week in healthy, active young men increased the concentrations of testosterone by 57 ng/dL and 150 ng/dL.^[125][126]

Conversely, 10 other trials (involving a total of 218 participants) looking at the effect of supplemental creatine at daily doses of 3–25 grams on testosterone levels for up to 12 weeks have found no statistically significant effect.^{[127][128][129][124][130][131][132][133][134][135]} The participants in the majority of these trials were healthy, active young men. With regard to the form of creatine used, 9 trials administered creatine monohydrate, whereas 1 trial administered creatine malate. It’s worth noting that no trials have looked at the effect of creatine on testosterone in men with abnormally low testosterone levels.

Taken together, the available evidence suggests that supplementing with creatine is unlikely to increase testosterone levels, at least in young healthy men whose testosterone levels are within the normal range.