A foot mounted, inline/concentric gear reducer using planetary gearing. Splined input and output shafts isolate internal gearing from external forces. Heavy duty roller bearings on the output shaft are subject to external forces only - not internally generated gear forces. Modular sun and carrier gearing is used to achieve multiple reducer ratios. Heavy duty roller bearings and grease purgeable seals provide maximum protection in extreme environments. High and low speed shaft bearings and seals are commercially available. Efficiency is 97.5% at each reduction stage.