The objective of this study was to use magnetic resonance (MR) imaging to investigate long-term changes in muscle and tendon morphology following a hamstring strain injury.
MATERIALS AND METHODS:
MR images were obtained from 14 athletes who sustained a clinically diagnosed grade I-II hamstring strain injury between 5 and 23 months prior as well as five healthy controls. Qualitative bilateral comparisons were used to assess the presence of fatty infiltration and changes in morphology that may have arisen as a result of the previous injury. Hamstring muscle and tendon-scar volumes were quantified in both limbs for the biceps femoris long head (BFLH), biceps femoris short head (BFSH), the proximal semimembranosus tendon, and the proximal conjoint biceps femoris and semitendinosus tendon. Differences in muscle and tendon volume between limbs were statistically compared between the previously injured and healthy control subjects.
Increased low-intensity signal was present along the musculotendon junction adjacent to the site of presumed prior injury for 11 of the 14 subjects, suggestive of persistent scar tissue. The 13 subjects with biceps femoris injuries displayed a significant decrease in BFLH volume (p < 0.01), often accompanied by an increase in BFSH volume. Two of these subjects also presented with fatty infiltration within the previously injured BFLH.
The results of this study provide evidence of long-term musculotendon remodeling following a hamstring strain injury. Additionally, many athletes are likely returning to sport with residual atrophy of the BFLH and/or hypertrophy of the BFSH. It is possible that long-term changes in musculotendon structure following injury alters contraction mechanics during functional movement, such as running and may contribute to reinjury risk.
So on to this study. The abstract didn’t mean a lot to me before I took an in depth look at the anatomy. They found the LONG HEAD of the biceps femoris (the larger of 2 heads of the 3 muscles that make up the hamstrings) was generally what was strained in 13 out of the 14 injured, and was 10% smaller when measured between 5 and 23 months post injury. The biceps femoris SHORT HEAD was 13% larger. And the proximal conjoined tendon of the LONG HEAD biceps femoris and semitendinosus (another of the 3 hamstring muscles) was 85% larger. This was AFTER the athlete had completed their physical therapy and had returned to sport.
So what I learned from this is that the long head tendons being 85% larger is indicative of increased scar tissue that is still there as long as 23 months post injury. The LONG HEAD of the biceps does not recover full strength in spite of typical rehabilitation, but the SHORT HEAD becomes larger apparently to compensate for the injury of the LONG HEAD. Unfortunately the physical therapy rehabilitation exercises were not standardized so it’s unknown what exercise were performed. This meant something to me, but still not a lot until I looked up the particular attachments of the LONG HEAD and SHORT HEAD of the biceps femoris and saw that only the SHORT HEAD only crossed the knee joint and didn’t act at all to extend the hip, but only flexed the knee. The LONG HEAD in contrast crossed both the knee and the hip acting as both a hip extensor and a knee flexor.
So my thought is that these athletes were likely rehabilitated with hamstring strengthening exercises that act only on the knee, like leg curls, (both seated and prone) and to a lesser extent the Nordic Hamstring Curl, (which acts a lot at the knee and only a little at the hip). In contrast a Romanian Deadlift (RDL) acts primarily at the hip and I would expect would better target the LONG HEAD of the biceps femoris, and this might be what was missing from these athletes physical therapy protocols. SHORT HEAD atrophy of the biceps femoris, resulting from RDLs being a missing part of rehabilitation might also be why so many athletes, soccer players in particular injure and strain their hamstrings. It might also be why you test an injured athlete’s hamstring strength with knee flexion (a leg curl) and it might seem strong but they go right out and reinjure when running at high speeds, which requires strong hip extension.
So continuing to think out loud the Nordic Hamstring Curl has the advantage of particularly targeting eccentric strength of the hamstring, but the RDL being both eccentric and concentric does a better job at increasing strength in hip extension, plus better stretching the LONG HEAD, so the combination of the two exercises might be ideal. What I still don’t know is how strong an RDL an athlete should have in relation to their other exercises for safe return to sport, but based on my experience in therapy and at the NAU Weight room it should be AT LEAST as high as the persons back squat. But then you still get into problems of what kind of squat, high bar or low bar, how deep, etc. I also think this brings in need for isokinetic testing of hip extension both concentric and eccentric in normal players and players with hamstring strains much like it is done for the same muscle at the knee.
Further thinking out loud, it also gave me an idea for a new exercise I just made up called the “3 bounce RDL” where the person goes down to the bottom stretch position and bounces 3 times before returning upward. It might increase the eccentric strength component of the exercise and I think it most certainly will work to increase hamstring flexibility combined with strength. The problem I foresee however is that though you might stretch more, I don’t know if it would really cause any additional increase in eccentric strength as the athlete would almost certainly train with a lighter weight. So maybe it’s worthwhile only if the athlete has tighter hamstrings. Anyway makes me want to start looking for my own isokinetic muscle tester to one day gather dust and take up space in my office.
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Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.