Most running studies have considered level running (LR), yet the regulation of locomotor
behaviour during uphill (UR) and downhill (DR) running is fundamental to increase
our understanding of human locomotion. The purpose of this article was to review the
existing literature regarding biomechanical, neuromuscular and physiological adaptations
during graded running. Relative to LR, UR is characterized by a higher step frequency,
increased internal mechanical work, shorter swing/aerial phase duration, and greater
duty factor, while DR is characterized by increased aerial time, reduced step frequency
and decreased duty factor. Grade also modifies foot strike patterns, with a progressive
adoption of a mid- to fore-foot strike pattern during UR, and rear-foot strike patterns
during DR. In UR, lower limb muscles perform a higher net mechanical work compared
to LR and DR to increase the body's potential energy. In DR, energy dissipation is
generally prevalent compared to energy generation. The increased demands for work
as running incline increases are met by an increase in power output at all joints,
particularly the hip. This implies that UR requires greater muscular activity compared
to LR and DR. Energy cost of running (C r) linearly increases with positive slope
but C r of DR decreases until a minimum slope is reached at -20 %, after which C r
increases again. The effects of slope on biomechanics, muscle contraction patterns
and physiological responses have important implications for injury prevention and
success of athletes engaged in graded running competitions.