Hamstring strain injuries tend to occur in activities that involve high speed running. It is the most common injury among sprinting and the second most common injury among NFL team, with 8-25 days lost to injury. It has 30 % of re-injury rate as well. The challenge with hamstring strain injuries is the high rate of re-injury that we see. There’s data suggesting that upto one out of every three athletes who undergo successful rehabilitation will ultimately re-injure and need further care.

If you want to learn more about this topic, you can watch Bryan Heiderscheit's lecture here:

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WHAT ARE THE RISK FACTORS?
When we consider the risk factors of hamstring strain injury, some of the common factors are prior injury and age of the athlete. Apart from this, the other risk factors include:
1. Hydration and nutrition
2. Fatigue
3. Overload
4. Weakness
5. High speed running
6. Acceleration and Decelaration
7. Change of direction

ARE THERE ANY AFTER EFFECTS OF HAMSTRING STRAIN INJURIES?
1) Scar tissue formation
MRI’s show that 2 months post hamstring injury there is formation of scar tissue. We also know that regarding the athletes cleared to return to play; it’s not as if the muscle is fully healed. We continue to see evidence of injury that’s present, suggesting that the injury is still healing.
 

2) Denervation edema injury 
In a case study published by Wille and Heiderscheit in 2019, it highlighted a unique presentation of hamstring strain injuries. A first time hamstring strain injury of a 20 year old football player which involved the biceps femoris long head and semitendinosus was scanned shortly after the injury and about 3 months later. Post 3 months the injured side showed some edema in a unique form which was low- grey, low level edema and uniformly diffused throughout the biceps femoris long head and just a bit through the proximal aspects of semitendinosus. It was identified as a denervation edema injury. It was suspected that the player partially denervated the BFLH and the ST and created a low-grade edema response that persisted for several months.
 

3) Muscle volume changes 
Consistent changes in muscle volume were found especially in those who have reoccurring injuries. It was found that, those with the biceps femoris long head injury, even after 2 to 3 years later there was roughly 12 % atrophy. Even though the course of the injury is short i.e 2 – 4 weeks we still see some of these changes.
 

4) Fatty infiltration into muscle 
In addition, in athletes that are a little bit older i.e in their early thirtys and have had reoccurring injuries, there is evidence of fatty infiltration into these muscles. It is significant because the fat infiltration will prevent force production or will alter force production such that the quality of the muscle isn’t there.

If you want to learn more about this topic, you can watch Bryan Heiderscheit's lecture here:

Click here

SOURCES:
1.    ‘Hamstring strain injuries’ lecture by Bryan Heiderscheit