It has oftentimes become a practice to see NBA players take up working out in different sports in the offseason to keep their body toned and ready for the upcoming season.

San Antonio Spurs great Tim Duncan, during his heyday, had used the offseason to partake in MMA workouts—particularly kickboxing—over the last decade. According to Joon Lee of Bleacher Report, his trainer Jason Echols revealed that Duncan once ripped his biceps while training.

“One time, I tore my bicep just trying to move with him at a higher-level pace. He’s so big and his elbows are like spears and his bones are really sharp. Just interacting and punching with him, I hit him with a right hook and his elbow caught the inside of my bicep and tore it right off, just from moving around. Whatever pace I’m at, he sets it. The roaring lion is his passion to learn, his passion to pick up the movements. He’s really, really passionate and into the idea of martial arts. It’s cool to watch.”

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It turned out to be quite a poor decision by Echols that caused a significant injury that could have been much worse. Not only does Tim Duncan have a significant height advantage over him, he possesses a large edge in his strength.

This may have been quite a painful experience given the amount of strength and force of the blow to his bicep. The decision to speed up the workout increased the likelihood of getting accidentally struck by Duncan given his large size standing at 6-foot-11 with a wing span that stretches out to 7-foot-3.

It provides another prime example of the intensity and passion that the five-time NBA champion possesses even when away from the basketball court.