Michelle Rodriguez suffers for her art in high-action movie scenes because her knee is always popping out of place.
The actress has no anterior cruciate ligament (ACL) and reveals she has to wear a brace under her trousers to keep everything in place in sequences when she has to run and jump around.
And she admits she often gets so carried away by the moment, she forgets to put her brace on.
She tells WENN, "Sometimes I forget to put my knee brace on under the gear."
But Rodriguez admits the action onset is nothing compared to the brutal and grueling military training some of the roles she plays call for.
She really struggled in the boot camp before her latest alien war film "Battle: Los Angeles."
The actress explains, "I was thankful for the physical therapy we had after that because the physical training was gnarly. It was running two miles every day from five o'clock in the morning to five o'clock in the afternoon just non-stop carrying 30 pounds of gear with guns and bullets."
But she had it much easier than her male co-stars: "I didn't stay with them; I went home at night. And they had to eat rations, army rations... really nasty-tasting carb-infested rations. There were a couple of incidents of throwing up because the work-outs were intense."
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