Tendon Stiffness and Jump Performance: Practical Applications for Strength and Conditioning Coaches

INTRODUCTION

In high-performance sports, explosive actions such as vertical jumps are central to athletic success. Whether it’s a volleyball spike, a basketball dunk, or a sprint start, the ability to rapidly generate force is key. To truly measure and train this ability, tools like vertical jump test equipment, jumping sensors, and vertical jump sensors offer valuable data. And beyond muscle strength and neuromuscular coordination, flywheel exercise machines and eccentric training methods help us explore a crucial yet often-overlooked factor: the elastic properties of the tendons.

The study by Kubo et al. (1999) sheds light on how the stiffness of tendon structures can impact jump performance—particularly the difference in output between a squat jump (SJ) and a countermovement jump (CMJ). In this article, we’ll explore the practical implications of tendon stiffness for strength coaches, how to identify individual profiles, and how to tailor training strategies accordingly.

THE BASICS: WHAT IS TENDON STIFFNESS?

Tendon stiffness refers to the resistance of the tendon to elongation when subjected to force. A stiffer tendon deforms less under load, while a more compliant tendon stretches more. In the stretch-shortening cycle (SSC), this property determines how much elastic energy is stored and released during explosive movements.

Kubo et al. measured tendon elongation in vivo using ultrasonography during ramp isometric knee extensions. By examining the relationship between muscle force and tendon elongation (dL), they calculated stiffness as the slope of this relationship above 50% of maximal voluntary contraction (MVC)—a range where measurements reflect true tendon deformation rather than joint motion or slack.

KEY FINDINGS OF THE STUDY

• Average tendon stiffness: 143.8 N/mm, with a wide range between individuals (104 to 186 N/mm).
• Stiffness not correlated with jump height: Both CMJ and SJ heights were not significantly related to tendon stiffness.
• Prestretch augmentation and compliance: The greater the tendon compliance (i.e., lower stiffness), the greater the performance benefit observed from using a countermovement.

This means that while absolute jump height may not depend on tendon stiffness, the efficiency of energy storage and release in the SSC is clearly influenced by it.

WHY DOES THIS MATTER IN COACHING?

Understanding tendon stiffness offers a new dimension to performance profiling. Athletes with more compliant tendons can benefit more from SSC-based activities like plyometrics. On the other hand, athletes with stiffer tendons might rely more on concentric strength and rate of force development (RFD).

JUMP PROFILING IN PRACTICE

A simple way to assess an athlete’s SSC efficiency is by comparing CMJ and SJ performance:

• High CMJ > SJ difference (>10%): Suggests good use of elastic energy and likely compliant tendons.
• Low CMJ > SJ difference (<5%): May indicate stiffer tendons or poor utilization of SSC.

This practical test (often called the “Reactive Strength Index”) allows coaches to make informed training decisions without the need for expensive equipment.

TAILORING TRAINING TO TENDON PROFILE

If your athlete shows signs of high compliance:

• Emphasize plyometrics: depth jumps, hurdle hops, bounding.
• Include fast SSC activities: short ground contact drills.
• Monitor volume: compliant tendons may be more prone to overuse.

If your athlete has stiffer tendons:

• Focus on heavy strength work: trap bar jumps, squats, Olympic lifts.
• Train RFD: sled pushes, concentric-only jumps.
• Gradually introduce SSC drills: start with low amplitude exercises.

LONG-TERM ADAPTATION AND TENDON TRAINING

Tendon properties are not fixed. Long-term training can shift stiffness levels. Eccentric training, isometrics, and plyometrics have all been shown to affect tendon behavior. Importantly:

• Eccentric loading tends to increase tendon stiffness.
• Isometrics may improve stiffness and reduce pain (especially in tendinopathies).
• High-velocity training may increase compliance.

Thus, coaches can design periodized programs that intentionally modulate tendon stiffness depending on the sport’s demands and the athlete’s profile.

BEYOND THE TENDON: OTHER FACTORS IN JUMP PERFORMANCE

While tendon stiffness plays a role in SSC efficiency, it explains only part of the picture. Muscle thickness, joint kinematics, neuromuscular activation, and technique are all critical. In the Kubo study, the prestretch benefit explained about 21% of the variation in jump output—meaning that 79% was due to other factors.

So, while stiffness profiling is valuable, it should be combined with:

• EMG analysis (when available)
• Force plate data (for take-off kinetics)
• Biomechanical analysis (joint angles, velocity curves)

CONCLUSION: THINK ELASTIC, THINK SPECIFIC

Kubo et al.’s work opens a new path for thinking about explosive performance. Rather than just focusing on building stronger muscles, we should also consider how the muscle-tendon unit behaves as a system—especially when using flywheel squat machines, flywheel resistance training, or flywheel training protocols. Some athletes might need to stiffen their tendons for better force transfer, while others may benefit from more compliant tendons to enhance elastic return. As strength and conditioning professionals, our job is to detect these needs, interpret them, and build targeted programs that bridge the gap between physiology and performance. Because in the end, it’s not just about jumping higher—it’s about jumping smarter with the right flywheel tools and testing technologies.