It’s estimated that there are over 2+ million scientific papers published each year, and this firehose only seems to intensify.

Even if you narrow your focus to fitness research, it would take several lifetimes to unravel the hairball of studies on nutrition, training, supplementation, and related fields.

This is why my team and I spend thousands of hours each year dissecting and describing scientific studies in articles, podcasts, and books and using the results to formulate our 100% all-natural sports supplements and inform our coaching services. 

And while the principles of proper eating and exercising are simple and somewhat immutable, reviewing new research can reinforce or reshape how we eat, train, and live for the better. 

Thus, each week, I’m going to share three scientific studies on diet, exercise, supplementation, mindset, and lifestyle that will help you gain muscle and strength, lose fat, perform and feel better, live longer, and get and stay healthier. 

This week, you’ll learn whether caffeine’s effects diminish with use, how long to rest between supersets, and how “productive daydreaming” makes dieting easier.


Regular coffee drinker? Caffeine supplements can still boost your workout performance. 

Source: “Can I Have My Coffee and Drink It? A Systematic Review and Meta-analysis to Determine Whether Habitual Caffeine Consumption Affects the Ergogenic Effect of Caffeine” published on May 10, 2022 in Sports Medicine (Auckland, N.Z.).

Almost every pre-workout supplement is stiff with caffeine because it improves athletic performance in virtually every way. For example, it boosts strength, endurance, and power, and reduces fatigue and the perception of effort.

And all of this is why three-quarters of elite athletes consume caffeine before they compete.

There’s a downside to habitually guzzling gogo juice, though: caffeine’s stimulating effects wane with regular use, and tolerance doesn’t take long to develop.

Which begs the question: How much do caffeine’s performance-boosting effects diminish over time?

To help answer this question, scientists at the University of São Paulo conducted this meta-analysis. 

They analyzed the data from 60 studies containing a total of 1,137 participants (958 men and 179 women). Of these 1,137 people, 718 were “trained,” 400 were “untrained,” and 19 were “elite.”

The researchers then dug into each study, noting the participants’ age, weight, sex, training experience, and habitual caffeine consumption, what exercise they did during the study, how they consumed caffeine (coffee, energy drinks, capsules, etc.), and the results of each study.

The results showed that caffeine boosts strength, power, and endurance in trained and untrained men and women, regardless of whether they consume caffeine regularly or not. They also showed that caffeine exerts these effects whether you take a smaller or larger dose than usual and that abstaining from caffeine for a period doesn’t amplify its effects.

The only thing that appeared to make caffeine less effective was taking more than 6 milligrams per kilogram of body weight (2.7 mg per lb. of body weight), which tends to cause negative side effects.

This was a particularly thorough and comprehensive meta analysis, which is why we can probably say with confidence that caffeine . . .

  • Still offers some benefits to people who habitually consume it
  • Boosts performance across a range of different exercise types (strength, power, and endurance)
  • Is equally effective for trained and untrained men and women
  • Works best when you take 3-to-6 milligrams per kg of body weight

This is similar to the conclusions of a randomized controlled trial I reviewed a few months ago, which found that cyclists who took a much higher dose of caffeine than they were used to performed significantly better in a series of time trials. In this case, though, the researchers concluded that athletes could still benefit even from taking their “normal” dose. 

Before we get too giddy about the near-infinite ergogenic effects of caffeine, there are a couple of important caveats to consider. 

First, most studies (including most in this meta analysis) gather data about caffeine consumption using questionnaires, which are prone to inaccuracies. 

Second, there are no objective standards across studies about what constitutes a high, moderate, or low caffeine intake, and most of the studies (76%) included in this meta-analysis didn’t report the volunteers’ average habitual caffeine consumption. What this means is that someone who normally drinks, say, 150 mg of caffeine per day might be classified as having a “high” intake in one study and a “low” intake in another, depending on how much the other participants consumed. This makes it difficult to compare results between studies. 

Third, although meta analyses help you understand broad trends in research, it’s still instructive to look at individual randomized controlled trials if you’re gunning for more specific conclusions. And in this case, most of these studies show caffeine’s performance-boosting effects to sag with repeated use (although probably don’t disappear entirely, as some claim).  

At the end of the day, what this meta analysis shows is that taking 3-to-6 mg of caffeine per kilogram of body weight boosts athletic performance for most people most of the time and the benefits fade with continued use but don’t dissipate completely. 

And if you want an all-natural pre-workout supplement that contains a clinically effective dose of caffeine as well as five other ingredients designed to increase energy, improve mood, sharpen mental focus, increase strength and endurance, and reduce fatigue, try Pulse.

(Or if you aren’t sure if Pulse is right for you or if another supplement might be a better fit for your budget, circumstances, and goals, then take the Legion Supplement Finder Quiz! In less than a minute, it’ll tell you exactly what supplements are right for you. Click here to check it out.)

TL;DR: Caffeine’s performance-boosting effects probably do wane over time, but the benefits don’t disappear entirely. 

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This is how long you should rest between supersets to get stronger.

Source: “The Effect of Different Rest Intervals Between Agonist-Antagonist Paired Sets on Training Performance and Efficiency” published on March 1, 2022 in Journal of Strength and Conditioning.

I recently summarized a narrative review investigating the most time-efficient way to train. One of the recommendations in that study was to incorporate supersets wherever possible and practical.

This subsequent study by scientists at the Federal University of Rio de Janeiro builds on that recommendation by investigating the most efficient way to include antagonist paired sets—a type of supersets—in your training.

Antagonist paired sets involve alternating between two exercises that train different muscle groups and resting either a short time between each exercise or slightly longer once you’ve completed both exercises back-to-back.

For example, you could do a set of bench press (which trains your chest, shoulders, and triceps), immediately followed by a set of pull-ups (which trains your back and biceps), and then rest 2-to-3 minutes. Then, you’d continue this pattern until you’ve finished all of your sets for both exercises. Or, you could do a set of bench press, rest ~1 minute, do a set of pull-ups, rest ~1 minute, and then continue until finishing all of your sets. 

With either strategy, you can perform the same amount of work in less time without your performance skidding.

This study aimed to find the optimal rest duration for antagonist paired sets that allows you to do the most high-quality work in the least time (to optimize an already efficient process, basically).

The researchers had 18 male Brazilian military personnel complete 4 workouts. Each workout consisted of 3 sets of 4 exercises, paired into 2 “antagonist paired set sequences” (more on the specifics soon). The only difference between each workout was how long the participants rested between each antagonist paired set sequence. 

The four possibilities were 1, 2, or 3 minutes of rest between each antagonist paired set sequence, or the participants self-selected their rest interval, which meant they rested as long as it took to feel ready to do the next antagonist paired set sequence.

The antagonist paired set sequences were as follows:

In other words, the soldiers did a set of bench press, then, without resting, a set of bench row, then rested according to the protocol they’d been given that day and repeated this three times.

Afterward, they used the same protocol but swapped the bench press and bench row for the lat pulldown and overhead press.

The results showed that the longer soldiers rested between sets, the more reps they could perform in a workout and the longer their workouts lasted—not surprising.

Although resting just 1 minute between sets helped the soldiers do more volume load (weight x sets x reps), their strength declined significantly as the workout wore on compared to when they used longer rest intervals. They were able to do more total “work” with short rest intervals, but the quality of their workout dipped dramatically. 

When given the option to rest as long as they wanted, the soldiers generally rested 2.5 minutes, so their performance was about the same when they rested 2 or 3 minutes.

Everything considered, 2-to-2.5 minutes was the “sweet spot” for rest intervals—long enough to maximize workout performance, while short enough to get in and out of the gym as fast as possible. 

(And if you’d like more advice about how to make the most of your time in the gym, take the Legion Strength Training Quiz, and in less than a minute, you’ll know the perfect strength training program for your circumstances and goals. Click here to check it out.)

TL;DR: Two to two-and-a-half minutes is the “sweet spot” for rest intervals between antagonist paired sets—more than this is generally unnecessary, and less than this significantly hurts your performance.

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Focusing on the future makes dieting easier in the present.

Source: “Episodic future thinking reduces eating in a food court” published on October 28, 2015 in Eating Behaviors.

Most of us like to imagine we’re forward-thinking, but research shows this simply isn’t true—we almost always prefer immediate gratification even when the future reward is bigger and better. 

For example, imagine you’re given the choice of $90 now or $100 in two weeks. Most people would take the $90 now and be happy. Even when they know the extra $10 is only 14 days away, the idea of having something good now versus something great later is too tempting to pass up. 

This proclivity for shortsightedness—known as hyperbolic discounting—is as disastrous for our fitness as it is our finances. 

Many studies show that it underlies a host of self-destructive behaviors, including substance abuse, pathological gambling, risky sexual behavior, and most notably for us, an inability to commit to health-promoting habits. For instance, we might want to look good and feel confident in our swimsuit at the beach, but all too often we succumb to the siren song of short-term pleasures like sugary treats and cozy couch-bound laziness.  

You can countervail this pernicious mind virus with what scientists call episodic future thinking (EFT), which is essentially productive daydreaming. All that’s required is to imagine a specific, personal, and detailed future event linked to a personal goal.

Lab research shows that EFT can help obese and non-obese adults and adolescents and children control of their impulses, which then leads to faster weight loss.

For example, in a study conducted by scientists at the University at Buffalo School of Medicine and Biomedical Sciences, researchers gave 29 overweight or obese women who wanted to lose weight the opportunity to eat whatever they wanted in a food court full of deliberately tempting, unhealthy food. 

The day before the participants were exposed to this cornucopia of calories, the researchers split everyone into two groups: 

  1. Group one used an episodic future thinking (EFT group) protocol.
  2. Group two used an episodic recent thinking (ERT group) protocol.

The researchers asked the participants in the EFT group to think of 5 future health goals they would like to complete in the next 3 weeks and 5 future events they had planned or anticipated would happen in the next 3 weeks. The researchers also helped participants pair their goals with the events and encouraged them to imagine the events vividly (location, time, emotions, context, and so on.)

Their final goals looked something like this:

“In three weeks, I will go to the concert with my friend. We will sit near the back so we can chat more easily. I will be feeling strong and proud of myself after having achieved my goal of going to the gym three times per week. I will be feeling excited and happy to see the band play for the first time.” 

This encouraged the participants to project their thinking into the future.

The researchers asked the participants in the ERT group to list 5 things they did regularly and enjoyed and rate their importance. They also asked them to think of 5 events that had happened in the past 24 hours, again remembering them in terms of vividness, emotions, and context. This encouraged the participants to think about the recent past.

All participants recorded themselves reading each of their goals or memories on an mp3 player and on the following day, played the recordings back to themselves while they ate at the food court. 

The results showed that the EFT group consumed significantly fewer calories (~540 vs. ~749) and chose foods containing less fat (24% vs. 37%) and more protein (26% vs. 19%) than the ERT group without any prior guidance about food choices from the research team.

Thus, simply getting people to think about the future helped them make better eating decisions in the present. 

If you have trouble sticking to your health and fitness goals (or any goals for that matter), EFT is a low-risk, potentially-high-reward strategy that’s worth trying. Here’s an example to show you what you need to do to succeed:

Imagine your wedding is on the horizon, and you want to ensure you fit nicely into your dress or suit for the big day. Every time you’re tempted to renege on your diet, take a second to remind yourself why you want to lose weight and imagine things such as:

  • Where you’ll be on your wedding day.
  • How happy you’ll be to see your closest friends and family.
  • How pleased you’ll be with the event, including the room decorations, the entire wedding party, and your dress or suit.
  • How satisfied you’ll be for sticking to your diet and exercise plan, and how confident you’ll feel standing in front of all those people.
  • How comfortable you’ll feel having your picture taken, knowing you achieved the body you wanted.

Do this for as long as it takes to feel that day—taste the flavors and smell the smells—and your lucid vision of success can outshine the luster of immediate gratification.

(And if you’re looking for more information about how to diet successfully and want advice about what diet you should follow to reach your fitness goals, take the Legion Diet Quiz, and in less than a minute, you’ll know exactly what diet is right for you. Click here to check it out.)

TL;DR: When you feel like throwing in the towel while dieting, vividly imagine what it will feel like to have achieved your goal at a specific time and place in the future. 

+ Scientific References