Greetings!
Welcome to the Physiology Friday newsletter.
ICYMI
On Wednesday, I published a post about the recent evidence on high-volume exercise and atherosclerosis in athletes.
Details about the sponsors of this newsletter including Examine.com and my book “VO2 Max Essentials” can be found at the end of the post!
“Those who think they have not time for bodily exercise will sooner or later have to find time for illness.” — Edward Stanley, Earl of Derby (1826-93)
Exercise is the fountain of youth, but despite the overwhelming evidence that engaging in it reduces the risk of death from nearly all diseases, people still don’t get enough.
Getting more people to exercise more has been a goal of exercise scientists and public health experts for decades. Heavy investments have been made in addressing one of the main barriers that people cite as a reason for not exercising: a lack of time.
Life gets busy. People have jobs and kids and social obligations. Who has the time to exercise for 150 minutes per week or more (in addition to the 2 strength training sessions as a minimum)?
High-intensity interval training (HIIT) and the more vigorous sprint interval training (SIT) offered the hope of alleviating this barrier to exercise by providing a “time-efficient” alternative to longer, steady-state aerobic training.
HIIT and SIT can lead to improvements in cardiorespiratory fitness that are equal to or greater than those achieved with longer-duration moderate-intensity training, typically in less than half the time per week.
Alas, though the benefits of HIIT and SIT have been proven in numerous randomized controlled studies, their adoption outside of the lab is limited, and we haven’t seen the “fitness revolution” that these time-efficient modes of exercise promised to ignite. “Time” may not be the only barrier after all. Logistics may also play a role. People don’t seem to want to set aside time during the day to workout, for whatever reason. We need a way to weave exercise into daily life.
Exercise snacks are short bursts of high-intensity exercise engaged in throughout the day. They don’t require equipment, a change of clothes, or a shower after.
One variation of exercise snacking involves a total of three 20–30 second all-out sprints during the day with a rest period of 1–4 hours in between. Exercise snacks can also involve body weight squats, stair climbing, or even resistance-based exercises like pushups, pullups, or burpees.
No matter the “snack” you choose, the idea is that you go hard for 2 minutes or less, then do it again a few hours later, and repeat a few times that same day. Simple (but not easy).
Exercise snacks are referred to by another name: vigorous intermittent lifestyle physical activity or VILPA. Exercise snacks and VILPA are not structured exercise per se, but rather, are “interruptions” of your day.
The benefits of exercise snacks have been demonstrated in numerous studies and include:
improvements in V̇O2peak
enhancements in blood glucose and lipid metabolism
improvements in vascular function during prolonged sitting/sedentary time
Spreading out activity during the day into shorter bouts is without a doubt beneficial for metabolic health due to the benefits on glucose control and blood flow, even for people who already engage in a lot of exercise. Pro tip: walk after meals.
I’m a huge advocate of taking regular walk breaks of 10–15 minutes during the day as a way to de-stress and avoid the detrimental effects of prolonged sitting.
But should exercise snacks replace your low and moderate-intensity training during the week? Getting in at least one long (60–90+ minutes) exercise session per week seems to be beneficial for improving fat oxidation ability and, of course, can contribute to improvements in V̇O2max. So-called “base training” is essential.
To date, no studies have compared exercise snacks to moderate-intensity continuous training, but a new study put these two interventions head to head.1
For the 6-week study, the participants (42 total including 18 men and 24 women with an average age of 22) were assigned to one of three groups: exercise snacks, moderate-intensity continuous training, or a no-exercise control group.
The participants in the exercise snacks group completed three 30-second bouts of “all out” stair climbs per day on 3 days of the week. The rest period between each stair climb was one hour or more. In total, they completed 54 sessions of stair climbing (~27 minutes) during the intervention.
These stair climbing sessions were supervised in the lab and thus, all of the participants climbed the same set of stairs (6 flights with 126 steps total).
The moderate-intensity training group performed cycling exercise for 30–50 minutes at a heart rate between 60% and 70% of their age-predicted maximal heart rate.
Before and after the intervention, all of the participants completed a maximal exercise test to determine V̇O2peak, maximal fat oxidation, and other exercise variables. Body composition and blood pressure were also assessed.
Results
First, let’s talk about the exercise snacks. During the stair climbs, the participants’ average heart rate was 79% of their age-predicted max and peaked at 90% of age-predicted max. Pretty impressive given that each session lasted only 30 seconds!
Exercise snacks increased V̇O2peak by 7% or 2.5 ml/kg/min. In contrast, moderate-intensity training failed to improve V̇O2peak significantly (a 1 ml/kg/min increase was observed), while VO2 max declined in the control group (nonsignificantly) by 5% or 1.7 ml/kg/min.
Exercise snacks increased peak power output by 26 Watts; however, power output didn’t change in the moderate-intensity training or control group. Exercise snacks also increased the percent of V̇O2peak where the lactate threshold occurred. In other words, the participants were exercising at a higher intensity (power output) at their lactate threshold.
None of the interventions improved fat oxidation or blood pressure. There were also no significant changes in body composition, including weight, fat mass, fat-free mass, skeletal muscle mass, and waist circumference in any of the groups. Not surprising given that diet and physical activity outside of the intervention didn’t change.
The major finding here (in my opinion) is that a total exercise duration of less than 5 minutes per week achieved via stair climbing improved V̇O2peak by almost 1 metabolic equivalent (3.5 ml/kg/min) — an improvement that’s been associated with an 11% decrease in the risk for all-cause mortality.
What’s even more surprising is that even in this group of inactive adults, moderate-intensity training didn’t improve V̇O2peak. This was unexpected because almost any exercise will improve cardiorespiratory fitness in people who don’t exercise. The baseline V̇O2peak of the participants in this study was 32–35 ml/kg/min. That ranks these ~22 year olds as “poor” in terms of cardiorespiratory fitness and indicates that the thrice weekly protocol may have been insufficient in intensity and/or volume to yield fitness improvements. Even at the maximum of 50 minutes 3 times per week, they were barely getting the minimum recommended amount of weekly aerobic exercise.
In any case, it would appear that moderate-intensity training is inferior to high-intensity exercise snacks for improving V̇O2peak, but I should note that this study did not statistically compare these two interventions.
Exercise snacks may have performance benefits too! At baseline, the lactate threshold of the participants in the exercise snacks group occurred at around 58% of their V̇O2peak. After the study, lactate threshold occurred at around 64% of their V̇O2peak, indicating a modest improvement in submaximal exercise performance.
If you’re looking to improve your body composition, weight, or fat-burning ability, exercise snacks may not be effective, and longer-duration, higher-volume training is probably necessary. The zone 2 advocates got it right here! Thus, we arrive at the inevitable conclusion that exercise snacks are probably a worthy supplement to your exercise routine, but probably can’t replace some of the benefits of low- and moderate-intensity training.
How can you apply these findings?
For me, these results are exciting because they offer a way to accumulate more weekly activity (“training”) without setting aside more time for training!
If you’re already working out every single day and don’t have a problem finding the time to exercise, you can still do exercise snacks to grab a few extra percentage point improvements in your aerobic capacity, power output, or race performance. The added benefit is that these snacks aren’t likely to cause extra fatigue or take away from your ability to train or recover from your main session.
If you’re not working out as much as you’d like, then you should be reassured that a massive time commitment isn’t required to reap the benefits of exercise, at least in the shorter term. Use exercise snacks when you’re on a time crunch or when you’re away from home and without your usual gym amenities.
Take this stair climbing protocol and integrate it three times per week. Most of us will encounter stairs at least 3 times each day. When you do, climb, sprint, or bound up them for around 30 seconds. You might have to go up and down a few times depending on the length of your staircase.
I’m definitely going to try this in the next week and even measure my heart rate while doing so. I’ll be curious to see if I experience any noticeable benefits and implore you to join me.
Thanks for reading. I’ll see you next Friday.
~Brady~
The VO2 Max Essentials eBook is your comprehensive guide to aerobic fitness, how to improve it, and its importance for health, performance, and longevity. Get your copy today and use code SUBSTACK20 at checkout for a 20% discount. You can also grab the Kindle eBook, paperback, or hardcover version on Amazon.
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Lifestyle seems to be the biggest barrier to not moving enough.
I’m thankful I’ve had the time and space to structure mine to promote sufficient movement and improve my health while being an at-home dad over the last 5+ years.
While transitioning back to more working, I plan on continuing these lifestyle practices while living more of a “working” lifestyle.
For example, I’ll go outside, do rope flow, run, or climb trees for 20-30 minutes in the morning. Then, I go work for an hour or two.
That 20-30 minutes of movement outside gives me a sharp mind to work and energy for the rest of the day.
‘If you’re already working out every single day and don’t have a problem finding the time to exercise, you can still do exercise snacks to grab a few extra percentage point improvements in your aerobic capacity, power output, or race performance.”
The study was done on inactive young adults, do you think that active fit healthy individual who are accumulating much more than the 150 minutes of moderate to vigorous physical activity a week could actually see benefits from exercise snacks like this? Running up a flight of stairs may be enough for the folks in the study to trigger adaptations but for someone who is already fit and active;y training my thought would be that they need more stimulus than a sprint up a flight of stairs to get improvements.
Regardless though it certainly can’t hurt to try, you won’t get less fit by doing them 😜