Magnetic resonance imaging as an index of muscle activation during uphill and downhill running

The purpose of this study was to investigate the usage of the lower limb muscles (quadriceps femoris:QF, m. vastus lateralis : VL, m. rectus femoris :RF, m. vastus medialis :VM, m. vastus intermidialis:VI, hamstring: HM, m, gastrocnemius :GN, tibialis anterior: TA) and blood lactic acid concentration during uphill ( : UR + 5 %) and downhill running ( : DR - 5 %). We used magnetic resonance imaging (MRI) as one of the major indices. Seven healthy male volunteers participated in this study. T2-weighted MR imaging, muscle surface temperature and blood lactic acid concentration were measured before and after UR and DR. In MRI imaging, the T2 value was defined as the area in which a high signal appeared after exercise. The value of the blood lactic acid concentration of UR was higher than that of DR (p < 0.001). After DR, the muscle surface temperature of RF was lower in comparison with other muscles (p < 0.05). After UR, the T2 value of RF (p < 0.05), HM (p < 0.01) and GN (p < 0.05) was higher than after DR exercise. During DR, a positive correlation (r = 0.818) existed between the T2 value of GN and blood lactic acid concentration (p < 0.05). During DR, a positive correlation (r = 0.739) was also observed between the T2 value of QF and blood lactic acid concentration (p < 0.05). From these results, we conclude that (1) the pattern of usage of lower limb muscles differs during UR and DR, (2) the most mobilized muscles in the lower limbs for UR are GN and HM, and (3) the most mobilized muscle in the lower limbs for DR is QF, respectively. These findings show that different exercises affect the blood lactic acid concentration differently.