Eccentric vs Concentric strength training:
In Strength training a count of 1-2-3-4 is an oft used rule of thumb. The concentric movement is done to the count of ‘1’, and the eccentric rotation 2-3-4. By concentric I’m referring to typical contracting muscle action which shows the muscle bulging, as in the the classic strong man bicep pose. The eccentric movement is what many consider the relaxation phase.
The explosive movement comes from developing the fast concentric rotation, ie, good for sprinters. However, these days, it is firmly considered that the most benefit comes from the controlled eccentric rotation.
Muscles work only by contraction. The concentric action tries to maximise the number of 000’s of minute muscle components to trigger instantly. If one just relaxes then the brain tries to switch off as many of those minute components as fast as is safe to do so. But as an exercise, we endeavour to control the switching off process, to delay it, thus working the muscle components. It is the slow controlled eccentric that leads to the strength gains, particularly for endurance athletes.
Once again, how you do your strength training really matters.