Still Think It's The Thigh Muscles?

I have seen many patients who have had an anterior cruciate ligament (ACL) tear over the years.  Some patients chose not to go under the knife but most had reconstruction done. ALL of them were taught to focus their strengthening on their quadriceps (or thigh) muscles.

So not surprising that a recently published study by Alzobi et al (2026) found that patients who did not opt for surgery exhibited progressive hamstring muscle atrophy.

A total of 1,207 thighs were examined. There were 92 with ACL tears and the other 1,115 acted as controls. The average age of the subject group was 61± 9 years.

Over 4 years, the ACL deficit thighs were smaller by an average of 28.18 mm, all due to progressive hamstring atrophy. The differences ranged from 13.92 to 42.43 mm smaller. The sartorius muscle also atrophied by an average of 3.02 mm.

There were no significant differences in the quadriceps or adductor cross sectional area. hamstring force was decreased significantly whereas quadriceps force showed no significant change.

The researchers concluded that muscle deterioration occurred in the posterior thigh muscles (hamstrings) with minimal changes in the front thigh muscles (quadriceps) over time. And for ACL deficient knees, it is really important to target long term rehabilitation strategies focusing on hamstring preservation. 

We already know that one of the reasons women sustained ACL tears is that their hamstrings were significantly weaker than their quadriceps muscle strength.

If you have been reading our previous blog articles, you already know that the quadriceps (thigh muscles) and gastrocnemius (calf muscles) increases load on the ACL due to anterior shearing forces at the tibia (shin bone). This is especially so when the knee is straightened (Maniar et al, 2022).

The hamstrings and soleus (deeper calf muscles) help to unload the ACL by generating posterior tibial shearing forces (Maniar et al, 2022).

So for those of you who have torn your ACL, whether or not you choose to go for surgery, make sure you focus on your hamstrings and soleus muscles instead.

References

Alzobi O, Mohajer B, Fleuriscar J et al (2026). Thigh Muscle Changes In The ACL-Deficient Knee: A 4-Year Lonitudinal MRI Study of 1,207 Patients. JBJS Am. 108(3): 219-226. DOI: 10.2106/JBJS.25.0064

Maniar N, Cole MH, Bryant AL et al (2022). Muscle Force Contributions To Anterior Cruciate Ligament Loading Sports Med. DOI: 10.1007/s40279-022-016743