Acute Effect of Different Resisted Sprint Loads on Joint Kinematics and Electromyographic Activity in Experienced...

The aim of this study was to investigate the acute effect of different active resisted sprint loads upon joint kinematics and leg electromyography (EMG) activity in experienced sprinters.

Thirteen experienced male sprinters (age: 20.5 ± 1.3 years, body mass: 66.8 ± 4.5 kg and body height: 1.74 ± 0.06 m) with best 100-m times of 11.24 ± 0.34 s performed a 50-m sprint with maximal effort from three-point start. Afterwards, they performed different resisted sprints with maximal effort provided by a robotic pulley system that resulted in 65%, 50%, 25% and 10% reduction of peak velocity for, respectively, 10, 20 and 30 m in randomised order while spatiotemporal parameters, joint kinematics and EMG of nine leg muscles were measured from the point which sprint velocity plateaued.

The main findings were that increasing velocity-decrement conditions resulted in reduced sprint velocity, shorter step length, lower step frequency and prolonged ground contact time together with joint kinematics changing to a more flexed posture and forward leaning at touch down and less extension at toe off, with lower, maximal angular velocities during contact times. These adaptations resulted in more quadriceps dominant activity with increased stabilizing activity of gluteus medius, while hamstring activity decreased due to the lower angular knee extension during flight times with increasing resisted loads.

This study suggests that while resisted sprinting is an effective tool for increasing force production demands, higher resisted loads (> 50% velocity decrement) are associated with progressively different kinematic and neuromuscular patterns, likely reflecting the combined effects of increased force demands and thereby reduced running velocity.