The Soleus: A Running Coach’s Take on Your “Second Heart”

As a running coach, I spend a lot of time looking beyond pace charts and mileage totals. The real breakthroughs in endurance performance often come from understanding how the body works. One muscle that deserves far more respect from runners is the soleus—often called the body’s second heart. 

The idea of a “second heart” isn’t poetic fluff. It’s rooted in physiology. 

Your heart pumps blood to the lower body, but gravity makes it hard to get that blood back up to the heart. That’s where the soleus muscle, a deep calf muscle that sits underneath the gastrocnemius, plays a critical role. When it contracts, it squeezes the deep veins of the lower leg, pushing blood back toward the heart. This mechanism is known as the calf muscle pump. 

Unlike many muscles, the soleus is built for endurance. It’s made up predominantly of slow-twitch (Type I) muscle fibres, which means it can work for hours without fatiguing. Every step you take while walking or running activates it. Over thousands of steps, this pumping action significantly improves venous return, supports circulation, and helps maintain oxygen delivery to working muscles. 

In simple terms: 
A strong, active soleus helps keep blood moving, just like a heart does. 

The soleus crosses only one joint—the ankle—which makes it especially active when the knee is bent, such as during running, climbing, and long steady efforts. Its main jobs are to: 

• Control ankle dorsiflexion as your foot hits the ground 

• Store and release elastic energy during push-off 

• Stabilise the lower leg over long durations 

During endurance running, the soleus works constantly, even at slower paces. While the bigger calf muscle (gastrocnemius) helps with explosive movements like sprinting and hill surges, the soleus is the quiet workhorse that keeps you moving efficiently kilometre after kilometre. 

For endurance runners—marathoners, ultra runners, trail athletes—the soleus may be one of the most important muscles in the body. 

Here’s why: 

1. Improved Oxygen Delivery 
   A well-trained soleus improves venous return, which supports better cardiac output and oxygen circulation. This can delay fatigue and improve endurance efficiency. 

2. Energy Efficiency 
   The soleus stores elastic energy in the Achilles tendon and releases it with each stride. Stronger soleus muscles mean less energy cost per step—huge over tens of thousands of steps in a long race. 

3. Fatigue Resistance 
   Because it’s slow-twitch dominant, the soleus is designed to work all day. When it’s weak or undertrained, other muscles compensate, leading to early fatigue and breakdown in running form. 

4. Injury Prevention 
   Many common running injuries like Achilles tendinopathy, calf strains, plantar fasciitis and even knee issues, can often be traced back to poor calf and soleus strength. A resilient soleus reduces load on surrounding tissues. 

5. Late-Race Performance 
   Ever noticed how runners “lose their legs” late in marathons or ultras? Often, it’s not cardiovascular failure, it’s peripheral muscular fatigue. A strong soleus helps maintain stride integrity when everything else wants to shut down. 

Runners love chasing their VO₂ max status, weekly mileage and Strava kudos.  All those matters, some more than others, but none work well without a strong foundation. The soleus doesn’t get Instagram glory, but it quietly supports circulation, efficiency, and durability. 

If you’re an endurance athlete, think of soleus training as an investment in: 

• Longer-lasting legs 

• Better economy 

• Fewer injuries 

• Stronger finishes 

Strengthening the Soleus: Practical Exercises for Runners 

From a coaching perspective, the soleus doesn’t need flashy workouts. It needs consistent, targeted loading that matches its endurance-based role. Because it works best with the knee bent, soleus exercises should differ slightly from traditional straight-leg calf work. 

Below are some of the most effective, runner-specific ways to strengthen it. 

1. Bent-Knee Calf Raises (Soleus Raises) 

This is the cornerstone exercise for soleus strength. 

How to do it: 

• Stand with feet hip-width apart 

• Slightly bend your knees (about 20–30 degrees) 

• Rise slowly onto the balls of your feet 

• Lower under control 

Progressions: 

• Bodyweight → single-leg → weighted (holding dumbbells or wearing a pack) 

Prescription for runners: 

• 3–4 sets of 12–20 reps 

• Slow tempo (3 seconds up, 3 seconds down) 

Coaching tip: Keep the knees bent throughout the movement—straightening them shifts the load to the gastrocnemius. 

https://youtube.com/shorts/uQAIX2jrvYYsi=0hZRzUEmUKCgrPR 

2. Seated Calf Raises 

This closely mimics the knee-bent position of running. 

How to do it: 

• Sit on a bench or chair 

• Place weight (barbell, dumbbells, or kettlebell) across your thighs 

• Lift heels off the ground and slowly lower 

Prescription: 

• 3–5 sets of 15–25 reps 

• Focus on full range of motion 

This exercise is excellent for endurance runners because it isolates the soleus while minimising hip and knee fatigue. 

https://youtube.com/shorts/nLysrEHspKQ?si=4lx-qS-SxXGZ1YWA 

3. Isometric Soleus Holds 

Isometrics are gold for both strength and tendon health, especially for runners dealing with Achilles or calf issues. 

How to do it: 

• Perform a bent-knee calf raise 

• Hold the top position on your toes 

Options: 

• Double-leg or single-leg 

• Add load once bodyweight becomes easy 

Prescription: 

• 3–5 holds of 30–60 seconds 

This builds fatigue resistance—exactly what the soleus needs for long races. 

https://youtube.com/shorts/ysSo1ro7n30?si=8FS3eP600pVPC73L 

4. Eccentric Heel Drops (Bent Knee) 

Eccentric strength is essential for absorbing load during landing and downhill running. 

How to do it: 

• Stand on a step with heels off the edge 

• Bend your knees 

• Rise up using both feet 

• Lower slowly on one foot 

Prescription: 

• 3 sets of 8–12 slow reps per leg 

• 4–5 seconds lowering phase 

This is especially useful for trail and ultra runners who spend long periods braking on descents. 

https://youtube.com/shorts/kpserlCZeXX8?si=YCDRxsJSMHmH9z9T 

5. Walking Lunges with Heel Raise 

This integrates soleus strength into a functional, running-specific pattern. 

How to do it: 

• Step into a lunge 

• At the bottom of the lunge, lift the back heel 

• Push forward into the next step 

Prescription: 

• 2–3 sets of 20–30 steps 

This builds strength under fatigue and teaches the soleus to work while the body is moving—just like running. 

https://youtube.com/shorts/kr9rqSU8p54?si=DJxvJKwwY0aDJS1L 

6. Uphill Hiking or Incline Treadmill Walking 

One of the most underrated soleus exercises. 

Why it works: 

• Uphill movement keeps the knee slightly bent 

• Long time under tension 

• Low impact but high muscular demand 

Prescription: 

• 10–30 minutes 

• Moderate incline (5–10%) 

This is perfect for recovery days or for runners returning from injury. 

If you’re an endurance runner and you’re not training your soleus deliberately, you’re leaving performance and durability on the table. 

Strong feet don’t start at the toes—they start in the deep calf. 
Train your soleus, support your “second heart,” and you’ll run farther, stronger, and longer.