Research Roundup #3: Activation Exercises to Boost Glute Growth, the Problem with the 5:2 Diet, the Best Time of Day to Do Cardio, and More

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 five 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 “activation exercises” help you build more muscle, how effective the 5:2 diet is for preserving muscle while you diet, whether you burn more calories doing cardio in the morning or evening, and more.

Table of Contents

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• Glute “activation” exercises boost glute activation during squats.
• The 5:2 diet may not be as effective at preserving muscle while cutting as continuous dieting.
• Supplementing with vitamin D may reduce injury risk and boost performance.
• Blood flow restriction training helps you gain muscle just as effectively as traditional training, even if you don’t take sets to failure.
• When it comes to fat loss, it doesn't much matter what time of day you do cardio.

Glute “activation” exercises boost glute activation during squats.

Source: “Activation training facilitates gluteus maximus recruitment during weight-bearing strengthening exercises” published on February 9, 2022 in Journal of Electromyography and Kinesiology.

Many personal trainers tout the benefits of “activation exercises,” which are basically warmups designed to help a particular muscle “fire” harder during your workout. And while the benefits of activation exercises are often oversold, a recent study conducted by scientists at the University of Southern California shows they have some merit. 

In this study, the researchers hooked 12 men and women up to an EMG and measured how active their glutes were during 3 sets of 3 reps of bodyweight squats and split squats. The participants then went home and performed “glute activation training” twice per day for a week before returning to the lab to repeat the squat session.

The glute activation training consisted of three exercises: Side-lying clamshells, side-lying hip abduction (lifting your leg up), and quadruped fire hydrants. The participants completed three one-minute isometric holds for each exercise and used resistance bands to make the exercises harder as necessary.

The results of the second squat session showed that following a week’s worth of glute activation exercises, the participants’ glutes were 57% and 53% more active in the squat and split squat, respectively.

It’s important to remember that more muscle activation doesn’t always lead to more muscle growth, but given that it’s a low-risk strategy that could yield positive results, doing daily glute activation training may be worthwhile if growing your glutes is high on your priority list.

Withal, a counterargument is that it’s also possible any benefits from glute activation exercises could disappear as you get stronger on exercises like the barbell squat, which will force your glutes to activate regardless of how “sleepy” they are generally. In other words, it’s possible that doing bodyweight warmup exercises before heavy squats to get your glutes firing is like blowing on a bullet to make it fly faster.

(If you like training tips like this and want an even more in-depth guide to how you should train to build your best body ever, check out my fitness books for men and women, Bigger Leaner Stronger and Thinner Leaner Stronger.)

The Takeaway: Performing “glute activation exercises” such as side-lying clamshells, side-lying hip abduction, and quadruped fire hydrants twice per day significantly increases how active your glutes are during bodyweight squats and split squats, which could help you get more glute growth out of your lower-body training.

The 5:2 diet may not be as effective at preserving muscle while cutting as continuous dieting.

Source: “Intermittent Fasting and Continuous Energy Restriction Result in Similar Changes in Body Composition and Muscle Strength When Combined With a 12 Week Resistance Training Program” published on January 27, 2022 in European Journal of Nutrition.

Diets that involve fasting have become very popular as a weight-loss strategy in recent years. Still, many people are reluctant to try them because it’s unclear how effective they are at helping you preserve muscle. A recent study conducted by scientists at Swinburne University of Technology investigated this concern.

The researchers took 17 untrained 18-to-45-year-old men and women and split them into two groups: A continuous diet group that maintained a 20%-calorie deficit and consumed 1.4 grams of protein per kilogram of body weight per day, and a 5:2 diet group who ate at maintenance on 5 days per week, and in a 70% deficit on the other two. The 5:2 group also had to consume 1.5 grams of protein per kilogram of body weight per day on non-fasting days, and eat all of their calories between 12 p.m. and 6 p.m. and 1.1-to-1.2 grams of protein per kilogram of body weight per day on calorie-restricted days. 

These dietary stipulations ensured that all participants averaged a daily calorie deficit of 20% across the week and consumed an average of 1.4 grams of protein per kilogram of body weight per day (which is slightly below optimal, but not terrible).

The participants also performed a strength test at the beginning and end of the study, which consisted of a three-rep max test on the bench press and leg press and a single set of as many reps as possible on each exercise using 70% of the participant’s one-rep max. In addition, the participants performed three resistance training sessions per week consisting of 3 sets of 12-to-15 reps of push-ups, squats, rows, lunges, bicep curls, and dips.

The results of the strength tests revealed what you’d expect: both groups gained about the same amount of strength, but this is likely because all the participants were new to weightlifting and thus hypersensitive to its strength-building effects.

The body composition results were more interesting. According to the DXA results taken before and after the trial, both groups lost about the same amount of weight and retained about the same amount of muscle. However, results from the ultrasound and CT scans showed that the group that dieted continuously experienced larger increases in a few measures of muscle size.

While most of these measurements failed to reach statistical significance, they probably would have if the study had lasted longer than 12 weeks. And this suggests that continuous dieting may be better for maintaining muscle while dieting (or gaining muscle while losing fat if you’re new to weightlifting) than the 5:2 diet.

(And if reading this has got you wondering what kind of diet is right for your circumstances and goals, then take the Legion Diet Quiz! In less than a minute, you’ll know exactly what diet is best for you. Click here to check it out.)

The Takeaway: If you’re cutting, you’ll probably retain more muscle and lose the same amount of fat using a continuous calorie deficit instead of following the 5:2 diet.

Supplementing with vitamin D may reduce injury risk and boost performance.

Source: “The Effect of Vitamin D Supplementation in Elite Adolescent Dancers on Muscle Function and Injury Incidence: A Randomised Double-Blind Study” published on June 12, 2018 in International Journal of Sports Physiology and Performance.

Many people take a vitamin D supplement because of the myriad ways it optimizes your health, but this study shows that D might also have benefits for people who are focused on performance.

The researchers at the University of Wolverhampton split 71 elite young dancers into a vitamin D supplement group and a placebo group. Both groups gave blood samples at the beginning of the trial and then took 120 pills over 4 days. In the vitamin D group, the pills contained a total of 120,000 IU of vitamin D, and in the placebo group, the pills were inert.

(This may sound like a huge amount of vitamin D to take, and it is, but research shows that it’s safe and effective provided you have clinical supervision.)

The participants then tested their strength using an “isometric mid-thigh pull” (a machine exercise that’s similar to a rack pull) and power using different jumping exercises. For the rest of the four-month trial, the participants recorded all of their injuries and consumed no other supplements. At the end of the study, the participants gave another blood sample, then retested their strength and power.

The results showed (unsurprisingly) that the vitamin D group increased their D levels significantly more than the placebo group. They also increased their strength by around 7%, while the placebo group lost a little bit of strength, which is interesting, but not mind blowing.

The most surprising finding, though, was the effect vitamin D had on injury rates.

The participants in the vitamin D group were more likely to be injury-free (40% vs. ~36%) and far less likely to have a “traumatic injury” (~11% vs. ~32%) than the placebo group.

This suggests that taking vitamin D might make you less prone to injuries (and traumatic injuries in particular) and give you a little performance boost to boot, making it a beneficial supplement for most athletes. The exact mechanisms behind this aren’t clear, but given vitamin D’s role in supporting the immune system, and the immune system’s role in muscle recovery and tissue repair, it seems possible that vitamin D boosts the body’s ability to repair itself. 

(And if you want a multivitamin that contains a clinically effective dose of vitamin D, as well as 30 other ingredients designed to enhance your health and mood and reduce stress, fatigue, and anxiety, try Triumph for men and women.)

The Takeaway: Participants who supplemented with vitamin D increased their strength by a small amount and lowered their risk of suffering an injury compared to participants who took a placebo.

Blood flow restriction training helps you gain muscle just as effectively as traditional training, even if you don’t take sets to failure.

Source: “Acute cellular and molecular responses and chronic adaptations to low-load blood flow restriction and high-load resistance exercise in trained individuals” published on September 23, 2021 in Journal of Applied Physiology.

Many bodybuilding stick-in-the-muds still view blood flow restriction training (BFR) as futile fitness flimflam, but according to the results of this study (and many others), it’s a technique that deserves more attention.

In this nine-week study, scientists at The University of Queensland compared the effects of training with light weights and BFR and training with heavy weights without BFR (traditional strength training) on strength and muscle growth (they also examined various other molecular processes, but they aren’t relevant for this discussion).

The researchers split 21 experienced male and female weightlifters into a BFR group and a traditional training group, then instructed them to perform 3 lower-body training session per week, consisting of squats, leg press, and knee extensions on days 1 and 3, and Bulgarian split squats and knee extensions on day 2.

The high-load group began the study using weights that were ~75% of their one-rep max for each exercise and did 4 sets of 8 reps with 2 minutes rest between sets. The BFR group started using weights that were ~30% of their one-rep max for each exercise and did one set of 30 reps, followed by 3 sets of 15 reps, with 45 seconds of rest between sets.

All participants recorded how many reps in reserve they had after each set. Participants in the high-load group increased their weights if they had more than two reps in reserve after two consecutive sets, and participants in the BFR group increased their weights if they had more than four reps in reserve after two consecutive sets.

The results showed that squat one-rep max increased in both groups, though it increased significantly more in the traditional training group (9 kilograms in the BFR group versus 19 kilograms in the traditional training group), and quad muscle size increased about the same amount in both groups.

The main upshot from all of this is that BFR training is just as effective for building muscle as traditional strength training, despite using much lighter weights and not taking each set to failure. While it wasn’t as effective at increasing strength, this isn’t surprising, since strength is highly specific to the rep range you train with. 

Thus, if you’re using BFR training to allow your joints to heal from an injury, do more volume, or just inject a little variety into your training, you can rest easy knowing that it’s not any worse for building muscle than traditional, heavier training. Plus, you don’t need to grind each set to failure to get the benefits, either.

The Takeaway: Blood flow restriction training with light weights helps you build just as much muscle as traditional, heavy strength training, even if you don’t take each set to failure.

When it comes to fat loss, it doesn’t much matter what time of day you do cardio.

Source: “Effect of Morning and Evening Exercise on Energy Balance: A Pilot Study” published on February 15, 2022 in Nutrients.

Recent research shows that our circadian rhythm causes our body to burn slightly more calories digesting food we eat in the morning than it does digesting food we eat in the evening. And this got scientists thinking: do we burn more calories doing morning cardio than evening cardio?

To explore this question, scientists at the University of Colorado recruited 33 overweight or obese 18-to-56-year old men and women and spilt them into a morning cardio group (6-to-10 a.m.) and an evening cardio group (3-to-7 p.m.). 

The participants did 4 cardio workouts per week during their prescribed time windows, and the workouts got more difficult as the 15-week study progressed—at the beginning, the participants burned about  750 calories per week from cardio, and by the end, they burned about 2,000 calories per week. 

At the beginning and end of the study the researchers collected several pieces of data about the participants, including their weight, body composition, total daily energy expenditure, and sleep habits using multiple reliable methods.

The results showed that the time you train does influence daily energy expenditure. Specifically, the data showed that the morning group experienced a larger increase in total daily energy expenditure and resting energy expenditure and a smaller decrease in non exercise activity thermogenesis, but a larger increase in energy intake (they ate more). 

And the effect of all this was that the evening cardio group lost marginally more total weight and fat than the morning cardio group. 

Unfortunately, this isn’t cause to get too excited. Aside from the fact this is just one, very small study that used good but not great data collection methods, the positive effect of doing cardio in the evening was so small that it didn’t meaningfully influence changes in body composition. One other potential confounder is that most people feel a bit more lusty in the afternoon and evening, so it’s also possible that this helped the evening-exercises push a little harder in their workouts.

TL;DR—when you do cardio doesn’t impact how many calories you burn to a meaningful degree. Just do it whenever works best for you.

The Takeaway: Do cardio whenever works best for you—whether you do earlier or later in the day has almost no influence on how many calories you burn.