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Soleus Health · Movement Science

The Science Behind the Soleus Muscle and Seated Health

Most people have never heard of it. Fewer still have been told what happens to it when you sit for 8 hours a day. This is the science behind the soleus, and why 2HEART is built around it.

5 min read
Definition
Soleus Health
(noun) · wellness category

The practice of activating and monitoring the soleus muscle during seated hours to support everyday body movement and responsiveness. Introduced by 2HEART as a new category in modern wellness.

Why researchers call it the second heart

The soleus is not just another muscle. It plays a unique role in how your body moves blood and maintains circulation, especially when you are seated.

Blood Return
The soleus acts as a venous pump. When it contracts, it pushes blood upward from the lower legs toward the heart, working against gravity.
Calf Pump Mechanism
The calf pump, driven largely by the soleus, is responsible for returning blood from the feet and legs back to the central circulation.
Soleus Function
Unlike muscles designed for bursts of power, the soleus is built for endurance. It can activate for hours without fatigue, quietly supporting the body.
Circulatory Support
During seated hours, the soleus becomes the primary driver of lower-body circulation. When it is inactive, blood flow slows.
What is the soleus

The muscle most people cannot name.

The soleus muscle is a muscle in your leg that sits beneath the gastrocnemius, the visible outer calf muscle. It is called the soleus. Most fitness programmes ignore it. Most conversations about body movement never mention it. What it does, quietly and without recognition, is keep your body in motion during seated hours.

Body mass
~1%

The soleus makes up roughly 1% of your total body mass yet during ordinary seated activity, it outpaces every other muscle in the body for energy use.

Muscle composition
70–80%

Slow-twitch muscle fibres, one of the highest proportions of any skeletal muscle in the body. This means it can work for hours without fatigue or discomfort.

Known as
Second heart

Published research describes the soleus as performing the role of a peripheral heart, the primary driver of movement from the lower leg back through the body.

Runs on a different fuel

Unlike other muscles, the soleus draws energy directly from your bloodstream during low-intensity activity. It does not rely on stored glycogen. This makes it uniquely suited to working quietly and continuously during seated hours.

Your body's movement engine

The soleus supports the body's internal movement when you are seated. When it activates, it compresses the deep veins of the leg, supporting movement of blood back through the body, a function the heart cannot perform alone from a distance.

Never tires

Its high proportion of slow-twitch fibres means the soleus can be activated repeatedly, at low intensity, across a full working day. No other major muscle in the body has this profile during seated posture.

Educational purpose only. This information is not medical advice. Consult your doctor with questions about your circulation or health.

Explore related topics

Venous Return → Calf Pump Function → Sitting vs Standing → Soleus vs Steps →
What sitting does

When you sit, it goes silent.

The soleus is effectively switched off when you are seated with your knees at 90 degrees. The gastrocnemius, the outer calf, bears almost no load in this position either. For the 8 to 10 hours most desk workers spend seated each day, the body's natural movement engine is not running. Read more about what happens when the soleus stops moving →

What this means for your body

The body is not designed for prolonged stillness. It expects movement. When the soleus stops working during long periods of sitting, the body feels the difference: reduced energy, heaviness in the legs, the familiar 3pm fog.

Over time, the absence of regular soleus activity accumulates. The body's natural movement patterns are disrupted not by disease, but by the simple architecture of modern desk work.

2HEART is built to address this gap: not with interruption, not with standing, but by activating the soleus during sitting and measuring what happens when it works.

The research foundation

The evidence behind the physiology

The scientific case for soleus activation during seated hours has been building in peer-reviewed literature for years. These findings belong to the independent researchers who produced them. 2HEART builds on this foundation; it does not claim to own it.

Hamilton et al. · iScience · University of Houston · 2022

In a laboratory setting using a specialised protocol, sustained soleus activation during seated time produced a significant reduction in post-meal energy response. The soleus became the dominant energy-consuming tissue in the body during the session. Read the full study summary →

Elek et al. · Sports Journal · 2025

A 2025 pilot study confirmed significant improvement in prediabetic individuals performing soleus activation during seated time, without any laboratory equipment. Read the study →

Houghton et al. · Blood Journal · Mayo Clinic · 2021

People with reduced soleus muscle activity were significantly more likely to experience serious health events over time. Read the full study summary →

Meta-analysis · 2017

Hedges' g effect size: 0.83 (p < .001) for calf pump interventions across 14 studies with 519 participants. This is a large, statistically significant effect and it's a meta-analysis, which carries more weight than any single study alone. Read the study →

See the full research index

All studies, attributions, and plain-language summaries.

View Research →
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