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MORPHOLOGICAL AND MECHANICAL PROPERTIES OF THE PLANTAR FASCIA FOLLOWING 400 M TRACK REPEATS UNTIL FATIGUE University of Idaho, Moscow, ID
The plantar fascia (PF) is a sheath of connective tissue extending across the plantar aspect of the foot. Injury, such as plantar fasciitis, often appears suddenly and unexpectedly. Thus, the mechanism and timeline behind PF injury are still unknown. Thickness and stiffness of the tissue have been proposed to provide vital information regarding prevention strategies. PURPOSE: To evaluate the effects of repeated 400 m sprints on PF thickness and stiffness. METHODS: Seven participants completed five maximal effort 400 m sprints with a 1:1 work to rest ratio, followed by additional maximal effort trials until fatigue. Fatigue was defined as two consecutive sprints below 5% of the mean sprint time calculated from the first five sprints. The work to rest ratio was adjusted after each lap, allowing participants to rest for the exact time it took them to run the preceding lap. Sprint times ranged from 63 to 97 sec (lap 1), and 72 to 112 sec (lap 7 or 8). PF properties were recorded via ultrasound (B-mode and shear wave elastography) before, immediately after, and 30 minutes after the run. Participants laid prone on a treatment table to allow for relaxation of foot and ankle. Three images for each PF property were taken at the calcaneal insertion after palpating and marking the site. Data were analyzed via repeated measures ANOVAs, and significant findings were further explored with post-hoc t-tests. RESULTS: Analyses indicated a significant PF thickness (p = 0.033) and stiffness (p = 0.009) effect. Post-hoc t-tests further revealed a PF thickness decrease immediately following the run compared to before approaching significance (p = 0.07; 3.5 ± 0.87mm; 3.8 ± 1.0mm respectively), and a significant decrease in stiffness (p = 0.037; 4.1 ± 1.3 m/s; 3.1 ± 0.7 m/s respectively). No significant differences were found in either thickness or stiffness between the measurements immediately and 30 min after the run (3.7 ± 1.0 mm; 3.8 ± 1.4 m/s). CONCLUSION: The findings indicate that one session of high intensity running following an interval type protocol alters both PF thickness and stiffness. However, after 30 minutes of recovery, PF properties appear to approximate pre-exercise values, indicating that any detrimental effects to the tissue may only be acute. These results provide essential information for understanding how PF injuries may develop.
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