The bone stress injury model: a new way to deal with stress fractures and stress reactions in runners

An MRI reveals a tibial stress fracture

Traditionally, overuse injuries to the bone in distance runners are divided into two distinct categories: stress reactions and stress fractures.  Runners who develop pain along one of their bones hope desperately that they have the former and not the latter, since the usual prescription for stress fracture recovery is six to eight weeks of no running whatsoever.  The usual restrictions for stress reactions depend on the doctor, but typically involve two to four weeks away from running.  Some doctors, coaches, and runners eschew the term "stress reaction" entirely because, in their view, you either have a stress fracture, or you don't—that's all there is to it.

Normally, the story unfolds something like this: a high school runner develops a sharp, aching, localized pain somewhere along a bone in his lower body.  It doesn't improve much with icing and lowered training volume, so his coach or trainer refers him to a doctor.  The doctor orders an X-ray, examines it, but sees no evidence of calcification, so he orders the runner to ease back into training, but return if pain continues.  The high schooler gives running a shot, but continues to have pain.  The doctor then orders a bone scan or an MRI, which shows bone marrow edema or increased metabolic activity at the location of pain.  This is deemed to be a stress fracture, and the runner is put in a boot, forbidden from running for six to eight weeks, and his season is effectively over.  Sound familiar?

The reason for caution with stress fractures is well-known.  If you have a stress fracture and continue to run recklessly on it, it can worsen and eventually lead to the bone splitting in two—a true fracture.  This can lead to heaps of complications and could end your running career.  There is also a category of "high risk" stress fractures that occur in particular areas like the femoral neck, the navicular, and the sesamoid bones, which are known to have a significant risk for poor healing or nonunion.¹ These require even more time off and a much slower return to running.

Problems with the old model

However, doctors and physical therapists are starting to learn what coaches have already picked up on: the traditional approach to low risk stress fractures (as the vast majority are) is inadequate on a number of points.

The case for a new approach to bone injuries in runners was laid out in an exhaustive review article published in October of last year by Stuart Warden, Irene Davis, and Michael Fredericson, three extremely prolific running injury researchers.² They propose using the term "bone stress injury" or BSI, which is intended to encompass all overuse injuries to bone that runners sustain. 

Under Warden, Davis, and Fredericson's model, bone stress injuries exist on a continuum.  On the most severe end of this spectrum are true stress fractures: a fracture line is observable on an MRI or CT scan, and there is edema (swelling) in the bone marrow and periosteum, the membrane that covers the surface of the bones.  A stress fracture is accompanied by a sharp pain or ache during weight-bearing activity that sometimes persists even when you're resting. 

The next step down the continuum of bone stress injury is the stress reaction: pain and aching during or after weight-bearing that is associated with bone marrow edema (on an MRI) or increased bone remodeling (as imaged by a bone scan), but lacks a visible fracture line. 

Further down the bone stress injury spectrum lies asymptomatic areas of bone remodeling.  As it turns out, if you were to schedule weekly MRIs for a group of high-level runners in heavy training—say, a college cross country team—you would quite often find runners developing transient areas of bone marrow or periosteal edema that would be indicative of a stress reaction, except that they have no pain associated with them, and never develop problems in the area.³ 

The biology of bone remodeling

One of the core paradoxes of stress fractures and stress reactions is why they occur in fairly experienced runners.  All medical students can recite Wolff's law—bone responds to stress by becoming stronger.  So, theoretically, running more should lead to stronger bones, not stress fractures.

Using the Tempo Trainer for pacing interval workouts on the track

The Tempo Trainer

As a high school coach, one of the toughest things to teach young runners is proper pacing.  Everyone has seen a high schooler who takes off far too fast in a mile or two-mile race, only to stagger home disappointed and out of energy at the end.  Pacing in races is obviously important, but so is pacing in workouts.  An improperly-paced interval session can ruin the intended purpose of the workout.

Take, for example, a staple high-end aerobic session: "cruise interval" kilometer repeats done at the anaerobic threshold.  A high school runner who is currently in 9:55 3200m shape might be looking to run 6x1km at around 3:30 per kilometer with a minute's rest between each.  When done properly, running each repeat at an even pace, this is a fairly relaxed workout.  However, if poorly paced, it quickly becomes a lot more challenging. 

For an experienced runner or a coach, it can seem baffling when a new runner is incapable of pacing.  Younger runners haven't developed their own internal sense of pacing yet, so they struggle to hit prescribed workout paces, even if the workout isn't inherently difficult. 

Can't you just check your watch every 200 meters? Frequent watch-checking is the most obvious solution, but this brings along a host of problems.  First, you're relying on all of the runners you are coaching to remember to bring a watch, which can be its own struggle.  Second, a watch only allows you to check cumulative times; adding up splits in your head can be a little tricky if you aren't running a mathematically convenient pace.

The proper pace for a 3:30 kilometer is 42.0 seconds per 200 meters.  What I'll often see when a group of high school runners attempts to run this pace is wild variation in the per-200m split, alternating between too fast and too slow.  So, a group might run the assigned pace of 3:30, but will do it with intermediate splits of 39 - 41 - 44 - 44 - 42.  Hardly ideal! You can take a split each 200 on your watch, but then you can't report your overall time to your coach.  Using the watch to gauge pacing can also lead to overcorrection: running a 40-second 200 to "get back on pace" by 400 meters, following a first 200m split of 44 seconds, for example. 

Discovering the Tempo Trainer

Through a combination of luck and resourcefulness, I stumbled across a more robust solution.  In the fall, I suffered a case of Achilles tendonitis which led to a few weeks of aqua-jogging in the pool to maintain my fitness.  I shared pool space with a club swimming team which occasionally used a small pacing device called the Tempo Trainer to help them set their stroke rate (much like some runners use a portable metronome to assist with setting their stride rate).  The waterproof unit was meant to be tucked inside a swimmer's swimcap and was loud enough to be heard underwater. 

It wasn't until I mentioned the Tempo Trainer to a swimmer friend of mine that I realized that it could be used for pacing interval workouts as well.  My friend remarked that she often used its pacing function so she could hear a "beep" at a prescribed interval during long repeats in the pool.  So, for example, if she wanted to swim a 100 yard repeat in 66 seconds, she'd set the Tempo Trainer to beep every 16.5 seconds, so she'd hear it each time she pushed off each wall in a 25 yard pool.  By judging whether the beep was early or late, she'd be able to tell whether she was ahead, behind, or on pace.

Hearing this reminded me of a special workout called the "Faraggiana-Gigliotti Test" that Italian running coach Renato Canova conducts on his top marathon runners.  The test involves taking blood lactate samples after a series of 2km repeats at a range of potential marathon paces to get a reasonable estimate of an athlete's current marathon fitness.  To ensure his athletes pace each two-kilometer repeat as efficiently as possible, the coach sets out cones every 25m and uses a loud beeper set to beep at the proper interval for the required pace.  As John Kellogg has pointed out, doing so requires the beeper to be placed in the center of the infield, so you don't get pacing variations due to the speed of sound as you round the track.  One central beeper also has to be loud enough to be heard from the other side of the track, and you can only use it for one workout group at a time.  Finally, unless a coach manually resets it or changes the beep interval, the athlete has no control over it. 

The Tempo Trainer circumvents all of these limitations.  It's small enough to easily be carried in your hand during a workout, and it is loud enough to be heard even while running in a group, but not so loud that everyone within a quarter-mile can hear. A large track or cross country team could use one Tempo Trainer for each workout group.  Finally, if you get sick of it, you can turn it off and toss it on the infield.  It also comes with a clip that you could use to attach it to your shorts, but I found it easier to just carry it in your hand.  After doing some research, I bought one and tested it out.