The effect of running on functional MRI measures of hindfoot muscle activation due to ground reaction force

This study explored the effect of ground reaction force on hindfoot muscle activation during jogging and recovery using functional magnetic resonance imaging (fMRI). Eight adult male volunteers (average age, 36 +/- 8.3 years; average height, 1.73 +/- 0.03 m; average weight, 70 +/- 9.9 kg) were asked to jog for 3000 meters on a treadmill at a velocity of 9 Km/hr and ground reaction force was measured using the Pedar (R) insole system. Muscle fMRI of each hindfoot muscle was performed immediately post exercise and compared to baseline imaging and imaging after 10, 20, 30 min, and 24 hours of rest. Significant positive correlation was observed between ground reaction force, expressed as Max force (r = 0.353, P = 0.002), peak pressure (r = 0.312, P = 0.008), force-time integral (r = 0.236, P = 0.046), and percent activated volume. T2 value was most pronounced in abductor digiti minimi (ADM) (lateral hindfoot territory). The most prominent activated volume was within posterior ADM. Greatest maximum force (33.17 N) occurred within flexor digitorum brevis (FDB) (central hindfoot territory). Ground reaction force resulted in metabolic changes on fMRI as reflected by percent activated volume within hindfoot muscles during jogging and this change was most pronounced immediately after exercise.