Flexor demand is a biomechanical concept describing the instantaneous or cumulative mechanical requirement imposed on the deep digital flexor apparatus to generate the internal flexion moments necessary to maintain equilibrium, control distal interphalangeal (DIP) joint mechanics and facilitate breakover while opposing externally generated extension moments during locomotion (Figure 1).

Throughout the stance phase, the ground reaction force acts on the hoof, creating external moments whose magnitude depends on the position of the center of pressure relative to the joints, hoof geometry, limb posture and the direction of loading. These external moments tend to extend the distal joints and must be balanced by internal flexion moments generated primarily through the deep digital flexor tendon (DDFT), together with contributions from its musculotendinous unit and associated passive structures. The greater the external moment, the greater the internal moment required to maintain mechanical equilibrium.^1,2

Flexor demand is therefore not synonymous with DDFT force (Figure 2). Rather, it represents the overall mechanical demand placed on the flexor system, with tendon force being one expression of that…