DYNAMIC EVALUATION OF EXERCISING LEG MUSCLE IN HEALTHY-SUBJECTS WITH ECHO-PLANAR MR-IMAGING - WORK RATE AND TOTAL WORK DETERMINE RATE OF T2CHANGE

Echo planar MR imaging of the leg was performed in nine healthy volunt eers to better understand the dynamic relationship between exercise an d changes in muscle T2, Imaging and T2 calculation was performed befor e, during, and after ankle dorsiflexion exercises using a TR of 9 seco nds and a TE of 60 msec. performing g-second duty cycles, six of the s ubjects exercised for sets of 12 duty cycles, three with a graded seri es of weights and pulleys and three with an isometric orthotic device graded in varying percentages of maximum voluntary contraction, The ot her three volunteers performed duty cycles to fatigue, Gastrocnemius a nd soleus muscle T2 relaxation times were unchanged before, during, an d after exercise, The tibialis anterior muscle showed an initial brief 1.7-6.2% decrease in T2 values after starting exercise, followed by a linear increase. Maximum T2 values and percent changes were higher fo r higher work rates (P<.05), and the rate of T2 change increased in a linear fashion with increasing work rates, By using rapid serial MR im aging, we show that the rate of muscle T2 change bears a simple linear relationship to muscle work, This technique may be exploited in both diagnostic and rehabilitation procedures.