An experiment of three parts was designed to compare: Prone knee flexion (KF) and seated knee extension (KE) cost:work ratios (c:w); 60 and 80 percent one-repetition maximum (1 RM) KF and KE c:w; and one-leg KF c:w with the hip extended and with the hip flexed. After determining resting oxygen uptake ((Formula presented)O2) for five minutes, (Formula presented)O2and vertical work were measured during KE or KF. Recovery (Formula presented)O2was measured until resting (Formula presented)O2was reached. Energy cost was estimated by multiplying five times net O2(L), and total work was determined by summing the vertical work done on limbs and weights. In the first part, seven subjects were tested four times, at 60 and 80 percent of 1 RM for both KE and KF. A sets x repetitions scheme of 4 x 10 was used in the 60 percent 1 RM tests, and 4x5 was used in the 80 percent 1 RM tests. In part two (five minutes of continuous work), 10 subjects were tested twice, at 25 percent of 1 RM KE and KF. In part three (five minutes of continuous work), five subjects were tested twice, at 25 percent of 1 RM KF with hip extended and hip flexed. Even though subjects had higher work values during KE than during KF, significantly higher net (Formula presented)O2and c:w values were seen during KF in parts one and two. A trend toward higher c:w for the 80 percent 1 RM c:w was found, but the difference between the 80 percent 1 RM and 60 percent 1 RM was not statistically significant (p = 0.07). Knee flexion with the hip extended had significantly greater net (Formula presented)O2and c:w values than KF with the hip flexed, even though KF with the hip flexed had higher work values than KF with the hip extended. The results of this study indicate that KF and KE economy is probably affected by exercise intensity, and that hip position affects KF economy. © 1992 Journal of Applied Sport Science Research.