A good part of the scientific process is to critically discuss potential pitfalls and problems of new ideas, even debate the issues. This helps everyone with diverse perspectives to all hopefully move closer to advancing the science and discovery of the hidden truths about physiology (how the body works). We have recently received many questions; too many to answer in detail individually. One of the purposes of this website is to make it feasible and time efficient to respond to inquiries.
Frequently Asked Questions
1. What is the most distinctive aspect of SPU activity?
It’s specifically designed to sustain muscle metabolism for hours, not minutes.
2. What do you mean by minutes?
The prevailing viewpoint by researchers and the advice by medical organizations like the CDC or WHO is about adding minutes per day of activity.
3. If there was one take home point to remember about this what is it?
Pay attention to “the units of time” when you think about metabolism. We know that people are on average sitting 600 minutes per day at a low metabolic rate. This low muscle metabolism counteracts good health. So what’s the logic in thinking you can keep muscle metabolism humming all day by making it a goal with your Fitbit or Apple watch to take a 60 second break at the end of the hour? Even a good hard 60 min workout is but 10% of your sitting time. And muscle metabolism plummets with a half time of 30 seconds when it stops contracting.
4. Following in this last point about why we tested these indefatigable soleus contractions. We pointed out in the research article that we are unaware of any studies in either lab rats or humans that previously working muscle can sustain an elevated carbohydrate oxidation once the contractions stop. Thus the particular mechanism of being able to “burn more sugar” is not a biological reality once an exercise bouts ends.
5. People need to focus on “the why” and less on “the how”. Even people who exercise or have a large muscle mass still have a low metabolic rate when sitting. That has unavoidable consequences that are rapidly induced each time you sit. The 2 we focused on this particular study was postprandial carbohydrate oxidation (burning carbohydrate as a fuel) and fat metabolism when fasting between meals.
6. Related to this, the most fundamental yet misunderstood metabolic concept is that muscle as a tissue has a much lower metabolic rate when sitting than people realize-that rapidly harms key metabolic processes.
7. Simply put, what is special about SPU activity?
It is a Muscular activity specifically targeting the soleus muscle making it possible to raise muscle metabolism for hours per day, not minutes.
8. How far can you say we can generalize this to other kinds of movement?
We were careful to spend much more valuable space in the discussion of the article than is normal to offer limitations.
9. People need to focus on “the why” before “the how”. Even people who exercise or have a large muscle mass still have a low metabolic rate when sitting. That has unavoidable consequences that are rapidly induced each time you sit. The 2 we focused on in this particular study was postprandial carbohydrate oxidation (burning carbohydrate as a fuel) and fat metabolism when fasting between meals.
10. So how much does muscle energy expenditure need to increase to improve glucose and lipid metabolism?
That’s a huge question. It’s a major key to understand why and how we did this study. But it’s also surprisingly not asked enough. As far as I know, as shocking as it seems, this is the first study to have done a dose response analysis for the effects of 3 levels energy expenditure in this range of energy expenditure with respect to glucose tolerance. With this soleus muscular activity, we carefully measured the increase in energy expenditure above the inactive sitting control level.
11. What is the simplest way to describe this method of activity?
Muscular activity specifically targeting the soleus muscle.
12. Was this the first study to raise the hypothesis that a high duration of contractile activity throughout the day could be a necessary component of metabolic health? No, see below.
13. Was this the first study about local contractile activity of the soleus muscle throughout the day? No, see below.
14. Was this the first study to suggest that low effort contractile activity could cause large metabolic health benefits? No, see below.
A good place to start in answering all three of these questions is to read the introduction and discussion of the iScience article published in September 2022 (found here). Then, there are seven additional articles to start with. This website will be updated with easy to understand annotations of those and many other articles. The goal is for anybody to be able to answer these and other related questions for themselves after feeling more confident about how the body works.
A note about the rationale for the nomenclature to describe “the SPU” contractions (Soleus Pushups)
The language of biomedical research and preventive medicine is never perfect for everyone.
Most importantly, discussing new physiological concepts about how the body actually functions is a terrific way for people to use their intellectual curiosity (and valuable time). Controversy about what you call a muscular activity isn’t as productive or enjoyable.
For the sake of efficiency and transparency, here is the thought process and rationale behind why my laboratory has been using the term SPU contractions.
The nomenclature of any muscular activity is minor.
As a physiologist, I find it useful to identify the targeted muscle, and to describe the motion to help people understand it.
Like I’ve said publicly when asked by my university media relations department, what you see on the outside isn’t clearly reflecting what happens inside the body.
I found that some research participants incorrectly used other muscles if they tried to “lift” or “raise” their heels and legs.
With this particular type of low resistance plantarflexion, it’s better to think of pushing the ball of the foot down into the ground and the contraction of the soleus will shorten the muscle to cause the ankle joint to bend and lift up the leg.
This endurance activity shouldn’t be confused with a type of resistance training. There is no need for adding an external load and it is preferable if the soleus muscle is passive during the downward motion (no eccentric contraction).
The purpose and methods of an SPU are different than a type of resistance training already called heel lifts or calf raises. In contrast, the latter involves lifting and lowering a weight and both an eccentric and concentric contraction phase.
There is actually much more to this story. The development of this fascinating story involves insights about the cellular mechanics of muscle physiology. Because that involves a deep dive into other things my lab has been doing, we can write about it later.
Potential Confusion and Controversies
The iScience article wrote about the potentially high duration of soleus contractions made possible by SPU activity. Some asked if that is a limitation in the study and even offered negative responses about that fact. To make an informed opinion on the matter, consider this question for yourself:
When did the ability to get more of something rather than less of something that is good for you become a limitation or flaw?!
The explicit purpose in the study for developing and testing the SPU contraction was to be able to test the hypothesis that sustaining oxidative metabolism for hours (not minutes) would be able to cause improvement in systemic metabolic responses. The limitation to traditional shorter bouts of higher intensity exercise and other therapeutic approaches in being able to sustain elevated rates of oxidative metabolism for prolonged periods was discussed in detail in the Discussion section. Please feel free to study those references; they are hot linked in the journal article to gain access.
One last important point to notice in the Results section of the paper (Table 3); the SPU contractions had already quickly reduced blood glucose significantly within less than 30 min after first ingesting the 75 gram glucose load (19 mg/dL less in the moderate level of SPU contractions of 1.1 kcal/min above inactive control).