Running injury prevention with better footwear

Running shoes for all seasons

The repetitive nature of running is a big cause of lower limb injuries. Heel impact forces peak at three to six times body weight; shock-induced acceleration at the level of the tibia has been found to be between five and 15 times the force of gravity; and one mile of running involves approx 500 foot strikes. Multiply all that by the length of your average training run and then by the number of sessions per week and it all adds up to a whole lot of stress being absorbed by your body.

The good news is that the repetitive nature of running has also been cited as the most important of all of the modifiable risk factors for lower limb injury in runners (if you are going to alter one thing, it should relate to the impacts). For many years shoe manufacturers have spent a lot of time developing new and improved shock absorption systems. Modern materials and technologies have transformed the humble trainer, and modern running shoes now boast innovations such as air cushions, gel, hydroflow, EVA and polyurethane foam. It may therefore come as a surprise to learn that the ability of these materials to absorb shock can be affected by exposure to different temperatures (‘Effects of environmental temperature on shock absorption properties of running shoes’, Clinical Journal of Sports Medicine 2005; 15(3):172-176).

Researchers in the United States took four different running shoes representing common shock absorption systems: Nike Air Triax (Nike Air-Sole unit); Asics Gel Nimbus IV (gel cushioning system); Adidas a3 cushioning (polyurethane-based cushioning system); Adidas Supernova cushion (EVA-based cushioning system), and monitored the changes in cushioning properties of the shoes when exposed to a range of ambient temperatures (-20°, -10°, 0°, +10°, 20°, 30°, 40°, and 50°). Shock absorption was measured using an impact tester. The researchers collected data for five impacts at each temperature level, compared with five pre-impact data sets (impact data collected at ‘normal’ temperature).

The findings of the study indicated that shock absorption significantly decreased as temperature decreased in all of the shoes. This is the first study of its type to suggest that the shock absorption properties of modern day running shoes are significantly reduced as a function of low temperature. The Adidas a3 struggled to cope when the temperature began to drop and showed significantly less shock absorption at lower temperatures compared to the other shoes. Among the rest, the Nike Air Triax performed the worst, followed by the Asics Gel Nimbus IV and the Adidas Supernova. Considering the wide range of extreme weather conditions in which people train, their running shoes are taken through extreme temperatures that could be very close to the temperatures tested in this study.

The next time you are going out for a run during the depths of winter it’s worth remembering that your running shoes may not absorb as much shock as you are hoping for. More research is needed but it’s worth considering adjusting your training volumes and intensities during the winter and opting for an alternative low-impact training method such as pool- based running.

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