Saturday, November 4, 2017

Weightlifting Shoes: What Does Research Tell Us About WL-Shoes' Effect on Performance, Form & Muscle Activity?

Nice gimmick or must have gym equipment? Answer: "it depends".
People are investing more in gym-gear than ever before. $150, for example, for 25% discounted Adidas Weightlifting Shoes - is that a bargain or just a waste of money? Today's SuppVersity review will help you decide if weightlifting or O-lifting shoes, of which Bloomberg writes that they are among the fastest growing markets in sportswear (Bloomberg 2017), are a good or useless investment.

The distinguishing feature of all weightlifting shoes is the raised heel: the exact heights differ, but range from three-quarters of an inch to one inch and are implemented by solid wood or another hard, rigid material. With laces and a strap to tighten and narrow the fit, the shoes facilitate an optimal transfer of force to the ground... that's at least what the theory and shiny adds will tell us.
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Practically speaking, however, there's astonishingly little research to support a general advantage of weightlifting- over running-, or minimalist shoes for gymgoers. "Little" is not none, though, and thus reason enough for me to summarize the "little" science we have.

With the majority of the research involving squats, it makes sense to focus, at least for this basic research overview, on studies in which the squat performance, biomechanics and muscle activation with running shoes and/or minimalist/no shoes were compared to weightlifting shoes.
Table 1: Overview of studies comparing squatting in weightlifting shoes to other shoes/barefoot.
All in all, I was able to dig up 14 studies with 7-32 subjects (both male, female and mixed), each. Almost all subjects had previous squatting/weightlifting/strength training experience, were normal-weight and healthy. The various weightlifting shoes (as you would have expected, brands and models differed significantly) were mostly compared to running shoes and/or squatting barefoot. Alternatively, some studies used Vibrams or similar minimalist shoes as a comparison. A medium intensity (~60% 1RM) was chosen in most studies to prevent that high weights would compromise the form.

The study outcomes included 2D/3D kinematic analyses of the actual squat, measurements of the EMG activity of the subjects' leg (and in some cases trunk) muscles, the force (re-)distribution during the squat (measured with force plates = scales that can determine the gravitational force different parts of your feet exert on the ground), and direct measurements of the joint angles (vs. 2D/3D video analysis) by the means of electrogoniometers... all that with very heterogeneous results, I've briefly summarized for each of the N=14 studies in Table 1.

Let's take a look at some of the results to give you an idea of how much of a difference we're talking about

What the tabular overview in Table 1 doesn't really give you, though, is a visual representation of the differences that were observed in some studies. That's a problem because not every statistically significant difference is also practically relevant. Let's take a look at Fortenbaugh et al.  (2010; Figure 1), for example.
Figure 1: Comparison of squat kinematics between running and weightlifting shoes (Fortenbaugh 2010).
In their study, the scientists observed significant effects on horizontal trunk displacement and ankle peak flexion. With a quantitative difference of only 10% and 3%, respectively, and in the absence of measured shear forces, it is yet difficult to tell how practically relevant the "more vertical shank position and erect posture during squatting" (Fortenbaugh 2010) actually is. The fact that the optimal biomechanics will also depend on your individual physique (e.g. the ratio of leg to torso length, etc.) and variables like bar-positioning were often not even standardized within the individual studies (let alone between studies), doesn't make it easier to interpret the results.
Knees behind the toes? Not for everyone! And not thanks to weightlifting shoes. It is not necessarily a bummer that weightlifting shoes don't seem to have the general ability to allow lifters to keep their knees behind the toes while squatting. In fact, Legg et al. (2017) highlight that "limiting or restricting anterior knee translation results in compensatory movements at the hip and trunk"; changes of which coaches should know that they are, for some individuals, far more undesirable (e.g. greater trunk leaning = higher strain on the lower back) than the anterior shift of the knee.
The same goes for the results of a more recent study by Legg et al. (2017) whose 3D motion capturing study was more state of the art, but observe likewise only small magnitudes of changes in knee and ankle joint moments - and that without the often-advertised reduced chance of having your knees pass past your toes when squatting w/ the right gear: when depth and knee movement were unrestricted, the knees would very well be moving anteriorly beyond the toes during the squat movement, albeit with high inter-individual differences.

Heterogenous study design, heterogeneous outcomes

Even if we focus only on the more recent 3D (vs. older 2D) analyses of the movement patterns while squatting, studies by Wilkins et al. (2016), Sinclair et al. (2014) or Lee et al. (2017) report conflicting or null results with respect to the effect of using weightlifting shoes on the stability of the subjects' center of pressure. The same can be said for the results of EMG measurements, which reveal (in most cases) no relevant effect on trunk/leg muscle activation.

That some studies found (at least statistically) significant differences, while others didn't can be explained by dozens of confounding variables - with the three most important ones probably being:
  • differences in the weightlifting and control shoes that were used
  • the effect of training load which differed between studies (25-80% 1RM)
  • subject variables such as habituation to footwear, squat technique etc.
The number of studies is too small and direct comparisons (e.g. studies comparing different weightlifting shoes) as will as relevant data about the subjects (bar placement, habituation, etc.) are missing. Accordingly, I cannot make any definitive statements about the individual relevance of these and/or other factors with respect to null/conflicting results.

Let's assume there's a benefit. Who's most likely to see it?

While we have to handpick our studies to speculate about benefits, Legg's 2017 study suggests that people with limited hip mobility and those who are limited by their anthropometry (long legs) may benefit most from weightlifting shoes as these tools will allow them to squat deeper without having to compensate by leaning forward extensively (any heel wedge would probably do the same, though | cf. Charlton 2017 who used a 2.5-cm wooden block). The photo from

The more upright trunk position Legg et al. observed only in the unloaded trials and in novice athletes, though, could also be associated with a reduction of the strain on the lower back and makes weightlifting shoes attractive for people with pre-existing musculoskeletal problems. That the previously referenced study by Legg et al. confirmed that only for novice lifters, does yet put a bold question mark behind the practical relevance of this observation for the average SuppVersity reader.

Focus on quads?

Finally, it's also worth mentioning that the increase in knee flexion and thus quad involvement may come handy for athletes competing in sports where that's the muscle which makes the difference between victory and defeat.

On the other hand, we should not forget that anterior-/posterior-chain muscle imbalances (which usually favor the anterior chain) are pretty common. People who are already "quad dominant" will not necessarily want to increase their problem even more by squatting with weightlifting shoes.
Squats burn >35kcal+/min - regardless of the shoes you're wearing | more
What's the verdict, then? Long legs, problems w/ squatting deep and no muscular imbalances (quats >> glutes, hamstrings)? If that describes you well, you can but don't have to give weightlifting shoes a try. Overall, the changes in exercise kinematics seem to be small and consistent increases in performance and/or EMG activity haven't been recorded.

One thing we must not forget, though, is that everybody is different. Which is why the high inter-study and intra-study (inter-participant) differences are not surprising but rather in support of the importance of personal preference, as well as individual biomechanics. These will eventually determine if you're wasting your money or investing in a safer and more effective squat w/ weightlifting shoes for $100-250 | Comment!
References:
  • Beckham, G. K., Sato, K., Reed, J. P., Sands, W. A., & Land, D. H. (2014, May). EMG Activity Of Leg Musculature During The Back Squat With Weightlifting And Running Shoes. In MEDICINE AND SCIENCE IN SPORTS AND EXERCISE (Vol. 46, No. 5, pp. 822-822). 530 WALNUT ST, PHILADELPHIA, PA 19106-3621 USA: LIPPINCOTT WILLIAMS & WILKINS.
  • Charlton, J. M., Hammond, C. A., Cochrane, C. K., Hatfield, G. L., & Hunt, M. A. (2017). The Effects of a Heel Wedge on Hip, Pelvis and Trunk Biomechanics During Squatting in Resistance Trained Individuals. The Journal of Strength & Conditioning Research, 31(6), 1678-1687.
  • Fortenbaugh, D., Sato, K., & Hitt, J. (2010). The effects of weightlifting shoes on squat kinematics. In ISBS-Conference Proceedings Archive (Vol. 1, No. 1).
  • Hughes, G., & Prescott, S. (2016, May). EFFECTS OF FOOTWEAR ON SAGITTAL PLANE KINEMATICS AND CENTRE OF PRESSURE EXCURSION DURING THE BARBELL BACK SQUAT. In ISBS-Conference Proceedings Archive (Vol. 33, No. 1).
  • Josefsson, A. (2016). The Kinematic Differences Between a Barbell Back Squat Wearing Weightlifting Shoes and Barefoot.
  • Lee, S. P., Gillis, C., Ibarra, J. J., Oldroyd, D., & Zane, R. (2017). Heel-Raised Foot Posture Do Not Affect Trunk And Lower Extremity Biomechanics During A Barbell Back Squat In Recreational Weightlifters. The Journal of Strength & Conditioning Research.
  • Legg, H. S., Glaister, M., Cleather, D. J., & Goodwin, J. E. (2017). The effect of weightlifting shoes on the kinetics and kinematics of the back squat. Journal of sports sciences, 35(5), 508-515.
  • Nielsen, S. R. (2015). Posterior pelvic tilt in Barbell back squats: a biomechanical analysis (Master's thesis). 
  • Pilkinton, A. W. (2016). INVESTIGATION INTO THE BARBELL BACKSQUAT COMPARING WEIGHTLIFTING SHOES TO BAREFOOT CONDITIONS.
  • Sato, K., Fortenbaugh, D., & Hydock, D. S. (2012). Kinematic changes using weightlifting shoes on barbell back squat. The Journal of Strength & Conditioning Research, 26(1), 28-33.
  • Schermoly TP, Hough IG, Senchina DS. (2015). "The Effects of Footwear on Force Production during Barbell Back Squats. Journal of Undergraduate Kinesiology Research." Journal of Undergraduate Kinesiology Research 10 (2): 42-51.
  • Sinclair, J., McCarthy, D., Bentley, I., Hurst, H. T., & Atkins, S. (2015). The influence of different footwear on 3-D kinematics and muscle activation during the barbell back squat in males. European journal of sport science, 15(7), 583-590.
  • Southwell, D. J., Petersen, S. A., Beach, T. A., & Graham, R. B. (2016). The effects of squatting footwear on three-dimensional lower limb and spine kinetics. Journal of Electromyography and Kinesiology, 31, 111-118.
  • Teal, A. N. (2016) "The Effect of Sex and Footwear on Dynamic Changes during the Loaded Barbell Back Squat."  Masters Theses. 475.  http://commons.lib.jmu.edu/master201019/475
  • Whitting, J. W., Meir, R. A., Crowley-McHattan, Z. J., & Holding, R. C. (2016). Influence of Footwear Type on Barbell Back Squat Using 50, 70, and 90% of One Repetition Maximum: A Biomechanical Analysis. The Journal of Strength & Conditioning Research, 30(4), 1085-1092.
  • Wilkins, A. A., McLean, S. P., & Smith, J. (2016). Effects of Footwear on Performance in a Barbell Backsquat. In International Journal of Exercise Science: Conference Proceedings (Vol. 2, No. 8, p. 61).