Why hill sprints OR hill bounds, and not hill sprints AND hill bounds ? In fact, a good interpretation of the 2 workouts has a different goal.
1) HILL SPRINTS
The interpretation is : MAX SPEED, using high frequency with very high knees. Recovery is not important (1' or 2' or 3'), important is to start the next sprint when you are nervously ready. Physiological objective : RECRUITMENT OF THE HIGHEST POSSIBLE PERCENTAGE OF FIBERS in the muscules working.
This type of training is strictly connected with the nervous system. When an athlete runs slowly, he uses only a little percentage of the fibres of his muscles. Increasing speed, the percentage increases. Only running at the MAX possible speed it's possible to recruit the highest percentage of fibres. When for too long time an athlete doesn't use max speed, his ability in recruitment fibres decreases, and, when in competition he has to ask something to the FULL muscle, the answer is very poor. This is the only way for giving to the athlete the KEY for opening the door of the STORE, where he can find more energy for a final sprint (in case of lactic events like 800 / 1500m) or more fuel (after finishing glycogen in his slow fibers) in case of marathon.
So, short sprint uphill can enhance the ability in MAX SPEED (because there is an improvement in STRENGTH), and in ENDURANCE (in case of marathon runners), because they can find a reserve of fuel to use, coming from fast twich fibers.
The way to use hill sprints is as follow :
LENGTH / DURATION : 80/100m (12" / 15")
INTENSITY : Max
RECOVERY : Full
GRADIENT : 8-12 %
REPETITIONS : 10-15 (no more, because the nervous concentration, if the interpretation is ok, goes to decrease)
PERIOD : All the season. I used short hill sprints (10 x 60m) many times the morning of the day of the competition (if on track, by night), or the previous day in case of race in the morning. There is not really physical fatigue, as the production of lactate is very little. Full recovery is important in order to fully remove lactate.
2) HILL BOUNDS
This exercise is more connected with the development of MUSCULAR STRENGTH, less connected with the recruitment. The athlete has to bound using long jumps from one foot to the other, giving attention to the elastic reactivity of his feet. After a first period (during the GENERAL PERIOD of training, going to the FUNDAMENTAL) where this exercise is carried on distances of 30-50m, and the speed is not important, because the goal is to DEVELOP ELASTIC REACTIVITY.
After this first period, the athlete must increase the speed, bounding with steps longest possible, for the same distance (30-50m). In this case, this exercise has the goal to increase STRENGTH of the contractile fibres, not only the REACTIVITY of the elastic fibres.
The way to use HILL BOUNDS is as follows :
LENGTH : 30-50m
GRADIENT : 6-8 %
INTENSITY : 80% (general period), 90 % (fundamental period), 100% (special period)
RECOVERY : Full
REPETITIONS : 6-8 times
PERIOD : No in the SPECIFIC season
In the first long period of preparation (general and fundamental period, practically all Winter), athletes can use a MIXED system (Circuits for increasing STRENGTH ENDURANCE using both sprints and technical exercises : for example, 50m sprint + 30m bounding + 50m sprint + 30m heels to buttocks + 50m sprint + 30m skipping + 80m sprint, and at the end 10 squat-jumps on the same place). We need to use long recovery in this case (may be 6'/8') because in any case athletes must use MAX intensity in every part of the circuit, otherwise there is NO RECRUITMENT OF FIBRES IN LACTIC SITUATION.
This is the best system for building the ability in final sprint. Nothing to do with the MAX SPEED of an athlete, but with the ability in recruitment high percentage of fibres when muscles are full of lactate.