Many strength coaches repeat the same outdated concept over and over, stating that “sprint speed is determined by the amount of force you put into the ground.” Force is a vector quantity that has magnitude and direction. It’s not just the force you put into the ground; force relative to bodymass in addition to the direction of force application help determine sprint acceleration performance.
A recent study titled, Technical Ability of Force Application as a Determinant Factor of Sprint Performance, by Morin and colleagues, took a close look at sprint performance using 12 subjects including 2 sprinters. What they found was that speed was determined by high amounts of net horizontal force, which is calculated by subtracting braking forces from propulsive forces. They measured mean vertical, horizontal, and total forces, and what was very unique about this study is that they measured the forces during each step of the acceleration, which allowed them to calculate an index of force application technique involving the net direction of force per stride.
What the researchers found was that the direction of force application and the net horizontal ground reaction forces were significantly correlated with sprint performance, but vertical ground reaction forces and total ground reaction forces were not. The researchers concluded that:
The orientation of the total force applied onto the supporting ground during sprint acceleration is more important to performance than its amount.
In fact, the researchers elaborated on this during the study, stating the following:
A good example of the distinction between the technical and physical capabilities put forward in this study is that of the two typical subjects presented in Fig. 2B. Subject 11 is a national-level long jumper, has been training for sprint and long-jump for about 10 years, and has a personal best of 10.90 s in the 100-m. Subject 2 is a basketball and mountain-bike competitor, and not specialized in sprint. These two subjects have about the same body mass (68.1 vs. 69.9 kg) and similar values of maximal RF (Fig. 2B). Further, their capabilities of total force production over the acceleration phase were very close: FTot = 1.87 BW for Subject 11 and 1.89 BW for Subject 2. However, their DRF (-0.051 vs. -0.083) were the two extreme values for the population tested. This means that Subject 11 was able to maintain much higher values of RF when accelerating compared to Subject 2, despite similar RF at the first step. What is interesting and clearly illustrates the superior 100-m of Subject 11 (Smax of 9.96 vs. 8.80 m.s-1, t100 of 11.90 vs. 13.66 s, and d4 of 26.3 vs. 23.3 m) is that despite similar total force production capabilities, he had a better DRF during treadmill accelerated runs.
Mel Siff understood this many years ago. So did Charlie Francis when he said, “looks right, flies right” and prescribed his sprinters (including Ben Johnson) the reverse leg press; an anteroposterior hip extension exercise that focused on end-range glute strength, similar to the pendulum quadruped donkey kick.
The take home message for strength coaches, track & field coaches, and sprinters is that you really need to analyze vectors and forces and determine which ranges of motion require accentuated force development. Squats, Oly lifts, ballistics and plyos are staples, but end range hip extension strength and power is maximized by combining training methods including hip thrust variations, pendulum quadruped variations, back extensions and reverse hypers, sled work, horizontal jumps, and of course, sprints.