Good news for weekend warriors
Most national health guidelines recommend about 150 minutes of moderate exercise per week. And there's a good deal of research showing that people who meet this benchmark are healthier than those who don’t. But what if you are sedentary all week and then get your 150 minutes on the weekend?
My guess would be that this weekend warrior strategy would be inferior to one where physical activity is spaced more evenly throughout the week. It takes only a few hours of physical inactivity before there are measurable changes in physiology and metabolism. At some point the accumulated effects of these changes cannot be undone with a bunch of make-up work. But a new study suggests that this point doesn’t arrive before the weekend.
It compares the mortality of people who exercise at least 150 minutes on just two days of the week compared to those who got their exercise on at least three days. There were no differences in mortality during a ten-year period. I find this surprising and would like to see a comparison of weekend warriors with people who were active on at least six days instead of just three. But I will revise my priors accordingly.
Pain asymbolia and predictive processing
My last post was about pain asymbolia, which is a weird condition involving damage to the limbic system that causes pain that doesn't hurt. Here's a link to a paper discussing pain asymbolia from the perspective of predictive processing.
It explains why people with pain asymbolia often feel that the pain doesn't “belong” to them. The author argues this is a form of depersonalization, where pain is experienced, but not experienced as “mine”:
Pain asymbolia is a case in which nociceptive signals (of bodily damage) are not integrated with affective signals because of hypoactivity in the anterior insula. The mind, however, predicts that affective me will feel distress as a consequence of pain/nociception. The result is a prediction error that cannot be resolved because relevant affective and self-modeling mechanisms are deactivated. As a result, when an experience of pain, predicted to have a strong affective signature, does not produce affect, the subject feels as though it is not happening to her.
The author also argues that pain relief from opioids has a similar phenomenology and physiology.
The idea that the anterior insula is a substrate of the feeling of mineness for pain via its role in affective processing is consistent with the similarity between depersonalization experience for pain and mild opioid analgesia. In opioid analgesia, patients report that the pain is not extinguished but no longer matters. A key finding here is that that opioids target not only the PIC, as one might expect, but also the AIC and related limbic structures involved in emotional processing.
Why its hard to run at an an easy pace
Most amateur runners would probably benefit from spending more time running slower. Research by Stephen Seiler and others shows that elite endurance athletes spend about 80% of their training time moving at an “easy” pace. But amateurs do most of their runs at moderate or high intensity, thereby missing the unique benefits of zone 2 training. This presents an interesting question: why would people prefer to do something that's harder and less beneficial than something easier and more beneficial?
A recent study, written about by Alex Hutchinson here, explains why this might be. Everyone has a running speed that optimizes running efficiency, which is where you consume the least energy for a given distance. In general, running fast is less efficient than running slow, but the relationship is not perfectly linear, so the most efficient speed will not be the slowest. Imagine running at the slowest possible speed, barely faster than walking. This is not a natural way to move, and efficiency would improve by adding a little speed. It seems that people are attracted to running at an efficient pace, even though that pace is harder, and this may cause them to run faster than an easy pace. So people might choose efficiency over ease, even when efficiency is harder.
I have definitely noticed this in my own running. On days that I intend to run easy (defined as having my HR below 135), I take pleasure in the fact that I won't have to work very hard during my run. But then I find myself gravitating to paces that send my HR above 150. It takes discipline and attention to slow myself down, even though doing so brings the immediate reward of less exertion. Interesting.
Primate shoulder mobility
Last weekend I taught a four-hour online course about primal movements like reaching. (This was for a Japanese students. I might be offering a similar course online soon.)
One section was about the evolution of the human shoulder, which is well-adapted for swinging from tree branches. These adaptations provide us with excellent mobility in every direction, including overhead. But not as much mobility as this guy:
Exercise and immune system regulation
In a previous post I mentioned the Constrained Energy Expenditure hypothesis put forward by Herman Pontzer in his new book Burn. It is based on surprising research finding that exercise has less impact on daily energy expenditure than we might imagine. This is because the body tends to compensate for physical activity by spending less energy on other bodily functions throughout the day. Thus, the health benefits of physical activity might be more about changing HOW we spend energy rather than HOW MUCH energy we expend. For example, a physically active body might spend less energy on creating inflammation or stress responses to emotional events.
Pontzer just published a new study with evidence consistent with his hypothesis. It analyzed population data to find that people with higher levels of exercise also had lower levels of immune system activity and thyroid activity:
active adults had a lower levels of T4 and reduced slope of the TSH:T4 relationship. Similarly, greater physical activity was associated with lower CRP and fibrinogen levels (but not IgE) and lower white blood cell, basophil, monocyte, neutrophil, and eosinophil (but not lymphocyte) counts. Daily physical activity was also associated with lower prevalence of clinically elevated CRP, WBC, and lymphocytes in a dose-response manner. These results underscore the long-term impact of daily physical activity on both systemic metabolic activity (thyroid) and on specific physiological tasks (immune).
But the beneficial effects of exercise in inflammation levels is not linear. The relationship is complicated. Here’s a helpful note from the paper:
During exercise and immediately afterward, inflammation increases in proportion with exercise intensity. However, regular exercise leads to lower baseline inflammation levels and is associated with lower levels of white blood cells (WBC), neutrophils, and lymphocytes and a lower risk of clinical elevation in C-reactive protein (CRP) and fibrinogen (indicators of chronic inflammation), and WBC. There is also evidence that, when the energetic demands of physical activity are sufficiently high, exercise-induced immune suppression can be harmful. Intense exercise workloads such as those in elite athletes increase the risk of clinically significant suppression and functional impairment collectively referred to as overtraining syndrome or relative energy deficit syndrome.
Does a ruptured achilles tendon require surgery?
I'm usually pretty skeptical about the benefits of orthopedic surgeries, and have written some articles summarizing evidence that many of them don’t seem to work very well. But I've always assumed that getting surgery to repair a ruptured achilles tendon is a no-brainer.
A recent study (h/t to Paul Ingraham) presents a different view. It randomized 526 patients with an achilles rupture into three groups: open-repair surgery, minimally invasive surgery, or nonoperative treatment. After 12 months, each group had a similar improvements in their “Total Rupture Score.” The nonoperative group had more re-ruptures and the minimally invasive surgery group had more nerve injuries.
Orangutan picture courtesy of Wikimedia commons.
Thanks for the concise gifts for my hungry brain
Why not just walk at a brisk pace instead of running since it’s so hard to stay in zone 2 with running?