In the series “Our personal trainer“The Berlin fitness coach Sebastian Grüner helps us to become stronger, healthier and more beautiful. This article is part of TIME on the weekendissue 03/2026.

Did you know that we don’t just have one biceps in our upper arm? There is also a two-headed muscle in the thigh that provides the bi in biceps, in this case the Biceps femoris muscle. It may not be as easy to flex as the one in the upper arm, but it is still important: it bends the knee and extends the hip.