On my hill, 3 X 100 meters at max effort. I went in with no goal other than to get maximal stimulation with the minimal number of repeats. To get the most out of the least you have to give each interval 100%. The idea here is based more on the electrical (CNS) rather than the metabolic.
Swept the sand off the first 20 meters of road. 3 point starts. Focusing on stomping the ground after the first 20 meters (increased ground force = increased drive) and good arm swing. Head down, chin tucked for the first 20 meters. Good dorsi flexion in my ankles and sweeping back before ground contact.
All on 4:00 rest. Probably should have taken more.
Hamstrings and glutes started to ache after the third 100. I'm certain that a 4th would have been slower. Maximal stimulation with just 300 meters of running. Perfect. Huge neural demand/ stimulation with minimal metabolic/ hormonal stress = minimal recovery.
I have about 5 pages of writing done on a blog post that might be forthcoming. It's a long ramble about personality types in running. Ultrarunners VS sprinters specifically and the chemical/ neurotransmitter differences and how it applies to preferred training and race distances.