Over the past 10 years, Jeffrey Hausdorff has studied thousands of steps from hundreds of feet. The Harvard Medical School assistant professor says that complex patterns hidden in an ordinary walk will reveal changes in the brain and body caused by aging and disease. To compile his gait analyses, Hausdorff uses mathematical tools used to model climate changes and stock market fluctuations. Now a walk down the hall offers a way to evaluate the risk of falling in older adults. Hausdorrf has also devised a clever gadget to measure the timing of the heel and toe strike of each stride. The device is flatter than a typical shoe insert; it feeds data through a short wire to a small monitor worn around the ankle. Hausdorff’s findings target gait instability as a potentially reversible contributing factor to the risk of falling, a major public health problem.