Unilateral Leg Extension
The leg extension is the only exercise in which the quadriceps muscles can be trained in isolation from muscles such as the hamstrings, glutes, abdominals, and lower back.
In this variation, the exercise is performed with one leg at a time, either alternately or consecutively, instead of with both legs simultaneously.
Unilateral leg extension execution
-
1
Push one foot forward and upward until the leg is almost straight.
-
2
Lower and move your foot back in a controlled manner until just before the resting point (maintain tension).
-
3
Repeat with the same foot or alternate with the other foot.
Unilateral leg extensions
Muscles involved:
Legs:
- Quadriceps (vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris)
Unilateral leg extension setup
(also see the instructions on the machine):
- Adjust the seat to the correct distance. Your knees should be aligned with the machine's pivot point.
- Adjust the leg pad to the correct height so that it rests at the curve between the shin and the top of the foot.
- Sit down and place the leg pad as far back as possible before securing it.
- “Lock yourself in” by gripping the handles firmly.
Unilateral leg extension technique
The rectus femoris is the only quadriceps muscle that crosses two joints. Besides extending the knee, it also functions to bring the leg forward and upward. In a seated position, as during seated leg extensions, it is therefore the only one already shortened because the leg is already raised forward. In this so-called “active insufficiency” state, the already shortened muscle cannot produce maximum force. This means that the other quadriceps muscles have to take over part of the load.
During squats and the leg press, the rectus femoris is also already shortened before the leg is extended at the knee. When you descend in the squat, your thighs move forward, after all. The difference from leg extensions, however, is that the thighs become aligned with the torso again while rising in the squat and pushing out in the leg press. While the rectus femoris is shortened at the knee during the rise or press, it is lengthened at the pelvis. As a result, compared with leg extensions, there is less “active insufficiency” and the rectus femoris can produce more force.
Leg extensions are therefore not a complete alternative to exercises such as the leg press and squat and should instead be viewed as a supplement.
Alternatives
- Cable leg extensions
- Leg extensions
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