What Is Impact Loading?
Impact loading describes the mechanical stress your body experiences with every step you take while running. It consists of two key components, both essential for understanding how forces travel through your body.
Impact magnitude reflects how much impact is exerted on your body after landing. It is measured in G, representing how many times your bodyweight is loaded with each step.
Impact duration represents how quickly the impact travels through your legs. It is an important indicator of how effectively your muscles and tendons absorb the shockwave that’s traveling through your body.
- A longer impact duration suggests better (more active) shock absorption.
- A shorter impact duration signals limited (more passive) absorption, meaning the impact reaches your joints more abruptly.
Why Is Impact Loading Important?
Every step contributes to your cumulative mechanical load. Running mechanics, muscle coordination, and landing strategy all shape how much load your body must handle.
A low(er) impact magnitude is generally desirable for endurance running, but it doesn’t create the full picture. The impact duration is equally important. Certain landing patterns, such as overstriding, reduce active shock absorption, forcing your joints and passive structures to handle more load.
Your muscles, particularly the calves, hamstrings, and quadriceps, play a crucial role in shock absorption. Their timing and coordination determine how well the legs share forces and dissipate impact.
Burke et al., 2022 show that runners with a recent injury often display reduced loading patterns compared to healthy runners. This may be either a cause or a consequence of injury, highlighting the importance of addressing impact loading.
How Is Impact Loading Measured?
Impact loading is a kinetic (force) parameter traditionally measured using force-plate instrumented treadmills, equipment typically limited to research laboratories.
However, inertial measurement units (IMUs) have transformed the landscape. These smart sensors enable the measurement of impact loading in real-world settings, such as on the road, track, or in clinical practice.
Sensor placement is critical; research consistently supports measuring accelerations near the hips (pelvic acceleration) for the most reliable measures of impact loading Vanwanseele et al., 2020; Refai et al., 2020; Patoz et al., 2022. Use of foot and shin sensors remains debated among experts for quantifying lower-limb mechanical load Sheerin et al., 2019; Kerns et al., 2023; Xiang et al., 2024; Tu et al., 2024; Willy et al., 2025.
Impact Loading Profiles
Understanding your numbers starts with identifying your impact loading profile. This is shaped by the relationship between impact magnitude and impact duration. To simplify interpretation, we use four distinct profiles:
- Excellent Loader
- Poor Loader
- High Loader – Active Absorber (typically a bouncy runner)
- Low Loader – Passive Absorber (typically a grounded runner)
Tap to read each profile 👇
How to Train Your Impact Loading?
Your impact loading profile determines the direction of your intervention. Each pattern benefits from specific exercises and technique cues.
For a detailed guide on how to improve your impact loading through exercise, we refer you to our dedicated article on training impact loading.
