Strength Imbalance and Running Injury Part 1

I’m seeing it quite a bit these day, in runners of all levels. Whether they’re running their splits in 6 minutes or 12 minutes, 5ks or 50ks, strength imbalances are ever present in injured runners. The reputation of strength imbalance is growing, the annoying sidekick to some classic running-related overuse injuries.

They’ve likely been there for years and you haven’t even noticed. Strength imbalances can occur between two sides, say the difference between your left quadriceps and right, but this article is going to focus on single sided imbalances within a particular functional muscle group.

These imbalances often create a gross asymmetry that lies undetected or insignificant until the next time you try to push it at a hard race or increase your weekly mileage. Human bipedal gait is incredibly complex, a true marvel of evolution. What we as movement scientists know of it continues to grow, but is based largely on norms that we observe in the laboratory. The problem with this can be summed up in one word: variability.

There are some constants in human propulsion, but equally importantly, there is also a large continuum of variability in movement patterns. We know what ‘typical’ looks like, and a half dozen variations, but the headache lies in the question of ‘when to correct gait patterns?’

Do you have to have ‘textbook’ gait mechanics to set a world record or to make it to the Olympic trials? No. But if your injury, pain, or performance issues correlate with a dysfunctional movement pattern, that’s when some changes may be warranted.

My name is Dr. Allan Buccola, Physical Therapist and owner of Impetus Physical Therapy in Greensboro, NC. This post details a brief description of some common muscle imbalances seen in runners, that when identified early, can stop injury in its tracks.

This is part one of a multi part series. I'll also link some research I've recently stumbled across that is related in some way. 

#1 Quads, Glutes, & Hamstrings

This triad of power controls arguably 90% of propulsion, or the gross movement we think of in straight plane walking to running. If you look at bipedal movement along a continuum from slow walking to all-out sprinting, theses muscles work together in a ways that are equally as variable. This is easily demonstrated in the contrasting builds between sprinters (heavy glute max development) and distance runners (heavy quads development).

Since this first example has three muscles working together in a multitude of complex ways, we have lots of examples of how imbalances can lead to injury. I’ll be brief and stick to just a few of the most common that I see.

In runners with with quadriceps development that rivals the glutes, it’s common to see problems with patellafemoral pain and iliotibial band syndrome. These runners are also likely to experience trigger points and muscle pain in the glute max on days where they attempt sprint intervals, especially at distances less than 400m or greater than 90% effort running. This is often difficult pinpoint and typically is perceived as 'low back pain.'

An imbalance in these runners also leads to greater vertical oscillation (the amount of up/down bounciness that takes place during running) which in turn leads to greater loading forces and all of the injuries associated with those mechanics (tibial stress fractures, femoral stress fractures.) A glute max dominant gait can also lead to patellar tendon pain.

Clinical determination of this particular imbalance can be tricky, as it requires both functional and nonfunctional means of assessment of these muscle groups.  This requires a lot of data collection and analysis: in short, extra time. Gait analysis alone is not always sufficient, as patterns in running are not merely dictated by strength imbalances; they can also be resultant of joint abnormalities, poor endurance, or poor neurological activation, among other things.

There has been a fair amount of research investigating strength ratios between the quadriceps and hamstrings. The focus has been largely related to hamstrings injuries, and the goal, to find the ideal ratio for injury prevention/protection. Unfortunately, no consensus has been found in the literature, although it remains an important topic.

Here are some interesting reads on the topic for those of you who follow the research: nerd-out below.

Hamstring-to-quadriceps fatigue ratio offers new and different muscle function information than the conventional non-fatigued ratio

Age-related effects on maximal and rapid hamstrings/quadriceps strength capacities and vertical jump power in young and older females

Hamstrings to quadriceps peak torque ratios diverge between sexes with increasing isokinetic angular velocity

Quadriceps effort during squat exercise depends on hip extensor muscle strategy

Hip-Extensor Strength, Trunk Posture, and Use of the Knee-Extensor Muscles During Running

#2 Hip Extensors (glute max/hamstrings) and Plantarflexors (gastroc-soleus)

This one I see quite a bit, typically presenting as apparent calf weakness, but in the faster runners (sub 7” milers), the imbalance can also stem from an inhuman amount of force produced through the glutes. This makes it easy to miss, because at a glance, the calves may appear to be sufficiently strong. Additional digging will be needed.  

Most PTs are aware that hip range and ankle range are intimately related in gait, wherein a lack of mobility in either will lead to inefficient mechanics and potentially injury. Strength imbalances between these two seem to be less common, but almost always seem to lead to calf strains or Achilles' pain, and typically both.

If you are runner with chronic Achilles' or calf pain, a good first investigation should assess calf strength, especially when there are no other glaring gait abnormalities. Often in these cases, the propulsive forces of the total limb slightly exceed the stabilization capabilities of the calf. As in many calf issue, these problems will be exacerbated with speed work, fast tempo runs.  

#3 Hip Flexors (Iliopsoas, rectus femoris) and Abdominals (rectus abdominus, external oblique)

Imbalances in core strength can manifest in several ways, but a lack of core stability will ultimately lead to poor power output in every athlete. Those with core weakness, or an acquired imbalance between the hip flexors and the abdominals, will not be able to stabilize the pelvis and trunk during the push-off or landing phases. 

It's analogy time! I equate this to trying to drive your car while the lug nuts are partially loosened. In the transference of power from the engine to the tires, there can be no mechanical lags. When the gas is punched, any movement that occurs between the lugs and the wheel not only delays the onset of optimal power, it eventually leads to serious mechanical problems.

The ‘core’ has taken on its own persona in popular culture in the last 10 years, but it’s critical to realize that the core is more than just ‘six pack abs.’ The core is more than just a pretty face and includes several muscle groups that are often forgotten. The ability to fully determine that strength imbalances in the core are contributory to running dysfunction, or that they exist in the first place, can be a tricky endeavor and should be left to the running experts.

But the magazines say that planks will save me! 

Obligatory strengthening won’t always solve the problem either. Typically what happens is someone continues to do generalized strengthening, and the body continues to overcompensate with the strong muscles to pick up the slack for the weak ones. The strong get stronger, and the weak...well, if you're lucky, they don't do anything. For the unlucky, additional pain will follow these fruitless attempts. 


If you consider the plank exercise, this is a perfect example. The plank is considered the go-to exercise for strengthening the abs, but it’s critical to acknowledge the other muscles involved. If someone has weakness in their abdominals, they may continue to plank in positions that are dysfunctional because they are simply easier, and are none the wiser.

Another option is that because of their abdominal weakness, the plank becomes dominated by the hip flexors. If you over-rely on the hip flexors in the plank, eventually it’s likely you’ll try to stabilize your core with them while on the run too. This simply won’t work, as they are busy doing other things while you’re running. So plank on, but don't expect miracles if that's all you're doing. 

I find these runners will fall into excessive arching of the low back while running, especially once in a fatigued state. On the run, this often results in altered firing of the hip flexors, too great a magnitude of movement in the lumbar spine, and higher loading forces at foot strike. These runners will complain of injuries associated with high loading forces, as well as back pain, possibly knee pain, and often demonstrate some knee instability.

More nerdom.

A proximal strengthening program improves pain, function, and biomechanics in women with patellofemoral pain syndrome.

Mechanics of the muscles crossing the hip joint during sprint running

Hamstring strain injuries: factors that lead to injury and re-injury

Is there an easy fix?

OK, this is good reading and all, but I would argue that if you are not dealing with injury at the moment, there’s no inherent need to start making drastic changes in your gait. If you suspect your running mechanics line up with some of these profiles and you are dealing with injury, find a human movement specialist who can not only assess your gait, but also perform an in depth analysis of your functional and isolated strength.  

In running research, the biggest predictor of a future injury is a history of that same injury. I believe this is because in rehab/recovery, injuries are often addressed locally, but little long-term changes are achieved in resolving strength imbalances, training errors, and other contributory factors.

Think of this in the context of massage, foam rolling, or stretching: if you have pain, these things are helpful in the moment to calm the system down, but they are insufficient to resolve the actual problem. Let’s take injury rehab and prevention into the 21st century, and not just mask pain, but change the way we move for the better! 

Thanks for reading and check back for part two on this topic wherein I’ll cover 3 more common strength imbalances. Until next time, keep moving!