Is it horizontal or vertical?
Is one more important during certain phases of acceleration vs top-end speed?
Why the confusion?
Let's take a look into both Horizontal and Vertical forces and clear the air about both of them.
Recent research has shown high levels of horizontal force application is related to faster sprinting speeds, especially acceleration speed. Horizontal forces can be seen in two lights
- Those that propel us
- Those that brake us
With that being said, there has been a barrage of recent research showing the contributions of horizontal forces and impulses as being major players in sprinting speed.
In fact, it would be safe to summarize that it appears horizontal forces are of greater importance to sprinting speed than vertical forces - but there may be some caveats.
There are a few constants in our life - taxes, death, and GRAVITY to name a few.
Gravity is the force that we cannot avoid discussing as it will always be there and will always play a huge role in sprinting speed. Like it or not, gravity acts on all of us as we sprint.
- As we push and drive off the ground, we fight gravity.
- As our center of mass falls back to the ground after the flight phase, we must fight gravity.
- At ground contact, we must be resilient and resist crumpling, must of which has to do with gravity.
The fact that no one on earth can hide from gravity, makes it pretty clear that during the sprinting cycle, we must fight the forces of gravity and these forces are inherently vertical.
The popularity of vertical forces can be traced back to the most famous study in sprinting history - Peter Weyand's sprinting study done in year 2000 at his famous SMU sprinting laboratory. Weyand et al (2000) looked at correlations between vertical forces and sprinting speed of 33 subjects. Vertical forces were found to be significantly greater in faster runners than slower ones (7).
Since, this study has been the backbone for the vertical force side, but we must also realize the correlation coefficient between vertical force and running speed was only (r = 0.39), which is considered low by most standards. Also the researchers did NOT test for horizontal forces - so there were no comparative measures.
Still, it is undeniable that vertical forces play a role in sprinting performance.
Acceleration Speed vs Top-End Speed
It appears that both horizontal and vertical forces play a role in sprinting speed, but do different phases of sprinting - acceleration vs top-end - have different levels of horizontal vs vertical importance?
Let's breakdown a few studies and see what the literature says...
Buchheit et al (5) analyzed the horizontal forces of 86 elite youth soccer players during sprinting. The researchers found that horizontal force was significantly correlated with acceleration speed (10m) but not maximum sprinting speed, suggesting horizontal forces may be more important for acceleration performance than maximal sprinting performance.
Morin et al (4) looked at different phases of a 40m sprint. The researchers found that net horizontal impulse and propulsive horizontal impulse were strongly correlated to sprinting performance in the 40m sprint, but vertical impulses was not (4). Now the 40m dash is a combination of both acceleration and top-end speed, but most would argue acceleration performance is probably more important than top-end speed.
Almost 30-years ago Mero (1988) analyzed the sprints of elite Finnish sprinters over 10m from a block start. Mero found a couple of important nuggets. First, at the first foot contact, even though the foot landed behind the COM by over 10cm, there were still horizontal braking forces to overcome. So even a positive angle at foot contact BEHIND the COM still equaled horizontal braking forces, demonstration that no matter what there will be horizontal forces to be overcome.
Friction = needing to overcome horizontal forces = slowing down.
Second, Mero found correlation between horizontal forces in the first step and at 10m and sprinting speed. These same correlations, however, were not found in regards to vertical forces (3).
De Lacey et al. (2014) looked at 39 rugby players from the National Rugby League. They looked at the 10m and 40m dashes on a non-motorized treadmill and compared the differences between backs and forwards. They found faster players produced significantly greater relative horizontal force and power. The researchers concluded that developing force and power in the horizontal direction may be beneficial for improving sprint performance in professional rugby league players (6).
Morin et al (2) analyzed 13 male subjects with different sprint performance levels ranging from novice to world class ability. The researchers found that peak sprinting velocity was related to both vertical and horizontal forces, but the correlation for horizontal was stronger (r=0.59 vs r=0.79).
We already reviewed Weyand et al. (2000) and this remains the vocal research paper for the vertical forces group.
Brughelli et al (1) looked at 16 high level Australian soccer players as they sprinted over a Woodway force treadmill at speed ranging from 40-100% max sprinting speed. The researchers found that as speed increased from 40 to 60%, peak vertical and peak horizontal forces increased by 14.3% and 34.4% respectively. But as the subjects increased speed from 60-80% speed, changes in peak vertical and peak horizontal forces were 1.0% and 21.0% respectively. Finally, as the subjects increased speed from 80-100% speed, changes in peak vertical and peak horizontal forces were 2.0% and 24.3%. Overall, the researcher concluded it would seem that increasing maximal sprint velocity may be more dependent on horizontal force production as opposed to vertical force production (1)
Kale et al. (2009) looked at 21 male sprinters and ran these subjects through a gamet of tests. They found that ability to produce vertical force, in the form of a depth jump, was the most strongly correlated test to 100m dash sprinting speed. In conclusion, vertical power and force in the form of a depth jump was an effective way to reflect maximum running velocity. The thought process of the researchers is that this same vertical force in the depth jump, is very applicable to the manner of force application during max velocity. But as we know, correlation does not equal causation (8).
Running fast cannot be zoned into just a single force or factor, speed is multi-dimensional with many different aspects being intertwined. If anyone says it's just a single force or single factor... run, run away fast!
The other factor that seems obvious to me, is the action of the body is very similar in both stages - acceleration and top-end speed - and the difference seen in forces is just a outcome of body positioning.
As Mike Young has said - "Acceleration is just top speed turned on it's side".
The actions of the body are the similar/same, it's just body orientation in relation to the ground that differs and this is where changes in forces is seen.
Take a look a Usain Bolt accelerating in the picture below.
Now what's interesting is in Weyand's first study back in 2000, most S&C coaches interpreted the results from that study - more vertical force = more speed - as a need to increase an athletes squat and deadlift strength and that will increase speed.
Well, we know it doesn't really work that way. We know GCT is under .20 for acceleration and .10 for top-end speed, not even close to enough time to put maximal muscle force into the ground.
Also, I haven't seen a study done, but I would be really interested in seeing if gains in strength in the back squat or deadlift actually increase vertical and/or horizontal ground forces.
I really don't think if adding pounds onto an athletes squat or deadlift will actually carryover to greater ground forces. It would be interesting to see a correlation done on these weight room strength numbers and ground forces (both vertical and horizontal). I think in novices there may be a slight relationship, but I highly doubt at higher ability levels you'd see any relationship.
This isn't to say lifting isn't important, I feel it improves qualities in other realms that transfer to ground forces. Things like stiffness, resisting deformation, body composition, motor unit recruitment, rate coding, and muscular coordination/timing. These will all help speed in different ways, but I truly believe it's not as simple as more force in the weight room = more force applied during sprinting, otherwise the strongest people would also be the fastest.
That's all for now. Stay tuned for our next installment on muscle actions/activities.
Go Get 'Em!
1) Brughelli, M., Cronin, J., & Chaouachi, A. (2011). Effects of running velocity on running kinetics and kinematics. The Journal of Strength & Conditioning Research, 25(4), 933-939.
2) Morin, J. B., Bourdin, M., Edouard, P., Peyrot, N., Samozino, P., & Lacour, J. R. (2012). Mechanical determinants of 100-m sprint running performance. European journal of applied physiology, 112(11), 3921-3930.
3) Mero, A. (1988). Force-time characteristics and running velocity of male sprinters during the acceleration phase of sprinting. Research Quarterly for Exercise and Sport, 59(2), 94-98.
4) Morin, J. B., Slawinski, J., Dorel, S., Couturier, A., Samozino, P., Brughelli, M., & Rabita, G. (2015). Acceleration capability in elite sprinters and ground impulse: Push more, brake less?. Journal of biomechanics.
5) Buchheit, M., Samozino, P., Glynn, J. A., Michael, B. S., Al Haddad, H., Mendez-Villanueva, A., & Morin, J. B. (2014). Mechanical determinants of acceleration and maximal sprinting speed in highly trained young soccer players. Journal of sports sciences, 32(20), 1906-1913.
6) De Lacey, J., Brughelli, M. E., McGuigan, M. R., & Hansen, K. T. (2014). Strength, Speed and Power Characteristics of Elite Rugby League Players. The Journal of Strength & Conditioning Research, 28(8), 2372-2375.
7) Weyand, P. G., Sternlight, D. B., Bellizzi, M. J., & Wright, S. (2000). Faster top running speeds are achieved with greater ground forces not more rapid leg movements. Journal of applied physiology, 89(5), 1991-1999.
8) Kale, M., Asçi, A., Bayrak, C., & Açikada, C. (2009). Relationships among jumping performances and sprint parameters during maximum speed phase in sprinters. The Journal of Strength & Conditioning Research, 23(8), 22