The debate over which type of exercises are the most beneficial for athletes has been going on as long as I can recall being interested in strength and conditioning; without a definitive or conclusive answer. Bilateral exercises are those performed in a two legged stance, while unilateral exercises are those performed in a single leg stance. It clearly depends on the focus of the session, exercise and where each piece of the puzzle fits. Changing from bilateral to unilateral not only changes the overall load but can also change the position of the load on the body and the actual resistance implement (barbell>dumbbell>kettlebell).
To build raw strength, it is a no brainer that you will be able to lift a greater load with a bilateral back squat compared with a unilateral squat e.g. a rear foot elevated split squat. From what I have read (and listened to) the monsters at Westside Barbell are not performing single leg dumbbell squats on their way to back squatting 1000lbs. There is a clear relationship on the force-velocity curve which demonstrates how overall strength will influence power metrics. But, chasing numbers and overall strength is rarely the defining factor as to who shows the highest level of readiness to play next Saturday, nor who will cross the finish-line first in the Olympic 100m final. Some sports and subsequent positions demand pure raw strength; most however do not. The chicken-egg concept with strength and power is a tough one; so where should you place your focus? 1 leg or 2 legs?
My answer… I use a combination of both. I will generally cycle these throughout the preparation phase and then although not exclusively, stabilize around single leg dynamic movements for in-season strength and power development. Frans Bosch is a major advocate for unilateral training; developing various conventional (and unconventional) special strength exercises, however I do not necessarily believe in all his innovations nor am I convinced on the actual transfer of the training. I have seen Dan Pfaff discussing how Greg Rutherford, 2012 Olympic Gold Medallist Long Jump, performed single leg Olympic lifts (snatch, cleans), which I am not opposed to, but again there is a transfer question (compared to the bilateral), along with the complexity of the movement which must considered.
The movement pattern of running is probably the most common form of locomotion used across all sports. It is effectively a series of rapid or pedestrian single leg coordinated plyometrics propelling the athlete in various directions down the field of play. Considering this, it stands to reason we should focus on developing force in a single leg stance. Some S&C professionals are completely against unilateral exercises citing that you cannot develop enough force with these exercises when compared with the bilateral version. This would be correct if we put them on a Keiser plate and measured the force. However, I believe there are various other factors which are important to the athlete which makes using unilateral exercises beneficial:
- Decreases spinal load (unilateral exercises are usually not supported across the shoulders or are a significantly reduced load than bilateral in the same position)
- Decrease the overall load which can decrease (complex issue) the chance of injury to muscles and connective tissue
- During the season, can maintain bilateral strength and power levels through contralateral transfer
- Can identify and isolate areas of weakness which are protected in the bilateral version of exercise
- Can isolate and strengthen specific muscle groups which are not effectively targeted in the bilateral version
- Identify and address limb strength deficits
At a previous ASCA conference, I have heard Dr Greg Haff state something to the effect of ‘If you are not getting stronger, you are getting weaker’. Physiologically and theoretically, this is correct. It is similar to the acceleration-deceleration continuum of a 100m sprint. However, as I stated previously, during the competitive season, scarcely the aim is to improve strength levels (perhaps only if injuries have occurred), rather maintenance and stimulation is the key.
Once the season starts and the intensity, velocity and sense of urgency increases, I do cycle between both types of exercises (> velocity with bilateral movements; reduced load) but I lean more towards unilateral training where it is appropriate (I have to admit I am highly influenced by texts and podcasts I have read/heard from Mike Boyle (MSBC), and his preference to favor unilateral work. He presents a logical and common sense approach to the training which sits well with me). Of course we want our athletes to remain strong during the season, but to chase numbers mid-season by loading up the rack and back squatting to 1RM is fraught with danger and irresponsible.
Have your athletes achieve a high state of readiness to compete in their chosen sport; not chasing numbers and showing elements of fatigue and soreness come game day.