Monthly Archives: October 2012

Midsole hardness and dynamic balance

 

I forbindelse med det tidligere indlæg med en masse fantastiske quotes omkring (forfods)sko- og løb, faldt jeg over et studie inden for samme emne (1). Studiet undersøgte forskellige grader af “midsole hardness” på dynamisk balance. Forsøgspersonerne (FP) (n = 12) iførte sig 3 forskellige par sko med variende hårhed af mellem-sålen, samt gik barfods. FP gik på en 8m walkway, og i 25% af tilfældene signallede en lyd at de skulle stoppe deres gang. Udsving i tyngdepunktet under “stop-fasen” blev målt og brugt som indikator for dynamisk balance.

 

“In conclusion, the present study suggests that variations in midsole material and even the presence of it, impairs the dynamicbalance control system.”

 

Som det fremgår af konklusionen, blev den dynamiske balance ringere som mellem-sålen blev hårdere.

Alt andet lige, forestiller jeg mig balance-elementet er værd at have med ved løb. I praksis vil det sandsynligvis betyde en øget risiko for at falde under løbeturen, hvis mellem-sålen er hård som sten (hvilket den ofte er).

 

Jeg forestiller mig det nemt kan have noget at gøre med føddernes store antal af baro-receptorer, som – foruden det visuelle og vestibulære system – fodrer hjernen information omkring kroppens position. De traditionelle hårde løbesko vil mindske følsomheden af disse receptorer (de da ikke bliver stimuleret i samme grad), hvilket alt andet lige vil have en effekt på balancen. At løbeturens intensitet muligvis bliver mindre af samme årsag (grundet større opfattet trussel via nedsat balance-evne), er et andet potentielt problem.

 

(1) Influence of footwear midsole material hardness on dynamic balance control during unexpected gait-termination. 2007

 

 

 

Science Update

 

Konditionstræning og kognitiv funktion

En meta-analyse fra 2012 (1) undersøgte effekten af træningsperioder med hhv. kognitive træning og konditionstræning på udførelsen/præstationen af ukendte kognitive tests. Forfatterne søgte litteraturen fra 1966-2010 og fandt 42 egnede studier som inkluderede 3.781 sunde, ældre (>55 år) voksne.

Resultatet: Grupperne som dyrkede konditionstræning havde en lige så stor fremgang som grupperne som trænede kognitivt, på præstationen af ukendte kognitive tests (choice reaction time, memory, and executive function).

 

Meta-analysen viser derfor dels at konditionstræning er en effektiv måde at træne/vedligeholde sin kognitive kapacitet på, og dels at ældre voksne (stadig!) har potentiale for at optimere den kognitive funktion.

 

 

Back problems. What actually works?

I 2009 udkom et review i The Spine Journal (2), som undersøgte litteraturen af forebyggelsen af ryg-problemer (BP) hos voksne. Studiet havde høje kriterier for inklusion (RCT), og kun 20 ud af 185 fundne studier opfyldte kravene for “high-quality research”.

 

 

“Results: Only exercise was found effective for preventing self-reported BPs in seven of eight trials (effect size 0.39 to >0.69). Other interventions were not found to reduce either incidence or severity of BP episodes compared with controls. Negative trials included five trials of education, four of lumbar supports, two of shoe inserts, and four of reduced lifting programs.”

 

Dette review viser at det – af de undersøgte interventioner – kun var exercise som havde en positiv effekt på BP. Derimod havde sko-indlæg, ryg-støtte, nedsat træningsmængde og uddannelse inden for området, ingen positiv effekt. De kommer dog ikke nærmere ind på hvilken type “uddannelse” der er snak om, da det tidligere er vist at “pain-education” er en meget potent intervention ift. smertelindring (se arbejde af Moseley). Det er sandsynlig at uddannelse i dette review er mere relateret til “do and dont´s” vedr. BP end til neurobiologien bag smerte.

Herudover er det interessant at hverken sko-indlæg, nedsat træningsmængde eller nedsat bevægelse af lænde-ryggen, viste positiv effekt på BP. Det er ligeledes lidt tankevækkende, da disse interventioner ofte er de mest anvendte. Det er tilsyneladende også mindre vigtigt hvilken type træning/bevægelse der er tale om, da de inkluderede studier havde gang i alt fra passiv udstræk til styrketræning; – med den samme effekt på BP.

 

 

 

(1) Extended Practice and Aerobic Exercise Interventions Benefit Untrained Cognitive Outcomes in Older Adults: A Meta-Analysis. 2012

(2) High-quality controlled trials on preventing episodes of back problems: systematic literature review in working-age adults. 2009

 

 

Oh no, not the shod!

 

Jeg faldt over et par gode quotes vedr. de potentielle negative aspekter ved at pakke foden ind i moderne løbesko. Yderligere læsning/litteratur inden for området kan ligeledes findes i den tidligere post “Forfodsløb – to do!”.

 

 

During barefoot running, the ball of the foot strikes the ground first and immediately starts sending signals to the spinal cord and brain about the magnitude of impact and shear, getting most of its clues about this from the skin contact with the surface irregularities of the ground. Take away this contact by adding a cushioned substance and you immediately fool the system into underestimating the impact. Add a raised heel and the shod runner is forced to land on it. Strap the cushioning on tightly with the aid of a sophisticated lacing system and you block out shear as well, throwing the shock-absorption system even further into the dark…. The cushioned midsole of the modern running shoe robs the system of important sensory information necessary for ankle, knee and hip response to impact. The arch support (or orthotic) in modern running shoes not only prevents the arch suspension system from absorbing energy by preventing flattening but eventually leads to intrinsic muscle atrophy and complete loss of active muscular control of the arch leaving only the inelastic plantar fascia as a checkrein to flattening. The barefoot runner’s ‘foot position awareness sense’ which relies heavily on sensory input from the sole of the foot minimizes his risk of sustaining an ankle sprain on uneven ground. The shod runner is at marked increased risk of ankle sprains because his ‘foot position awareness sense’ is handicapped by the paucity of sensations coming from his soles.

- Joseph Froncioni

 

 

Research on foot impact by Robbins and Waked (1997) suggests that balance and impact are closely related, that a person coming down on a soft surface (like a gymnast landing on a thick pad or runner on a spongy shoe) intentionally, though non-consciously, comes down harder in order to find a stable surface. The spongier the landing material, theoretically, the harder the impact because the body seeks to compress the material to find some sort of stable footing.

- Joseph Froncioni

 

People who habitually wear shoes wind up shaping their feet developmentally in distinctive ways. From the point of view of our feet – if I can be so anthropomorphizing – the shoe becomes the ‘environment’ in which feet are grown. Factors like temperature, abrasion, constriction, and the like become the environment with which the foot must contend adapt to, and rely upon. Shoes are a kind of developmental niche for feet, and like any ecological niche, exert their own influence on the anatomical unfolding of the foot’s anatomy. Of course, other factors in addition to shoes make up the foot’s ‘environment’, such as the very act and amount of walking we do, the surfaces we walk on, the sorts of forces exerted upon the bones in the feet by factors like our body size, built environment, athletic activities… and all of these can be affected by shoes, too.

In other words, from the point of view of the feet, a whole constellation of things make up the developmental environment, some of which are truly ‘outside’ us – like cold or wet or surfaces – but some of which are very much under human control, including activity patterns and habitual footwear. To the foot, the leg is part of the environment, and how the leg is used becomes one of the environmental factors feeding into how the feet develop. If we wear a pair of shoes that changes how our legs work (such as high heels or thickly-soled running shoes), these shoes affect the feet directly, but they also impact the feet indirectly through what they do to the leg and the dynamics of our gait and our patterns of activity.

- Greg Downey, 2009

 

The natural foot is the naked, unclothed foot; and its arched conformation is not an element of weakness in design calling for artificial help, but of structural strength acquired through countless generations of unaided weightbearing. Occasionally we hear shoes referred to as a “natural support for the arch.” The suggestion should move our hearts in pity toward all primitive peoples were it not for the fact that they have no foot troubles, as well as no shoes. The phrase is one of many in which glibness overshadows accuracy, and unfortunately tends to promote erroneous ideas about the foot and its welfare.

- Dudley Morton, 1964(!)

 

The arch support, which is present in all running footwear, would interfere with the downward deflection of the medial arch on loading. Furthermore, the use of orthodics, or other structures that are fitted to the mold of the soft tissues of the foot, could cause similar difficulty. Such designs occur when an engineer looks at the foot as an inflexible lever which is delicate and thus requires packaging. Various myths persist about foot behavior due to poor understanding of its biology.

- Robbins and Hanna, 1987

 

Patterns of bone growth and remodeling due to use (commonly referred to loosely as ‘Wolff’s law) suggest that a shift in toe use and the increased support for the bones of the feet provided by habitually worn shoes, will lead to differences in bone structure between habitually shod and unshod populations. Bound together laterally and ‘supported’ by an arched shoes, the foot cannot act as efficiently as a shock absorber; at the same time, less dynamic loading on the bones means that the bones will be less robust. Shoes, then, have a range of developmental effects, from low-level, constant pressure and abrasion to a form of protection which leads to greater fragility.

- Greg Downey, 2009

 

The researchers observed increased joint torques at the hip, knee and ankle with running shoes compared with running barefoot. Disproportionately large increases were observed in the hip internal rotation torque and in the knee flexion and knee varus torques. An average 54% increase in the hip internal rotation torque, a 36% increase in knee flexion torque, and a 38% increase in knee varus torque were measured when running in running shoes compared with barefoot.

These findings confirm that while the typical construction of modern-day running shoes provides good support and protection of the foot itself, one negative effect is the increased stress on each of the 3 lower extremity joints. These increases are likely caused in large part by an elevated heel and increased material under the medial arch, both characteristic of today’s running shoes.

Remarkably, the effect of running shoes on knee joint torques during running (36%-38% increase) that the authors observed here is even greater than the effect that was reported earlier of high-heeled shoes during walking (20%-26% increase). Considering that lower extremity joint loading is of a significantly greater magnitude during running than is experienced during walking, the current findings indeed represent substantial biomechanical changes.” Dr. Kerrigan concludes, “Reducing joint torques with footwear completely to that of barefoot running, while providing meaningful footwear functions, especially compliance, should be the goal of new footwear designs.

- Kerrigan et al., 2009