Here's what you need to know...

  1. Explosive unilateral exercises have been shown to improve Rate of Force Production (RFD) and contribute to overall power output.
  2. High-load eccentric or negative training is one of the most powerfully effective ways to pack on muscle.
  3. Single-leg exercises are valuable since you can use one leg for the eccentric (lowering) portion and two legs for the concentric (lifting) portion.
  4. Single-leg training can increase hamstring length, which has benefits for activities like sprinting.
  5. Single-leg exercises are great for metabolic conditioning.
  6. It takes twice as long to train each leg individually. That means at least twice the metabolic cost.

One Leg, Twice the Results

Single-leg exercises have become a staple in many strength and conditioning programs:

  1. They allow athletes and bodybuilders to continue training around an injury.
  2. They correct left-right strength and size asymmetries.
  3. They improve general balance and proprioception.
  4. They're similar to athletic movements such as running and bounding and therefore have a strong motor carryover to sport.

When you dig a little deeper, there are even more hidden benefits that make single-leg exercise a powerful training tool.

1 – More Explosive Power

Explosive power training has long been considered the exclusive jurisdiction of the bilateral (two-limbed) lifts. Heavy, complex movements like barbell squats, deadlifts, and presses stimulate the growth of cellular proteins. Lighter, ballistic strength exercises like barbell cleans and plyometric drills improve neuromuscular output, timing, and efficiency.

But that doesn't mean single-leg exercises don't have a seat at the power-development table. Unilateral exercises, which are performed from a small base of support and present a high degree of sensorimotor challenge, have been shown to improve Rate of Force Production (RFD), one of the most important factors that contribute to overall power output.

RFD is the physiological equivalent of a race car's 0-60 mph time – it measures how long it takes a muscular contraction to get off the starting line before hitting peak levels of force production. RFD is typically divided into two-phases: The initial onset stage, which measures how quickly you can initiate a voluntary contraction, and the late stage, which measures terminal velocity.

Traditional bilateral resistance and/or explosive exercises improve RFD by developing the speed and amplitude of commands being generated from the pool of motor neurons in our brain. In other words, heavy-loaded exercises are excellent tools to improve your ability to generate outgoing (efferent) messages from "central command" to working muscle tissue.

Unilateral exercises, on the other hand, improve RFD in a somewhat reverse manner. The small base of support created by having only one foot on the ground at a time stimulates the pool of motor neurons at our spinal level (afferent), increasing their contribution relative to the overall force development equation. These types of improvements can be thought of as forcing "outside-in" adaptations, rather than traditional "inside-out" ones.

Although the research in this area is not as clear as we'd like it to be with regard to the exact mechanisms by which this occurs, we know that sensorimotor exercises improve RFD through some combination of improved motoneuron recruitment, firing frequency, and/or synchronization patterns in a way that's just different from the way heavy resistance training does.

None of this is to say that you should ditch bilateral lifts in favor of unilateral ones; heavy bilateral lifts should always form the foundation of your power program. However, unilateral exercises may make for a far better, more response-specific power exercise option than they're typically given credit for, especially in terms of improving early stage contractile power.

There are no clear-cut rules to maximize the power-enhancing properties of the single-leg lifts, but here are a few thoughts. First, single-leg deadlifts, single-leg squats, and strict step-ups are the most logical resistance training exercise choices, providing the smallest possible base of support and requiring the greatest proprioceptive response.

Second, using an offset load – holding a dumbbell or kettlebell on the opposite side of your working leg – seems to make sense. Asymmetrical loading increases rotational torque on the body, which in turn increases the balance demand and stimulates a stronger neural response.

Offset Step-Ups

Keep the weights heavy and the tempo steady on loaded exercises, much as you would during a bilateral exercise. Splurge on high-speed contractions for medicine ball exercises or bodyweight plyometric drills.

2 – Improved Strength

We've known for decades that focused, high-load eccentric training – where a muscle is actively lengthened under mechanical tension – is one of the most powerfully effective ways to pack on massive amounts of muscle tissue and dramatically increase strength and output.

But the reality is that most strength programs still under-emphasize, or outright ignore, the eccentric component of most exercises. This is doubly true when it comes to lower body exercises.

There are some practical obstacles for why this happens. Our muscles can handle 15-30% more weight when functioning eccentrically versus concentrically, which means we need two different sized weights for each half of each rep, one weight that you can lower under control and one which, by definition, you can't lift back up on your own again, to realize the full benefit of muscular overload.

A good workout partner or access to specialized equipment that picks up and releases weights from the bar can make this process a lot easier, but both are luxuries that aren't available to all. This is where single-leg exercises are worth their weight in gold since you can use the same weight on both halves of your rep – using one leg for the eccentric and two legs for the concentric portion – with two different loading schemes.

Loading the eccentric with 100-120% of your concentric 1RM (known as accentuated eccentric training) has been shown to be a more effective way to increase strength than standard concentric training or higher volume eccentrics where a sub-maximal concentric weight is simply slowed down over the course of a set.

Here's how it would work using a single-leg deadlift as an example of a posterior chain eccentric: Begin at the top position of your deadlift with a barbell loaded with 100-120% of your single-leg concentric 1RM. Remove one foot from the floor and lower the weight to the ground using only one leg. Take 3-5 seconds. Once the weight is down, bring the other foot back to the ground and explosively pull the weight back up to the beginning position using both legs.

Repeat this process for 1-2 sets of 1-3 reps at the beginning of your workout and it'll help to prime your nervous system to preferentially recruit fast-twitch fibers during the rest of your lifts.

Single-Leg Deadlift Accentuated Eccentrics

The same method can be applied to single-leg squats.

Single-Leg Squat Accentuated Eccentric

3 – Increased Hamstring Range of Motion

If you've been geeky enough to read research in the area of hamstring strain prevention and rehab, you know that in addition to the strength-building effects of focused eccentric training comes the corollary benefit of increased hamstring range of motion. The reason this happens is kinda cool.

In the short-term, we know that among other things, eccentric loading causes microscopic damage to the chains of sarcomeres that make up our muscle tissue. This is the first stage in the process that leads to delayed-onset muscles soreness (DOMS).

One of the big net positive results with DOMS is an increase in something called the "series compliance" of our muscle tissue. Series compliance can be thought of as our tissues' willingness to lengthen during a stretch. The higher the compliance, the less force is needed to affect length change.

Over the course of a training cycle, where subjects are regularly exposed to eccentric stress, we start to see quantifiable increases in fascicle length, which suggests an addition of sarcomeres in series within the muscle.

These types of adaptations cause a shift in the hamstrings' optimal length – the knee angle at which our hamstrings can generate the highest possible amount of torque – in the direction of longer muscle length. In other words, it gives your hamstrings the ability to produce peak force in a longer position without needing to overstretch.

This has obvious benefits for activities like running and sprinting, which require the hamstring to rapidly decelerate hip flexion and knee extension at the terminal phase of leg swing. It's also why you see eccentric training featured so prominently in the literature about hamstring strains.

But it stands to reason that the increased length/force relationship would also benefit any movement that required force production when the hamstrings are in a stretched position, like at the bottom position of a deadlift, kettlebell swing, glute-ham raise, or, arguably, at the bottom of a squat.

This could be particularly useful to help people with limited range of motion to improve their deadlift starting position off the floor.

We also know this shift in optimal length occurs more readily during unilateral exercises, like single-leg deadlifts, than during bilateral ones since the hip extension moment created by lifting the contralateral acts to limit posterior pelvic tilt that would otherwise short-change the elongation stress on the hamstring attachment.

Here are two stiff-leg deadlift (SLDL) variations that use eccentric contractions to build awesome power and functional strength:

Eccentric Single-Leg Deadlift From Deficit

Single-Leg Deadlift Medicine Ball Slam

4 – Identify and Close Energy Leaks

Removing 50% of your normal stabilizing platform dramatically increases the demand on multi-directional stability, particularly in the frontal and transverse planes. This has a powerful magnifying glass effect on any energy leaks caused by muscle imbalances, movement deficits, and left-right asymmetries that drain muscular efficiency and increase the metabolic price tag for applying force during a lift.

In terms of economy of motion, the application of unfettered strength and power carries the cost of proper positioning. Good positioning means that your joints are able to travel freely around an optimal center of rotation equally, and reciprocally, on both the left and right sides.

Movement inefficiencies can often hide within the wide margins of a bilateral pattern, drawing metabolic resources away from prime movers like energy-sapping parasites. When this happens, we see knees that collapse inward during a lunge, a trunk that side-bends during a step-up, or a hip that rotates outward during a single-leg deadlift.

The rehabilitation world has devised a myriad of manual muscle tests and isolative assessments to identify energy leaks or correct underlying muscle weaknesses, but these types of static diagnostic screens don't always transfer well to dynamic performance on the field or in the weight room.

Rather than spending precious training time performing complicated assessments to hunt down energy leaks, it's often more time efficient and psychologically manageable to repurpose single-leg exercises as both training tools and movement-specific assessments.

I'll often use a sagittal plane exercise like a step-up or step-down as an opportunity to assess frontal plane trunk, hip, knee, and ankle stability. Step-ups work better for assessing frontal plane control because there's much less rotational torque than during other single-leg exercises, so I can get a very clear picture of frontal plane insufficiencies.

Valgus Collapse

In the video you should have seen a significant degree of mechanical faults – valgus knee collapse, foot pronation, and compensatory side bending – that indicate a lack of motor control and/or strength in the frontal plane.

In the transverse plane, nothing brings a mobility or stability dysfunction to the surface quicker than observing a single-leg deadlift. The video below shows an open rotated hip position, a very common left/right imbalance that shows up in many people's movement profiles indicating an inability to properly internally rotate and adduct the hip joint during forward bending.

Single-Leg Deadlift Fault – External Rotation

In addition to their value as assessment tools, making small tweaks to these single-leg exercises allows them to double as both a training exercise and a movement corrective.

To do so, I use a version of Reactive Neuromuscular Training (RNT), a technique that uses external force, usually in the form of band resistance, to accentuate an existing stability problem in order to heighten proprioception and elicit a reflexive postural correction.

RNT Step-Up for Medial Knee Collapse

RNT Single-Leg Deadlift for Hip Internal Rotation

5 – Cardio (Without Doing More Cardio)

The powerful cardiovascular and metabolic advantages of single-leg exercises are often hidden in plain sight.

I remember they hit me like a donkey kick to the chest halfway through a set of heavy, high-rep dumbbell lunges I was doing as part of a high volume program. By the end of the set, my heart rate was north of 185 beats per minute and all of the reasons I hadn't included high-rep lunging in one of my programs were coming sharply back into focus.

It obviously takes exactly twice as long to train each leg individually as it would to train them both at the same time. (The true time cost is actually higher if you factor in speed of movement and readjustments to accommodate for balance).

All of that means at least twice the amount of time under tension, twice the metabolic cost, twice the number of challenged breaths, and twice the number of heartbeats for the same exercise performed on two legs.

Single-leg exercises are now a staple in my metabolic conditioning programs. Here are two of my favorite finishers that combine a variety of single-limb movements into a concerted lower body blitzkrieg.

Circuit #1

  Exercise Sets Reps
A1 Dumbbell Forward Lunge 2-3 10/side
A2 Bodyweight Single-Leg Bench Hip-Thrust 2-3 10/side
A3 Dumbbell Goblet Side Lunge 2-3 10/side
A4 Explosive Bodyweight Step-up 2-3 10/side

1 minute rest between sets.

Circuit #2

  Exercise Sets Reps
A1 Dumbbell Rear Leg Elevated Split Squat 2-3 10/side
A2 Lateral Skate Hop 2-3 10/side
A3 Dumbbell Single-Leg Deadlift 2-3 10/side
A4 Prowler Sprint (or Treadmill Sprint) 2-3 45 sec.

1 minute rest between sets.

Related:  10 Best Unilateral Exercises

Related:  More on eccentric training