Echo planar MR imaging of the leg was performed in nine healthy volunteers to better understand the dynamic relationship between exercise and changes in muscle T2. Imaging and T2 calculation was performed before, during, and after ankle dorsiflexion exercises using a TR of 9 seconds and a TE of 60 msec. Performing 9-second duty cycles, six of the subjects exercised for sets of 12 duty cycles, three with a graded series of weights and pulleys and three with an isometric orthotic device graded in varying percentages of maximum voluntary contraction. The other three volunteers performed duty cycles to fatigue. Gastrocnemius and soleus muscle T2 relaxation times were unchanged before, during, and 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 for 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 imaging, 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.