Experimental setting: Schematic illustration of stretch-shortening cycle and force, kinematic and electromyographic activity.

(A) Experimental setting. (B) Schematic illustration of the stretch-shortening cycle with an active stretch (eccentric contraction) of a muscle, followed by immediate shortening (concentric contraction). (C) Modulation of the ground reaction force (GRF; bottom), ankle, knee and hip joint kinematics (middle) as well as electromyographic (EMG) activity of shank (SOL, GM and TA) and thigh muscles (RF, BF Gmax) for one representative subject in the known (solid line) and unknown condition (dotted line) on hard ground. GCT is marked as the time between GC and take-off; the relevant EMG phases PRE, SLR, MLR and LLR (bottom) are also marked. Data comprise the means of 15 jumps for each condition. EMG activity in shank and thigh muscles was mostly reduced in PRE, SLR, MLR and LLR from known to unknown. Concomitantly, GCT duration was lengthened, and the peak force decreased from known to unknown conditions.