Work your smooth muscles to strengthen your circulation.
Every fitness blogger talks about to build or keep skeletal muscle, because more skeletal muscle looks good and promotes health and longevity.
But almost no one talks about smooth muscle.
Skeletal muscles attach to bones via tendons. They operate under (mostly) voluntary control. They're the muscles that control our limbs and that we can build up by working out.
Smooth muscles attach to our stomach, intestines, bladder, arteries, and veins. They operate under involuntary control, which means there are no workout videos or fitness machines for strengthening smooth muscle tissue.
Smooth muscles perform several important functions in the body, including:
propulsion of food through the digestive tract,
expulsion of urine,
regulation of blood flow and pressure,
contractions during pregnancy & childbirth, and ejaculation,
standing hairs on end.
Smooth Muscle Health
Irregularities in smooth muscle function are linked to asthma, high blood pressures, atherosclerosis, and varicose veins. Moreover, smooth muscle function typically declines with age (Chi et al. 2019, Greaney et al. 2015).
Because smooth muscle control is involuntary, exercising your smooth muscles is different from the activities that exercise your skeletal muscles.
For a smooth muscle work out, you need an ice bath.
Vasoconstriction & vasodilation
When the thermoreceptors in your skin identify cold temperatures, they signal vasoconstriction, which is a smooth muscle contraction in the arteries that control blood flow to the extremities. This is partly why your toes and fingers hurt when submerged in ice water. Although it feels uncomfortable, vasoconstriction is a thermal defense mechanism that automatically protects your core from being exposed to cold blood returning to your heart from your cold limbs.
Afterdrop is a phenomenon that happens when you emerge from the cold water. As your skin rewarms, the smooth muscle tissue in your limbs relaxes to allow blood to return to the cold muscles in your arms and legs. Although your extremities get warmer, your blood gets colder. Then, when cold blood from your limbs returns to your heart, your core temperature may keep dropping as your body temperatures rebalance.
That's why you sometimes don't start really shivering until after you are out of the Forge.
Thermal contrast therapy -- where you go from cold to hot and back again -- is like a workout for your smooth muscle tissue. Cold contracts it. Heat relaxes it (via vasodilation), and every time you switch back and forth is like doing another "rep" in your smooth muscle workout.
Use dry heat for thermal contrast therapy
Ironically, immersion in warm water can also result in vasoconstriction. For example, the wrinkles that appear on skin of your fingertips when you've been too long in the hot tub are caused by vasoconstriction (Wilder-Smith & Chow 2013). Ordinarily, your warm body would increase blood flow to the skin, where sweat evaporation would help cool the body and prevent overheating. However, when you're in a hot tub, sweat can't evaporate, because you're submerged in water. In a process called hidromeosis, the body senses warm water on the skin and signals smooth muscle tissue to shut down circulation minimize heat gain.
Thermal contrast therapy works best for your smooth muscle tissue when you go from the wet cold of the ice bath to the dry heat of the sauna, rather than to the hot tub.
Do you need vasoconstriction?
Although there are no studies that relate thermal contrast therapy to indicators of smooth muscle fitness, it stands to reason that a smooth muscle workout might slow ageing and extend healthspan, because those who perform thermal contrast therapy typically enjoy fewer adverse outcomes related to markers of smooth muscle dysfunction. For example, elderly subjects who practiced sauna experience better cold intolerance and less constipation and incontinence (Sugie et al. 2020). Moreover, studies in Finland and Japan reinforce the hypothesis that thermal contrast vasoconstriction-vasodilation cycling results in improved cardiovascular outcomes (Heinonen & Laukkanen 2017). Given the critical role that smooth muscle tissue plays in regulation of blood flow, adding a smooth muscle workout to your health regimen is likely to improve digestion and elimination, stabilize blood flows and pressures, improve sexual and reproductive functions, and may slow ageing or wrinkling of your skin.
About the Author
Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience. Subscribe to https://seagertp.substack.com/ for more information from Seager on taking charge of your own physical & mental health.
Here's an update on vasoconstriction from my Forge (and why I never combine ice bath with hot tub).