Effect of speed and gradient on plantar force when running on an AlterG® treadmill

Abstract

Background Anti-gravity treadmills are used to decrease musculoskeletal loading during treadmill running often in return to play rehabilitation programs. The effect different gradients (uphill/downhill running) have on kinetics and spatiotemporal parameters when using an AlterG® treadmill is unclear with previous research focused on level running only. Methods Ten well-trained healthy male running athletes ran on the AlterG® treadmill at varying combinations of bodyweight support (60, 80, and 100% BW), speed (12\u2009km/hr., 15\u2009km/hr., 18\u2009km/hr., 21\u2009km/hr., and 24\u2009km/hr), and gradients (−\u200915% decline, −\u200910, −\u20095, 0, +\u20095, +\u200910\u2009+\u200915% incline), representing a total of 78 conditions performed in random order. Maximum plantar force and contact time were recorded using a wireless in-shoe force sensor insole system. Results Regression analysis showed a linear relationship for maximum plantar force with bodyweight support and running speeds for level running ( p \u2009<\u20090.0001, adj. R 2 \u2009=\u20090.604). The linear relationship, however, does not hold for negative gradients at speeds 12 & 15\u2009km/h, with a relative ‘dip’ in maximum plantar force across all assisted bodyweight settings. Conclusions Maximum plantar force peaks are larger with faster running and smaller with more AlterG® assisted bodyweight support (athlete unweighing). Gradient made little difference except for a downhill grade of −\u20095% decreasing force peaks as compared to level or uphill running.