The influence of running shoe design towards a sub two hours marathon

Discussion

The world marathon records in the 1960s were broken on minimalistic footwear. When the running boom hit the world in the 1970s, running shoe designs were developed to provide shock absorption through the heel. However during fast running humans tend to land on their forefoot. In order to absorb the high gravitational forces during the first part of the stance phase in running, the ankles eccentrically plantar flex over a greater distance than when the landing is on the heel. A basic application of the second law of Newton shows that a touch down with the ball of the foot reduces the stress on the body, as compared to a heel strike. A range of descriptive and experimental studies^{(4, 5, 6, 7)} have indeed shown that landing on the ball of the foot (metatarsal heads) is preferential in terms of impact forces and running speed. Fast athletes run with their foot striking on the ball of the foot (metatarsal heads). Such athletes particularly use the calf musculature as vertical force decelerator and providers of energy return; the muscles absorb the body weight with eccentric contractions plus passive elasticity and push the body back up and away every step of the way.

Ever since the running boom in the 1970’s scientists and shoe brand manufacturers studied the science of distance running in order to develop tools to prevent injuries and aid performance. The limiting factor for marathon running times is fatigue and soreness in the leg muscles which provide this spring like action. To meet the need of protection from the hard road, the sole needs to have a certain amount of shock absorption to complement the natural shock attenuating function of the leg extensor muscles of the runner. The shoe sole also needs to be light weight to ensure the minimum resistance to the running action. Attempts to provide footwear with minimal weight and optimal shock absorption concentrated on the rear part of the shoe sole for 28 years despite the fact that, increasingly, elite marathon runners made little use of the heel of the shoe. This heel focus in the development of footwear might well explain the low rate of 5.6 seconds per year improvement of the world marathon record in the period of 1970-1998. In the beginning of the 21^st Century various footwear designs have been developed to reduce the impact of such forefoot strike on tarmac roads or hard synthetic running tracks. Theoretically such footwear can delay the point at which the marathon runner has to slow down due to the fatigue in the muscles. Sound biomechanical evidence has been provided with regards to the effectiveness of cushioning provided by the shoe sole through in vivo laboratory studies on runners, in vitro testing of shoe soles and related mathematical modelling⁽⁸⁾.

Recent laboratory studies on running efficiency comparing shod running with barefoot running have resulted in contradictory findings with regard to footwear and running economy^{(9, 10, 11)}.

World record marathon runners in the 1960s ran with a very similar running style compared to the world record marathon runners in the 21^st Century: with a forefoot strike. An increase in cushioning in the forefoot is likely to reduce the muscle fatigue induced by running fast for more than 2 hours non-stop. However the cushioning material used gave the athlete considerable energy loss due to hysteresis of the material and increased weight of the running shoe. In recent years new materials with better energy return and new shoe designs have become available. Some of these developments have filtered through to the marathon runners trying to break world records, but not yet all.

Road running shoes for racing are considered optimal if the sole material provides both cushioning and energy return (to prevent muscle fatigue and soreness) and if they are lightweight (to minimise resistance to the running movement). Several biomechanics studies confirm the value of low weight, cushioning and energy return⁽¹²⁾ to promote running speed and reduce muscle fatigue. Arguably the improvement of world marathon records from 1998 to 2012 at a rate of 14.2 seconds a year is linked to footwear development. Although running footwear has stayed conventional with only small changes, there has generally been a focus away from the heel to the sole part below the midfoot and forefoot, especially in racing shoes. If this current development of footwear, continues, it can be predicted that a sub 2 hour marathon will be achieved in 2026.

In other sports more radical new designs have led to a more rapid progression of world records. For example, in the late 1990s the Dutch invention the “klapschaats” (“clap skate”) brought about sudden and marked reductions in the world record times in speed skating. More radical running shoe designs might bring about a quicker change in best marathon times.

One such future improvement option in road running shoes is the Healus Footwear concept, which replaces the heel with a shock plate which provides Sole Force Distribution and Sense Enhancement⁽³⁾. The latest prototype of this concept, for road racing, has considerable cushioning in the forefoot areas, and low shoe weight (158 grams). In the footwear industry which is renowned to be conservative such radical approach might well assist the elite runner in breaking the 2 hour barrier not later but sooner than Joyner et al’s prediction⁽¹⁾ of 2021.