Please note this doesn’t only have to be about hamstrings. The important thing is we are talking about preventable injuries. Preventable in that we can reduce risk with proper training. These injuries are characterized by occuring without physical contact with another object. An example is the baseball player who comes up lame while running out a ground ball — nothing touched him, so why did he get injured??
The obvious thought is the hamstrings weren’t strong enough.
This is logical, but it doesn’t mean its always true.
The body is a bunch of connected pieces, so the answer lies somewhere amongst these connections as well. In other words its usually not an issue with one single aspect/muscle/imbalance.
Let’s look at the large leg and hip muscles which perform movements similar to the hamstrings:
If we look at movement, the hamstring does hip extension and knee flexion. The big calf muscle does knee flexion too. The glutes and adductors perform hip extension too. They key is the glutes are the main hip extender. And the hamstring “main job” is knee flexion. Sometimes though the glutes don’t do their job well (this is very common without proper training actually), so what happens? The hamstrings are dialed in to pick up the slack.
Well if they now have 2 “main jobs” because the glutes can’t fulfill their main role and main hip extender, there is a greater chance of hamstrings getting worked to the max. If they work more than “to the max”, the hamstring gets pulled.
Now, this doesn’t mean the best solution is to just get the hamstring stronger. The imbalance still remains: the glutes can’t fully perform their job, so they ask hamstrings to help out more than they should. Getting the hamstrings stronger just basically means next time there will be a higher threshold (for level of force) before the hamstring gets pulled. The problem is this doesn’t address the cause.
It will be far more effective in the long-term to determine the cause of the hamstring pull and address the necessary areas. This is where we look at these other muscles as well as what’s too short, too long, etc. The common things tend to be weak glutes and/or poor activation of them combined with tight hip flexors.
So remember, any injury not cause my body contact with another person or object, it is smart to look at all the connecting pieces as addressing the root cause of the injury lies is some issue(s) involving these other structures too.