Plantar fasciitis is a relatively common injury that occurs in running athletes. The disease entity is a good example of an overloaded process of the plantar fascia at its calcaneal insertion. This study was designed to examine the strength and flexibility findings in the muscles that are put on tensile load during running, and which are responsible for controlling the forces on the foot during stance and pushoff, thus modifying the overload. Three groups of athletes underwent physical examination, including checking ankle range of motion in plantar flexion and dorsiflexion. Cybex peak torque measurements were taken at 60 and 180 deg/sec. The groups were a control group of 45 athletes with no symptoms, a group that included 43 affected feet with symptomatic plantar fasciitis, and a group that included the 43 unaffected contralateral feet. Analysis of data showed dynamic range of motion deficits in 38 of 43 affected feet, static range of motion deficits in 37 of 43 affected feet, deficits in peak torque at 60 deg/sec in 41 of 43 affected feet, and deficits in peak torque at 180 deg/sec in 37 of 43 affected feet. Statistical comparison of range of motion showed that the group with symptomatic plantar fasciitis was significantly restricted compared to both control and unaffected contralateral feet groups. Statistical comparison of peak torque showed that the symptomatic plantar fasciitis group was significantly lower than both other groups at both velocities. This study documents strength and flexibility deficits in the supporting musculature of the posterior calf and foot that are affected by plantar fasciitis.(ABSTRACT TRUNCATED AT 250 WORDS)