To compare the effects of forward walking and backward walking on surface electromyographic analysis of quadriceps muscles at treadmill grades of 0%, 5% and 10%, subjects were randomized to eleven athletics (5 females, 6 males), with a mean age of 17.8 years, and a SD of 4.66 years. The values of the surface electromyographic (SEMG) activity of the rectus femoris (RF), vastus lateralis (VL) and vastus medialis oblique (VMO) were measured during forward walking and backward walking on a treadmill at grades of 0, 5 and 10%. The subjects walked for approximately 10 seconds at 4.0 km/h. The data were analyzed by repeated measuring of the two-way ANOVA and analyzed by a paired t-test between forward walking and backward walking. The SEMG activity levels of the RF, VL and VMO were the highest when both the forward walking and backward walking increased incrementally for treadmill grades of 0% to 10%, but the VMO/VL ratio had no significant changes. The SEMG activity levels of the RF, VL and VMO were significantly different between directions. However, SEMG activity levels of the RF, VL, VMO and VMO/VL ratio did not show significant difference among the treadmill grades. No statistically significant interactions were detected between the direction of walking and treadmill grade. Backward walking on the treadmill at 4 km/h and grades of 0%, 5%, 10% elicited a greater SEMG activity on the quadriceps muscles than did forward walking under the same conditions. The results suggest that the quadriceps may be effectively activated by performance at treadmill grades of 10%. This investigation confirms that backward walking up an incline may place additional muscular demands on individuals.