Home » How to Run Faster » Best of Strength and Conditioning Research in August: Part I, Studies on the Psoas

Best of Strength and Conditioning Research in August: Part I, Studies on the Psoas

The focus of this month’s research is on a deep muscle attached to the front of the spine that most trainers and athletes don’t even consider in their training programs. If you look at the research, you will realize that the psoas muscle (and its close friend the iliacus) is of key importance if you are looking to become a faster athlete with healthy strong hips.

The recent issue of Strength and Conditioning Research was described by author Chris Beardsley as “The Spine Edition”, with many studies on spinal biomechanics, pain, and musculature. The one that I enjoyed the most had to do with the psoas and it’s role in sprint performance and spinal curvature.  If maximally developing speed in athletes is of importance to you, read on!

hip flexor strength
Hip flexor strength is very important in sprinting

Current Strength Research on the Hip Flexors

The Effects of Psoas Major and Lumbar Lordosis on Hip Flexion and Sprint Performance

Copaver, Hertogh and Hue

Research Quarterly for Exercise and Sport, 2012


In this study, we analyzed the correlations between hip flexion power; sprint performance, lumbar lordosis (LL) and the cross-sectional area (CSA) of the psoas muscle (PM). Ten young adults performed two sprint tests and isokinetic tests to determine hip flexion power. Magnetic resonance imaging was used to determine LL and PM CSA. There were correlations between hip flexion power, sprint performance, and PM CSA, but LL showed no correlation with any parameter The impact of hip flexion power and LL on sprint stride pattern efficiency was considered. Hip flexion might not have a simple role in the passive knee replacement of the stride pattern; instead, it may be an active parameter. Other investigations are needed to determine the influence of pelvic architecture on sprint performance.

The world of sport science in regards to sprinting is getting better and better.  Thank God we have some great current research to offset rubbish as seen in the video below:

Can’t teach a deep squat correctly?  Don’t care at all about loading patterns of sprint specific musculature?  Being paid by a chiropractor to give your athletes back issues? No problem! Have athletes quarter squat instead!

Back to the real world of sports training…. the current study at hand is focused on the psoas mucle.  For those of you not familiar with the anatomy of the hip musculature, the psoas is a large hip flexor designed to bring your knee towards your chest.  It works closely with it’s neighbor on the spine, the iliacus and together they are referred to as the iliopsoas complex.  There are actually around seven hip flexor muscles (iliacus/psoas, tensor fascia lata, rectus femoris, sartorius, pectineus, adductor brevis and the gracilis).hip flexor muscles

When an athlete has weak psoas muscle, this creates issues, because the iliopsoas complex happens to be the only two muscles that can create flexion in the hip greater than 90 degrees.  This is due to the mechanical leverage that the psoas has (it originates on the spine, which is higher than the origins of it’s other hip flexor brethren).

Aside from that, the iliopsoas is vital for controlling the head of the femur in it’s socket.  If your body is relying on the other 5 muscles besides the iliopsoas to bring your hip into flexion, you will be losing power and increasing chances of injury due to the mechanical disadvantage of those muscles.  Poor psoas strength causes poor control of the femur in it’s socket.  Needless to say, if your psoas is having problems, and you want to be a fast sprinter, you are in big trouble. 

The way that coaches and trainers approached training the hip flexors (including the psoas) was, in many cases, diminished during the “Weyand-Mania” that occurred in an aftermath of the landmark study by Peter Weyand in his 2000 study “Faster top running speeds are achieved with greater ground forces not more rapid leg movements”.  The rundown of the Weyand study was that world class sprinters are faster because they put more force into the ground, and not because they are swinging their legs faster through the air.  After this study, myself and other trainers pretty much discounted training athletes hip flexors, because it now didn’t matter how fast a person could swing their legs through the air, all that mattered was how much force they put in the ground!  This really wasn’t the right attitude at all, and other authors had the same change of heart that I did.  Check out Kelly Baggett’s excellent article on the same subject.

Eventually, my thoughts started to change a bit.  My mental process transformed to “some of athletes have trouble getting their knees up when they sprint”, and I figured this was a combination of poor core strength, hip strength and poor mobility (which is true for many athletes).  What I still lacked though was the knowledge of the importance of proper psoas functioning in sprint performance.  Studies are pouring in highlighting the importance of psoas strength and sprint ability, and they cannot be ignored.

Consider the following studies: 

  • Effects of Hip Flexor Training on Sprint, Shuttle Run, and Vertical Jump Performance The Journal of Strength & Conditioning Research. 19(3):615-621, August 2005.  (This study found a 12.2% increase in hip flexor strength improved 40 yd dash and shuttle run times by 3.8% and 9.0% respectively.)
  • Influence of the psoas major and thigh muscularity on 100-m times in junior sprinters. Med Sci Sports Exerc. 2006 Dec;38(12):2138-43.  (This study found that the bigger the psoas was in relation to the quadricep muscle group, the faster the 100m time was.)
  • Muscular strategy shift in human running: dependence of running speed on hip and ankle muscle performance Tim W. Dorn, Anthony G.  Schache and Marcus G. Pandy J Exp Biol 215, 1944-1956  (This study showed that when an athlete moves from a fast jog to a sprint, the three muscles that are of top importance are the hamstrings, glutes and hip flexors.)

So based on the info above, we realize that the function of the psoas is of just a little importance if an athlete wants to be a powerful sprinter.  Weyand said that sprinters don’t move faster because they swing their legs any faster in the air, but the psoas works in other ways to help speed.  As mentioned above, it is an extremely important muscle for femoral control.  It also helps to provide a strong base of support for the glutes to fire, in fact, training the psoas in a deficient athlete can bring about increases in glute firing.

The most recent study looking into the psoas just put another nail in the coffin of ignoring the hip flexor complex in sprinters.  It also gives us a darn good reason to look into ways to promote the optimal function of this muscle group in our athletes.

Discussion of the 2012 Copaver Psoas Study:

The Effects of Psoas Major and Lumbar Lordosis on Hip Flexion and Sprint Performance

For this particular study, 10 male athletes were assessed in their hip flexor strength, size, level of lumbar lordosis, and sprint speed.  The cross-sectional  area of their psoas and angle of lumbar lordosis was measured by MRI.  The athletes were then assessed in a 50m sprint and a 120m sprint with complete recovery between efforts.  Hip flexor strength was assessed isometrically at 120 and 180 degrees.  This study was unique in that it determined if increased strength in the psoas would pull the spine into an undesirable position.

lumbar lordosis

Lumbar lordosis:  The theory this study disproved was that strong psoas muscles may pull the spine forwards into lordosis (Tip: Lordosis will cause a lot of problems)

The study found that bigger psoas muscles were linked to increased hip flexion strength.  Larger, stronger psoas muscles also had no effect on static lordosis, so increased strength and size in these muscles will not pull an athlete into poor posture.  A more accurate theory is that tight psoas muscles may pull an athlete into lordotic posture, and we are often both tight and weak (this is what happens when you sit all day) in the iliopsoas, so proper stretching of this muscle is a must.  Unfortunately, there was no gauge as to how the strong psoas muscles affected lordosis while actually sprinting, but my guess it that the disadvantage would be minimal considering the higher sprint speeds and the other research that is out there.

Copaver found that there were positive correlations between hip flexion strength at 180 degrees and performance in the 120m sprint.  There were also positive correlations between psoas cross sectional area and performance in the 50m sprint.  We don’t know 100% how the role of the psoas changes during acceleration vs. long sprinting, but in general terms, it is obvious that a bigger, stronger and well-functioning psoas muscle is important for developing speed in athletes.

Summary of the Copaver Study:

  • Greater cross-sectional area of the psoas had significant relation to a 50m sprint
  • Greater strength of hip flexion at 180 degrees was correlated with 120m sprint performance
  • Stronger psoas muscles will not cause lumbar lordosis in static positions

Practical Applications:

In order to achieve the highest performance, an athlete must optimize the function of their psoas.  A combination of strength, stretching, and soft-tissue will help athletes improve their athleticism.

Strengthening: To hit the psoas maximally and separate it from the other hip flexors, you need to be training your hip at greater than 90 degree angles.  To see how good of psoas function and strength you have, strength coach Mike Boyle has this simple test: Stand against a wall and bring one leg to your chest with your hands.  Release your hands and try to keep that knee has high as possible.  If you have proper psoas function, you should be able to hold your knee there for a good 15 seconds.  Athletes that rely on other muscles to flex the hip will notice a quick drop in the thigh once they release their hands in this particular exercise.

Honestly though, whether you are deficient or not, you should still be hitting your hip flexors hard, if you perform poorly on this test however, you’ll have to start extra light.  The following exercises are nice ways to train the hip flexors for improved sprint power.

Wall Knee Raises

These are as basic as it gets.  Bringing the thigh about 90 maximizes the psoas involvement.  Add an elastic band for more difficulty.
Seated Hip Flexor

This is a basic exercise to isolate the iliopsoas complex.  You can add difficulty to this by using a band, plate, or kettlebell on your thigh.  Since the psoas is a relatively large muscle and offsets the glute, I recommend working up to at least 30-40lbs for 10-12 reps.

Psoas activation off of a box

Mike Boyle uses this as a staple exercise to work the psoas and separate it from the other hip flexors.
Hurdle Mobility

The first three exercises are “modern”, but if you want to use something tried, true, and simple, just remember that hurdle mobility is a great dynamic way to work the hip flexors.  Make sure your athletes are lifting their knees towards their armpits to maximize psoas involvement.

Stretching: A tight psoas will keep your glutes from firing maximally through “reciprocal inhibition”.  Research by Sandberg (1) demonstrated significant gains in vertical jump height following static stretching of the hip flexor group vs. a control.  Our psoas grows tight from sitting around all day, so it’s prime length must be reached through stretching

Basic Static Psoas Stretch

A basic stretch to lengthen the psoas.  Best done after soft tissue release work.

Overhead Walking Lunge

We typically include these as part of our warm-up for my track athletes.  Cue the athlete to reach for the sky as high as possible and take big steps.

Releasing:  Often times inhibited or weak muscles are loaded with knots, trigger points and neural issues.  Soft tissue work such as softball or foam rolling can help to restore function, but the problem with the psoas is that it is a very deep muscle, and hard to get to.  The videos below provide some very useful material in releasing the psoas manually.  Don’t overlook this aspect of your training, after all, we are after that last couple % points of improvement, so get to the release!

Active release of the psoas with a plate

Releasing the psoas, mobility WOD style

So with that, I give you three methods to improve your psoas function and get a step, or eight, ahead of your competition.  If you are not accustomed to hip flexor training, I recommend you start by using release and stretching methods each day for the next two weeks.  Accompany this with a few sets of basic bodyweight strengthening in both seated and standing positions.  Performing this should help you feel more power from your hips in dynamic movement.  You will love the results!


  • Recent research has shown a link between psoas size and strength, and sprint performance
  • Increased psoas strength will aid in femoral control, and allow the glutes to fire more powerfully
  • Increasing the cross-sectional area and strength of your psoas shouldn’t bring you into anterior tilt
  • The function of the psoas should be trained through soft tissue release, stretching, and strengthening. 

Other References:

Sandberg JB,Wagner DR, Willardson JM, Smith GA. Acute effects of antagonist stretching on jump height, torque, and electromyography of agonist musculature. J Strength Cond Res. 2012 May;26(5):1249-56.


  1. An electromyograph detects the electrical potential generated by muscle cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect medical abnormalities, activation level, recruitment order or to analyze the biomechanics of human or animal movement. ‘.”,

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  2. Hi Joel,
    Are you aware of any correlation between hip flexion strength AT 90 degrees and sprint speed? And could you tell me about any anecdotal evidence you have seen or know of for increased sprint speed from strengthening the hip flexors above 90 deg?

    • Hi Tom,

      I don’t have any exact evidence, but I can tell you that the explosive firing potential of the glutes (in sprinting, not in hip thrusts or deadlifts) is regulated by the strength of the psoas. If you improve the strength of the psoas, your glutes can hit harder. Kelly Baggett wrote a good anecdotal article about this. Here is the link: http://www.higher-faster-sports.com/hipflexors.html

      Kind regards,


  3. What do you think about progressively increasing the size/strength of the psoas muscles? My 1 rep max on cable knee drives is around 30 pounds…if i double that, should i be a lot faster? At what point will an increase in psoas musculature not yield any more benefits? Thanks!

    • Hi Umair,

      Increasing psoas strength is important to becoming a better athlete, but of course, there is a limit to how much it will help you. To become a faster sprinter, doing barbell hip thrusts is useful,. but there is a limit, and point where extra hip thrust strength will no longer transfer; and the hip thrust itself helps all other athletic movement to be more powerful.

      For psoas work, the cable knee drive is a nice lift, but it is where the leg is above 90 degrees flexion that only the psoas and illacus can work, so you’ll want to focus more on that range. You don’t need much resistance to do it either, just a few pounds. More reps is generally better in this scenario, as the more exposure you can give your psoas the better; and you’ll feel the difference in regular athletic movement after several weeks. Once you have improved movement, you’ll only need to maintain the psoas strength.


  4. Hi Joel, in your article you say that in Copaver’s study, “Hip flexor strength was assessed isometrically at 120 and 180 degrees.”
    The study actually assessed hip flexor strength isokinetically at 120 – 180 degrees/second. 180 degrees/second being the angular velocity of the isokinetic machine.

    I really enjoy reading your articles, thanks for all the great info and insights!

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