The Effect of a Hip Strengthening Program on Mechanics During Running and During a Single Leg Squat.
Willy RW, Davis IS. J Orthop Sports Phys Ther. 2011 Jul 12. [Epub ahead of print]
In a previous post, we reviewed an article examining the effect of a medially applied load to the knee on hip muscle activation. Although the study determined effective exercises to activate the gluteal muscles it did not delineate the role hip strengthening has on frontal plane running mechanics and thus injury prevention. Therefore, the purpose of this study was to determine the effect of hip strengthening and movement control, via a single-leg squat, on the running and squatting mechanics of healthy females with abnormal running mechanics. For this study, 20 healthy female runners with abnormal running mechanics were identified through instrumented gait analysis. Abnormal running mechanics were defined as 20° or greater peak hip adduction (HADD). If peak HADD was > 20° bilaterally in a single subject, the lower extremity with the greatest peak HADD was used. All subjects were within an 18-35 age range and running at least 10 km a week. Exclusionary criteria consisted of any form of lower extremity resistance training for at least 90 days and prior musculoskeletal injury or surgery. The runners were randomly assigned to either a training group (TR) or a control group (CON), and then matched on age and running distance. All subjects were blinded to the kinematic criteria for enrollment, so that conscious changes to running mechanics were avoided. MVICs for hip abduction (HABDS) and hip external rotation (HERS) was also collected. The strength values were then normalized to body weight and lever arm length (%Bw*m). The subjects assigned to the TR group completed a 6 week program targeting the hip abductors and external rotators. All exercises were performed bilaterally and 2 sets of 10 repetitions were completed. Every week the participants were given 2 new exercises to perform. Exercises during weeks 1 and 2 were performed non-weight-bearing then progressing to weight-bearing for weeks 3-6. During weight-bearing exercises verbal cues and visual feedback, through the use of mirrors, were given to participants to help maintain proper lower extremity alignment. The single-leg squat was introduced at week 4 and progressively became more difficult each week by decreasing external support and eventually adding a resistance band around the leg which imparted an adduction force. The control group, however, did not undergo a hip strengthening program and only required to continue their weekly running distance for the remainder of the study. After 6 weeks, all participants returned for follow-up strength and motion analysis utilizing the same techniques as described earlier. While the training program was able to improve the strength of the TR group (HABD 41.6%+21% Bw*m, HERS 40.0%+12.5% Bw*m), there was no significant reduction in peak HADD, hip internal rotation (HIR) and contralateral pelvic drop (CPD) overtime during running or compared to the CON group at either baseline or post-training. However, peak HADD, HIR and CPD while performing a single-leg squat did improve after the intervention. Also of note, the contralateral pelvis of the TR group was elevated by nearly 4° during the single leg squat.
Although significant strength gains were found in the TR group, that alone may not be enough to improve abnormal knee frontal plane running mechanics. The authors suggest that activity-specific neuromuscular training might be indicated to improve running mechanics. The improvements found in the single leg squat were encouraging and are commonly thought to translate to dynamic function. However, due to the lack of improvements in running mechanics this study raises the question about the use of a single leg squat to evaluate overall function. In addition, although all of the subjects were classified as having abnormal running mechanics, all subjects reported to be perfectly healthy, which leads us to ask: 1. Should hip strengthening be used clinically to improve running mechanics, or is muscular endurance and neuromuscular training potentially more important? 2. If a runner has “abnormal” running mechanics, but no injury, is there any point at attempting to correct their mechanics?
Written by: Mark Rice
Reviewed by: Stephen Thomas
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I am one of the co-authors on the paper, so perhaps I can provide some insight into our participants that might help answer your questions.
Our participants all had abnormal proximal mechanics during running, which we operationally defined as excessive HADD. While they did not have any active injuries, I did ask them about their injury history. Of the 20 who qualified (we kinematically screened 43 "healthy" runners), 4 reported a previous tibial stress fracture, 6 reported previous Iliotibial band syndrome, 5 reported previous episodes of PFPS, 4 reported plantar fasciitis. Obviously, some reported a combination of those injuries. In fact, 2 of the control subjects eventually developed PFPS in the next 12 months and ended up as volunteers in an intervention study on PFPS that we did. I think this is pretty reflective of the high rate of injury typically reported by runners (van Gent, 2007).
A second point that was made in the review is interesting as well: "this study raises the question about the use of a single leg squat to evaluate overall function." Willson, 2008 suggested that females with PFPS who run with abnormal proximal mechanics, tend to squat and jump with them as well. What our findings merely suggest is that just because we alter the mechanics of one of those therapeutically, you might not see changes in the mechanics of the other activities occur in turn.
To reiterate a point in the article, we only looked at changes in peak torque production. Obviously, there are other gluteal muscular performance factors that may affect mechanics in a similar cohort that we did not examine(endurance, rate of force production, timing and duration of activation.
Thanks for reviewing the article!
Richard Willy, PT, PhD, OCS
Thank you for taking the time to read this post and provide feedback. Having one of the co-authors chime in to help bring us more clarity and insight is great! Anything that we can get our hands on to be able to apply it clinically is a bonus.
You mentioned an PFPS intervention study following this one. What types of variables are you looking at and were you able to apply anything from this study to it's methodology?
Mark Rice MS, ATC
We looked at essentially the same variables, but also with step descent. We focused on a more neuromuscular intervention for PFPS.
The possible reason for the lack of improvement in running mechanics from the improvements in the single leg squat could be explained from the fact that running occurs primarily in sagittal plane. Although the single leg squat is also a sagittal plane motion, the benefits from the single leg squat training in this study are reduced hip adduction, hip internal rotation, and contralateral pelvic dro, which are not constricted in a single plane. These improvements might be critical factors in preventing injuries in other sports where multi-plane activities, such as cutting and pivotting are common. However, running mechanics are invovled with single plane activities compared to other sports.
Maya, Thanks for the comment. Another thing to consider is that there is an explosive nature to the movements of running. Running requires a rapid transition from heel strike to toe off. Instead the squat is more gradual and controlled. It could be a specificity of training issue. It's definitely true that running is predominantly a sagittal plane activity but there's also a lot of activation of hip rotators and abductors as they try to ensure sagittal movements without deviations into hip adduction or rotation.