How kangaroo rats jump higher: muscle dynamics from in vivo measurements

Kangaroo rats use vertical leaps to outjump predators. To investigate how these animals achieve higher jumps, we used sonomicrometry (SONO) and electromyography (EMG) techniques in the vastus lateralis (VL) muscle, a large knee extensor, and lateral gastrocnemius (LG) muscle, a large ankle extensor, while these animals were jumping at different heights. To achieve higher jumps these animals do not shorten their muscle fibers more, but they do activate more muscle fibers. This suggests that increased mechanical output, needed for a higher leap, is achieved through more muscle force and not through greater length changes in muscles.