SCIENTIFIC RESEARCH ON HEELLESS RUNNING AND JUMPING AND ON HEALUS SHOES
Reduced impact forces in heelless running shoes
Authors: Hartveld, A., Chockalingam, N., Greenhalgh, A. & Dunning, D.
Presented at Staffordshire Conference Clinical Biomechanics, 12th May 2006
Stoke on Trent, UK.
Running is beneficial for health but the high impact forces during heel strike contribute to a high injury rate amongst runners (Hreljac 2004). Landing on the heels during running and jumping is associated with high vertical impact forces (Hartveld & Chockalingam 2004, Williams et al 2000, Pratt 1989). A new shoe has been developed to reduce the initial increase in impact force during the foot strike. The Healus shoe is a shoe without a heel, but with a slanted sole, force transmission, force distribution and sense enhancement features, which allow the runner to avoid heel contact (Hartveld 2005a, b &c).
Kinetics of four mature male distance runners were assessed with a strain gauge force platform while running at 4.0 m/sec., 8 trials in conventional running shoes (Reebok Premier Competition) and 8 trials in Healus Technology shoes (Slant Sole – HSDXXV). The chronological time order was varied. They were instructed to run comfortably as they used to in real environments. The runners adjusted their stride 10 meters in front of the force plate and did not adjust their stride when running close to or on the force plate.
To compare the shoe effects on the vertical ground reaction force (Fz) variables two sample T-tests were performed and a significance level of p<0.01 was chosen. The results indicated significant reductions in Fz at 25msec into the stance phase for all 4 runners (27.0% - 58.8% average reduction) when running in the Healus Technology shoes. The maximum Fz was only significantly reduced with one runner (-0.6% - 4.5% average reduction when in the Healus shoes). The initial loading rates when running in the Healus shoes were significantly reduced with 3 out of the 4 runners (31.4% - 84.5% average reduction). The maximum loading rates when running in the Healus shoes were significantly reduced with 2 out of the 4 runners (-3.9% - 43,6% average reduction). There were no significant order effects.
The results led to conclude that Healus Technology has the potential of reducing impact forces, which would allow runners to run more often and for longer without injuries.
Shock absorption during jumping barefoot and in shoes
Authors: Hartveld, A.1 & Chockalingam, N.2
1Staffordshire Exercise Partnership (StEP), Stoke on Trent
2School of Health, Staffordshire University, Leek Road, Stoke-on-Trent
High impact forces during jumping contribute to the development of overuse injuries. This investigation uses a single subject and measures vertical ground reaction forces whilst jumping down from a platform with different movement strategies. The maximum vertical ground reaction force (Fz) and the loading rate during the landing phase of jumping down was much reduced when the subject was instructed to jump with maximum knee flexion and with forefoot landing [mean Fz of 1,718 ± 283 N as opposed to 5,406 ± 968 N (p<0.001) and a mean loading rate of 33,831 ± 13,426 N/sec as opposed to 446,431 ± 204,685 N/sec (p<0.001)]. There were no significant differences in impact forces between the barefoot and shod conditions (p = 0.05). The results of this study indicate that impact forces are reduced when a person jumps with increased knee flexion and lands more on the forefoot. Furthermore, this study suggests that although the soles of basketball and running shoes might have the capacity to reduce impact, this effect is often cancelled out as a result of adapting various movement strategies.
Increased levels of physical activity reduce people’s risk of coronary heart disease, hypertension (National Service Framework [NSF] Coronary Heart Disease 2000), depression (NSF Mental Health 1999), diabetes (NSF Diabetes 2001), osteoporosis (NSF Older People 2001), some cancers and stroke. Running and jumping activities are convenient, habit-forming, in-expensive and easy forms of exercise, which need to be promoted and supported. In most sports, which involve running and jumping, repetitive amounts of vertical force with high loading rates are applied to the body. These forces are a major factor in the development of overuse injuries (Hreljac et al 2000, Whittle 1999). Reducing these forces through the training of shock absorption (Novacheck 1998) and the use of shock absorbing shoes (de Wit et al 2000, de Wit et al 1995) could reduce the rate of injuries. This would enable people to exercise more regularly and more frequently resulting in numerous health benefits.
Previous investigations have demonstrated that the amount of impact (shock) during landing when jumping is predominantly determined by the movement strategy a person adopts (Zhang et al 2000, Caster & Bates 1995, Gross & Nelson.1988). When a person fully utilises knee and ankle flexion, the vertical ground reaction forces (Fz) are greatly reduced (Devita and Skelly 1992). Various studies emphasising landing strategies reported on subjects demonstrating a “toe-heel” landing, after hanging from a pole above a force platform. Gross and Bunch (1989) assessed the impact loads of basketball players during vertical jumps. Although all subjects first contacted the ground with their forefoot, the highest vertical forces were experienced later in the landing phase during heel contact; despite the advantage of a 2.5 times thicker midsole under the heel than under the forefoot. The magnitude of heel impact was related closely to individual landing technique. There were no significant differences between shoe material conditions in peak Fz, both at forefoot and at rearfoot contact. However the peak stress beneath the calcaneus (as measured by the transducers in the shoes) was significantly less when the subjects were wearing shoes with midsole material that was more like an accommodating spring. This material combined an ability to deflect with minimal viscous properties and as a result, decreased heel impact stress.
Dufek et al (1991) and Caster and Bates (1995) reported that although the initial contact was with the forefoot in all subjects, the highest Fz values were recorded when the subjects’ heels contacted the ground. There were significant variations in Fz between subjects and between two types of basketball shoes used. This study recommended multiple measurements and a within-subject analysis to get reliable and statistically significant difference between shoe conditions. As suggested in these studies, current investigation used a single subject design with multiple measurements to study the shock absorption during landing technique.
For the remainder of the article see: Int. J. Podiatric Biomech., Summer 2004.
Reduced impact forces whilst running in heelless running shoes
Authors: Hartveld, A. 1, Chockalingam, N. 2, Greenhalgh, A. 2 & Dunning, D.
1 Staffordshire Exercise Partnership (StEP)
2 Faculty of Health and Sciences, Staffordshire University, Leek Road, Stoke-on-Trent
Running is beneficial for health but the high impact forces on heel strike contribute to a high injury rate amongst runners. Runners can avoid this heel strike by changing their running style and by changing their running shoes.
Kinetics of four mature male distance runners were assessed with a strain gauge force platform while running at 4.0 m/sec. The subjects were instructed to run relaxed and not to change their running style. Each subject ran 8 trials in conventional running shoes (Reebok Premier Competition) and 8 trials in heelless running shoes (Healus Technology – HSDXXV). To compare the shoe effects on the vertical ground reaction force (Fz) variables two sample T-tests were performed and a significance level of p<0.001 was chosen.
The cumulative results indicated significant reductions in Fz at 25msec into the stance phase (Mean (SD) 13.28 (5.16) v 34.87(21.42)) and in the initial loading rates (Mean (SD) 1.00 (0.46) v 1.68 (0.46)) and the maximum loading rates (Mean (SD) 99.36 (30.03) v 131.15 (27.40)) when running in the Healus Technology shoes. The maximum Fz when running in the Healus shoes was not significantly reduced (Mean (SD) 2.48 (0.37) v 2.53 (0.34)). There were no significant order effects, but strong individual variances.
These results led to conclude that Healus Technology running shoes have the potential of reducing the loading rate of impact forces, which would allow runners to run more often and for longer without injuries.
Running is a convenient, low-cost and habit-forming activity, which contributes to a slower development of disability in older people (Fries et al 1994). However, various epidemiological studies of recreational and competitive runners have estimated that between 27% and 70% of runners sustain overuse injuries during any 1-yr period (Hreljac 2004). Previous studies have established that running produces high vertical ground reaction forces (Fz) and high loading rates (Hamill et al 1984, Keller et al 1996). When vertical ground impact forces (shock) on foot strike are too high and when applied too frequently, the body tissue breaks down (Hreljac 2004, Mueller & Maluf 2002, Hreljac et al 2000). The high impact forces on heel strike have also been implicated in the development of osteoarthritis (Radin et al 1991). The peak impact force and maximal initial loading rate are higher in older runners than in younger runners when running at the same pace (Bus 2003). This is due to a decrease in shock absorbing ability of the muscles and of other structures such as the heel pad (Hsu et al 1998). However, Fries et al (1994) showed that older people who run, do not have a higher rate of degenerative joint changes than less active older people.
The impact forces during foot strike can be easily reduced by reduction of speed (Stergiou et al 1999, Keller et al 1996, Ricard & Veatch 1994). However running with increased speed is often desirable for the development of fitness, to increase enjoyment and to increase competitiveness. Impact forces on foot strike are greatly dependent on the movement strategy the person adopts (Novacheck 1997, Lafortune et al 1996). The extensor muscle groups of the legs can be activated to a greater extent, providing more shock absorption and therefore relieving the joints from such sudden high forces (Zhang et al 2000, Oakley & Pratt 1988). Such timed activation can be achieved through guided running practice as explained by Arendse et al (2004) and Williams et al (2000). In both studies the runners, who normally strike their foot with the heel, were instructed to land on their midfoot / forefoot. The runners were quickly able to convert their strike pattern and adapt to run to landing on the balls of their feet. This resulted in a clear reduction of the loading rate on impact in both groups. Scholten et al (2002) showed that recreational runners who normally adopt a heel strike running style, automatically adapt their strike pattern to a forefoot strike when needing to run over low obstacles, such as a block of wood with 35cm height. This neuromuscular response limits the vertical impact forces on foot strike and therefore prevents musculoskeletal injuries.
A range of shoes has been developed with the purpose of reducing impact during running. Subject tests, which have been performed using a force platform to measure the ground reaction forces during actual running, have produced contradictory results (de Wit et al 1995). Various studies showed the paradox that softer running shoes with soles with higher shock absorbing capacity do not reduce the impact peak of vertical ground reaction force (Milani et al 1997, Hennig et al 1996, Frederick 1986, Clarke et al 1983). There appears to be an adverse neuromuscular response to such soft soles, i.e. a reduction of shock absorbing activity by the leg extensor muscles (Hardin et al 2004, McNair & Marshall 1994). When the runner strikes the floor with a more definite heel strike the impact forces are high. A midfoot or forefoot strike would reduce the impact (Williams et al 2000, Pratt 1989) and probably when running on harder shoes this is how runners adapt their running style to avoid high heel impacts (Milani et al 1997). Hennig et al (1996) showed that runners do this by a rapid unloading of the heel and increased weight bearing on the forefoot structures.
In jumping activities there is comprehensive evidence that landing on the forefoot, i.e. with more ankle plantar flexion on foot strike results in much lower Fz loading rates and initial Fz values (Hartveld & Chockalingam 2004). Both in running and jumping the initial impact forces are reduced when the person strikes the foot with a more plantar flexed ankle. The eccentric plantar flexion movement during the first part of the stance phase provides effective deceleration to the body hitting the ground.
Based on these observations Hartveld (2005, 2006a,b&c) developed Healus Technology shoes with its Heelless Shoe with Force Transmission, Slant Sole TM, Sole Force Distribution TM and Sense Enhancement TM features, which encourages the runner to strike the ground with a plantar flexed ankle. The aim of this shoe construction is to increase the distance over which the calcaneus is decelerated and therefore to decrease the vertical ground reaction forces on foot strike. Healus Technology shoes have a compliant midsole which allows the ankle to dorsal flex during the first part of the stance phase to aid in the gradual deceleration of the downwards movement of the body. Through a replicated single subject experimental design Hartveld et al (2005) showed that the vertical impact forces could be reduced through changing the shoes with a Healus Technology shoe sole.
The remainder of this article is available from Adri Hartveld at firstname.lastname@example.org or
Professor Nachiappan Chockalingam PhD, CEng
Faculty of Health and Sciences
Stoke on Trent ST4 2DF