I know I said I'd post about the strength speed continuum for horizontal force and power development but I thought I'd explain the importance of horizontal force first :) We've all been told that in order to get faster, we just have to get stronger and squat and power clean more. But is this really the case? Here is a nice and short overview of why horizontal force and power is so important to improve short sprint speed.
A study by Morin et al. (2012) looked at the 100m sprint which involved 9 physical education students. 3 national level sprinters and 1 world class sprinter. Since this little review is focused on short sprint speed, only the 4sec distance will be talked about.
The authors found significant correlations between the index of force application, horizontal GRF (ground reaction force) and 4sec distance (r=0.683 & r=0.773 respectively). However, no significant correlations were found between vertical GRF and 4sec distance. Average and maximal power output were also significantly correlated with 4sec distance (r=0.903 & r=0.892 respectively). NOTE: correlation of 1 means a perfect correlation, e.g. if power was correlated with speed at r=1, whenever power goes up, speed would go up, if power went down, speed would go down.
Just squatting more to get faster may not be the answer
This has been further backed up by a recent paper by de Lacey et al. (2014). 10m and 40m sprint performance were measured comparing backs and forwards in elite rugby league players. Backs were found to be significantly faster than forwards in both sprints, however there were no significant differences found in vertical force or sprint kinematics. Significant differences in relative horizontal force (effect size/ES=0.87) and relative power (ES=1.04) were found between forwards and backs. In contrast, no significant differences were found in relative isokinetic strength even though sprint times and kinetics were different.
What does this all mean?
These data suggests that the direction force and power is applied in (horizontal direction) is more important than the magnitude (how much) of force and power produced when it comes to short sprint performance. Furthermore, with relative force being equal between athletes, further improving horizontal force production may potentially improve short sprint performance.