There are many benefits of full squat training that make it superior to partial squatting as the “go-to” squat, including better knee joint function, enhanced muscle coordination, and greater athletic strength.
A classic study that compared the effect of full front, full back, and quarter back squat training for 10 weeks found that full back squats produced the greatest overall strength development when trainees were tested in all three variations. Both the full front and back squat programs produced robust increases in maximal strength of 25 to 30 percent.
In contrast, the quarter-back squat group experienced a decrease in their capacity to produce force by about 15 percent. The also experienced performance losses in isometric and explosive strength measurements. The one area the quarter squatters improved was at quarter back squatting (no surprise there), increasing 1RM by 37 percent.
Researchers suggest the reason quarter squats are so ineffective for developing usable strength is that the back becomes a limiting factor due to the high loads required. Small range-of-motion training requires much heavier loads than full-range training, and in the case of the quarter squat, the thoracic spine would collapse under loads heavy enough to induce training stimuli on the lower body musculature.
The opposite occurs with deep squat training: Because lighter loads are used with full squats, they are safer and more manageable for the spine, while applying greater neuromuscular stimuli to more motor units throughout the lower body.