The “Second Heart”: How Your Calves Support Circulation and Blood Sugar

Most people learn that the heart is solely responsible for pumping blood through the body. While that’s true, it’s only part of the story.

Your cardiovascular system has a powerful partner in your lower legs: the calf muscle pump, especially the deep, endurance-oriented soleus muscle. Because of its role in venous return, this system is often described as a “second heart” or “peripheral heart.”

When the calf pump is underused—most commonly during prolonged sitting—blood and fluid can pool in the lower limbs. This contributes to heavy legs, swelling, fatigue, and in some people, venous disease. When activated regularly, the calves act as both a mechanical pump and a metabolic regulator, supporting circulation and blood sugar control.

How the Calf Muscle Pump Improves Circulation

Gravity makes venous return difficult. Blood from the feet must travel upward against a vertical column to reach the heart.

This is where the musculovenous pump becomes essential.

The deep veins of the lower leg run between the calf muscles and contain one-way valves. Each time the calves contract—during walking, standing, or calf raises—they compress these veins, pushing blood upward and preventing backflow.

Classic hemodynamic studies show that rhythmic calf contractions can reduce venous pressure in the legs by 50–60 mmHg, significantly limiting blood pooling and edema. Reviews of skeletal muscle blood flow consistently identify the calf muscle pump as a major contributor to venous return during upright activity and exercise.

Key insight:In many otherwise healthy people, sensations of “poor circulation” or heavy legs reflect an inactive calf muscle pump, not a failing heart. Persistent or severe symptoms, however, should always be medically evaluated.

Key references:

• Laughlin MH. Skeletal muscle blood flow capacity: role of muscle pump in exercise hyperemia.https://pubmed.ncbi.nlm.nih.gov/3318504/

• Meissner MH. The hemodynamics and diagnosis of venous disease.https://pubmed.ncbi.nlm.nih.gov/18068561/

• Joyner MJ, Casey DP. Regulation of Tissue Oxygenation and Exercise Hyperemia.https://www.ncbi.nlm.nih.gov/books/NBK57139/

  
  

The Soleus Muscle and Blood Sugar Control

While blood sugar regulation is often associated with intense exercise, newer research highlights the unique metabolic role of the soleus muscle.

The soleus is predominantly slow-twitch and highly oxidative. It’s designed for endurance, posture, and prolonged low-intensity activity. When activated gently and continuously, it can use circulating glucose and fats efficiently with minimal lactate production.

The Soleus Pushup Study

In 2022, Marc Hamilton and colleagues published a landmark paper in iScience describing a seated movement called the Soleus Pushup (SPU). The goal was to maximally activate the soleus while sitting, without triggering high-intensity exercise responses.

In controlled laboratory conditions, the researchers found that:

• Sustained SPU contractions increased soleus oxidative metabolism for hours without fatigue

• After a glucose drink, participants experienced a ~52% reduction in post-prandial blood glucose spikes

• Insulin exposure dropped by ~60% compared with uninterrupted sitting

These findings suggest the soleus can function as a metabolic “sponge,” helping regulate blood glucose and lipid levels during prolonged sitting.

This research is promising but early-stage. It does not replace exercise, nutrition, or medical care, but it highlights the importance of frequent, low-intensity muscle activation for metabolic health.

Key references:

• Hamilton MT et al. A potent physiological method to magnify and sustain soleus oxidative metabolism improves glucose and lipid regulation.https://www.cell.com/iscience/fulltext/S2589-0042(22)01302-5https://pmc.ncbi.nlm.nih.gov/articles/PMC9404652/

• University of Houston summary:https://stories.uh.edu/2022-soleus-pushup/

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One System, Multiple Benefits

The “Second Heart” works because several physiological systems overlap:

• Circulatory: Calf contractions improve venous return and reduce venous hypertension

• Metabolic: Soleus activation increases glucose and fat uptake

• Lymphatic: Muscle contractions help propel lymph and clear interstitial fluid

Long, uninterrupted sitting doesn’t just reduce calorie burn—it switches off an auxiliary pump that supports circulation, metabolism, and tissue health.

How to Activate Your “Second Heart”

Seated Soleus Pushups (Desk Exercise)

1. Sit upright with feet flat and knees near 90 degrees

2. Keep toes relaxed and in contact with the floor

3. Raise your heels slowly, contracting the calves

4. Lower with control

5. Repeat continuously at a comfortable rhythm

Aim for:5–10 minutes at a time, several times per day during long sitting periods.

Standing Calf Raises (Movement Breaks)

1. Stand near a wall or desk for balance

2. Rise onto the balls of your feet

3. Pause briefly at the top

4. Lower slowly

Perform 15–20 repetitions once per hour during prolonged sitting or standing.

This simple habit improves venous return and serves as a proven activity break for cardiometabolic health.

Safety Considerations

Persistent leg pain, swelling, skin color changes, numbness, or cold feet may indicate conditions such as chronic venous insufficiency, peripheral arterial disease, neuropathy, or heart failure and require medical evaluation.

Calf-focused exercises should complement—not replace—overall physical activity, nutrition, and medical care. People with advanced diabetes, cardiovascular disease, foot ulcers, or recent surgery should consult a clinician before starting new routines.