Point-Counterpoint: Can Toning Shoes Have A Legitimate Impact?

Author(s): 
David Y.S. Yee, DPM, FACFAOM, and Eric Fuller, DPM

Yes.

Aside from the toning shoes’ benefits on muscle toning and core strengthening, this author says one can also incorporate the shoes into treatment plans for numerous podiatric conditions.

By David Y.S. Yee, DPM, FACFAOM

In recent years, rocker-sole toning shoes have garnered an increasing share of the athletic shoe market. Patients in my practice have asked about them on a weekly basis and many new patients have presented wearing toning shoes when establishing care with my office.

   Just as television and magazines have heightened patient interest in brand-name prescription drugs and driven physician prescribing habits, media impressions have driven patient interest in rocker-sole shoes. This has forced us to look into the possibility of prescribing these shoes or at least have a working knowledge of them.

   How do they work? Rocker-sole shoes, according to advertiser messages, improve balance, improve muscle strength and tone, maximize calorie burn, reduce joint impact, improve circulation and improve posture.1,2 Their effect is a result of the inherent instability of the shoe’s design, which facilitates sagittal plane motion. The foot and lower leg “rock” forward as weight transfers from the heel to toe during gait in a smooth progression. This changes the forces acting on the joints and activates muscles to control some of the instability.3,4

   While the recent, highly publicized American Council on Exercise study refutes the claims that rocker-sole shoes impact exercise intensity, calorie consumption, muscle strength and muscle tone, be aware that the study design had many shortcomings.5 The test subject group was small, the timeframe of the study was short and the study only measured the shoes’ effects on muscles proximal to the ankle joint instead of the smaller extrinsic foot muscles that researchers believe are neglected when people wear more traditional athletic shoes.6 By comparison, numerous studies have confirmed the small but definite benefits of rocker-sole shoes in the areas of muscle workload, postural sway and metabolic activity.6-9

What The Literature Shows About The Clinical Benefits Of Rocker Sole Shoes

In addition to their advertised, exercise-associated benefits, rocker-sole toning shoes can also be helpful in treating a variety of foot problems.

   Metatarsalgia. Whether due to bursitis, capsulitis, neuroma or osteoarthritis, metatarsalgia is aggravated by abnormally high forefoot pressures during weightbearing and gait. The use of rocker-sole shoes can allow for a smoother, faster progression of weightbearing pressures across the foot and distributes weightbearing pressure onto the heel and arch, away from the metatarsal heads.10

   Digital fractures. Rocker-sole shoes decrease forefoot pressures during gait but paradoxically increase pressures on the tips of the toes.11 While this finding would suggest that this would cause pain and inflammation in patients with digital fractures, the stiff midsole of the rocker-soled shoe will prevent movement of the fracture fragments. Whether patients use it alone or with a forefoot “stiffener” made of cardboard or wooden tongue depressors, the rocker-sole shoe can be an “inconspicuous” postoperative shoe.

   Hallux limitus/hallux rigidus. The stiff midsole and rocker sole allow smooth transition of weightbearing pressures from heel to toe without causing dorsal jamming of the first metatarsophalangeal joint.10

   Plantar fasciitis. The raised heel elevator/soft rearfoot wedge relaxes the tension on the plantar fascia and reduces heel strike pressures. The raised heel elevator also relaxes the Achilles tendon and therefore reduces the tension on the plantar fascia from the windlass mechanism.10

   Achilles tendinitis and retrocalcaneal bursitis. The heel elevator/soft rearfoot wedge also relaxes the tension on the Achilles tendon and reduces inflammation and pain.8,12,13 The rocker sole aids in forefoot roll-off and increases ankle joint dorsiflexion at initial contact and greater plantarflexion at toe-off. The rocker sole causes increased ankle joint range of motion. The sole also places the Achilles on an active stretch during the midstance phase of gait and may serve as a mild stretching force.

   Pre-ulcerative keratosis in patients with diabetes. Rocker-sole shoes can reduce pressure under the heel and metatarsal heads by 35 to 65 percent.6,14,15 Patients can use rocker-sole shoes prophylactically to treat patients at risk for rearfoot and central ray ulcerations.6 One can further improve the efficiency of the shoe by the presence of accommodative insoles.14,16

   Knee osteoarthritis. Preliminary studies have shown that rocker-sole shoes can reduce knee pain in overweight patients.6 Theories behind this effect include: reduced joint loading and pain by strengthening the small pedal muscles; increased quadriceps activity during mid-to-late stance while walking; reduced peak knee adduction movement; and/or increased knee flexion angles.

What Are The Caveats For Using Rocker-Sole Shoes?

While rocker-sole shoes may have exercise-related and therapeutic indications, their use is not completely without risk. Anecdotal reports have linked the use of rocker-sole shoes with sciatica, hip fractures, ankle fractures and Achilles strains.4,17-18 As a result, I suggest addressing several issues prior to prescribing rocker-soled footwear.

   1. The patient should review the DVD or instructional booklet that accompanies the shoes. The stretching program should start prior to the use of these shoes, especially in tight, “out-of-shape” patients at risk for straining their Achilles. An “active stretching program” (i.e., night splints, therapeutic stretching and/or physical therapy) may also be necessary to prevent injury.4

   2. One should correct limb length discrepancy to prevent musculoskeletal aches and pains. While most patients with limb length discrepancy are asymptomatic while using conventional shoegear, increased pedal movements secondary to the inherent instability of the rocker may cause unilateral pains in the foot, ankle, leg, knee, thigh, hip and/or back. This is a result of excessive strains on the “longer” lower extremity as it goes through pronation-induced malalignments to get the foot on the “shorter” leg to the ground. One should correct for structural and functional components when using rocker-sole shoes.

   3. Patients cannot use rocker-sole shoes with foot orthotics, a fact noted in the instruction materials supplied with the shoes.1,2 The inherent instability of the shoes runs contrary to the concept of the stabilizing effect on the function of the foot imparted by a custom-molded foot orthotic.19 The instability of these shoes may exert high torques on the joints of the foot and ankle, and excessive tension on ligaments and tendons. This may result in overuse injuries. With that said, I do sometimes fit rocker-sole shoes with heel lifts, prefabricated scaphoid pads and metatarsal cookies to provide small, nondescript “generic” corrections on foot function if the patient is still symptomatic despite the use of this footwear.

   4. One must evaluate equinus prior to the use of rocker-sole shoes. Equinus is a deformity characterized by a decrease in ankle joint range of motion, usually less than 10 degrees ankle joint dorsiflexion.20 Evaluating the type of equinus (i.e., osseous versus soft tissue) and the means by which the patient compensates for the equinus during gait will improve the efficiency of shoe gear.13 A more flexible foot allows for greater compensatory pedal movements in a rocker-sole shoe while a more rigid foot type will place more torque on the pedal joints due to excessive range of motion on the pedal joints.

   5. Patient selection is essential to the success of prescribing rocker-sole shoes. Healthy, able-bodied adults, obese patients and patients experiencing plantar foot pains will benefit from the use of rocker-soled shoes. On the other hand, do not prescribe rocker-sole shoes to patients at risk for falls, patients with compromised balance and patients who are severely out of shape.6

In Conclusion

While more studies need to occur to establish the efficacy of rocker-sole shoes on exercise, they will become a fixture of every podiatric practice simply because the aggressive advertising campaigns of the manufacturers place them front and center in the minds of almost every patient entering our offices.

   Every podiatrist needs to have a basic understanding of the shoes’ effects on the human foot in order to take proper precautions and place shoes in an appropriate position in the treatment armamentarium.

   Dr. Yee is in private practice in Honolulu and is a member of the staff of Straub Clinic and Hospital in Honolulu. He is a Fellow of the American College of Foot and Ankle Orthopedics and Medicine.

References
1. Skecher Shape Ups instructional DVD.
2. MBT physiologic shoegear instructional pamphlet.
3. American Academy of Podiatric Sports Medicine statement on toning shoes, 2011. Available at http://www.aapsm.org/toningshoes.html .
4. Cheskin M. The rocker sole revolution. Podiatr Manage. 2010; 29(8):89-96.
5. Porcari J, Greany J, Tepper S, Edmonson B, Foster C, Anders M. Will toning shoes really give you a better body? American Council on Exercise. 2010; 8:1-4.
6. Landry SC. Unstable shoe designs: functional implications. Lower Ext Rev. 2011; 3(3):31-36.
7. Landry SC, Nigg BM, Tecante KE. Standing in an unstable shoe increases postural sway and muscle activity of selected smaller extrinsic foot muscles. Gait Posture. 2010; 32(2):215-19.
8. Myers KA, Long JT, Klein JP, Wertsch JJ, Janisse D, Harris GF. Biomechanical implications of the negative heel rocker sole shoe: gait kinematics and kinetics. Gait Posture. 2006; 24(3):323-330.
9. Gasser BA, Stauber AM, et al. Does wearing shoes with unstable shoe construction stimulate metabolic activity in lower limbs? University of Bern Switzerland, 2008.
10. McCurdy B. Study says toning shoes don’t live up to the hype. Podiatry Today. 2010; 23(9):12.
11. Stewart L, Gibson JNA, Thomson CE. In-shoe pressure distribution in “unstable” (MBT) shoes and flat-bottomed training shoes: a comparative study. Gait Posture. 2007; 25(4):648-51.
12. Long JT, Klein JP, et al. Biomechanics of the double rocker sole shoe: gait kinematics and kinetics. Gait Posture. 2007; 40(3):2882-2890.
13. Kirby KA. The effect of shoe design parameters on foot function. March 1987. Foot and lower extremity biomechanics: a ten-year collection of Precision Intricast newsletters. Precision Intricast, Inc., Payson, AZ, 1997, pp. 87-89.
14. Praet SF, Louwerens JW. The influence of shoe design on plantar pressures in neuropathic feet. Diabetes Care. 2003; 26(2):441-5.
15. Brown D, Wertsch JJ, Harris GF, Klein J, Janisse D. Effect of rocker soles on plantar pressures. Arch Phys Med Rehabil. 2004; 85(1):81-86.
16. Foster JB. Forefoot plantar pressures respond to rocker bottom diabetic footwear. Lower Ext Rev. 2011; 3(5):11.
17. Can rocker sole shoes cause sciatica? Available at http://bit.ly/v3dsC4 .
18. Skechers Shape-Ups shoes blamed for hip injuries/Injury Board Kansas City. Available at http://bit.ly/rERLEc .
19. Busman P. Letters to the editor: rocker bottoms. Podiatr Manage. 2011; 30(5):30.
20. Root ML, Orien WP, Weed JN. Normal and abnormal function of the foot, vol. II. Clinical Biomechanics Corp., Los Angeles, 1977, p. 38.

   For further reading, see “Key Principles To Evaluating Athletic Footwear” in the September 2010 issue of Podiatry Today.

No.

Although this author acknowledges that toning shoes may have some positive impact for people with certain conditions, he cites biomechanical concerns and a lack of evidence that the shoes cause increased muscle activity and increased toning.

By Eric Fuller, DPM

The most common way to strengthen a muscle is to use it. Conversely, non-use of a muscle results in the muscle becoming soft and a corresponding loss of muscle tone. For a toning shoe to work, it has to make the person use the muscle. For a toning shoe to be better than a regular shoe, it has to work the muscle more than a regular shoe without increasing the risk of injury.

   One of the problems with the question of whether toning shoes are effective is that there are so many different modifications of shoes and shoe manufacturers claim these modifications make the shoes toning shoes. However, it is important to consider the biomechanical impact of different aspects of shoes in relation to the shoes’ ability to significantly increase muscle activity.

A Closer Look At The Biomechanical Effects Of Toning Shoes

In a search for toning shoes, I found several different types of shoes with manufacturer claims of being toning shoes. The first category is the sagittally unbalanced shoe. The Masai Barefoot Technology (MBT, MBT Marketing and Trading) is a classic example of this. The thickest part of the shoe’s midsole is approximately 50 percent of its length. If you were to try and stand with the sole of your foot parallel to the ground, you would have to balance on a point. It is like trying to stand on a narrow stick that is perpendicular to the length of your foot. It is possible to balance on this stick but it will take some effort to do so. Some will choose to put all their weight on the heel and stand with the foot dorsiflexed at the ankle. Others may stand in a plantarflexed position with their weight on the forefoot.

   In each case, balancing with the foot level and the weight on the heel or the forefoot, the muscles of the lower leg will have to work harder than in regular standing. In regular shoes or even barefoot, the anterior tibial and triceps surae muscles shift weight under the foot to control postural sway in the sagittal plane. If the shoe wearer chooses to put weight on the forefoot, then the triceps surae will be working harder.

   Therefore, one can make a case for toning the calf muscles if shoe wearers make the subconscious choice to put weight on the forefoot. The shoe wearers may not necessarily do that because they still have the option of trying to balance with the foot level or putting the weight on the heel. Therefore, there is a potential upside of increased toning.

   On the other hand, there is a potential downside to using a sagittally unbalanced shoe. If the shoe wearer chooses to put weight on the heel with the foot dorsiflexed and the anterior tibial muscle contracting, this may cause some injuries. Constant contraction of the anterior tibial or triceps surae could cause tendonitis in the tendons of those muscles. When people are balancing over these shoes, they will be standing on a smaller surface area in comparison to regular shoes. Most normally healthy people should be able to balance over this reduced area but anyone with concerns about balance or falls probably should not use these shoes.

   I had a patient recently who had Achilles tendonitis that got worse with wearing this style of shoe. I know many people who choose to wear the sagitally unbalanced shoes for many different reasons. The shoes will change how you walk and this change may benefit some people. These shoes are generally rigid, which can also benefit people with problems like hallux rigidus. However, beyond the effect on the calf muscles, there is no reason to believe the gait changes will firm the buttocks and thighs.

   There are also claims of anterior rocker soles being a form of toning shoes. This type of shoe has equal thickness of the midsole in the posterior 60 to 80 percent of the shoe and tapers to essentially zero thickness at the very tip of the shoe. This type of shoe has been in use for a long time to reduce the pressure on the forefoot in the treatment of plantar ulcers. The rocker effect happens when the person tries to put weight on the forefoot. The shoe cannot push back but it can roll forward. What this does is shorten the lever arm of ground reaction force at the ankle. In other words, there is less resistance for the ankle plantarflexors. Therefore, this type of shoe will not act as a toning shoe at all. On the other hand, it would be good for someone with Achilles tendonitis.

   A third type of shoe is unstable in the frontal plane. One type of this shoe has a partial sphere or spheres on the bottom of the sole. The effect is the same as balancing on a narrow stick that is parallel with the length of the foot. Just as with the sagittally unbalanced shoe, the shoe wearer has to make some conscious or unconscious decisions on how to stand in the shoe. The shoe wearer can choose to either invert or evert the foot so the sole contacts at the edge and the bottom of the spheres to create a relatively more stable platform or an attempt to balance on that “stick.” The muscles that would have increased activity would be the invertors or the evertors. These muscles are relatively small and are not going to burn a significant amount of calories to qualify this shoe as a shoe that will tone the calf, thighs and buttocks.

   As with the other aforementioned shoe types, there has to be some concern about problems that may surface. To balance on a narrow base of support, the invertors and evertors will be working constantly. Feet that are prone to either posterior tibial or peroneal tendonpathy will be at risk with this increased activity of the muscles. If the shoe wearer chooses to stand highly inverted or everted, there is further chance for strain on various anatomical structures. In gait, these shoes could also be increasing the risk for ankle sprains in feet that are already laterally unstable.

   A final category of toning shoes is the heelless shoe. These shoes have a platform under the forefoot and the heel is suspended in the air. To stand in these shoes, patients will constantly need to contract the gastroc soleus muscle group. Obviously, patients will be using the gastroc soleus muscles in these shoes more than other shoes in general. Would patients then be using these muscles too much? Another question is how much work patients need to do to increase muscle strength. Do they really need to be constantly contracting their triceps muscles to increase strength?

   This question is also relevant for all the other types of toning shoes. If you look at weightlifting as a way of increasing strength, experts suggest anywhere from six to 20 repetitions of lifting a weight is sufficient, noting that patients do not need to have constant contraction of a muscle to increase strength.

What Recent Studies Reveal About Toning Shoes

To test the effectiveness of the shoes and evaluate the claims behind them, Porcari and colleagues designed a pair of studies.1 One study evaluated patients’ exercise responses to walking in traditional athletic shoes versus toning shoes. The second study focused on patients’ muscle activation in regular athletic shoes in comparison to toning shoes.

   For the first exercise response study, researchers evaluated 12 physically active female volunteers, ranging in age from 19 to 24.1 All patients completed a dozen five-minute exercise trials in which they walked on a treadmill for five minutes wearing a traditional running shoe (New Balance) and a toning shoe. The shoe order was randomized as patients walked at 3.0 mph with a 0 percent grade hill; at 3.5 mph/0 percent grade; and at 3.5 mph/5.0 percent grade. The authors also monitored patients’ oxygen consumption, heart rate, ratings of perceived exertion and expenditure of calories.

   To measure muscle activation in the second study, Porcari and colleagues evaluated physically active female volunteers, ranging in age from 21 to 27.1 Similar to the first study, these patients performed a battery of five-minute treadmill trials, rotating between traditional and toning shoes at random. Using electromyography (EMG), the researchers measured muscle activity in six areas: the gastrocnemius, the rectus femoris, the biceps femoris, the gluteus maximus, the erector spinae and the rectus abdominis. To determine the baseline for electromyography analysis prior to testing, researchers used manual muscle techniques to study maximum voluntary isometric contractions in all muscles.

   In both studies, researchers found that none of the toning shoes showed statistically significant increases in either exercise response or muscle activation during any of the treadmill trials.1 Although Porcari and co-workers said that at times patients favored the running shoes and at times favored toning shoes, they noted nothing statistically significant. The authors concluded that there is no evidence to support the hypothesis that toning shoes will aid shoe wearers in exercising more intensely, burning more calories or improving their muscle strength and tone.

   How do researchers account for the anecdotal evidence (found on blogs and other sources) from those who wear toning shoes and claim their muscles get sore, which must mean the shoes are working?

   Porcari and colleagues explain that since patients are walking on an inch of cushioning, their feet feel different in the toning shoes and they may be sore because they are using different muscles.1 However, the authors note that patients’ muscles would be sore while wearing any shoes they are not used to wearing and that feeling of soreness will not translate into toning glutes, hamstrings or calves.

In Conclusion

There are some legitimate uses for some of these shoes. An anterior rocker shoe can help reduce the load on the Achilles tendon or the forefoot. The sagittally unstable shoes certainly have a lot of testimonials to their success. However, if the studies show there is no increase in muscle activity of the muscles of the thigh and buttocks, then there is no reason to expect that toning shoes will have a legitimate impact on increasing the tone of those muscles. There is also no reason to expect that these shoes will cause people to burn any more calories than if they are out exercising anyway.

   Dr. Fuller is in private practice at Berkeley Foot Specialists in Berkeley and Orina, Calif.

Reference

1. Porcari J, Greany J, Tepper S, Edmonson B, Foster C, Anders M. Will toning shoes really give you a better body? American Council on Exercise. 2010; 8:1-4.

   For further reading, see “Study Says Toning Shoes Don’t Live Up To The Hype” in the September 2010 issue of Podiatry Today or the DPM Blog “Are The New Rocker Sole Sneakers Worth The Hype?” at http://bit.ly/bzX7SH .

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