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The Importance of Impact Loading

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.

Visualisation of the impact curve

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.

Key shock-absorbing muscle groups

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.

Average impact curves of injured v.s. Non-injured runners

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.

Application of the Runeasi belt on a runner by physio
Runeasi measures pelvic acceleration

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:

  1. Excellent Loader
  2. Poor Loader
  3. High Loader – Active Absorber (typically a bouncy runner)
  4. Low Loader – Passive Absorber (typically a grounded runner)

Tap to read each profile 👇

1. Excellent loader

Frequently seen in excellent distance runners

Smooth, efficient loading with low impact magnitude and longer impact duration. This reflects strong, well-coordinated shock absorption throughout the lower limbs.

Benefits

  • Excellent distribution of forces across joints and muscles
  • Reduced injury risk due to effective shock absorption
  • Efficient mechanics suitable for sustained endurance running

What to Focus On

  • Maintain strong shock-absorbing mechanics
  • Continue strengthening key muscles that support smooth loading (e.g., calves, quads, hamstrings, glutes)
  •  

2. Poor loader

Frequently seen in Recreational runners / Start-to-runners

High impact magnitude with short impact duration, creating sharp and abrupt forces. These runners often land stiffly with limited active shock absorption.

Consequences

  • Increased injury risk due to excessive loading on joints and passive tissues (e.g., knees, shins, plantar fascia)
  • Fatigue builds quickly because the body cannot dissipate forces efficiently

How to Improve

  • Running technique: encourage softer landings, better leg positioning, smoother transition into stance
  • Strengthening: target key shock-absorbing muscles (calves, quadriceps, hamstrings, glutes)
  • Running drills: exercises that enhance neuromuscular control and timing of lower-limb musculature

3. High Loader – Active Absorber

Frequently seen in explosive athletes / sprinters

Higher impact magnitude but longer impact duration. These runners usually bounce more vertically, storing large amounts of elastic energy.

Benefits

  • Use of tendon elasticity at high speeds
  • Improved running economy in fast-paced or sprint conditions
  • Strong athletic qualities that rely on elastic recoil (Achilles tendon , plantar fascia,...)

Consequences

  • Increased stress on elastic structures (Achilles tendon, plantar fascia)
  • Movement strategy becomes inefficient and potentially risky during slower runs
  • Excess vertical motion increases unnecessary loading for endurance-style running

How to Improve

  • Reduce excessive vertical bounce to lower impact magnitude and improve efficiency at lower speeds
  • Strengthen key tissues (calves, Achilles tendon, plantar fascia) to build resilience and tolerate elastic loading

 

4. Low Loader – Passive Absorber

Frequently seen in ultra-runners / recreational runners

Lower impact magnitude due to minimal vertical motion, which is beneficial. However, forces are often absorbed passively and locally, commonly at the knee and hip. This can be linked to overstriding or prolonged push-off.

Benefits

  • Low vertical loading helps conserve energy
  • Lower impact-related stress on the foot and ankle

Consequences

  • Overreliance on passive structures (ITB, hip stabilizers, knee joints)
  • Increased knee motion may elevate risk of patellofemoral pain or ITB irritation
  • Longer ground contact time may reduce stability and reactive capabilities
  • Potential imbalance in load distribution over long distances

How to Improve

  • Develop greater reactivity: quicker, more elastic ground contact
  • Run technique cues that reduce overstriding and encourage more efficient foot placement

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.

5 rEASONS TO USE OUR APP

1. Global movement quality

Track and improve your client’s Runeasi running quality. Identify their weakest link with our advanced visualisation.

2. individual recommendations

Get individual training and cueing recommendations to improve your client’s weakest link.

3. Real-time feedback

Engage your clients through visual gamification and watch how they self-optimize to your verbal cues.

 

4. Session trends

Learn more about your client’s running quality during daily training. Our session trends show when and where the quality drops with fatigue.

5. Quick comparisons

Compare pre-post data to show intervention effects on the movement quality. 

3 REASONS TO CAPTURE DATA USING THE RUNEASI BELT

1. No motion artifacts. The Runeasi belt is secured tightly against the body and the skin to capture the actual movements of the body’s center of mass. Attaching or clipping the sensor directly to the pants would allow the sensor to wobble from side to side (i.e., measuring the wobbling of the pants, and not the human body.

2.  Easy to standardize the sensor’s positioning. The Runeasi belt makes it easy to consistently position the sensor close to the center of mass. Attaching the sensor directly to the pants would dramatically affect the reliability of the outputs as the height and tightness of the pants will affect the results. Moreover, these pants attachments often shift sideways while running which further decreases the data quality. 

 3. Comfortable to wear.  Hundreds of runners confirmed that they immediately forget about our belt while running. This allows them to move without any restrictions and allows us to capture movements that are representative of a client’s true biomechanics.

SENSOR SPECS

LAB GRADE SENSOR

Accurately captures full range of motion and kinetic parameters by leveraging wide sensing range (16 Gs) & high sampling frequency (1000 Hz)

WATER & SCHOCK PROOF

Built to withstand high intensity training and sweating. Suitable for the outdoor elements, come rain or shine. Robust to handle the repetitive and ruthless impact shocks of running.

Lightweight & SLIM

Seamlessly integrates onto the body to support movement without restrictions. Weight: 9.4g/0.33oz with battery. Dimensions (36.6mm/1.44” dia. X 10.6mm/ 0.42” thick)

No charging wireless

Replaceable coin-cell battery with operating time up to months, depending on the usage. Bluetooth® 5.0 radio for effortlessly transmitting data real-time or post-session.