Straight-Leg vs Bent-Knee Calf Raises: Gastrocnemius vs Soleus Length-Tension

If your calves refuse to grow even though you smash seated calf raises every week, the exercise is probably the problem. In the straight leg vs seated calf raise comparison, the straight-knee version wins for the big visible calf muscle (the gastrocnemius), because bending your knee takes most of its tension away. Seated raises still train the soleus, the muscle underneath.

This is one of the clearest examples of the length-tension ideas in our guide to range of motion and stretch-mediated hypertrophy. Below: what each muscle does, what the trial data show, and a simple way to program both.

Why does knee angle change a calf raise?

Your calf is really two muscles that share the Achilles tendon. The soleus attaches below the knee and crosses only the ankle. The gastrocnemius (the two-headed muscle you see from behind) starts above the knee, so it crosses both joints. It plantarflexes your ankle and also helps bend your knee.

That two-joint design is the whole story. A muscle can only produce good force within a certain length range. Bend the knee to 90 degrees and the gastrocnemius is shortened from its upper end, so it has less ability to contribute. Straighten the knee and it is held at a longer length, where it can produce more force. This is the same logic we cover in active vs passive insufficiency in biarticular muscles.

What does the research say about gastrocnemius vs soleus?

Several lines of lab evidence agree, though most are small studies in healthy young adults.

• Torque drops with a bent knee. In nine active men, maximal isometric plantar flexor torque was about 40% lower with the knee flexed than extended (about 93 vs 154 N·m) (Kovács et al., 2024). Gastrocnemius size tracked torque with the knee straight, but only soleus and total calf size tracked it with the knee bent.
• Motor units hand off. During a light, steady calf contraction, moving the knee into flexion lowered gastrocnemius motor unit firing, with most units de-recruited near full flexion, while soleus activity rose (Lauber et al., 2014).
• Same pattern with knee extension. Adding knee extensor effort to plantar flexion lowered medial gastrocnemius EMG and raised soleus EMG in ten men (Suzuki et al., 2014).

Notice the limits. These are acute measurements, not growth outcomes, and EMG is only a rough proxy for how much a muscle will grow. The growth data come next.

Does standing really grow more calf than seated?

The best direct test is a 12-week within-person trial. Fourteen untrained adults trained one leg with standing, straight-knee calf raises and the other with seated raises at a 90-degree knee bend. Both legs did 5 sets of 10 reps at 70% of 1RM, twice a week, and MRI measured muscle volume (Kinoshita et al., 2023).

The results were not subtle:

• Lateral gastrocnemius: 12.4% vs 1.7% (standing vs seated)
• Medial gastrocnemius: 9.2% vs 0.6%
• Whole triceps surae: 5.6% vs 2.1%
• Soleus: 2.1% vs 2.9%, with no significant difference

The seated leg’s gastrocnemius growth was not statistically significant at all. The soleus grew about the same either way.

A systematic review of range of motion studies points the same way for the lower body: full-ROM training tends to beat partial ROM for hypertrophy there, though the review included only six studies and noted the response may be muscle-specific (Schoenfeld and Grgic, 2020).

Which calf muscle gives the “diamond” look?

From behind, the rounded, diamond-shaped bulk is mostly the two heads of the gastrocnemius. The soleus lies underneath and shows up as extra width and thickness toward the lower calf, especially from the side and front. I would not promise any specific shape change from any exercise, because tendon length and genetics also shape how calves look. But if you want the muscle most people mean by “big calves”, straight-knee work should come first.

You may see the soleus described as a slow-twitch, endurance-type muscle. That is a common teaching point, but I did not find a source I could verify here, and the programming advice below does not depend on it.

How do I train both properly?

Here is how I would set it up for a lifter in a normal commercial gym.

Straight-leg options (gastrocnemius priority):

• Standing calf raise (machine or smith)
• Donkey calf raise
• Leg-press calf raise with the knees straight but not hard-locked
• Single-leg standing raise on a step with a dumbbell

Bent-knee options (soleus priority):

• Seated calf raise
• Smith-machine or barbell raise with the knees bent
• Bent-knee raise with a dumbbell on the thigh

A simple weekly layout:

Session	Exercise	Sets	Reps
Day A	Standing calf raise	3	8-12
Day A	Seated calf raise	2	10-15
Day B	Leg-press or donkey raise	3	8-12
Day B	Seated calf raise	1-2	10-15

That lands at roughly 9-10 hard sets a week, in line with our usual 6-10 range, and puts about two-thirds of the work on the gastrocnemius. You can check your numbers with the training volume calculator or drop these into a leg day plan.

How deep should I go at the bottom?

Deep. The bottom of a calf raise is where the gastrocnemius is longest, and that is the position that seems to matter. Let the heel drop below the platform, hold the stretch for about a second so you do not bounce off the Achilles tendon, then rise to a full top squeeze.

The most common mistake here is bouncing through half reps with a heavy stack. It looks like a lot of weight, but the stretched range is exactly the part being skipped.

Some trials suggest the lengthened range may be especially useful for gastrocnemius growth:

• In 23 untrained men over 10 weeks, adding past-failure partial reps in the lengthened (dorsiflexed) position grew the medial gastrocnemius by 9.6% vs 6.7% for sets to failure alone, with the authors reporting strong Bayesian support (Larsen et al., 2025).
• In 16 untrained men, half as many sets with lengthened partials after full-ROM failure produced the same 8% thickness gain as standard sets, which means more growth per set but not more growth overall (Goli et al., 2026).
• In 23 resistance-trained men and women over 8 weeks, partials in the stretched range from the first rep edged out full-ROM sets finished with partials at the top, but the evidence for a difference was only anecdotal and both approaches worked (Larsen et al., 2025).

So the picture is: lengthened-range work looks good, but which exact method is best is unsettled, and every one of these was short-term. More on this in our guide to lengthened partials.

What about stubborn calves?

Calves have a reputation for a reason. The authors of the MRI trial describe the triceps surae as relatively unresponsive to resistance training compared with other muscles, though prone to shrinking when inactive (Kinoshita et al., 2023). Here is the checklist I would run:

1. Are you doing straight-knee raises at all?
2. Do you reach a deep stretch every rep?
3. Are you finishing within 1-3 reps of failure?
4. Do you train them at least twice a week?
5. Are you adding reps or load over months, or just repeating the same numbers?

Quick comparison

	Straight-knee raise	Bent-knee raise
Main target	Gastrocnemius (plus soleus)	Soleus
Gastrocnemius length	Long, more tension	Short, little tension
MRI growth, gastroc (12 wk)	9-12%	Under 2%
MRI growth, soleus (12 wk)	2.1%	2.9%
Best use	Base of calf training	Add-on for soleus

Where this fits with the rest of your calf training

This article is about one variable: knee angle, and what it does to each calf muscle. Volume, frequency, rep ranges and the full weekly picture live in our calf hypertrophy guide to standing vs seated raises. The short version holds either way. Keep the knee straight for most of your sets, go deep, and push hard. Protein matters for every muscle, calves included, so check your daily target with the protein calculator, whether you eat meat or rely on dal, paneer and curd.

When to see a doctor

Normal calf soreness fades in a few days. Sudden sharp pain, a swollen, warm or red calf on one side, or calf pain after a long trip needs medical assessment, since it could be a muscle or tendon injury or a clot. Do not train through it.

The bottom line

Bending your knee removes most of the gastrocnemius from the exercise, and the soleus takes over. For visible calf growth, build the base from straight-knee raises with a deep stretch, then add seated raises for the soleus. The best direct data are one 12-week MRI trial in untrained adults plus lab studies of muscle activation, so expect to refine the details, not abandon the principle. Pair this with a sensible weekly plan and enough protein, and give it a few months.