Unlocking Speed: The Benefits of the Clark 105 Exercise for Sprint Performance
Discover the power of the Clark 105 Exercise, inspired by the research of Dr. Ken Clark, PhD, who identified the critical role of the thigh split angle in sprinting performance. Introduced to this groundbreaking concept by Chris Korfist, a leading Chicago speed coach, I developed this isometric training method to enhance top-end speed, acceleration, and running mechanics. By strengthening the muscles that control peak thigh split positions—especially the glutes and hip flexors—athletes can achieve faster, more efficient strides while reducing injury risks. Ideal for both youth and elite athletes, the Clark 105 is a safe, effective solution for improving sprint performance.
Understanding the Thigh Split and Its Importance
The thigh split refers to the angle between the thighs during the early flight phase of a sprint—when one thigh reaches peak extension while the other reaches peak flexion. Essentially, it represents the total range of motion (ROM) that the thighs cover during the swing phase of a running stride.
Achieving an optimal thigh split is crucial, but an even more critical determinant of top sprinting performance is the ability to reverse the movement at the peak split position. This is often described as the capacity to “block at the top”—rapidly accelerating the thighs back in the opposite direction with high angular force. This reversal generates the momentum required for maximum speed and stride efficiency.
Typical values of the thigh split vary based on athletic specialization:
- Track and field athletes: ~100 to 105 degrees (range: 95-115 degrees)
- Team sport athletes: ~95 to 100 degrees (range: 85-110 degrees)
Several factors influence an athlete’s ability to achieve and maintain an effective thigh split, including:
- Strength and mobility in the hip flexors, glutes, and other related muscles.
- Sprint movement patterns, influenced by neuromuscular coordination.
- Control strategies, such as the vertical force applied during ground contact.
Introducing the Clark 105 Exercise
To address these critical performance factors, I developed the Clark 105 Exercise—an isometric drill that places athletes in a greater-than-105-degree thigh split position and requires them to hold this stance under maximum muscular tension. This position replicates the demands of sprinting by activating the same muscles involved in high-speed running, such as the glutes and hip flexors.
Clark 105 Torque Isometric Overcoming
How the Clark 105 Improves Performance
Research and training experience have shown that strength in the peak thigh split position has a significant impact on several key aspects of athletic performance:
- Top-end speed: Strengthening this position enhances an athlete’s ability to maintain efficient strides at high velocity.
- Acceleration: Athletes develop better control during rapid changes in direction and short-burst sprints, improving overall explosiveness.
- Running mechanics: The exercise helps athletes achieve better hip extension and flexion, leading to more powerful and efficient strides.
- Safety and injury prevention: By training isometrically, athletes strengthen stabilizing muscles, reducing the risk of strains and imbalances.
How to Perform the Clark 105
The Clark 105 can be executed in various ways to target different aspects of strength and motor control:
- Basic Isometric Hold: Athletes hold a greater-than-105-degree thigh split for 5 to 10 seconds per side, with maximum muscular effort. Repeating this hold for 3 to 6 sets per session has yielded significant results.
- Dynamic Pulsing Variation: Athletes turn their muscles on and off quickly—maximally contracting for less than a second, relaxing, and then contracting again—for a duration of up to 10 seconds. This variation enhances the neuromuscular system’s ability to generate rapid force.
- Rotational Core Activation: Athletes twist their upper bodies during the hold, adding an element of core stability training. This helps improve coordination and control during dynamic movements.
- Torque Generation: In some variations, athletes squeeze their legs inward to create additional torque, strengthening hip and thigh stabilizers.
Why the Clark 105 Is Safe and Effective for All Athletes
One of the greatest benefits of the Clark 105 Exercise is its safety, particularly for youth athletes. Since the exercise is isometric, it places minimal joint stress while still delivering high-intensity muscle activation. The controlled nature of the movement ensures that athletes can safely build strength without overloading their bodies.
Transform Your Sprinting with the Clark 105
Athletes who incorporate the Clark 105 into their training routines have reported dramatic improvements in both speed and strength. By targeting the critical thigh split position, this exercise enhances performance across sprinting phases—from initial acceleration to sustained top speed. Whether you’re a sprinter aiming for a new personal best or a team sport athlete looking to improve agility, the Clark 105 is a powerful addition to any training program
Digging Deeper: What Makes the Clark 105 So Effective
One of the coolest things about the Clark 105 is that it doesn’t just build hip flexor strength — it actually teaches your body how to connect everything together. Most people don’t realize how big a role the pelvic floor plays in sprinting. It’s like the bridge that transfers force from one side of your body to the other.
When you hold that 105-degree position, you’re not just strengthening muscles — you’re training the entire system that coordinates movement from your hips through your core and spine. That’s why the Clark 105 improves not only hip function, but also posture, balance, and how efficiently your body moves when you’re at top speed.
Timing, Reflexes, and the Hidden Connection
Power is great, but timing is what makes speed look effortless. During the back phase of sprinting, the hip flexor loads up like a spring. If it fires reflexively at the right time, momentum takes over and the leg cycles forward without wasted effort.
I’ve actually tracked this pattern in video work, and it’s fascinating — the reflex from the hip flexor connects all the way up through the arm swing. Sprinting really is a full-body coordination event, not just a leg exercise.
If you want to see how that connection works, check out my Thoracic Tuck Method. It shows how the spine, thoracic control, and leg recovery all tie together when you’re running efficiently.
Common Compensations: When the Wrong Muscles Take Over
Here’s something I see a lot — even with advanced athletes. Their abs and quads start doing the work that should belong to the hip flexors. You’ll know it’s happening when their chin starts jutting forward or their upper body drifts ahead during movement. The RPR Reflexive Performance Reset Cheat Patterns.
That pattern doesn’t show up overnight; it comes from years of compensating. And even after I reactivate someone’s hip flexors, they sometimes fall right back into that same pattern if the core isn’t doing its job. The Clark 105 helps break that cycle by forcing proper sequencing between the core and hips. Once that pattern is fixed, everything else — posture, stride, and stability — falls into place.
Why I Trust Isometrics More Than Traditional Lifts
People often ask about oscillatory lunges or single-leg RDLs. They have their place, but when it comes to developing power in a specific range of motion, isometrics are unmatched.
That’s what makes the Clark 105 so powerful — it locks you into the exact range that matters most for sprinting and teaches you to create maximum tension there. You’re not just getting stronger; you’re training your nervous system to apply that strength precisely where you need it.
Plus, because it’s isometric, it’s incredibly safe. You can train hard without putting extra stress on the joints.
The YURI and Cable Variations
Let’s talk about the YURI for a second. It’s not redundant with the Clark 105 — far from it. The YURI is one of the most advanced ways to potentiate top-end speed. I haven’t released a version yet that adds a hip flexor pull to the forward leg, but it’s in the works. Once I find a way to make it team-friendly, it’ll add a whole new layer to speed development.
You can also try Clark 105 cable variations after building a solid isometric base. The cable adds a dynamic resistance element, letting you apply that strength in more athletic, movement-driven ways. It’s a great bridge between raw strength and real-world performance.
(More on this here: Unlocking Speed – The Triphasic Standing Horizontal Hip Variation)
Adding Rotation: Training the Slings That Protect You
The rotational Clark 105 — sometimes called the Three-Way Foot Variation — is another step up. Here, the “rotation” mainly comes from the lower body, as the legs drive inward to create torque through the hips and pelvis. The upper body stays tight and slightly coiled, helping you learn how to control and transfer that rotational energy.
This type of training strengthens what we call the myofascial slings — the interconnected muscle chains that stabilize the body during fast, multi-directional movement. Strengthening these slings doesn’t just make you faster; it makes you far more resilient to injuries.
I go deep into this concept in my Non-Contact ACL Prevention Course, where I show how improving these rotational patterns can actually help predict and prevent ACL injuries before they happen.
Big Picture Takeaways
Here’s the short version of everything we’ve talked about:
The Clark 105 builds more than muscle — it builds coordination, timing, and control.
Sprinting trains the velocity side; the Clark 105 locks in strength where it matters most.
Isometrics like this one are the fastest route to real, functional power.
The YURI adds a layer of top-end speed potential.
Cable and rotational variations make your gains more transferable to sport and help prevent injuries.
Final Thoughts
When it’s done right, the Clark 105 connects strength, movement, and speed like few other exercises can. It’s the missing link between the weight room and the field — helping athletes not only get faster but also move more efficiently and stay healthier.
It’s a perfect example of what Triphasic Training is all about: taking complex physiological ideas and turning them into practical, high-impact tools that any athlete can use.
A List alternatives and variations of the exercise
Clark, K. P., Meng, C. R., & Stearne, D. J. (2020). ‘Whip from the hip’: Thigh angular motion, ground contact mechanics, and running speed. Biology Open, 9(10), bio053546. https://doi.org/10.1242/bio.053546
Murphy, A., Clark, K. P., Murray, N., Melton, B., Mann, R., & Rieger, R. (2021). Relationship between anthropometric and kinematic measures to practice velocity in elite American 100 m sprinters. Journal of Clinical and Translational Research, 7(5), 682. https://doi.org/10.xxxx
Alt, T., Komnik, I., Ryan, L. J., & Clark, K. P. (2024). Top speed sprinting: Thigh angular motion and eccentric hamstring strength in faster vs. slower sprinters. Human Movement Science, 98, 103280. https://doi.org/10.1016/j.humov.2024.103280
