Biomechanics

New horizons in iliotibial band biomechanics in runners

The iliotibial band, or IT band, is a thick strip of fibrous tissue on the outside of your thigh. It’s the fifth most common location of injury among runners, and it’s also a very weird anatomical structure.

Two completely different muscles, with seemingly different roles during running, both connect to the IT band: 100% of the fibers of the tensor fascia lata, on the side of your hip, connect to the IT band, but so do about 50% of the fibers of the gluteus maximus (one of the prime movers of the hip joint).

Another strange thing about the IT band is that it seems to be a uniquely human structure: chimpanzees and other primates do not have an IT band (almost all of their gluteus maximus fibers connect directly to the femur, and their TFL muscle inserts on a shorter fascia that terminates above the knee).

Despite its anatomical uniqueness, and its high rate of injury, we—meaning the biomechanical and sports medicine community—don’t really understand a whole lot about what the IT band is doing during running (or walking or cycling, for that matter). All of the most popular “musculoskeletal models” of the body used for gait analysis don’t have a true IT band: they just have a TFL that goes down the side of the leg, and a gluteus maximus that inserts along the femur.

I have just published a new preprint that addresses this problem. The title tells it all: “A full-body musculoskeletal model with an anatomically informed iliotibial band.”

You can read the full preprint below, if you want the technical details, or read on for some highlights on how this model of the IT band works and I think it will be very useful for studying IT band mechanics during running.

📄 Read the full paper here

Something to understand: this paper is a beginning, not the end, for my research on IT band biomechanics. The big centerpiece—simulating five gait cycles of running at 8:30/mi pace for one runner—won’t blow you away, though it is a big technical accomplishment, and it  does produce some nice visualizations. This study, and this IT band model, are a foundation for future research (some of which I’m working on already) into many different aspects of IT band biomechanics.

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What can Garmin RunDynamics and Stryd data tell you about biomechanical training load?

I just published a new scientific study—this paper was basically the centerpiece of my PhD dissertation, and the title more or less gives away the premise: “Predicting Achilles tendon and patellofemoral joint forces during running with consumer-grade wearable sensor data.”

In this study, “consumer-grade wearable sensor data” means RunDynamics from a chest-worn Garmin heart rate monitor and similar data from a Stryd foot pod. If you aren’t familiar with these devices, they use on-board sensors to estimate biomechanical parameters like your cadence / stride length, vertical oscillation, ground contact time, and so on.[1]

There are a few issues with the gait metrics you get from these kinds of devices, though. First, are they accurate? And second…do they actually tell you anything about what’s going on inside your body?

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A comprehensive guide to the science of cadence for runners

Your cadence is the number of steps you take per minute while running. Simple measurement, right? But there are many questions surrounding it, including how it differs across runners, how it changes as you run faster, whether a higher cadence is more efficient, whether a lower cadence causes injury, and whether you should aim for a specific number.

It almost goes without saying that there is an enormous amount of erroneous information circulating around when it comes to cadence, to such an extent that—with a few exceptions—I’m mostly going to avoid trying to refute everything wrong about cadence you may have seen elsewhere, and instead focus on the (correct) biomechanics of cadence in running.

Cadence is squarely in my scientific wheelhouse; I spent most of my time during my PhD collecting and analyzing biomechanical data. One of the chapters of my dissertation is even focused on the merits of cadence (and other gait metrics) as a predictor of biomechanical loading. So, buckle up—we’ll be covering everything you need to know about cadence.

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Understanding tissue loading, tissue damage, and running injuries

In my article on biomechanical training load, I covered the basics behind how biomechanical loading is related to the development of running injuries.

The basic idea is pretty straightforward: every time you take a step, your tendons, bones, and joints experience a loading cycle: a build-up and release of mechanical force.

Each loading cycle does a tiny amount of damage, depending on the magnitude of the force and the structural integrity of the tissue. If this damage accumulates faster than your body can repair it, the result is an overuse injury.

In this article, we’re going to take a deeper dive into exactly how this process of tissue damage works. Our goal is to build up an understanding of cumulative damage: a way of quantifying “how much damage” you’ve done to a specific piece of tissue.

We’ll use the recurring example of damage done to the Achilles tendon, since it’s a common injury and a relatively straightforward tissue in terms of understanding both its biomechanical loading and its tissue properties.

So, what is the actual mechanical process behind tissue damage in running? Let’s dive in and find out.

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A high-level picture of biomechanical training load for runners

What do we mean when we say “training load”? This is the second article in a three-part series aimed at answering that question.

My core argument in this series is that there are three distinct types of training load you should consider—physiological training load, biomechanical training load, and psychological training load.

Today, we turn our attention to the second of these types of load. What exactly is biomechanical training load? In short:

Biomechanical training load describes the mechanical force—and ultimately, the mechanical damage—experienced by the load-bearing tissues of your body: bones, tendons, muscles, ligaments, and joint surfaces.

When talking about biomechanical training load, what we mean is “how much physical damage are you doing to your body.”

Proper biomechanical training load drives health and structural integrity: the ability to avoid injury and increase your body’s ability to sustain higher levels of training in the future.

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Why a pure lateral crosswind slows you down when running

Let’s say you’re running at 6:00/mi, heading straight north on a day with a 10 mph wind from the east. You’ll certainly notice this stiff crosswind. But will it slow you down?

Earlier this summer, I made a headwind and tailwind calculator for runners that uses the latest scientific work on the metabolic cost of overcoming headwinds and tailwinds. It calculates a “wind-adjusted pace,” and unlike any other calculator on the internet, it also allows you to specify the direction of the wind you’re encountering, so you can calculate the effects of not just a headwind or a tailwind, but lateral winds coming at you from any angle.

However, the first version of this calculator made a subtle mistake! After publishing the calculator, I got an email from reader Dave Clark, who noticed that pure lateral crosswinds—such as the east wind in the intro example—seemed to produce no effect on your pace. I assured him that this was expected: my calculator assumed that the lateral component of the drag force imposes a negligible metabolic cost. 

Dave responded with some back-of-the-envelope math that made me realize I’d made an error in how I implemented the drag equation! The calculations were still correct for pure headwinds and pure tailwinds, but anything involving a crosswind was slightly off. But it’s fixed now!

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Running in the lab versus running in the real world: why they differ and what to do about it

My article from a few weeks ago on Emile Cairess’ training before his 3rd-place finish at this year’s London Marathon was one of the most popular articles I’ve written in a long time. However, it actually wasn’t the only article I published that week! A few days prior, one of my dissertation studies was published, and it was titled:

“Are Gait Patterns during In-Lab Running Representative of Gait Patterns during Real-World Training?”—and the answer is “not really.”

I’d like to go over both what we did in this study and what implications it has for people (like me!) who want to apply findings from biomechanics research to real-world training.

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Check out my new book on marathon training!