How do I activate the soleus muscle?

Activating the Soleus Muscle

To selectively activate the soleus muscle, perform plantar flexion exercises (heel raises) with the knee extended, or add knee extension activity during plantar flexion, which preferentially recruits the soleus while suppressing gastrocnemius activity. 1

Exercise Selection for Soleus Activation

Heel Raise Training (Primary Method)

• Perform standing heel raises with knees straight to maximize soleus recruitment 2
• Execute 100 repetitions daily for optimal hypertrophy of the soleus, which contains approximately 90% slow-twitch muscle fibers 2
• This low-intensity exercise requires no special equipment and can be performed safely across all age groups 2

Combined Knee Extension and Plantar Flexion

• When knee extensor activity is added to plantar flexion, soleus EMG activity significantly increases while gastrocnemius activity is suppressed 1
• This selective activation occurs because the gastrocnemius acts as a knee flexor (antagonist during knee extension), while the soleus is purely a plantar flexor 1
• Perform isometric plantar flexion at 10-30% maximum effort while simultaneously adding knee extension at 50-100% maximum effort 1

Neuromuscular Electrical Stimulation (NMES) for Soleus

When to Use NMES

• NMES is indicated when minimal volitional muscle activation is present or for patients unable to perform conventional exercise 3
• Particularly useful for severely deconditioned individuals, bed-bound patients, or those with acute disease exacerbations 3

NMES Parameters for Soleus

• Pulse duration: 200-700 milliseconds 3
• Duty cycle: 2-10 seconds on / 4-50 seconds off 3
• Intensity: Increase current (mA) until visible muscle contraction occurs or to maximum tolerated level 3
• Frequency: 3-7 days per week 3
• Duration: One to two sessions daily, totaling 20-60 minutes per day 3
• For optimal force development, use stimulation frequencies of 70-80 Hz, as NMES requires higher frequencies than physiological nerve firing due to synchronous motor unit recruitment 3

NMES Benefits for Soleus

• Microcurrent electrical nerve stimulation (10 μA, 0.3 Hz, 250 msec pulse width) facilitates regrowth of atrophied soleus muscle by activating protein synthesis pathways 4
• Long-term electrical stimulation training preserves muscle characteristics and prevents development of fast-fatigable muscle properties in paralyzed soleus 5
• NMES increases phosphorylated levels of p70 S6 kinase and Akt, intracellular signals involved in protein synthesis 4

Progressive Resistance Training Protocol

Initial Phase (Weeks 1-4)

• Begin with isometric exercises (quad sets, short-arc quad sets) to avoid pain during knee extension 6
• Start with low resistance at 40% of 1-repetition maximum (1-RM) for 10-15 repetitions 3
• Perform exercises 2-3 non-consecutive days per week 3

Progression Phase (Weeks 4+)

• Progress to isotonic (dynamic) exercises, which closely correspond to everyday activities 3
• Advance to long-arc quad sets and closed-chain exercises (partial squats to 30 degrees) as pain allows 6
• Increase to 3-5 days per week, 20-60 minutes per session at moderate intensity 6
• Use 8-12 repetitions for adults under 50-60 years; 10-15 repetitions at reduced resistance for those over 50-60 years 3

Exercise Execution Guidelines

• Perform movements rhythmically at moderate to slow controlled speed through full range of motion 3
• Exhale during the contraction/exertion phase and inhale during relaxation to avoid Valsalva maneuver 3, 6
• Hold static stretches for 10-30 seconds before returning to resting length 3
• Include 5-10 minute warm-up with low-intensity range-of-motion exercises and 5-minute cool-down with static stretching 3

Rehabilitation Following Nerve Injury

Exercise Timing and Intensity

• Intermittent mid-intensity treadmill exercise (not slow continuous running) improves soleus muscle reinnervation following nerve crush injury 7
• Mid-intensity intermittent exercise enhances functional muscle recovery and increases autophagy-related markers (LC3) 7
• Slow continuous running exercise worsens functional outcomes and should be avoided during nerve regeneration 7

Common Pitfalls to Avoid

• Do not hold your breath during exercises, as this increases intra-abdominal pressure and cardiovascular stress 6
• Avoid performing heel raises with bent knees, as this shifts activation toward the gastrocnemius rather than the soleus 1
• Do not use slow continuous exercise protocols during nerve injury recovery, as they impair functional outcomes 7
• When using NMES, ensure proper electrode placement and gradually increase intensity to prevent excessive muscle soreness 3
• Avoid excessive initial resistance that prevents completing the prescribed repetition range, as this increases injury risk 3