Biarticular Muscles - Gastrocnemius
Bi-articular muscles are muscles that cross 2 joints and influence the movement at both. Uniarticular muscles are those that only attach to and influence one joint. The benefit that biarticular muscles have over uniarticular muscles is that biarticular muscles influence joint activity by contracting and possibly preventing movement at one or both joints that it crosses (Floyd, 2021). Discovering the optimal length and tension on biarticular muscles will have different outcomes as joint angles are altered. Biarticular muscles also exert a greater force when lengthened.
There are nine biarticular muscles that cross the knee joint. The gastrocnemius is the only one that crosses the knee and ankle joint. The gastrocnemius inserts at the posterior surface of the calcaneus (Achilles tendon) and has two origins: The medial head is on the posterior surface of the medial femoral condyle and the lateral head is on the posterior surface of the lateral femoral condyle. The gastrocnemius is responsible for plantar flexion of the ankle and flexion of the knee. The soleus is a uniarticular muscle and also assists in plantar flexion at the ankle joint. The soleus and gastrocnemius together form the triceps surae. The soleus activates when the knee is flexed, due to reduced effect of the gastrocnemius. (Floyd, 2021, Pg. 322).
Today I will be discussing the optimal length of the gastrocnemius and the angles of knee flexion and ankle plantarflexion that make this possible. Also, rehabilitation practices for ACL injuries and ankle instability, and discuss the kinetic chain and correlation between these ACL injuries and ankle instability, via the gastrocnemius.
The first study was a review on biarticular muscles of the lower extremities.They measure which knee and ankle joint combinations produce the greatest force by the gastrocnemius.
One of the tests consisted of 10 females and 7 males. Knee flexion moments produced by the gastrocnemius were measured with 24 knee and ankle joint positions. The angles analyzed at the knee were 0 (extension), 15, 30, 45, 60, 75, 95, and 105 degrees, and were compared with the ankle joint at neutral (0) and 15 degrees of plantar flexion and dorsiflexion. The results showed that when the knee is in flexion from 0-30 degrees, the maximum moment is influenced more by the ankle joint moving from dorsiflexion to plantarflexion. However, the knee flexion moment did decrease by 50% moving from 0-30 degrees. Furthermore, when the knee was in flexion greater than 45 degrees, the knee flexion moment started to drastically decrease, and at 75 degrees the gastrocnemius had nearly no effect on the knee flexion moment. Therefore, what this tells us is that as knee flexion increases, the knee flexion moment decreases, causing the gastrocnemius to have minimal force. Also, the gastrocnemius has the most influence when the knee is at 0 degrees (extension) and 15 degrees dorsiflexion. The Plantar flexion joint moment found the same results - A fully extended knee and dorsiflexed ankle created the greatest force. From a training perspective, this explains the common use of the elevated calf raise, in order to strengthen your gastrocnemius. (Landin, D., Thompson, M., & Reid, M. , 2016).
One of the groups of authors from the review, Li et al., used this study to evaluate ACL injuries and the correct rehabilitation practices to use. The results of this study display that keeping the knee flexed under 30 degrees, while performing weight bearing exercises will help keep the knee stabilized. Anything over 30 degrees, the gastrocnemius starts to contribute less impact, causing the knee to be less stable. A plethora of different rehabilitation exercises that involve single plane balancing movements, while keeping the knee under 30 degrees of flexion and the foot at neutral to approximately 15 degrees of dorsiflexion were displayed here. One specific exercise was a lateral lunge, coming back to balance on 30 degrees of knee flexion, with the ankle at approximately 15 degrees of dorsiflexion. (Li, L., Landin, D., Grodesky, J., & Myers, J. 2002 & Wilk, K. E., Arrigo, C., Andrews, J. R., & Clancy, W. G., 1999)
While these movements make sense, I also considered how an ACL injury or reconstruction could harm the ankle joint as well, due to the instability of the knee during the injury and recovery period. If you’re training someone with an ACL injury, what preventative measures can you take to avoid the negative effect of the kinetic chain?
An article by Thomas, A. C., Villwock, M., Wojtys, E. M., & Palmieri-Smith, R. M. in 2013 studied lower extremity muscle strength after ACL injury and reconstruction. They studied eight males and seven females with an ACL injury. Preoperatively the ACL injured group displayed a greater weakness in the ankle plantar flexor strength. Although they found that ankle flexor strength was not influenced postoperatively, meaning that the strength could have occurred early on in rehabilitation. Furthermore, they concluded that because the gastrocnemius crosses the knee joint, that the weakness in plantarflexion could have been a direct outcome of the ACL injury. (Thomas, A. C., Villwock, M., Wojtys, E. M., & Palmieri-Smith, R. M, 2013)
This brings me back to my initial argument of working up and down the kinetic chain. For any injury and rehabilitation program, understanding the whole scope of the injury and every muscle involved is crucial for a positive outcome, especially when dealing with lower extremity-weight bearing-biarticular muscles. When working with an ACL injury, exercises strengthening and lengthening the gastrocnemius should be looked at in detail. Exercises to stabilize the knee should be performed at knee flexion under 30 degrees. Various balancing exercises, performing different movements on a single leg and progressing to a balancing pad will encompass both knee and ankle stability. Gastrocnemius strengthening exercises could involve calf raises from the floor, with a progression to elevated calf raises when the patient is ready. This will also help strengthen the ankle joint.
References
Floyd, R.T. (2021). Manual of structural kinesiology (21st ed). McGraw Hill.
Landin, D., Thompson, M., & Reid, M. (2016). Actions of Two Bi-Articular Muscles of the Lower Extremity: A Review. Journal of clinical medicine research, 8(7), 489–494. https://doi.org/10.14740/jocmr2478w
Li, L., Landin, D., Grodesky, J., & Myers, J. (2002). The function of gastrocnemius as a knee flexor at selected knee and ankle angles. Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 12(5), 385–390. https://doi.org/10.1016/s1050-6411(02)00049-4
Thomas, A. C., Villwock, M., Wojtys, E. M., & Palmieri-Smith, R. M. (2013). Lower extremity muscle strength after anterior cruciate ligament injury and reconstruction. Journal of athletic training, 48(5), 610–620. https://doi.org/10.4085/1062-6050-48.3.23
Wilk, K. E., Arrigo, C., Andrews, J. R., & Clancy, W. G. (1999). Rehabilitation after anterior cruciate ligament reconstruction in the female athlete. Journal of athletic training, 34(2), 177–193.