Most women can identify one problem area that seems to lag behind other areas of their bodies despite a dedicated approach to their training programs. Sometimes it’s the result of neglecting areas that are harder to train than others. In other cases, it’s because they rationalize that an area is already getting enough work, so it doesn’t need extra work. The thighs are especially notorious for fitting into these categories. They are often hard to firm up, yet many women expect that the time invested in cardio or pounding miles on the treadmill should take care of the thighs. After all, the thighs seem to get tired after these exercises, don’t they? Unfortunately, the thigh musculature may not be adequately shaped and firmed by cardio alone. Cardio is certainly needed, but it has a different function, which is to “burn” body fat stores and improve the function of the heart and lungs. The exercise that the thighs receive in cardio is usually not intensive or direct enough to provide the tone, shape and firmness most women desire. Thus, a more direct approach is needed, and this can be achieved by adding a few sets of resistance exercise that directly activate the thighs. There are several exercises that will accomplish the task of shaping and firming the front (anterior) part of the thighs. Leg extensions are among the best exercises that directly recruit the muscle fibers along the inside, outside and middle portions of the thigh from the hip to the knee.
Thigh Muscles: A Closer Look
The anterior (front) of the thigh is made up of four primary muscles that collectively are called the quadriceps femoris muscle (“quadriceps” or “quads” for short). The muscles in the quadriceps include the rectus femoris and the three vastus muscles. The fibers of the rectus femoris muscle (rectus=straight) run vertically down from the hip, along the front of the thigh, to join the quadriceps tendon above the kneecap (patella). The rectus femoris extends the leg at the knee joint. However, because the rectus femoris begins at the hip, it is slackened and therefore, functionally weaker, when the hip is flexed in exercises like seated leg extensions. For this reason, seated leg extensions will emphasize the vastus muscles more so than the rectus femoris muscle in the quadriceps group.
The vastus medialis muscle covers the medial (inner) part of the thigh just above the knee. Shaping this muscle tightens the area of the thigh that’s on the medial side of the thigh just above the patella (kneecap). The vastus intermedius is positioned in the middle of the quadriceps muscle group. It lies between the vastus lateralis and the vastus medialis muscle, but it’s deep to the rectus femoris muscle, so you can’t see it. The vastus lateralis muscle resides on the lateral (outer) part of the thigh. It gives the lateral part of the thigh the sweep and shape from the knee to the hip. The three vastus muscles are anchored to the femur bone of the thigh just below the thigh joint, and all attach to the upper border of the patella by the quadriceps tendon. The vastus lateralis, vastus intermedius and vastus medialis are attached to the lateral, middle and most medial parts of this tendon, respectively. The patella is attached to the tibia bone of the lower leg by the patellar ligament. As the muscles of the quadriceps contract, they shorten and pull on the tibia by way of the quadriceps tendon and patellar ligament, so the leg becomes extended at the knee joint. The three vastus muscles are not affected by hip angle, so they are fully active throughout the complete range of motion of the seated leg extension exercise.
1. Always warm up your knees thoroughly before doing leg extensions. This is especially important if knee extensions do not follow another thigh exercise. A few minutes of stretching and some stationary cycling are good time investments that will protect and warm the delicate knee joint.
2. Adjust the seat of a knee extension machine so the pivot point of the lifting arm is directly adjacent to the center of the side of your knee joint. Next, place the ankle roller of a knee extension machine so that it’s above your feet on the lower part of your legs (above the ankle joint). Set the extension unit to permit a knee flexion of 90 degrees. Greater flexion than this (especially at the beginning of the exercise) does increase the stretch on the quadriceps and improves the range of motion. However, it also greatly increases the risk of knee joint injury and therefore should be avoided.
3. Lift the weight slowly (three to four seconds) from the starting position rather than ballistically. This will help the tendons accommodate to the load, which is particularly important during the start of the very first repletion of each set. The subsequent lifts should always be slow (a count of “two” for the up movement) and controlled and not “jerked” upward or dropped downward. Rapid movements may result in tendon, ligament and/or knee cartilage injury you’ll want to avoid.
4. Continue extending your legs upward and straightening the knee joint. Stop at the top position of the extension where the knee is just slightly short of being totally straight (i.e., do not “lock” the knees out straight at the top of the lift). Furthermore, be careful that you do not “jam” the knee joint into a fully locked out position, because this could cause knee cartilage damage. Hold the top position for a count of two before lowering the weight.
5. Lower the weight slowly (over a count of three) as you return your legs back to the starting position. The downward movement should be slower than the upward phase because you’re resisting the pull of gravity. Therefore, to obtain the benefit of this eccentric (lengthening) phase of the lift, you must be in control of the weight as it’s being lowered (and not the other way around).
6. Stop the downward movement when your knee angle is flexed to 90 degrees. Do not rest at the bottom, but immediately continue the next upward lift to the top.
7. Take a short break after completing your first set (12-15 repetitions). If you can do 15 repetitions easily, then add more weight to the machine on your next set. If the resistance is selected correctly, it should be difficult to get all 15 extensions completed. Start with two sets if you have not done the exercise before. You may want to add a third set after a few weeks of training.
It’s worth reiterating that the extension phase of the exercise must not be done as quickly as possible. Some people seem to think if they kick the leg bar upward, the thigh muscles will respond just as rapidly as the weight is lifted. This is not the case. In addition to the tendency to increase the potential for tendon and joint injury, the fast movement reduces the stresses on the muscles because the machine’s momentum will help lift the weight upward. Fast movements may be easier and get the exercise over a bit sooner than doing it slowly, but the thighs will not achieve the same toning and firmness as if you do the exercise slowly. The slow movements guarantee that the muscle fibers are contracted and stimulated throughout each repetition while minimizing any potential to hurt the soft tissues around the knee joint. It is also important to ensure that your diet has adequate vitamins, especially iron, because this mineral has been shown to reduce muscle fatigability in exercising women.
In addition to possessing stunning quadriceps, your thighs will be stronger and firmer as a result of leg extensions. This will provide you with a new spring in your step when doing simple things like climbing stairs or more intense things like skiing. Furthermore, you will find that there will be a spillover to your cardio, such that the stepper and stationary cycling will become a bit easier to do.
Benn C. Forman K. Mathewson D. Tapply M. Tiskus S. Whang K. Blanpied P. The effects of serial stretch loading on stretch work and stretch-shorten cycle performance in the knee musculature. J Orthopaedic & Sports PhysicalTherapy, 27(6):412-22, 1998.
Brutsaert TD, Hernandez-Cordero S, Rivera J, Viola T, Hughes G and Haas JD. Iron supplementation improves progressive fatigue resistance during dynamic knee extensor exercise in iron-depleted, nonanemic women. Am J Clin Nutr, 77: 441-448, 2003.
Driss T, Vandewalle H, Le Chevalier JM and Monod H. Force-velocity relationship on a cycle ergometer and knee-extensor strength indices. Can J Appl Physiol, 27: 250-262, 2002.
Shinohara M. Kouzaki M. Yoshihisa T. Fukunaga T. Mechanomyogram from the different heads of the quadriceps muscle during incremental knee extension. Eur J Appl Physiol, 78(4):289-95, 1998.
Simeoni RJ and Mills PM. Bicoherence analysis of quadriceps electromyogram during isometric knee extension. Australas Phys Eng Sci Med, 26: 12-17, 2003.
Stewart D, Macaluso A and De Vito G. The effect of an active warm-up on surface EMG and muscle performance in healthy humans. Eur J Appl Physiol, 89: 509-513, 2003.
White KK, Lee SS, Cutuk A, Hargens AR and Pedowitz RA. EMG power spectra of intercollegiate athletes and anterior cruciate ligament injury risk in females. Med Sci Sports Exerc, 35: 371-376, 2003.
Wretling ML. Henriksson-Larsen K. Gerdle B. Inter-relationship between muscle morphology, mechanical output and electromyographic activity during fatiguing dynamic knee-extensions in untrained females. Eur J Appl Physiol, 76(6):483-90, 1997.
Zakaria D. Harburn KL. Kramer JF. Preferential activation of the vastus medialis oblique, vastus lateralis, and hip adductor muscles during isometric exercises in females. J Orthopaedic & Sports Physical Therapy, 26(1):23-8, 1997.