Donkey kickbacks are one of the top Smith machine exercises for glutes when it comes to developing a shapely butt.
Sure, a combination of heavy squats and hip thrusts is pretty much unbeatable for adding mass to your behind. However, if you want to build proportional glutes that even an IFBB Bikini Pro would be proud to own, then you need to perform unilateral exercises, too.
And, based on my coaching experience, few single-leg exercises are more effective than Smith machine donkey kicks for sculpting firm, symmetrical glutes.
So let's get into it...
As mentioned, you should aim to create a 90-degree angle between your upper and lower leg at the Smith machine glute kickback starting position. Obviously, this is easier said than done, since you can't exactly inspect your knee joint angle while you're on your hands and knees.
But, as a rule of thumb, if you feel the unmistakable, intense peak contraction in your glutes, then you know that your form is on point.
However, it's still possible to mess things up.
For example, If you lean too far away from the machine, then you'll feel more tension in your hamstrings. Conversely, if you position your torso too close to the machine then well...you'll probably press the bar into the hooks (and feel a whole load of tension in your quads).
Line up your joints during Smith machine kickbacks, and everything will be kosher.
Did you know that some Smith machine barbells can tip the scales at more than 20kg? While others can weigh as little as 3kg?
Unfortunately, when Jack Lalanne created the Smith machine, he invested a concept, not a product.
As a result, the bar weights are more diverse than the squat form in Planet Fitness.
However, this diversity isn't necessarily a bad thing as long as you know the bar weight before you start loading plates onto the machine.
If for whatever reason your Smith machine doesn't list the weight, make a note of the brand (and if applicable, the model) and perform a quick search either on our site or on your favourite search engine.
Of course, you might not give a toss about the bar weight, which is fine as well. Some people just want to train their glutes without worrying about minutia, and I completely get that.
Even more so than hip thrusts, Smith machine glute kicks rely on a strong mind-muscle connection to be effective (which is to say in order to fix your muscles imbalances).
As such, it's essential to pre-activate your glute with something like a hip circle if you want to enjoy the best effects from kickbacks.
Preactivation can be as simple as performing a couple of sets of bodyweight hip thrusts. However, if you're serious about glute training, then I recommend checking out Bret Contreras's book, Glute Lab: The Art and Science of Strength and Physique Training for some test-backed pre-activation techniques.
Like all glute isolation exercise, the most important part of the Smith machine donkey kick is the contracted position. Why? Because the glutes are most active during and near full hip extension.
Therefore, you must squeeze the heck out of your glutes at the top of the rep. Aim for stars, kick to the moon, pretend that some creep is chatting you up and that you're kicking him in the balls—whatever works for you. Just make sure to squeeze your glutes like your life depends on it.
Otherwise, Bret Contreras will not be happy.
If you want a gym accessory that warms up your hips and simultaneously builds up your gluteus medius, then I highly recommend investing in the Sling Shot Hip Circle By Mark Bell.
Admittedly, it's not much use for the Smith machine kneeling rear kick itself—but it's remarkably effective for firing up your glutes before your working sets.
Me and my wife have tried loads of hip circles over the years, and they've always ended up in absolute tatters (or in the bin).
And while the Mark Bell hip Circle isn't the cheapest hip circle, it's definitely the most durable.
I know what you're thinking: the resistance bands are for warming up your hips, right?
Remember when I said that glute kickbacks exhibit their peak tension at the top of the movement—in the contracted position?
Well, what I like to do is connect a band from the bottom of the smith machine (usually on the lowest weight peg) to the actual Smith machine barbell.
This setup dramatically increases the difficulty of the exercise. But, more specifically, it makes the glute contraction 10x more intense because you're forced to squeeze the heck out of your cheek in order to prevent the bar from lowering.
It would be remiss if I didn't give a big shoutout to Bret Contreras and his book, Glute Lab: The Art and Science of Strength and Physique Training.
This 608-page glute training mega guide removes the guesswork from building your glutes. With hundreds of well-illustrated pictures, countless exercise routines and more test-backed training techniques than I can remember, it's a must-have for anyone serious about sculpting a well-developed physique (of which I believe the glutes should be an integral part).
The glutes are the prime movers in the Smith machine donkey kick—hence why it's also called the "Smith machine squeeze" (or the Smith machine glute press). You're literally squeezing your butt cheek and then lowering the weight back down. Works like a charm as a finisher exercise .
The hamstrings become more active the further you lean away from the machine. Or, to be scientific, hamstring activation will increase in direct proportion the angle at your knee joint.
If you feel your hams burning too much, shift your hands and knees closer to the Smith bar—that'll put the tension back onto your glutes.
But just don't take it to the extreme. Otherwise...
If you position your torso too close to the bar, you'll increase knee flexion (and thereby quadriceps activation). This is undesirable for two reasons.
One, it robs your glutes of tension.
But second, since your knees and feet won't be lined up, you'll also end up kicking the bar into the hooks, which will ruin your rhythm (and your glute pump).
Your calves get worked isometrically during the Smith machine kneeling rear kick because they have to stabilise your ankle.
Many people complain that they don't feel their glutes working as much as they'd like during various hip-hinge exercises.
If you're one of these people, then I highly recommend performing the Smith machine kickback to increase your mind-muscle connection.
Specifically, you want to perform high reps in order to generate a strong pump and burn in the glutes. This sensation is easy to achieve with kickbacks since metabolic stress (better known as the pump) is most prevalent when a muscle is fully shortened, as is the case with the glutes during the Smith machine one leg kickback.
Also, make sure to hold the peak contraction for a second with your glutes. This way, you're creating strength in an area in which most people are weakest, which is to say full hip extension.
Heavy, eccentric-focused exercises like squats and Romanian deadlifts are hard to recover from quickly because they cause a ton of muscle damage. This is because they maximally lengthen your muscles under tension .
Exercises like the Smith machine kneeling rear kick are the exact opposite. As we just established, these squeeze-based movements are most challenging when the muscle's at its shortest. Naturally, this enables you to perform more training volume (and thereby stimulate faster glute growth) because these exercises cause less muscle damage on a per-set basis.
This is why you could get away with performing more sets of hip thrusts than squats, for example —the Strength Recovery Adaptation Curve is completely different. And it should definitely be taken into account when designing the optimal glute training program .
It's a well-established fact that the glutes are most activate at or near full hip extension (think hip thrust rather than good morning). 
As a result, you want to program a lot of exercises into your routine that display their peak tension (are most difficult) in the contracted position. The Smith machine kneeling rear kick is a prime example of such an exercise.
Nobody wants one glute that's bigger than the other.
But if you've been performing squats and hip thrusts for any length of time—without any unilateral work—then you probably already have muscle imbalances.
Of course, since virtually everyone has a dominant leg and a weaker leg, these so-called imbalances are completely natural. But that doesn't mean we shouldn't work on them.
Performing donkey kicks Smith machine style is a great way to ensure that each of your glutes receives equal work. Why? Because the exercise requires no stabilisation, meaning that you can focus 100% of your attention on getting the best glute workout possible.
The end result for you is a more symmetrical butt. And, of course, a stronger mind-muscle connection that carries over to every other glute exercise.
Besides the glute kickbacks machine, there are 3 amazing Smith machine kick up alternative exercises that you should consider.
The hip thrust is my favourite, and, by most accounts, the most effective Smith machine hip extension exercise that you can do to add mass to your glutes. While it doesn't quite provide the eye-watering peak contraction that you'll feel during Smith machine donkey kickbacks, it does enable you to overload the glutes more efficiently than virtually any other movement.
And, at this point in the glute training revolution, I think it's safe to say that some kind of bridging or thrusting movement is an essential part of any workout regime.
The Smith machine glute bridge is the less popular younger brother of the hip thrust. It's a great secondary movement for getting a pump because the relatively small range of motion is naturally suited to high reps. However, it provides minimal glute stretch, which as you probably know, is a crucial component of muscle growth. Still, it's a worthwhile Smith machine kickback alternative for building bigger glutes.
Smith machine kneeling squats are effectively a kneeling hip thrust, at least biomechanically-speaking. As such, it's little surprise that they elicit the highest EMG muscle activation out of any glute movement. It's a great glute activation exercise, but overall, I prefer Smith machine donkey kicks.