So You Want to be a Fitness Trainer: Controversial Exercise

Pumped up iron aficionados often like to demonstrate their strength in the weight room.
In my athletic prime I did it too. I used to lift the whole stack on the Nautilus Leg Extension Machine. I don't remember the exact weight but I think it was around 220 pounds or 100 kilograms. It wasn't a single lift but rather a set of 20 repetitions for one set. My quadriceps muscles would be screaming for mercy from the 12 Apostles by the 15th rep. Nothing could seem to match the leg extension machine for carving out the muscles of the front thigh. As for the sacred muscle pump, leg extensions reigned supreme.
Now, years later, I get episodes of nagging knee pain! Throughout my years of sporting life my knees were the rare joints that weren't injured. The evidence for me to blame Leg Extension Machines is only anecdotal but still compelling. However sports science seems to share my view.
Performing an exercise such as the squat causes compression force. The load of the weight is spread throughout the body with shoulders through the torso through the legs to the feet absorbing the gravitational force. The weighted load from a leg extension is at the upper ankle joint. This creates shear force pushing downward directly on the knee joint. Short term damage or sudden injury are unlikely. However years of accumulated grinding could lead to long term instability and in the extreme case conditions of osteoarthritis may occur.
The ligaments and tendons supporting this joint are not designed to withstand extreme or excessive shear force. The Anterior Cruciate Ligament(ACL), the Lateral Cruciate Ligament (LCL), the Medial Cruciate Ligament (MCL) and the Posterior Cruciate Ligament (PCL) all provide support for the knee. Ligament tissue receives little blood flow and does not get larger or stronger in response to exercise the way muscle does.
The Patella (kneecap) shields the underlying meniscus or articular cartilage that lubricates and cushions the 3 bones that join at the knee. Sudden stops, traumatic force or constant overuse can damage the intricate balance of this important location of the human organism.

The 4 muscles of the upper thigh are called the quadriceps. This is the anatomical profile:

Vastus Lateralis - Outer muscle of the upper thigh.
Vastus Intermedius- Middle muscle of the upper thigh.
Vastus Medialis- Inner muscle of the upper thigh. This muscle can take on a tear drop shape especially using a leg extension machine.
Rectus Femoris - Overlies the other 3 quadriceps muscles.

The leg extension machine is an isolation exercise. It isolates the quadriceps but does not engage the other muscles of the thigh, The hamstrings, the adductors, the abductors and the glutes are not participants in the movement, This exercise also enables movement only through the knee joint. The hip joint is not engaged.Hip flexor muscles muscles such as the Psoas, the Gracilis, and the Iliacus are mostly left out of the equation with the Leg Extension Machine.

This exercise is not functional to any practical movement or athletic motion. Squats, deadlifts, lunges or even walking or running stairs or hills mimic movements that are more realistic to normal motion. As for building strong muscular thighs, have you ever seen the legs of a sprint cyclist?. Hard brief intervals on a bike are super leg developers. Speed skating and sprint running also develop leg strength.

Is there anyone that might find use from the leg extension machine? Bodybuilders could benefit from such an isolation movement and the effect of creating visible separation of the quadriceps muscles. Even then, bodybuilders usually perform squats or leg presses first and use leg extension machines for fine tuning.
*** The most important muscles in lower body locomotion are the gluteus maximus muscles of the buttocks. If these muscles are weaker than the quadriceps then numerous postural problems can occur. The over active hip flexors can pull the body into anterior pelvic or sway back. Many distance runners can be skinny and have little belly fat but the front pelvic tilt makes it look like they have a gut.

All weight training movements have some potential for risk. Fitness Trainers should be aware of the risk / reward ratios of each prescribed exercise. The type of apparatus used is also a significant factor.
Some leg extension machines are poorly designed and can feel awkward and uncomfortable. Equipment such as Nautilus or Life Circuit are of superior design and safer to use.

The Leg Extension Machine does build strong and well developed front thigh muscles.
It does not develop functional strength that is specific to every day movement. It is an exercise that should be done carefully. It also should not be the only front thigh exercise used in any training program.

Until Next Time,....Keep Fit

Little Bobby Strong