Stay away from using the leg/knee extension machine utilizing heavy weights/workloads. Since it’s only a single-joint exercise (unlike squats or lunges), coupled with the likelihood of injuries with either too heavy a weight or a malaligned knee position in relation to the machine’s axis of rotation. If you choose to incorporate this exercise into your strength training regimen, then ask an experienced trainer about proper knee position (which should place the knee joint aligned with the axis of rotation – – See Figure 1.). Furthermore, use sets comprised of a higher number of repetitions (reps) at a light weight versus only 2-6 reps at heavy workloads. For almost all of my athletes and clients, I avoid this machine exercise altogether, and incorporate much safer and more effective multi-joint exercises. A couple of examples are wall squats with a Swiss/stability ball against the wall or on the Smith Machine or lunges, which allow you to position your feet far forward of the knee (See Figure 2.). By keeping the toes far forward of the bending knee, it places much less strain on the patellar tendons. Furthermore, these are multi-joint (knee and hip) exercises that not only work the quadriceps, but also target the glutes, hamstrings, and hip muscles (piriformis, pectineus, and iliopsoas) – which engage and strengthens more muscles, burns more calories, increases more hormone activation, and are more sport specific for a wide range of sports and activities.
Figure 1. (Two Proper Aligned, followed by Two Malaligned Leg/Knee Extension Machine Positions)
Figure 2. Proper Forward Position of Feet from the Knees during Wall Squats
Best of luck, and Train Safe!
P.S. If you are unable to view the Figure Photos or have additional questions, feel free to contact me at TP2Coaching@gmail.com