Horizontal vs Vertical Force: Why the Direction of Force Production Changes Everything
Summary
Sprinting is won and lost in the horizontal plane, but most strength testing measures vertical force. Understanding the difference—and training accordingly—separates good programmes from great ones.
Stand next to a strong athlete and ask them to jump. They go high. Ask them to sprint. They may or may not go fast. The two qualities are related but they are not the same thing, and the reason comes down to direction.
Sprinting requires the athlete to project force horizontally — into the ground and behind them, propelling the body forward. Jumping requires force directed vertically. These are not equivalent demands, and conflating them has led coaches to build programmes that produce athletes who test well vertically but perform poorly horizontally.
The Mechanics of Sprint Propulsion
During the acceleration phase of a sprint, the body is inclined forward. Ground reaction forces (GRFs) during this phase are large and directed backward relative to the athlete — meaning a significant horizontal component is pushing against the ground in the direction of travel. As the athlete approaches maximum velocity, the body becomes more upright and the GRF becomes more vertical, with the horizontal component serving to maintain velocity against deceleration rather than to generate it.
Morin et al. (2011) quantified this directly, demonstrating that mechanical effectiveness — the ratio of horizontal to total GRF during ground contact — is the variable that best distinguishes elite from sub-elite sprinters. Two athletes can produce similar total GRF magnitudes and have vastly different sprint performances, simply because one applies more of that force in the right direction.
This is the "force application technique" component of sprint performance. It is not a strength variable in the traditional sense — it is a coordination and technical variable, and it can be trained.
What This Means for Testing
If you are exclusively testing vertical force production — jump testing, force plate squats, Olympic lifts — you are only seeing part of the picture. For an athlete whose primary demand is horizontal (sprinting, change of direction, sled push), vertical testing is a useful proxy but a limited one.
The horizontal force-velocity profile changes how you interpret an athlete's deficit. An athlete who has high vertical GRF but poor sprint acceleration almost always has a mechanical effectiveness problem: they are pushing down when they should be pushing back. This will not show up on a vertical jump test.
Training the Horizontal Component
Horizontal force production is trainable. The most direct intervention is resisted sprint work — sleds, resistance bands, or friction-based devices — which exaggerate the horizontal demand and force the athlete to lean into the load. Research by Morin et al. (2012) showed that heavy sled work (loads producing >50% velocity decrement) specifically improves the horizontal force component of the profile, while lighter loads preserve velocity but produce less specific force adaptation.
The key principle is matching the training stimulus to the deficit. An athlete with good vertical but poor horizontal development needs more work in the horizontal plane. The reverse athlete needs less resisted sprint work and more vertical loading — which they are probably already getting.
Practical Implications
Do not abandon vertical testing. Jump testing remains one of the most practical ways to monitor neuromuscular readiness, training load response, and fatigue. But for athletes whose sport is primarily horizontal, supplement it with horizontal force assessment: sled sprinting, split times, or formal F-V profiling with multiple loads.
The direction of force matters. Build your testing and training around it.
References
Mark Fisher
Founder, Swift Performance
Mark Fisher is the founder of Swift Performance and has spent 30 years designing and building athlete testing equipment used by elite sport programmes and universities worldwide. He has worked alongside researchers and PhD candidates across biomechanics, sprint mechanics, and strength science — developing the hardware and software they use to collect and analyse performance data. His writing comes from three decades at the intersection of applied sport science and precision measurement technology.
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