Unilateral leg training is key for symmetrical muscular development, balance and coordination, and sound movement patterning. Lack of proper ankle, knee, and hip mechanics in a unilateral setting can spell D-I-S-A-S-T-E-R for many sport athletes relying on the fast, fluid, and involuntary joint actions to occur and produce large amounts of force.
Some of the most common unilateral training exercises are the Bulgarian split squats, lunges (any and all variations), and step ups; each offering coaches and athletes benefits and potential drawbacks to consider.
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In this article I will lay out each movement and discuss which movement may be best for a given situation, limitation, or athletic need.
Bulgarian Split Squat or Lunge vs Step Up: Unilateral Training
All three of these movements are considered unilateral lower body training exercises, meaning that they require and athlete to support oneself primarily on one limb.
Complexity
When determining exercise selection, the complexity of the movement can be both a pro and a potential drawback. For lifters or clients who lack balance, coordination, or basic strength, less complex movements may be a viable option to integrate them into more complex unilateral exercises. Conversely, as an athlete improves, he/she may need extra complexity to better build out their neurological and physiological abilities.
Step Up
The step up can be done at various heights and loads, and is often a good general starting point for nearly every athlete. The application to walking and daily activities (such as stairs, etc) makes it a very relatable exercise for most beginners ad/or injured athletes.
When performing, the lifter should remain upright, with the heel down and using leg drive to lift the body up, rather than shifting weight forward into the lift to gain momentum to overcome the deep knee flexion and lack of leg strength.
When looking to maximize leg hypertrophy and/or strength, load can be added easily, with little mental energy needed, making the step up a good option for starters and or athletes looking for a challenging exercise that doesn’t requires the most amount of balance.
Bulgarian Split Squat
The Bulgarian split squat may be one of the toughest exercises when it comes to complexity (however some lunge variations can be just as challenging).
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Unlike other unilateral movements, the lifter must place their back leg up on a bench or box, increasing the need for the glute, hamstrings, and quadriceps to support the lifter’s bodyweight and external load, while demonstrating balance and sound joint mechanics. This movement is very effective for increasing glute engagement and hip/knee stabilization (preventing valgus, aka, “knocked knees) in the squat, and can be adapted (front foot close or far in front) to increase quadriceps and/or hamstrings hypertrophy.
Lunge
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Lunges can be done in a magnitude of ways, whether to the front, back, front foot elevated, walking, etc. In general, lunges have a lifter start supported by both feet and move dynamically under load, transferring the majority of their bodyweight and external load to one leg. The lunge is also high in complexity in that it requires sound joint mechanics, strength, and balance and coordination, arguably slightly more than step ups and Bulgarian split squats (as the lifter is still stationary). The ability to also load most lunges with more weight may also have a positive impact of overall joint and muscular adaptation.
Application
The specific application of each of these movements is discussed below.
Squatting Movements
Increasing knee and hip stabilization, muscle development of the lower body and hips, and enhanced joint mechanics and balance during unilateral lower body movements can drastically improve squat health and performance. While it does not replace squats per say, many lifters can see good returns on their training investments in the event the add lunges, Bulgarian split squats, and/or step ups into their routing,
Human Locomotion
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Human locomotion (running, walking, jumping, skipping, biking, etc) are all often done while one foot is in support of the majority of the body through space. The ability to strengthen both the muscles, but also the nervous system to adequately absorb force, generate force, and do it involuntarily can drastically increase sports performance and injury resilience.
Muscular Balance and Joint Integrity
Unilateral training has been shown over and over to increase muscular activation, balance, coordination, and joint/neuromuscular performance. The ability to increase a lifter’s injury resilience, decrease muscular imbalances and/or aid in body awareness and balance is one coaches and athletes must take seriously. Failure to do so could result setbacks and potential injury.
Targeted Muscle Groups
There are slight differences in loading placed upon the quads, hamstrings, and gluteal muscles depending on the exercise, stance, tempo, or training variable manipulated; all of which are discussed below.
Quadriceps
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The quadriceps are responsible for knee extension, which during all three of these movements is needed to complete each repetition.
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The ability to pinpoint a specific knee flexion range (such as determining step up height) can increase demands specifically to the quadriceps. During other forms of unilateral movements, manipulating depth (minimizing hip flexion at end ranges to keep the loading upon the quadriceps), monitoring tempos, and not fully extending each repetition can drastically increase the quadriceps engagement and development.
Hamstrings
The hamstrings work to stabilize and control the lifter and load during the negative aspect (eccentric) of every repetition. During the Bulgarian split squat and some walking lunges, the eccentric aspect of the lift must be very controlled to remain balanced (unlike some step ups where the lifters drops back downwards). Wider stance (front foot out front) can also limit knee flexion, therefore demanding greater hip flexion and extension with a fixed bent knee, exposing the hamstrings to some serious muscle damage (good damage, as in microscopic tears, aka hypertrophy).
Gluteal Muscles
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The gluteal muscles are effectively engaged during all three of the movements, however slightly more during Bulgarian split squats and lunges, as the gluteal muscles are aid in the knee and hip stabilization required by these more complex movements. Increase range of motion, such as during Bulgarian split squats or lunges in which the front foot is elevated can also increase hip extension, bringing the gluteal muscles more into play for stability and force production at throughout the movement.
Final Words
All three of these movements are great ways to integrate unilateral movements into training regimens. With unilateral training, emphasis should be placed on sound joint patterning, muscle activation and engagement, and an understanding that they are to aid min lifts and movements, such as squats, pulls, etc. They are not to be done with maximal loading or to set heavy personal records, as the increase loading and stress placed upon the single joint could result in injury if done incorrectly, too often, or when not ready for loading.
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