Quick Hit Summary
The use of cushioned, arch supported shoes has long been championed as a way of preventing foot or lower body injury. However, the newest training craze, barefoot or pseudo barefoot (Vibram FiveFingers®, Nike Frees®) training, seems to fly in the face of conventional wisdom. Research indicates that barefoot training causes athletes to land on the balls of their feet when striking the ground. In contrast, individuals tend to strike the ground with their heels while wearing shoes. By striking the ground with the balls of one’s foot vs. heel, the initial impact, as well as the load felt by your knees and hip is reduced. Thus, it may be effective at preventing osteoarthritis. Additionally, barefoot training strengthens the intrinsic muscles of the foot, possibly preventing injuries such as plantar fasciitis. The use of other common footwear practices, such as wearing “cushy” gel inserts may not be the best idea in individuals with healthy knees as it too appears to have negative effects on both balance and joint function. Although barefoot training appears to have many benefits, I’m obligated to mention that long term studies are still required to support these initial findings. I strongly encourage you to work barefoot training into your exercise routine. Kick off your shoes while resistance training, moving about the house, etc. However, for endurance runners, I caution you against taking it to fast, as this may cause injury. Please refer to the advice of Harvard researcher, Dr. Daniel E. Lieberman, when implementing barefoot or pseudo barefoot training into your routine.
Barefoot Training
In Part 1 of my barefoot training series, we examined how barefoot vs. shod (shoe) running affected running biomechanics, activation of the intrinsic muscles of one’s foot and how to work this mode of training into one’s exercise program. In this concluding piece we’re going to shift our attention a little bit and focus on potential injury implications of barefoot vs. shod training. In addition, we’re going to expand our view a little bit and evaluate the role that specialized shoe inserts may have on injury outcome.
Barefoot vs. Shod on Injury Risk
Figure 1 Are traditional running shoes benefiting our feet?27
So far we’ve the examined biomechanics of barefoot vs. shod training as well a few potential implications for physical performance. However, if I had to guess, the underlying reason as to why most athletes purchase shoes probably has little to do with stride lengths or VO2. Rather, the motivation is probably injury prevention. In simplistic theory, this dogma makes sense:
Running/training shoes (or inserts) absorb impact—> less stress put on joints—> preservation of connective tissue (cartilage, meniscus) within joints—> Yahoo, we can train hard till we die!
Unfortunately, things are not quite this simple. As discussed in Part 1, wearing shoes alters our running mechanics. See Figure 2 Although traditional running shoes (cushioned soles with arch support) do absorb shock, there are no studies to date which have actually demonstrated that wearing them protects athletes from injury8. On the flip side of the coin, evidence is mounting that traditional running shoes may promote knee arthritis and other joint dysfunctions.
Figure 2. As seen in the top picture, front foot strikes, which occurs while walking/running barefoot, leads to a gradual rise in force upon striking the ground. Walking barefoot also leads shorter, but faster strides vs. wearing shoes. As seen in the bottom picture, rear foot strikes, which occur while wearing shoes, are characterized by a rapid spike in impact forces. Please note that this figure does not represent the images of any one specific study. Rather, it’s a general trend seen in most studies on this subject.
Knee and Hip Loads while Running Barefoot
{ Please note that for the remainder of the studies, I will be discussing forces felt by different joints while wearing shoes or going barefoot. However these are estimated forces/torques as current technology does not allow us to measure the true value. How well these estimates reflect the actual load is debated25 }
Recently, Kerrigan et al. had 68 endurance runners (15+ miles/week; 37 males, 31 females; mean age- 34), complete treadmill runs both barefoot and while wearing running shoes9. During each run, joint torques were analyzed for the hip, knee and ankle. {For those unfamiliar with torques… They can be thought of as the force required to spin something about an axis. An example would be pushing down on a wrench to loosen a nut. The rotational force felt by the nut would be the torque}. Significantly greater joint torques were observed in all lower body joints (ankle, knee, hip) while running in shoes. Of greatest importance to joint health, a 38% greater torque (varus) and a 54% greater internal torque were found in the knees and hips respectively while running in shoes. As noted by Kerrigan et al., greater varus torques (at knee) increase pressure on the inside part of the knee, the most common site for cartilage/meniscus degeneration in this joint. This load is somewhat alarming considering an increased varus knee torque of only 4% “is of extreme clinical relevance” while running10.
Knee and Hip Loads while Walking Barefoot
Shakoor & Block also found improved joint loading dynamics while walking barefoot11. In their study, 86 individuals (mean age- 59 years), with knee osteoarthritis (OA), were analyzed while walking barefoot and with shoes on. While walking barefoot, varus knee loads were reduced by 11% vs. shod conditions. Additionally, hip loads decreased by 4-11% (varied depending on type of load looked at- external rotation, internal, etc) when walking barefoot. Other studies have found similar reductions in varus knee loads in patients with OA12.
Recently, Shakoor et al. performed an interesting study looking at the effects of different popular shoe types and their effects on joint stress in 31 individuals (mean age- 57 years) with knee OA13. Each individual had their joint mechanics analyzed while they walked in the following foot wear types:
(Shoe model followed by characteristics)
- Dansko® clogs- rigid, stiff sole, provides cushioned support, heels elevated
- Brooks Addiction® stability walking shoes- “often prescribed for foot comfort and stability during walking.”13 Heels elevated and shoes are more rigid in design
- Puma H-Street®- “flat, flexible shoe allowing for significant foot mobility”13
- Flip Flops- made of flexible rubber
- Barefoot
After completing walking trials using each choice of shoe, it was found that the Dansko® clogs and Brooks Addiction® stability shoes increased stress on the inside part of the knee (ie- varus load) by 7-15% vs. all other conditions13. No significant differences were present on varus knee load between Puma H-Streets®, flip flops and barefoot walking. Additionally, the lowest impact forces upon striking the ground were found while barefoot. The research team went on to state that…
“It may be that the flexible movement of a bare foot is biomechanically advantageous. The natural flexion of the foot upon contact with the ground may attenuate proximal joint impact, compared to artificial “stomping” movement created by a stiffed-sole shoe.13”
and concluded by saying,
“In summary, we report that flat, flexible footwear are associated with significant reductions in dynamic knee loads during ambulation, compared to supportive, stable shoes with less flexible soles.13”
Shock Absorbing Cushions
In attempts to take a “proactive” approach to preserving knee health, many individuals buy cushioned sole inserts for their shoes. These inserts are routinely sold over the counter at many shoe stores. I’m guessing that at some point in your life a checkout man/lady has said to you… “Would you be interested in adding a pair of shoe inserts (shock absorbing) to that purchase?” Although the theory makes sense (see above dogma) from a simplistic point of view, full length shoe inserts have actually been shown to increases joint stress. This was observed in a study completed by Franz et al10. In their study, 22 healthy endurance runners (12 males, 10 females; mean age- 30 years), ran in running shoes as well as running shoes + full length, arch supported cushioned inserts. Compared to running in shoes alone, the research team found that the shoes+inserts increased varus knee torque by 4%. While walking under the same experimental conditions, varus knee torques were once again higher (6%).
Besides potentially increasing joint stress, cushioned inserts may also promote falls. In multiple studies led by Dr. Steven Robbins, it was shown that shoes with thick, soft midsoles decreased balance141516. These results were present in both healthy older men (25 participants; age >60 years)16 as well as younger men (13 participants; mean age- 32 years)15. For example, in the younger population, thick midsoles increased loss of balance by >50% (5.8 balance failures/100 attempts to 8.9 balance failures/100 attempts).
Shoes and Inserts Specific to Foot Design
The above studies looking at the differences of barefoot vs. shods and shods vs. shods+inserts used primarily neutral running shoes. In other words, they were fitted for size, but not necessarily specific to an individual’s foot arch (high arch, low arch, etc). Thus, it’s possible that shoes/inserts are only effective when fitted in accordance with foot design.
Knapik et al. examined if the use of shoes, specific to one’s arch structure, was more effective than “neutral” control shoes with respect to preventing injuries17. Their study involved 3062 men and women who were completing the US Army’s 9 week basic combat training. For the duration of the study, each individual trained in either a control shoe (neutral stability arch) or footwear that was specific to their arch type. At the end of the study, it was found that shoes specific to ones foot type were no more protective than standard shoes with respect to preventing injuries. This held true regardless of if you were looking at overuse injuries (shin splints, plantar fasciitis, etc), lower body only injuries, or a combination of all orthopedic injury types. In similarly designed studies, Knapik et al. found nearly identical results in 2676 individuals completing the US Air Force’s 6 week basic military training18as well as a 12 week study involving marines who were fulfilling their Basic Training requirements19. In personal communication with lead author, Dr. Joseph Knapik, ScD, I asked him if he felt results would differ if the study was carried out over an even longer time frame. In response he said,
“I cannot say for sure what would happen over a longer period. My guess is that the shoe assignment technique would not make any difference in the longer term.”19
On the other hand, there is research supporting the use of shoe inserts in individuals suffering from knee OA. Kerrigan et al. demonstrated a 6%-8% reduction in varus knee loads while wearing shoes with lateral wedge supports vs. shoes without lateral wedge shoe inserts20. Similar reductions in varus knee load have been shown in healthy individuals as well21. In a study completed by Maclean et al., it was found that wearing custom made foot orthotics for 6 weeks decreased chronic knee pain in 12 endurance runners22. Unfortunately, none of these studies examined barefoot vs. shoe insert conditions.
To my knowledge, only one study has examined barefoot vs. shoe inserts on varus knee loads. Kuroyanagi et al. actually found that lateral wedges decreased varus loads 8-13% vs. barefoot walking in a group of 21 older individuals (mean age- 72 years)23. However, there is a caveat worth mentioning. The study participants never actually wore shoes; rather special insoles (with lateral wedges) were strapped to their feet. If these same results would have been found while actually wearing shoes (vs. just the insoles strapped to feet) is unknown. That being said this study does show that some individuals may receive some benefit with lateral wedge inserts vs. barefoot conditions. From a clinical standpoint, I was informed by lead author, Dr. Yuji Kuroyanagi, that these lateral wedges are used quite often in Japan and do provide pain relief to those with knee OA28.
In summary of this “injury” section… There are a couple studies indicating that special inserts may reduce pain in those with existing injuries. However, there is no current evidence that specially designed arch supports or running/walking shoes prevent injury8. On the other hand, barefoot training does appear to have a positive impact on joint loads and strengthens the intrinsic muscles of the foot. However, I feel obligated to mention that there are no scientific studies to date that have shown that barefoot training leads to a lower rate of injury than wearing shoes. Long term studies are still needed in this area for more definitive proof.
Working barefoot into your program
(This section originally appeared in part 1 of this 2 part article. However, its worth stressing again.)
Many advantages appear to be present with barefoot training. I’d recommend switching over to barefoot resistance training as soon as you’re comfortable (Just don’t drop any weights… Speaking from experience, dropping a weighted implement onto your bare foot has a little more of an OUCH factor to it!). Also, for around the house type stuff, or going to the store type activities, kick off you shoes entirely or go pseudo-barefoot (ie- Vibram FiveFingers ® Nike Frees ®, etc).
If you’re interested working barefoot or pseudo-barefoot training into your endurance exercise program, I wouldn’t recommend quitting “cold turkey” with respect to your training shoes. Doing so would actually increase your risk of injury as you’d be putting demands on your body that it’s never experienced. For example, one’s calf and Achilles tendon face much greater stresses when barefoot training (due to FFS/MFS vs. RFS that occurs in shoes). In addition, after wearing shoes for our entire lives, our feet are actually misshaped. According to research conducted by K. D’Aou et al., wearing shoes appears to decrease both the length and width of our feet24. Thus, your lower body won’t be able to handle the physical demands of barefoot training as well as someone who grew up not wearing shoes. I’m not trying to discourage you from running barefoot, I just want to emphasize that you should BE SMART & TAKE IT SLOW!
With respect to working barefoot training into your endurance training program, I highly recommend taking the advice of Harvard researcher, Dr. Daniel E. Lieberman, lead investigator of the famous barefoot study that most advocates rally around in support of the movement25.
CLICK HERE FOR DR. LIEBERMAN’s RECOMMENDATIONS/TIPS
Bottom Line
Contrary to popular belief, the “less is more” approach seems to make sense with respect to foot wear. In comparison to traditional athletic shoes, barefoot training appears to limit stress on ones knee and hip joints. That being said, I must stress that long term studies are still needed in this area.
Also, there is no current research to support the idea of using special shoe inserts in healthy individuals. Buying “cushy” insoles actually appears to increase knee stress and decrease overall balance. On the other hand, for individuals with existing knee pain, customized shoe inserts appear to provide some relief.
In conclusion, short term studies indicate that barefoot walking helps reduce the stress placed on one’s knee and hip joints. However, one should SLOWLY work their way into barefoot training as recommended by Dr. Lieberman. If you start experiencing increased pain, by smart and back off.
Please know that I have no financial or other interest in any of the specific name brand shoes that I mentioned during this article.
References
8 Richards CE, Magin PJ, Callister R. Is your prescription of distance running shoes evidence-based? Br J Sports Med. 2009 Mar;43(3):159-62. Epub 2008 Apr 18.
9 Kerrigan DC, Franz JR, Keenan GS, Dicharry J, Della Croce U, Wilder RP. The effect of running shoes on lower extremity joint torques. PM R. 2009 Dec;1(12):1058-63.
10 Franz JR, Dicharry J, Riley PO, Jackson K, Wilder RP, Kerrigan DC. The influence of arch supports on knee torques relevant to knee osteoarthritis. Med Sci Sports Exerc. 2008 May;40(5):913-7.
11 Shakoor N, Block JA. Walking barefoot decreases loading on the lower extremity joints in knee osteoarthritis. Arthritis Rheum. 2006 Sep;54(9):2923-7.
12 Shakoor N, Lidtke RH, Sengupta M, Fogg LF, Block JA. Effects of specialized footwear on joint loads in osteoarthritis of the knee. Arthritis Rheum. 2008 Sep 15;59(9):1214-20.
13 Shakoor N, Sengupta M, Foucher KC, Wimmer MA, Fogg LF, Block JA. The effects of common footwear on joint loading in osteoarthritis of the knee.Arthritis Care Res (Hoboken). 2010 Feb 26. [Epub ahead of print]
14 Robbins S, Waked E, Allard P, McClaran J, Krouglicof N. Foot position awareness in younger and older men: the influence of footwear sole properties. J Am Geriatr Soc. 1997 Jan;45(1):61-6.
15 Robbins S, Waked E, Gouw GJ, McClaran J. Athletic footwear affects balance in men. Br J Sports Med. 1994 Jun;28(2):117-22.
16 Robbins S, Gouw GJ, McClaran J. Shoe sole thickness and hardness influence balance in older men. J Am Geriatr Soc. 1992 Nov;40(11):1089-94.
17 Knapik JJ, Swedler DI, Grier TL, Hauret KG, Bullock SH, Williams KW, Darakjy SS, Lester ME, Tobler SK, Jones BH. Injury reduction effectiveness of selecting running shoes based on plantar shape. J Strength Cond Res. 2009 May;23(3):685-97.
18 Knapik JJ, Brosch LC, Venuto M, Swedler DI, Bullock SH, Gaines LS, Murphy RJ, Tchandja J, Jones BH. Effect on injuries of assigning shoes based on foot shape in air force basic training. Am J Prev Med. 2010 Jan;38(1 Suppl):S197-211.
19 Knapik JJ. RE: RE: Injury rates in military recruits wearing shoes specific to arch type. Message to Sean Casey. May 6, 2010. Email.
20 Kerrigan DC, Lelas JL, Goggins J, Merriman GJ, Kaplan RJ, Felson DT. Effectiveness of a lateral-wedge insole on knee varus torque in patients with knee osteoarthritis. Arch Phys Med Rehabil. 2002 Jul;83(7):889-93.
21 Crenshaw SJ, Pollo FE, Calton EF. Effects of lateral-wedged insoles on kinetics at the knee. Clin Orthop Relat Res. 2000 Jun;(375):185-92.
22 MacLean CL, Davis IS, Hamill J. Short- and long-term influences of a custom foot orthotic intervention on lower extremity dynamics. Clin J Sport Med. 2008 Jul;18(4):338-43.
23 Kuroyanagi Y, Nagura T, Matsumoto H, Otani T, Suda Y, Nakamura T, Toyama Y. The lateral wedged insole with subtalar strapping significantly reduces dynamic knee load in the medial compartment gait analysis on patients with medial knee osteoarthritis. Osteoarthritis Cartilage. 2007 Aug;15(8):932-6. Epub 2007 Mar 27.
24 K. D’Aou, T.C. Patakyc, D. De Clercqd and P.The effects of habitual footwear use: foot shape and function in native barefoot walkers. Aerts. Footwear Science. Vol. 1, No. 2, June 2009, 81–94
25 Lieberman DE, Venkadesan M, Werbel WA, Daoud AI, D’Andrea S, Davis IS, Mang’eni RO, Pitsiladis Y. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature. 2010 Jan 28;463(7280):531-5.
26 Bergmann G, Heller MO. Re: The effect of running shoes on lower extremity joint torques. PM R. 2010 Apr;2(4):310-1; author reply 311.
27 Accessed June 11, 2010 from:flickr.com/photos/josiahmackenzie/3414064391/. Uploaded April 5, 2009, by Josiah Mackenzie.
28 Kuroyanagi Y. Effect of footwear on joint loads while walking. Message to Sean Casey. May 22, 2010. Email.