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Running Injury Prevention: Calf Muscle Power Deficits 

The calf muscles are an important source of shock absorption and propulsion during running gait (Hamner, Seth, Delp, 2010).  They function primarily as plantar flexors (extension) of the ankle and are made up of the gastrocnemius, soleus and plantaris (sometimes).

Image from Shutterstock

Strength testing standards currently involving using the calf raise test: a series of repeated single leg heel raises.  A systematic review in 2009 (Herbert-Losier et al) demonstrated that the normal number of single leg calf raises that healthy individuals should be able to perform are 27 repetitions for men and 19 repetitions for women.  25 repetitions is a commonly used standard, although the literature varies as evident by the above systematic review.

Bernard Lagat and his famous calf muscles.  
Photo Credit: Andre Zehetbauer, CC

The calf muscles are most active during the second half of the stance phase of running (foot on the ground).  They control the forward translation of the tibia (so you don't fall on your face) in an eccentric (controlled lengthening) manner.  Then the calf muscles quickly push the body forward concentrically by extending (plantarflexing) the ankle in late midstance to terminal stance.  During the swing phase (air born) of running gait, they are fairly quiet until the very end where they can prepare for landing if the subject is utilizing a forefoot or midfoot initial contact/landing pattern.

Image result for calf muscle anatomy runner
Image from Westcoast SCI

The gastrocnemius also crosses the knee joint and can assist with flexing (bending) the knee.   Thus the calf muscles support both the knee and ankle.  With this in mind, let's discuss how weakness of this muscle group can cause some running related movement issues and injuries.

ASSOCIATED RUNNING IMPAIRMENTS

Excessive Anterior Knee Translation

The calf muscles control the forward translation of the tibia during the stance (grounded) phase of running.  Meaning they also control how far forward the knee translates.  With poor muscular strength, there may be poor control of how far forward the knee translates.  As mentioned previously (see the link above for more information), there is some research on the increase load on the knee joint with a knee forward to toe position during lunging or squatting (Kernozek et al., 2018; Zellmer et al., 2017). As running has a great deal more impact load than either one of those activities, one can infer that this movement impairment may predispose individuals to an increased risk of patellofemoral (knee) pain.

Poor eccentric control of the tibia during midstance means excessive forward motion of the knee.
Image from www.bridge38physiotherapy.co.uk

ASSOCIATED INJURIES

Achilles Tendinosis

With excessive forward translation of the tibia comes excessive lengthening of the calf complex.  Excessive strain (ie excessive lengthening under excessive load) is a potential key mechanism in the irritation of tendons (Bogaerts et al 2016).  Hence why poor calf strength may lead to excessive tendon load and the path to achilles tendinosis (or itis in acute phases).

Patellar Tendinosis/Patellofemoral Pain 

As mentioned above, with an excessive knee forward to toe movement impairment, there may be excessive load through the patellar tendon or patellofemoral complex.  With the endurance component of running comes the risk of overuse injuries and the knee may be quickly put at risk.  The knee forward to toes movement impairment can put excessive load onto the posterior aspect of patella (knee cap) where it contacts the distal femur due to the excessive compression load with greater knee flexion.  There may also be excessive load through the patellar tendon due to strain on the tendon from excessive load through the quadriceps muscles.  Greater knee flexion may be associated with greater quadriceps compensation and overuse of the tendon for loading or support during the initial or midstance phases of running gait (Powers, 2018).

Plantar Fasciitis (Plantar Fasciopathy)

I must admit prior to discussing this relationship that this connection is from clinical experience and I have not been able to find much if any research looking into this.  However, since the calf and achilles are connected via fascial anatomy and the windlass mechanism (Myers, 2011), logically excessive strain on the achilles tendon via weakness of the calf muscles could lead to excessive strain on the plantar fascia.  The strength and flexibility of the surronding musculature is often overlooked in the treatment of plantar fasciopathy (the pathology is usually more chronic, thus is more correctly labeled fasciopathy).

Image from ESPN

CORRECTIONS

Given that the calf muscles are responsible for a large part of what moves the body forward during running (propulsion), it makes sense that having increased strength and power generation could also contribute to faster running!  So not only is it important to keep these healthy from an injury standpoint, but also from a performance standpoint.

Heel Raises


The current literature varies on how many single leg heel raises one should be able to do.  As mentioned above, the average is usually around 25 per leg.  These are a great way to build calf strength and can be done with the knee straight (gastrocnemius) or bent (soleus).  This should be a higher repetition exercise (3-5 x 20-25) as the calf muscles (particularly the soleus) tend to have a high percentage of slow twitch fibers (Gollnick et al., 1974).

Jump Rope

Image result for jumping rope
Image from AAPTIV

Jumping rope is a great introduction to plyometric exercise.  Plyometrics involved generating maximal levels of force in very short periods of time and are one of the best ways to increase power (the ability to generate strength quickly).  Running has a strong plyometric component to it, so improving muscle power is important not just for injury prevention, but also performance.  Jump rope forces athletes to be able to generate force quickly in order to get over that rope.  This should start as a 3 x 50 rep exercise, progressing to 3-5 sets of 150-200.  This can even be used as a form of cross training aerobically and can be done in carefully extended amounts of time.  

Single Leg Hops


One of the most functional exercises you can do for running.  Fast repeated single leg hops combined plyometric training of the calf, quad and hip along with working on pelvic and trunk stability.  Start slow with these (non-plyometric, just jumping) to work on control and force generation.  As your landing and stability improve, you can progress the speed to repeated single leg hops.  Progress far slower than the double limb jump rope above as single leg exercises are far more challenging than double limb (but they are also more functional and have bigger benefits).


Thanks for reading!

Dr. Matthew Klein, PT DPT OCS FAAOMPT
Doctor of Physical Therapy
Board Certified Orthopedic Clinical Specialist
Fellow of the American Academy of Orthopedic Manual Physical Therapists

***Disclaimer: As always, my views are my own.  My website should not and does not serve as a replacement for seeking professional medical care.  I have not evaluated you in person, am not aware of your injury history and personal biomechanics, thus am not responsible for any injury that you may incur from the performance of the above.  I have not prescribed any of the above exercises to you and thus again am not responsible for any injury that may occur from the performance of the above.  This website is meant for educational purposes only.  If you are currently injured or concerned about an injury, please see your local physical therapist.  However, if you are in the LA area, I am currently taking clients for running evaluations. 

REFERENCES

1. Bogaerts, S., Desmet, H., Slagmolen, P., Peers, K. (2016). Strain mapping in the Achilles tendon - A systematic review. Journal of Biomechanics, 49(9): 1411-1419. doi: 10.101/j.jbiomech.2016.02.057
2. Gollnick, P., Sjodin, B., Karlsson, J., Jansson, E. Saltin, B. (2974). Human Soleus Muscle: A comparison of fiber composition and enzyme activities with other leg muscles. Pflugers Archiv, 348(3): 247-255.
3.  Hamner, S., Seth, A., Delp, S. (2010).  Muscle contributions to propulsion and support during running.  Journal of Biomechanics, 43(14): 2709-2716.  doi: 10.1016/j.jbiomech.2010.06.025
4.  Kernozek, T., Gheidi, N., Zellmer, M., Hove, J., Hinbert, B., Torry, M. (2018). Effects of Anterior Knee Displacement During Squatting on Patellofemoral Joint Stress. Journal of Sport Rehabilitation, 27(3): 237-243. doi: 10.1123/jsr.2016-0197
5.  Myers, Thomas W. (2011).  Anatomy Trains.  London: Urban & Fischer
6. Powers, C. (2018). Evaluation and Treatment of the Injured Runner. (Lecture and Power Point). Los Angeles, CA.

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