Ask any bodybuilder "what do you do for hamstrings?", and I can guarantee that stiff leg deadlifts will be in there somewhere.
Stiff leg deadlifts add mass to the hams like nothing else. The problem with the free weight version, however, is that your stabilisers can often give out before your hamstrings.
Obviously, this is hardly optimal from a muscle growth standpoint. And if all you do is barbell stiff leg deads, then you're probably leaving a lot of your potential results on the table.
But all hope is not lost. Unlike barbell movements, Smith machine hamstring exercises remove most of the stabilisation from the equation, enabling you to achieve faster rates of muscle growth by focusing purely on your hamstrings.
Some may argue that Smith machine stiff legged deadlifts aren't "functional". But what exactly is functional about stretching your hamstrings with a heavy barbell, anyway?
If you want to perform functional training, go do some housework or some gardening—there's nothing functional about bodybuilding.
If, however, you want to beef up your hamstrings, then this article is for you.
As I'll explain later, the stiff-legged deadlift is different from the Smith machine straight leg deadlift. But for now, just know that you should always maintain a slight knee bend during the Smith machine stiff leg deadlift.
Doing so makes your hamstrings much less prone to injuries that result from overstretching. Also, even just a slight knee bend enables you to lift significantly heavier weights (and thereby build more muscle) than you can with completely straight legs. This is because the glutes are in a stronger force-producing position with bent knees.
It's tempting for beginners (and anyone else who just wants to start building their hamstrings ASAP) to bend at the waist rather than their hips. And yes, while doing stiff leg deadlifts this way can and does provide a significant hamstring stretch, it's usually at the expense of lower back health.
You see, when you actively reach down to the ground, rather than move towards the ground as a consequence of bending your hips, your spine naturally starts to round, which can cause all sorts of problems when you add a loaded barbell into the mix.
To be clear, the barbell shouldn't move because you're reaching with it to the floor. Instead, the Smith bar should move as a consequence of you flexing and extending your hips .
Keeping the bar close to your body is much easier to do with a Smith machine than with a free weight barbell. Unless, of course, your Smith machine is angled, in which case your stiff leg deadlift quickly becomes a straight leg deadlift.
But, presuming a linear Smith machine, this form tip is easy to master and has some pretty sweet benefits.
For one, keeping the bar close to your body recruits more of your hamstrings and less of your spinal erectors. Besides being brilliant for your back health, this vertical bar path also makes your legs grow faster and with fewer sets (because they get more of the tension).
This positioning naturally leads to the second benefit—increased strength. Obviously, a big muscle group like the hamstrings can handle far heavier weight than the comparatively smaller erector spinae. As a result, you can overload your legs with more resistance, which again, results in faster, more substantial muscle growth .
Having a set of sturdy lifting straps at your disposal is like having a second set of hands—even if your first pair gives out, the second set always has your back.
Lifting straps have increased my hamstring growth dramatically because they enable me to devote 100% of my attention to the working muscle. Unfortunately, most straps are incredibly uncomfortable, often increasing your grip strength at the expense of wrist health.
After trying half a dozen pairs, I finally settled on Versa Gripps.
Not only do Vera Gripps make it ridiculously easy to maintain a firm grip on the bar, but they also provide my wrists with a remarkable amount of support—even more so that some so-called "wrist wraps".
However, this isn't all that surprising considering that they're American-made (rather than in slapped together in some dodgy Chinese factory). Plus, it's great that us Brits can finally get our hands on Versa Gripps without taking out a second mortgage to pay for international delivery.
I'm not much of a powerlifting fella these day (especially since I tweaked my back doing deadlifts a few years ago).
Although I don't believe weightlifting belts are a silver bullet, I don't do any kind of deadlift without my RDX Powerlifting Belt for Weight Lifting.
It's made from sturdy cowhide leather, so it's no surprise that mine still looks like new after over a year of heavy usage.
Anyway, the biggest benefit is that my core strength has gone through the roof. Even on the Smith machine stiff leg deadlift, my core used to give out before my hamstrings. But with my RDX Weight Lifting Belt, that's not the case anymore. In fact, new PRs are a regular occurrence. And I'm just loving the progress!
I've also had good results from wearing the Dark Iron Fitness Pro Weight Lifting Belt, which I went ahead and ordered after reading a ton of positive reviews. Since this belt is constructed from 4mm Buffalo hide, it's incredibly durable, especially since it also benefits from dense double stitching.
However, the biggest benefit is that you can see instant results from wearing the Dark Iron Fitness Weight Lifting Belt. On average, users saw an increase of 10% on their major lifts, which could easily be 10-20kg if you're a relatively strong guy.
When I first started to see the benefits of using my Fit Nation Foam Roller, I laughed to myself.
No, not because the intense muscular massage gave me some weird laughing fit, it was because I realised what a waste of money most so-called "recovery supplements" are.
Foam rolling has decreased my mental stresses, loosened up my muscles and sped up my recovery more significantly than any supplement I've ever taken. And to think people still waste their money on dodgy supplements.
I suppose "self-myofascial release" doesn't have the same ring as "magic new supplement", does it?
Anyway, I've since upgraded to this 4 Piece Foam Rolling Set so that I can also work the knots out of my upper body by rolling the massage balls around my thoracic spine. Plus, all the gear's made from non-toxic materials, so it was a no-brainer considering that I'm pretty health-conscious for a man.
The hamstrings are the prime movers in the Smith machine stiff legged deadlift. Due to the massive weighted stretch, they take a ton of muscle damage, and as such, they can take a while to recover. That said, with good enough nutrition, stiff legged deadlifts will add mass to your hamstrings quicker than just about any other exercise.
The more that you flex your hips during stiff leg deadlifts, the more active your glutes become. Or, to put it another way, the deeper the stretch, the deeper the glute burn.
However, with a small form tweak, you can also change the movement into a glutes-first, hamstrings-second movement, turning it into what's known as the American deadlift .
Essentially, to emphasise your glutes, you want to posteriorly tilt your pelvis as you lockout the rep. The easiest way I can describe this is that you're essentially contracting your lower abs and curling your tailbone towards the sky.
Couple this glute squeeze with a slightly shorter range of motion, and you'll fire up your glutes significantly. Albeit, somewhat at the expense of your hamstrings.
The spinal erectors function to stabilise your torso, meaning that, the straighter you keep your legs, the harder your lower back has to work. This is because it's compensating for your hamstrings and glutes, which are in a relatively weak position when your knees are fully locked out (or, to be scientific, when you're in full hip extension).
Stiff leg deadlifts (or any deadlift variation for that matter) provide some pretty decent forearm stimulus, especially if you're performing high reps.
However, since most of us do the Smith machine version to eliminate our smaller, fast-fatiguing muscles—and thereby put the tension onto our hamstrings—I recommend using straps to ensure that your legs are always the limiting factor.
One thing's for sure. Doing leg curls, whether it be lying, seated or standing, creates a phenomenal pump in the hamstrings. However, they don't elicit that same, deep, unmistakable stretch, which only stiff leg deadlifts and the like can provide us with.
But why is the stretch so important?
Well, the science is pretty clear on this one. The weighted stretch (or eccentric muscle contraction) leads to more muscle growth than concentric contractions (such as squeezing your biceps).
This is why compound exercises (such as squats) that really emphasise the stretch are considered superior mass builders to movements like leg extensions, which focus more on the pump and contraction.
Take home message: never neglect the weighted stretch if you want juicy hamstrings .
Personally, I think deadlifts are vastly overrated from a muscle-building perspective. But I won't open up that can of worms now.
However, one flaw of the deadlift that no one can deny is that your lower back usually becomes fatigued before (and thus, at the expense of) your hamstrings and glutes.
With the Smith machine stiff leg deadlift, however, the exact opposite is true. Presuming good form, your hamstrings will almost always give out before our spinal erectors, which means less back pain and more leg growth.
Don't you just love a happy ending?
Research shows that strength-endurance training (high-rep stiff leg deadlifts) leads to less decline in hamstring strength than pure strength training (one rep max deadlifts, for example). 
What this means for you, is that you can perform more training volume because your hamstrings will naturally have a higher fatigue-resistance. This is important considering that training volume, not maximal strength, is the key driver of muscle growth itself .
So, no. Despite what bodybuilders might say, endurance-style training won't make your muscles shrivel up. In fact, it will probably make your legs grow faster since you're targeting the hard-to-fatigue, slow-twitch muscle fibres.
The Smith machine Romanian deadlift is yet another great exercise that enables you to focus purely on your hamstrings by taking virtually all of the stabilisation out of the equation. It's exceptionally similar to the stiff leg deadlift. The only real difference, as I explain below in more detail, is that you allow more knee bend, thus shifting the focus onto the glutes.
Depending on what kind of gym you train at, doing a deadlift on a Smith machine might get you a few dirty looks. Heck, if you slam the weight down, it might even get you kicked out of certain gyms.
In my opinion, if you want to truly deadlift, then you have to do it with a barbell off the floor. While it might stroke your ego to pull five plates on the Smith machine, it's never going to be a true deadlift because the barbell doesn't bottom out.
If you enjoy the core-strengthening benefits that free weight good morning provide, but also enjoy the safety offered by the Smith machine, then Smith machine good mornings are a brilliant exercise to include in your leg workouts.
As with the barbell version, Smith good mornings still work your core. However, since you can change your foot position without losing your balance, you can also preferentially target the hamstrings or the spinal erectors, leading to a more personalised leg workout.
The difference between a stiff leg deadlift and a straight leg deadlift is that, in the straight leg deadlift, you keep your legs completely straight and let the bar drift away from your body slightly. Naturally, this creates a deeper stretch in your hamstrings and glutes. However, it also engages more of your spinal erector muscles, so it's best avoided if you have existing back problems.
The difference between the stiff leg deadlift and the Romanian deadlift is that the Romanian deadlift aims to recruit the glutes more by increasing the knee bend, which in turn enables you to lift heavier weights.
However, the stiff leg deadlift is probably better for boosting your conventional deadlift strength as it requires you to lower the bar further towards the ground, thus improving your off-the-floor pulling power.
As you can tell, Smith machine stiff leg deadlifts are a great mass builder for the hamstrings. And, by my reckoning, just as effective as the free weight version.