Performance Mobility, Part 2: Trunk Rotation

Stay the Course[Author’s Note: This is Part 2 in a six-part series on functional-mobility self-assessment and restoration for runners. Check out Part 1, an introduction to the series and a discussion of hip mobility, Part 3 on foot and ankle mobility, Part 4 on knee mobility, Part 5 on trunk extension, and Part 6 on hip abduction and rotation mobility. ]

Last month, I introduced the concept of performance mobility. To reiterate, there are certain fundamental motions required for healthy, efficient running. These motions are related to the hips, trunk (spine and chest), knees, and ankles. The purpose and utility of performance mobility are to provide runners with a way to self-assess their motion and, if need be, improve and restore it. Moreover (and perhaps most useful), if the motion is full and normal, there is no need to stretch any more!

This concept, and the first metric, covering hip mobility, drew a great deal of interest, commentary, and criticism. Allow me to point out and shed some more insights on some of the comments.

Stretching Worsens Performance Research 

Several of you noted the substantial body of research demonstrating that stretching–namely static stretching, similar to what is noted in performance mobility–worsens performance by elongating the muscle-tendon unit and decreasing its power. I agree 100% with this theory. But it is important to note that there are many types of tissue mobility.

It’s well worth a trip back into the iRunFar time machine to January 2015, where I outlined the various types of tissue mobility in a similarly titled piece, Performance Flexibility: Joint, Spine, And Nerve Mobility For Runners. As the title implies, there are several types of mobility, besides the muscle-tendon, which is the primary unit studied in the literature.

The aim of performance mobility is not to elongate a muscle-tendon unit. Instead, it is to ensure that joint systems in the trunk, arms, and legs have full physiological motion.

Stretch Bands and Hinges

A good way to think of the difference in tissue mobility is by analogy. Consider the muscle-tendon as a stretch band. And while the stretch band cannot actively shorten the way a muscle-tendon does, it derives and stores much of its power in its elasticity. Indeed, the rationale of the anti-stretching research centers on the idea that overstretching the muscle-tendon reduces its elastic power. This could also happen with a stretch band: stretch too far and it may warp and lose tension.

Let’s continue our analogy. Beyond the stretch band is the hinge. A metal hinge is a good analogy for the articulation of a joint. One bone connected to another, and that unit must flex and extend. The hinge rides between two pieces, usually, a static wall and a swinging door. Compare that to a stable trunk and a swinging hip. For optimal function, that hinge needs to move through its full range, with very little friction. Seldom does a hinge have ‘too much motion,’ unless it becomes loose, thereby causing accessory motion (and uneven ‘swinging’ of the door). Otherwise, full motion is always preferred.

In the analogy, there is a stretch band connected on either side of the door–one to open it and one to close it. Implicit in the idea of performance mobility is that persistent range-of-motion loss is seldom due to tight stretch bands (muscles-tendons), but instead the result of a stiff, rusty hinge (joint)!

Moreover, a stiff, immovable hinge is far more likely to overstretch and damage the stretch bands! Thus, a regular check-in regarding ‘hinge mobility’ (and perhaps a spritz of WD-40) is extremely important in keeping that door fully and efficiently mobile! 

The following video demonstrates these two facets of performance mobility:

[Click here if you can’t see the video above.]

Performance Mobility is Not Evidence-Based

Others criticized the piece by arguing (as many do) that this theory lacks any research-derived evidence for its efficacy. And while I argued that much of what we do–as clinicians, as well as runners and coaches–does not have statistical evidence, yet still works, these mobility metrics are, indeed, scientifically and medically-derived.

The hip metric described in Part 1 of this series–the single-knee-to-chest test–is derived from an orthopedic special test called The Thomas Test. This is a ubiquitous sports-medicine test used to assess both hip and pelvic mobility (with associated muscle-tendon, joint, and other tissue mobility). All of the metrics outlined for performance mobility are grounded in the fundamentals of orthopedic tests and measures: what’s clinically normal and healthy, versus what is not.

In essence, the point of performance mobility is to bring these tests out of the examination room and into the hands of runners so that the runner can self-assess and stay ahead of any potential problem that comes from legitimate joint range-of-motion loss.

“The Research Says We Don’t Need to Stretch,” Part 2: Ultra Specificity 

More argument for the need for vigilance with range of motion comes from the specificity of ultrarunning and ultrarunners. Fodder for a future ‘Stay the Course’ column is a primer on how to best interpret and apply research studies. Among many factors is external validity. Can the results of a specific study be applied to me? Specifically, the question is, can the results of a given research study be applied to ultrarunners? To help answer that, allow me to point out:

  • For most of the stretching research cited, the study involves a population of young athletes (or, commonly, military recruits) engaging in short, high-intensity exercise.
  • The average ultarrunner (and iRunFar reader) is roughly aged mid-forties, a working professional (sitting most of her or his day), and runs for a long time (four to 24 hours) at moderate intensity.

As such, many studies on mobility fail to address the unique characteristics, needs, and challenges of the ultrarunner. As stated two years ago in our article on performance flexibility, the need to monitor and restore full functional mobility stem from those unique ultramarathon challenges, which include:

  • Running for a very long distance and time
  • Cumulative impact stress, from both distance and terrain
  • Fatigue-induced reductions in good posture and range of motion

And on top of that, we have our population-driven factors, which include:

  • Age-induced reductions in tissue (namely muscle-tendon and joint) mobility (for those of us aged 40-plus)
  • ‘Professional’ factors, such as sitting at a desk or in a vehicle for eight to 10 hours per day or more

These combined factors are a compelling argument for vigilance in monitoring and maintaining functional mobility! My hope is that this additional insight will help clarify the importance and relevance of performance mobility, especially for ultra-distance trail runners. Now, onto the second metric!

The Trunk-Rotation Metric

The running motion is a multi-dimensional, whole-body motion involving not only a forward-and-back leg, but a lengthening and rotating trunk. This metric assesses both the quantity and symmetry of that whole-body motion.

Details: Flat on the floor, flex a leg up to waist level, and then fold that leg across the body while using the opposite hand to push the flexed knee toward the floor.


  • Equal, symmetrical motion (left versus right legs)
  • Knee gets (close) to the floor (maintaining opposite elbow to the floor)

Common Deficits:

  • Overall range-of-motion deficit: a failure to get the stretch thigh (flexed leg) at least parallel to the floor
  • Asymmetry: one side stiffer than the other


Loss of trunk mobility may indicate a ‘stiff trunk,’ which lacks the normal, slight amount of side-to-side rotation while running, or an overall posture deficit, usually a forward slump during running, outside of running like while sitting at a desk, or both. Asymmetry of motion is most detrimental. Note that the test itself resembles running: one leg straight, the other flexed and ‘driving.’ Commonly, the stiffer side (one that fails to twist as far) indicates a whole-body (leg and trunk) push-off deficit.

Trunk Rotation Performance Mobility Metric

Joe Uhan performs the trunk-rotation test for performance mobility.

Restorative Exercises for Trunk Rotation

In this case, the restorative stretch is the same as the test: lying flat, flexing a thigh to the waist, and then folding across. There are a variety of ways to improve mobility. Prolonged holds (of 30 to 60 seconds) are useful in working on chronic-systemic (muscle-tendon as well as spine, rib, pelvis, and hip) stiffness. However, for those of you phobic of static stretching can also do repetitive on-and-off stretching of the knee toward the floor, using the hand.

Call for Comments (from Meghan)

  • So, did you pass Joe Uhan’s trunk-mobility test? If not, do you possess asymmetry between your left and right sides or do you have an overall loss of your range of motion?
  • We asked the same question in this series first article, and we’ll try it again here. What kind of flexibility training or stretching do you engage in, if any? Do you find that it helps you in specific ways? If so, can you describe them?
Joe Uhan

is a physical therapist, coach, and ultrarunner in Eugene, Oregon. He is a Minnesota native and has been a competitive runner for over 20 years. He has a Master's Degree in Kinesiology, a Doctorate in Physical Therapy, and is a USATF Level II Certified Coach. Joe ran his first ultra at Autumn Leaves 50 Mile in October 2010, was 4th place at the 2015 USATF 100K Trail Championships (and 3rd in 2012), second at the 2014 Waldo 100K, and finished M9 at the 2012 Western States 100. Joe owns and operates Uhan Performance Physiotherapy in Eugene, Oregon, and offers online coaching and running analysis at