OBJECTIVES: Plantar fasciitis, a common injury in runners, has been speculated 
to be associated with weakness of the intrinsic foot muscles. A recent study 
reported that atrophy of the intrinsic forefoot muscles might contribute to 
plantar fasciitis by destabilizing the medial longitudinal arch. However, 
intrinsic foot muscle volume difference between individuals with plantar 
fasciitis and healthy counterparts remains unknown. This study examined the 
relationship of intrinsic foot muscle volume and incidence of plantar fasciitis.
DESIGN: Case-control study.
METHODS: 20 experienced (≥5 years) runners were recruited. Ten of them had 
bilateral chronic (≥2 years) plantar fasciitis while the others were healthy 
characteristics-matched runners. Intrinsic muscle volumes of the participants' 
right foot were scanned with a 1.5T magnetic resonance system and segmented 
using established methods. Body-mass normalized intrinsic foot muscle volumes 
were compared between runners with and without chronic plantar fasciitis.
RESULTS: There was significant greater rearfoot intrinsic muscle volume in 
healthy runners than runners with chronic plantar fasciitis (Cohen's d=1.13; 
p=0.023). A similar trend was also observed in the total intrinsic foot muscle 
volume but it did not reach a statistical significance (Cohen's d=0.92; 
p=0.056). Forefoot volume was similar between runners with and without plantar 
fasciitis.
CONCLUSIONS: These results suggest that atrophy of intrinsic foot muscles may be 
associated with symptoms of plantar fasciitis in runners. These findings may 
provide useful information in rehabilitation strategies of chronic plantar 
fasciitis.