On Saturday Night, January 30th, NBA’s Primetime game with the Boston Celtics and the Los Angeles Lakers, Boston Celtic’s Marcus Smart was injured in the 4th quarter due to non-contact. He immediately grabbed for his lower leg. ABC later zoomed in on the video and one would immediately jump to the conclusion that he just tore his Achilles’ Tendon.
And a more zoomed in video that was displayed during the telecast.
According to ESPN’s Adrian Wojnarowski and Stadium’s Shams Charania the news was much better than initially expected.
Let’s review the calf muscles. There are two “main” muscles that create the posterior aspect of our leg. Many people are familiar with the “Gastrocnemius” and others are less familiar with the “Soleus” The Gastrocnemius is the more superficial muscle while the Soleus is the deeper of the two. Together the two muscles form the Triceps Surae. Sometimes the “Plantaris” muscle is also added but we will not include it in this discussion.
The Gastrocnemius is a phasic and primary mover muscle and is made up of a medial head and a lateral head. It functions better with knee extension than in flexion (active insufficiency). The Soleus is more of a tonic and postural muscle and functions as stronger plantar flexor when the knee is bent. Together the two muscles allow for the ankle to plantar flex and assist with push off from the ground.
The gastrocnemius, the muscle that has been diagnosed as “strained” has two heads to it. It has the medial head and the lateral head. Medial head gastrocnemius injuries are more common than lateral head injuries. And in the video, you can see that Marcus Smart “strained” the medial head.
One of the unique features about the gastrocnemius is that it does cross multiple joints. It crosses the knee joint, a weak knee flexion muscle, the talocrural (ankle) joint, a strong ankle plantar flexion muscle, and the subtalar joint, a weak inversion muscle.
The Soleus crosses the talocrural and the subtalar joint. As previously stated, the Soleus plays an important role in allowing us to plantar flex our ankle but also plays a vital role in helping us maintain balance when standing upright.

So when his lower leg was in complete knee extension and ankle dorsiflexion, that put the muscle on complete stretch and an eccentric load on it, it was a recipe for a potential injury. I would say he is fortunate that his tear did not occur closer to the Achilles’ tendon and occurred in the muscle belly.
Muscle has a greater blood supply network, compared to tendon, to allow for faster recovery times.
I am not nearly as optimistic about him being out for 1-2 weeks, as previously reported, considering the fasciculation you saw in the muscle and that this Grade I strain is potentially a Grade II strain. It may take at minimum of 2 weeks for him and team to consider a return and start a more rigorous rehabilitation schedule that consists of more than passive modalities and treatment. Considering how the Kevin Durant situation turned out in Golden State, the Boston Celtics may take a more cautious approach for Marcus Smart.