For many years, there has been a massive debate over which exercise is the ultimate mass builder. The squat seems to be the reigning king. Those who do not squat are often scorned and called "wimps" and other colorful names. But is the squats domination really justified? Let's take a look at the numbers surrounding the two exercises.
In order to compare the two, we must first explore their differences. The major difference is in the amount of weight that can be used in each. Using the 45 degree leg press allows for the use of very large poundages.
For the majority of trainees, larger tonnage on the bar equals greater muscle gains. The increase in weight, however, can be very deceiving, since the leg press's angle creates a sizable mechanical advantage.
To make a fair comparison between the two, then, we must first even the board by taking this advantage into account and compare the actual resistance that the trainee moves in each case. To do this we will have to delve into a little physics. Looking at a leg press weight of, for example, 700 pounds let's calculate the true resistance:
Without explaining too much about the equations for the calculation we find that:
F = W sin 45
where F = actual force generated, and W = weight (700 lbs), and "sin 45" accounts for the angle of force generated compared to gravity.
F = 700 (sin 45)
F = 700 (0.707)
F = 495 pounds of resistance.
For me, personally, 495 pounds is nowhere near my best 10 rep squat, it's much higher! However I could easily perform a 10 rep leg press with the 700 pound load mentioned. To be sure I could quantify the two here, I performed a little experiment using data from my training logs.
I took the most recent data for each of these exercises for the same rep range and compared them. Doing this I found that, on average, my leg press poundage is 1.8 times that of my squat poundage for the same rep range. So, from the 700 pound example I should be able to squat 389 pounds.
Actual Squat weight = 700/1.8
Actual Squat weight = 389 pounds.
Notice that my actual squat weight is much less than my leg press poundage. There is an actual poundage difference of 106 pounds! This would suggest that the leg press is the more productive exercise, right? Not so fast. There are other things to consider. The overall body stress is not the same for both exercises.
The Central Nervous System
The human central nervous system consists of the brain and spinal cord. These lie in the midline of the body and are protected by the skull and vertebrae respectively.
This collection of billions of neurons is arguably the most complex object known.
The central nervous system along with the peripheral nervous system comprise a primary division of controls that command all physical activities of a human.
Neurons of the central nervous system affect consciousness and mental activity while spinal extensions of central nervous system neuron pathways affect skeletal muscles and organs in the body.
One aspect of the squat that we cannot ignore is the difficulty involved in supporting large weights atop your body structure. Remember that in the leg press only your legs and hips actually support the weight. The squat on the other hand stresses, to varying degrees, all of the musculature of the back, delts, and traps as well.
If you have recurring back problems this is a desirable characteristic of the leg press. But because of this the squat could have a somewhat more stimulating effect on the central nervous system (CNS) and, therefore, have a stronger effect on the muscle growth processes.
Regardless of popular opinion it is the CNS that stimulates muscle growth and not the stress imposed upon the muscles themselves. This is one of the reasons that Static Contraction Training can have a profound effect on muscle growth. Merely supporting very large weights can cause the CNS stimulation necessary to cause muscle growth.
The CNS can determine whether the weight being handled is too heavy for you to handle. 300 pounds feels heavier than 200 whether you complete a rep or not. It's the CNS that tells you that the heavier load is too much and it responds by manipulating hormones responsible for causing increased protein synthesis in the involved muscles.
The heavier the weight, the greater the muscle tension created and, hence, more muscle growth stimulated. This is why Static Contraction Training can cause extreme rates of muscle growth in those who utilize it.
To get back to discussing the squat versus leg press, it would seem that you have good reason to incorporate both in your training. I would not recommend using both at the same time at maximum poundage, though. Doing so can easily lead to overtraining of the musculature involved.
There is, however, one other option. You could use the leg press because of the amount of poundage that you can support. This would cause the localized stimulation of the quadriceps, hamstrings, and calves that can lead to a massive lower body.
To cause some of the stimulation of the squat you can use the partial deadlift, from knee height, in a power rack. This system would allow the best of both worlds. The huge weights in the leg press, and the stimulation of a total body free weight exercise in the deadlifts. The king may not be dethroned but now has competition, it would seem...