As athletes strive for perfection, sports scientists need to exploit every technological¹ advance to help them achieve that goal. Researchers in New Zealand have now developed a new type of wearable impact sensor² based that can provide much needed information about the stresses and strains on limbs（四肢） for rugby（英式橄榄球） players, high jumpers, and runners. Writing in the International Journal of Biomechatronics（生物机电工程） and Biomedical Robotics, Kean Aw and colleagues in the department of Mechanical Engineering, at The University of Auckland, explain how novel（新奇的，异常的） materials known as ionic polymer（聚合物） metallic³ composites (IPMCs), produce an electrical current when compressed. These materials are flexible, lightweight and durable⁵ and so can be fashioned into wearable sensor devices to allow sports scientists to monitor directly impact forces without interfering⁶ with an athlete's performance.

IPMCs are usually made from an ionic polymer, such as Nafion or Flemion, which is coated with a conducting metal, platinum⁷ or gold. Previously⁸, researchers have experimented with IPMC materials as artificial muscles because applying a voltage causes them to flex⁴ as ions（离子） migrate causing electrostatic repulsion（静电排斥） within the composite material. The opposite effect, in which ion movement generated a voltage when the material is flexed⁹, is exploited in the sensor technology.

Impact sensors¹⁰ made from IPMC could be inserted into footwear to measure the impact energy of a foot striking a hard surface or they might be placed in a rugby player's shoulder pads to measure collision impacts or forces exerted during a rugby scrum（扭打，混打） . The data obtained from these sensors allows the athlete's performance to be quantified and analyzed¹¹ in terms of the forces acting¹² on their body with a view to improving their and also reducing the potential for injuries.

The researchers have tested IPMC sensors in the laboratory and compared the readings obtained for different applied¹³ forces with those from more conventional measurement techniques. Their analysis of the tests reveals that the IPMC sensors would have to be calibrated¹⁴（校准） with a high and a low impact force prior to testing with a performing athlete. However, the voltage spike¹⁵ and the slope of the voltage measurement obtained with an IPMC can be readily converted into an impact force measurement to within 10% accuracy.