The key to strengthening the soleus is bending your knee. This deep calf muscle sits beneath the larger, more visible gastrocnemius, and it only becomes the primary mover when your knee is flexed. Straight-leg calf raises hit the gastrocnemius hard but leave the soleus underworked. Bend the knee to about 90 degrees, and the soleus takes over.
Why the Bent Knee Matters
The gastrocnemius crosses both the knee and ankle joints, while the soleus only crosses the ankle. When your knee is straight, the gastrocnemius is in a lengthened position and fires aggressively. As you bend the knee, the gastrocnemius shortens and progressively shuts down. Research from motor unit recordings shows that gastrocnemius motor units begin to de-recruit at around 21 degrees of knee flexion, with soleus activity steadily increasing as the knee bends further. By the time you reach a full seated position with your knee at 90 degrees, the soleus is doing the heavy lifting.
This is why every effective soleus exercise shares the same setup: a bent knee. If you’ve been doing standing calf raises and wondering why the deeper part of your calf never grows, this is the answer.
What Makes the Soleus Unique
The soleus is roughly 70 to 90 percent slow-twitch muscle fiber. Compare that to the gastrocnemius at about 50 percent slow-twitch, or the quadriceps at around 32 percent. Slow-twitch fibers are built for endurance, not explosive power. They resist fatigue, generate force over long durations, and respond best to moderate rep ranges with controlled tempos rather than heavy, low-rep sets.
This fiber composition also explains the soleus’s role in daily life. It works constantly during standing, walking, and running to keep you from falling forward. It’s one of the hardest-working postural muscles in the body. And because it’s designed for sustained effort, training it requires a slightly different approach than you’d use for fast-twitch dominant muscles like the hamstrings or chest.
Best Exercises for the Soleus
Seated Calf Raise (Machine)
This is the gold standard. Sit with the pad resting on your lower thighs, the balls of your feet on the platform, and your heels hanging off the edge. Lower your heels as far as they’ll go to get a full stretch, then press up through the balls of your feet until your heels are as high as possible. The 90-degree knee bend ensures the gastrocnemius stays quiet and the soleus does the work. If your gym has a seated calf raise machine, use it as your primary soleus builder.
Seated Calf Raise (Bodyweight or Dumbbell)
Sit on a sturdy chair with your feet flat on the floor and knees bent at 90 degrees. Press through the balls of your feet to raise your heels as high as you can, then lower slowly. To add resistance, place a dumbbell or heavy book on your lower thighs near your knees and push down gently while you raise. This works well at home and is easy to progress by adding weight incrementally.
Bent-Knee Standing Calf Raise
Stand on the edge of a step with the balls of your feet on the surface and your heels hanging off. Bend your knees to about 90 degrees (a half-squat position) and perform calf raises from this position. You can hold dumbbells or a loaded backpack for extra resistance. This variation loads the soleus more than a traditional standing calf raise because the knee bend takes the gastrocnemius out of the equation.
Soleus Bridge
Lie on your back with your knees bent and feet flat, as if you’re doing a glute bridge. From the top of the bridge position, press through the balls of your feet and raise your heels off the ground. This combines hip extension with ankle plantar flexion and challenges the soleus in a way that carries over to running and jumping mechanics.
The Soleus Pushup
Sit in a chair with your feet flat on the floor. Raise your heels by pressing through the balls of your feet, then lower them back down. That’s one rep. It sounds simple, and it is, but research from the University of Houston found that sustained soleus contractions done this way reduced post-meal blood sugar spikes by 52 percent and insulin levels by 60 percent compared to sitting still. The metabolic benefits come from the soleus’s ability to burn fuel at a high rate when activated, even though the movement looks minimal. This isn’t primarily a strength builder, but it’s a useful tool if you sit for long hours.
Rep Ranges and Weekly Volume
Because the soleus is so heavily slow-twitch, it responds well to sets of 6 to 12 reps performed with a slow, controlled tempo. Hold the top position for a one to two second squeeze and take two to three seconds on the lowering phase. This keeps the muscle under tension longer, which is what slow-twitch fibers need to grow.
For weekly volume, 4 to 6 sets per week is a solid target for most people. You can split this across two sessions (two to three sets each) or do it in a single dedicated session. Advanced lifters may push toward 8 to 10 sets per week, but research on hypertrophy in trained athletes suggests that 4 to 6 sets per muscle group is often the sweet spot before diminishing returns set in. More isn’t always better, especially for a muscle that’s already active throughout the day.
Strength Benchmarks
If you want to know where you stand, sports physiotherapy benchmarks for the seated calf raise (which isolates the soleus) break down like this:
- General population: about 0.5 times your body weight
- Recreational athlete: about 1.0 times body weight
- Well-trained athlete: 1.25 to 1.5 times body weight
- Elite sprinters, jumpers, and field sport athletes: 1.75 to 2.0 times body weight
If you’re currently below the general population standard, you have significant room to improve, and you’ll likely notice the gains in your running, jumping, and overall ankle stability. These numbers refer to the load on the machine, not including body weight.
Common Form Mistakes
The most frequent error on seated calf raises is loading too much weight. When the weight is too heavy, you can’t lower your heels into a full stretch or raise them to full contraction. You end up working through a fraction of the available range, which limits both strength and muscle development. Drop the weight until you can go from a deep heel stretch at the bottom to a full squeeze at the top.
Bouncing is the second major issue. Instead of controlling the movement, people let the weight drop and then catch it at the bottom, using the elastic rebound of the Achilles tendon to bounce back up. This shifts stress away from the soleus muscle and onto the tendon, which increases injury risk and reduces the training effect. Every rep should be deliberate: slow on the way down, pause briefly at the bottom, then press up smoothly.
Soleus Strength for Injury Prevention
Weak soleus muscles are a common contributor to Achilles tendon problems, particularly in runners. Rehabilitation protocols for Achilles tendinopathy specifically include bent-knee calf raises to load the soleus and its tendon. A typical clinical protocol runs 12 weeks, performed twice daily, seven days a week, with 3 sets of 15 reps. The progression starts with eccentric-only work (lowering on the injured leg after raising on both) and adds load gradually, often with a weighted backpack, increasing by small increments like a bag of sugar at a time.
You don’t need to wait for an injury to apply this principle. If you run, play sports, or spend a lot of time on your feet, building soleus strength now creates a buffer against future tendon issues. The soleus produces enormous force during running, and a stronger muscle means less strain on the tendon with every stride. Two to three sessions per week of seated calf raises, progressed steadily over months, is one of the simplest and most effective forms of lower leg injury prevention available.