Even the slightest tweak in an exercise can drastically change the way it affects your body, and the pulldown is no exception. The lat pulldown is done with bent arms, and the straight-arm pulldown is done with -- you guessed it -- straight arms. This slight difference in technique causes a dramatic shift in the muscles that you use for each exercise.
In the conventional lat pulldown you sit down at an exercise machine, grab a handle that resembles a pull-up bar, and pull the bar down to your chest. It's commonly used as an alternative to the pull-up or chin-up because you can adjust the amount of weight you use, whereas in a chin-up or pull-up you have to work with your own bodyweight.
Read More: Muscles Used in a Lat Pulldown Machine
In the straight-arm pulldown you stand upright in front of a cable machine that has a straight bar attachment. You grip the handle with your palms facing down and push the bar down as far as you can while keeping your elbows completely straight. Some of the same muscles are used as in the lat pulldown, and some are different. The latissimus dorsi is still one of the major muscles used, since it extends your shoulder.
Muscles Used in Both
The two exercises both activate some of the same major muscle groups of the back.
The lat pulldown and straight-arm pulldown are both shoulder extension exercises, which primarily work the latissimus dorsi, which is the largest muscle in your upper body. The muscle spans from your lower back to the middle of your spine and out to your shoulder, where it attaches.
In the lat pulldown, the lats work harder if you use a wider grip. In the straight-arm pulldown, a narrow grip works best. A lat pulldown will work the lats more because you can use more weight. In the straight-arm pulldown other muscles, like your triceps, will give out before your lats do.
The posterior deltoid, part of the big muscle that covers your shoulder, contributes in the lat pulldown and straight-arm pulldown. This muscle is in the back of the shoulder, and helps pull your arm down and back during the movement. It assists the lat in extending your shoulder, which helps you pull the weight down in both exercises. It's used more in the lat pulldown than the straight-arm pulldown because your arms move out to the side as you pull down.
Both exercises use a smaller muscle called the teres major, a small muscle that spans from the bottom of your shoulder blade to the side of your arm. It helps extend the shoulder, just like the lat and posterior deltoid, but it's the weakest muscle of the three.
Your triceps, the muscles on the bottom of your arm, play a big part in the straight-arm pulldown, but not as much in the lat pulldown. In the straight-arm pulldown, they keep your elbows straight throughout the movement and they help you pull your arms down, aiding the lats. They also help you in the lat pulldown but they don't work nearly as hard because your elbow is bent, not extended.
Muscles Unique to the Lat Pulldown
The lat pulldown engages more muscles than the straight-arm pulldown. Keep this in mind when putting either exercise in your training plan.
As you pull the bar down, you use the lower part of your trapezius, which is a large muscle that connects to your neck, shoulder blades, spine and out to your shoulders. It has three parts: upper, middle and lower. The lower part helps you bring your shoulder blades down and together, which is an important part of the lat pulldown.
In the lat pulldown, your elbows bend as you pull down. The muscle that makes your elbows bend is the bicep, the muscle that sits on the front of your upper arm. This muscle is more active when you do a lat pulldown with your palms facing you.
Out of your four rotator cuff muscles, the one that contributes the most to the lat pulldown is the infraspinatus. This muscle sits on the back of your shoulder blades, and stretches from the part closest to your spine all the way out into your shoulder. It rotates your arm out, which means that it is not a major contributor to the lat pulldown, but it plays a part.
Muscles Unique to the Straight-Arm Pulldown
The straight-arm pulldown does engage your abs, an effect you don't get with the lat pulldown.
Read More: What Does a Straight-Arm Pulldown Work?
As you pull the bar down, the weight pushes back against you. This means that you have to fight to stay upright. If you don't, the weight will force you to lean back, which is known as a trunk extension. The muscles that prevent this are the trunk flexors, which are two specific abdominal muscles: the rectus abdominis and external obliques. The rectus abdominis is the muscle that forms the "six pack," and the external obliques are the muscles on the sides of your trunk.