Physiology Friday #134: Exercise "Snacks," Muscle Protein Synthesis, and Anabolic Resistance
Breaking up prolonged periods of sitting is a boon for muscle metabolism.
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Quick finding of the week: Is keto best for muscle building? A new systematic review and meta-analysis concluded that, compared to calorie-matched control diets (i.e., moderate- or high-carb diets), low-carb ketogenic diets were not better for improving lean muscle mass or reducing body fat during strength or resistance training. In other words — no apparent harm from keto, but no apparent benefit above and beyond other eating styles.
“Snacking” on exercise to enhance protein synthesis
Several recent studies have highlighted the importance of “getting your steps in.” The biggest improvement in health and reduction in all-cause mortality seems to occur somewhere between 7,000 and 10,000 steps per day, and I’ll be so bold as to say that further health improvements can probably be obtained from exceeding 10,000 steps per day.
It’s established: walking is good. Sitting is, on the other hand, not so good. But there’s probably nothing inherently wrong with sitting. Rather, inactivity — whether it be sitting, standing, or lying on the couch — isn’t good for us humans who are wired to move. Modern society has made inactivity quite easy. We take public transportation to work, sit for the majority of the day, and commute home. Even those people who work out for a few hours each day are likely spending a large portion of their waking hours in an “inactive” state.
The detrimental effects of inactivity are many and include cardiovascular and metabolic dysfunction. Inactivity also causes insulin resistance — which impairs our body’s ability to take up and utilize carbohydrates from meals, among other consequences.
There may even be more sinister and under-appreciated effects of inactivity that we’re now just beginning to realize. Studies have found that reducing step counts to below 5,000 steps per day can prevent some of the metabolic effects of exercise.
This is termed “exercise resistance.” A background of physical activity seems to be necessary to optimize the benefits of exercise.Inactivity can also lead to another type of resistance known as “anabolic resistance.”
Normally, when we exercise or consume a protein-containing meal, our body is stimulated to synthesize new proteins from amino acids and integrate those proteins into muscle. This is how diet, exercise, and their combination can work together to increase muscle size and strength.
Inactivity — sitting for too long or taking too few steps during the day — seems to reduce the muscle's ability to respond to these stimuli. In other words, exercise and protein are not as effective for increasing protein synthesis in “inactive” muscles as they are in the muscles of someone who is regularly active. Anabolic resistance is proposed as one cause of the decline in muscle mass with age, formally known as sarcopenia.
This may sound like unfortunate news. Many of us work desk jobs and sit for a good amount of the day. Are we compromising our health and gains? Fortunately, easy and effective strategies are at our disposal to prevent anabolic resistance in situations where prolonged bouts of inactivity are required (or voluntary).
One such strategy — termed “exercise snacks” — was investigated in a recent paper published in the Journal of Applied Physiology.
12 men and women with an average age of 23 were randomly assigned to complete three different conditions.
Prolonged, uninterrupted sitting for 7.5 hours (SIT)
Sitting for 7.5 hours with a 2-minute walk every 30 minutes (WALK)
Sitting for 7.5 hours with 15 bodyweight squats every 30 minutes (SQUAT)
A high-protein breakfast and lunch were provided to the participants during each trial at 7 a.m. and 10 a.m.
Every 30 minutes, participants had their blood drawn, and they also had a muscle biopsy taken from their leg before and after each condition. These samples were used to analyze the study’s primary outcomes which included the uptake of amino acids into muscle protein and myofibrillar protein synthesis. Researchers also measured the phosphorylation (i.e., “activation”) of a few key proteins that are involved in skeletal muscle anabolic signaling.
In the walking and the squat conditions, amino acid uptake and myofibrillar protein synthesis were higher than in the uninterrupted sitting condition. One protein — ribosomal protein S6 — was increased in the squat condition, but not in the walking or uninterrupted sitting conditions.
Obviously, we can’t infer that a single snapshot of protein synthesis will directly translate to significant differences in muscle strength or mass in the long term. However, if we assume that these experimental conditions mimic real life — someone sitting for 6-8 hours on 5 days of the week — it’s reasonable to assume that the cumulative effects on muscle quality and quantity could be significant.
The participants in this study drastically reduced their step counts in each condition — from a habitual ~8,000 steps per day to around 2,500 steps in the sitting and squat conditions and 5,000 in the walking condition. This is similar to the reduction in steps that can cause “exercise resistance,” suggesting there may be some step threshold below which metabolic consequences can occur.
In this same study (but a different publication),
the activity snacks also reduced participants’ insulin levels after the lunchtime meal, suggesting that breaking up sitting with exercise may also have benefits for postprandial metabolism and glucose regulation.
What I love about these findings is that they’re applicable to all of us. Anyone can perform activity snacks throughout the day. Even if you can’t walk around the block or the office, doing chair stands (squats) at your desk is an effective alternative. Many flavors of exercise snacks can work.
I sit for a large portion of the day. And while I typically do a structured, longer exercise bout in the morning, I’m prudent to include low-level activity throughout my day. Not only is this for the metabolic reasons we’ve discussed in the discussion above, but also it just helps me have more energy.
Here’s my “exercise snack” protocol for most days of the week.
A 30-45 minute walk around 12-1 p.m. after 3-4 hours of a.m. work to break up the day
150-200 pushups interspersed throughout the day (broken up into 6-10 sets total) as I work
6-10 sets of kettlebell swings, squats, or Romanian deadlifts (I recently purchased a trio of 25, 35, and 44 lb. kettlebells that are worth more than their weight in gold!)
I’ll do the sets of pushups and whatever kettlebell workout I have planned every 30-45 minutes. I find that this keeps my mind engaged, prevents bodily staleness from prolonged sitting, and allows me to accumulate some strength-building activity throughout the day. You can use this protocol or come up with your own exercise snack variation. Just keep active.
If you already have a daily activity ritual or protocol you use, share it in the comments below!
Thanks for reading. See you next Friday.
~Brady~
Vargas-Molina S, Gómez-Urquiza JL, García-Romero J, Benítez-Porres J. Effects of the ketogenic diet on muscle hypertrophy in resistance-trained men and women: a systematic review and meta-analysis. IJERPH. 2022;19(19):12629.
Coyle EF, Burton HM, Satiroglu R. Inactivity causes resistance to improvements in metabolism after exercise. Exercise and Sport Sciences Reviews. 2022;50(2):81-88.
Moore DR, Williamson EP, Hodson N, et al. Walking or body weight squat “activity snacks” increase dietary amino acid utilization for myofibrillar protein synthesis during prolonged sitting. Journal of Applied Physiology. 2022;133(3):777-785.
Gillen JB, Estafanos S, Williamson E, et al. Interrupting prolonged sitting with repeated chair stands or short walks reduces postprandial insulinemia in healthy adults. Journal of Applied Physiology. 2021;130(1):104-113.
There's another study--I may have seen it in your newsletter 😂--that shows the incremental benefit (reduced mortality rate) of daily steps doesn't slow down even up past 20,000 steps. In other words, you get as much incremental benefit going from 15K 20K steps per days as from 5K to 10K. Unlimited upside.