The squat is a bilateral movement that stresses a variety of muscles from head to toe. When performed correctly and too sufficient depth, the squat is a great exercise for building strength and power. However, over recent years the squat has faced some heavy criticism from strength and conditioning coaches. Some have gone as far as completely abolishing it from their programming because they feel that it is either too unsafe, or simply ineffective at transferring over to sport performance. Rather than performing bilateral movements, these coaches will opt for single leg (unilateral) variations instead.
Though most coaches will incorporate both bilateral and unilateral training into their programs, it is still worth understanding how training solely with one form or the other impacts performance. In a recent study by Fisher and Wallin (2014) from the Journal of Athletic Enhancement, the effects of unilateral only versus bilateral only training on speed and agility markers was tested. A total of fifteen collegiate male rugby players were split into a bilateral group and a unilateral group. Subjects trained twice per week performing both strength and plyometric exercises. Before and after the training program the subjects were all tested on the t-test, Illinois agility test and 10 m sprint.
The results showed that for the t-test, unilateral training resulted in a significantly greater reduction in time compared to bilateral (average change of -0.63 seconds and -0.11 seconds, respectively). For the Illinois agility tests, unilateral training again came out on top with an average change of -0.80 seconds compared to bilateral, of which showed a -0.50 second change. For the 10 m sprint, bilateral training was superior to unilateral training showing an average change of -0.07 seconds while unilateral times were virtually unchanged (0.01 seconds).
The authors conclude that unilateral strength and plyometric training appear to be more effective at improving change of direction ability while bilateral strength and plyometric training appear to be more effective at improving speed over short distances. A potential explanation for this discrepancy is that unilateral training tends to activate the hip abductors to a greater extent, which are highly active during frontal plane and change of direction type movements. A 10 m sprint is a measure of acceleration where the body must overcome the greatest amount of inertia to propel the body. Therefore, it would make sense that greater overall strength should facilitate better performance which is likely best developed with bilateral squatting. The take home message is simple. Include a combination of bilateral and unilateral training into your programs to develop both speed and change of direction ability.
Fisher, J., & Wallin, M. (2014). Unilateral versus Bilateral Lower-body Resistance and Plyometric Training for Change of Direction Speed. J Athl Enhancement 3, 6, 2.