Electromyography has limitations, but a consistent finding is that EMG amplitudes are typically lower during eccentric muscle actions than in concentric muscle actions (Douglas et al. 2016b). (strengthandconditioningresearch.com)
• Takes advantage of the stretch shortening cycle → Uses energy stored by eccentric muscle contraction (lengthening phase) quickly followed by concentric muscle contraction (shortening phase) to generate high amounts of power. (tomcoffeyfitness.com)
However, no training studies have yet measured whether voluntary activation can be preferentially increased in eccentric muscle actions after eccentric training (compared to in concentric muscle actions). (strengthandconditioningresearch.com)