My favorite eccentric training for clients involves “negatives”. They focus solely on the down phase. In this routine, I have clients lift at least 25% more weight than they normally do. I help them up in the concentric phase and they have to perform the eccentric phase at a count of 5 seconds. They do 2 to 3 sets of up to 6 repetitions (if they can do more than 6 reps, that means they need more weight). By the next day, they are very sore.
This routine, obviously, is recommended only for clients with at least a moderate level of strength who are looking for that extra edge. It should not be performed on special population clients, including but not limited to those recovering from injury, the elderly (provided they are able bodied and already have a significant level of fitness), pregnant women, and children, even if they are very athletic.
This routine can only be performed once a month for each body part/group, because of the strain it places on the musculoskeletal system. Performing negatives more than once a month on any body part/group can and will cause significant musculoskeletal damage.
If you guys have questions, let me know. I personal train at the LA Fitness in Seattle and host running clinics.