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 the health benefits of being a “weekend warrior,” how many calories weightlifting really burns, and how L-carnitine L-tartrate might enhance testosterone’s muscle-building effects.

You get most of the health benefits of exercise by training just once or twice per week. 

Source: “Association of the “Weekend Warrior” and Other Leisure-time Physical Activity Patterns With All-Cause and Cause-Specific Mortality: A Nationwide Cohort Study” published on July 5, 2022 in JAMA Internal Medicine.

The World Health Organization (WHO) pegs the minimum amount of exercise needed to stave off disease and support health as 150 minutes of moderate-intensity exercise, 75 minutes of vigorous-intensity exercise, or an equivalent combination of both every week.  


If you talk to most personal trainers, doctors, or just fit people, they’ll probably say that you should split this into three or four 30-to-45-minute workouts spread throughout the week, which is a fine workout frequency for most. 

What if you have an unpredictable or demanding schedule during the week, though? 

What if you’d rather just train on the weekends?

Would this be as effective as training throughout the week, or is exercising more like eating enough protein or getting enough sleep—something you need to do basically every day to reap the health benefits?

That’s the question scientists at the Federal University of São Paulo sought to answer in this study.

Instead of collecting original data, the researchers combed through the US National Health Interview Survey (NHIS)—a national survey conducted between 1997 and 2013 that collected health-related data from thousands of people, including information about their exercise habits. This means the study was retrospective—looking back at people’s habits and outcomes, teasing out connections, and then quantifying and validating them with statistics. 

Their initial search found 481,566 eligible participants, though the researchers later whittled this down to 350,978 people (~51% women, 49% men, with an average age of ~41 years old for both sexes) by omitting people who were already sick, didn’t provide details on their workout routine, or couldn’t exercise.

The researchers then classified the participants as either “weekend warriors,” who exercised no more than twice per week, or “regularly active people,” who exercised three or more times per week. They also quantified how much total exercise people did per week and how hard they trained. 

They found that how people divided their exercise throughout the week had no impact on their health—weekend warriors had the same risk of dying from all causes as regularly active folks—so long as they racked up equal amounts of total exercise. In other words, there was no downside to concentrating all of your time spent working out into one or two workouts per week.

The number one predictor of health was simply how much total exercise people accumulated over time. The more they worked out, the healthier and less likely to die they were. 

While this was an observational study and thus it can’t prove cause and effect, the results square with several previous studies which found that you don’t need to go “all in” on a rigorous workout regimen to stay fit and healthy. Just one vigorous ~75-minute workout per week dramatically reduces your risk of death, disease, and dysfunction (although more is still substantially better).

Keep in mind that this study only looked at improving health, not strength, muscle growth, or athletic performance, and these goals generally require a higher volume and frequency of exercise. 

If you need help deciding which training program to follow to reach your health and fitness goals, take the Legion Strength Training Quiz, and in less than a minute, you’ll know the perfect strength training program for you. Click here to check it out.

TL;DR: From a health perspective, how you split up your workouts throughout the week doesn’t matter. Doing one or two longer workouts is just as good as 3, 4, or 5+ shorter ones, so long as you do the same total amount. 

Weightlifting burns about 6 calories per minute (360 calories per hour)

Source: “Acute Behavior of Oxygen Consumption, Lactate Concentrations, and Energy Expenditure During Resistance Training: Comparisons Among Three Intensities” published on December 15, 2021 in Frontiers in Sport and Active Living.

As I’ve said before, burning calories shouldn’t be your main goal when lifting weights, but it’s a nice byproduct that makes losing weight a shade easier. 

How many calories do you really burn smashing steel, though? 

Wearable devices like the FitBit, Apple Watch, and Whoop are often used to estimate (albeit inaccurately) how many calories you burn during cardio workouts, but they’re essentially useless for estimating your calorie burn while weightlifting. 

A team of researchers at Metropolitanas Unidas College conducted this study to help us answer this question. 

They had 15 experienced male weightlifters do 3 workouts consisting of the chest press, pec deck, squat, lat pulldown, biceps curl, triceps extension, hamstrings curl, and machine crunch. 

The weightlifters performed these exercises with either 60, 75, or 90% of their one-rep max, doing the same number of total reps in each workout, and rested 2 minutes between sets and 48 hours between workouts. During the workouts, they also wore a spirometer (a device that estimates how many calories you’re burning by measuring how much air you breathe).

The weightlifters burned the most calories in the high-intensity workout, mainly because it lasted the longest (116 minutes vs. 44 minutes for the low-intensity workout). Regardless of the protocol, all of the weightlifters burned about 6 calories per minute of weightlifting (including the rest periods). 

Here’s a graph to illustrate this:

Calories Burned During Strength Training-v2

Of course, this is only one study looking at experienced male weightlifters, so it’s difficult to say whether the results apply to females new to weightlifting, for example. One limitation of this study is that the researchers didn’t measure how calorie expenditure related to body weight or strength (bigger, stronger people generally burn more calories), but any differences would probably have been minor. 

Given how consistent the results were (basically everyone burned between 4 and 8 calories per minute), ~6 calories per minute (including rest periods) is a reasonable rule of thumb.

Fun stuff, but how useful is this formula?

Should you start calculating how many calories you burn lifting weights? 

I don’t think so.

Reason being, so long as you accurately calculate your calorie intake over time, burning slightly more or fewer calories on any given day doesn’t matter. Put differently, if you consistently track your “calories in” and monitor how this affects your weight over time, you don’t need to micromanage your “calories out.” 

(And if you feel confused about how many calories you should eat to reach your health and 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: Most people burn about 6 calories per minute while lifting weights (including rest periods).

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L-carnitine L-tartrate may enhance testosterone’s muscle-building effects.

Source: “Androgenic responses to resistance exercise: effects of feeding and L-carnitine” published on July 1, 2006 in Medicine & Science in Sports & Exercise.

Aside from protein, basically no supplements directly build muscle (and protein is arguably more of a food than a supplement). Most, like creatine, beta-alanine, and L-citrulline, help you train harder and recover faster, but that’s not the same as actually building muscle.

Some scientists think L-carnitine L-tartrate may be different.

L-carnitine L-tartrate (LCLT) is an amino acid composed of L-carnitine bound to tartaric acid. The tartaric acid is essentially inert, however, and is included to stabilize and deliver the L-carnitine.

Research shows that LCLT helps you recover faster from exercise, though scientists still don’t fully understand how. At present, there are at least three major theories, one of which states that LCLT changes the hormonal status of cells by increasing their androgen receptor content, essentially helping cells “soak up” more testosterone and thus recover faster.

(An androgen receptor is the “gateway” through which androgens like testosterone enter cells and exert their functions.)

And it’s this theory that scientists at the University of Connecticut wanted to investigate with this study.

The researchers split 10 recreational male weightlifters into two groups. One group took two grams of LCLT per day, divided into two one-gram doses at breakfast and lunch, and the other took a placebo at the same times.

After 3 weeks, the participants completed 2 workouts separated by 48 hours, consisting of the squat, bench press, bent-over row, and shoulder press. The participants did 4 sets of 10 reps of each exercise with 80% of their one-rep max and rested 2 minutes between sets.

The researchers found that supplementing with LCLT boosted levels of androgen receptors in the participants’ quads even before they’d exercised. When the participants exercised, androgen receptor levels increased further.

Taking LCLT with water had no additional benefit, but when the participants took LCLT with protein and carbs after exercise, androgen receptor levels rose significantly more.

Specifically, when comparing the ideal trifecta of LCLT, protein, and strength training against the true control (placebo before exercise), androgen receptor expression increased by ~50%.

The researchers also found changes in several other hormones:

  • As androgen receptor levels increased, testosterone levels in the blood decreased, suggesting more testosterone was being sucked up by cells.
  • Taking LCLT with carbs and amino acids reduced cortisol levels more than taking a placebo with carbs and amino acids (high cortisol levels are generally “bad” for muscle growth).
  • Luteinizing hormone, which is involved in the production of testosterone in the testes, also increased similarly to testosterone.
  • Sex-hormone binding globulin (SHBG) increased with LCLT supplementation. Sometimes SHBG reduces sex hormone levels, but that wasn’t the case in this study.

The most titillating interpretation of these results is that LCLT could be a “testosterone synergist”—a compound that amplifies the benefits of testosterone, helping even young, active men reap additional benefits from their body’s natural hormone production. Hypothetically, this would mean LCLT could directly impact muscle building, rather than just acting as a muscle-recovery supplement.

A more clear-eyed interpretation would be that the transient tides of hormone levels often don’t correlate with real changes in muscle growth, fat loss, or other tangible benefits. For example, testosterone, insulin-like growth factor, and growth hormone all spike after lifting weights, but research shows these short-term changes in hormone levels don’t make a lick of difference in muscle growth. Likewise, HIIT workouts goose growth hormone levels, but don’t produce more fat loss than moderate-intensity cardio workouts that burn the same number of calories. 

Until we have more research on LCLT showing it directly causes muscle growth, it’s best to think of this supplement as “promising” rather than “proven.”

That said, there’s still good evidence that LCLT can indirectly improve muscle growth by reducing exercise-induced muscle damage and soreness and improving muscle repair and insulin sensitivity

All of this is why we decided to include two grams of LCLT in Legion’s post-workout recovery supplement, Recharge, along with two other ingredients that help boost muscle growth, improve recovery, and reduce muscle soreness.

(Or if you aren’t sure if Recharge 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: Supplementing with L-carnitine L-tartrate may amplify the effects of testosterone in the body, but it’s unclear whether this correlates with real-world changes in muscle growth, fat loss, or other tangible benefits.

+ Scientific References