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# What is a Weight Stack?

Article Details
• Written By: Micki Elizabeth
• Edited By: Lauren Fritsky
2003-2018
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A weight stack is a set of often flat, rectangular bars used to add resistance to some types of weight machines. Typically, each bar weighs the same amount so that one can add weight in increments. A pin may be inserted into the front of each bar in order for an individual to choose the total weight he desires for a particular exercise.

Weight machines may be referred to as “stack machines” when they use a weight stack. On these machines, the stack of weighted bars usually sits on top of one another vertically. Each weighted bar has two holes in it. The first, a hole from the top to the bottom of each bar, allows for a vertical metal stake to be inserted down the middle of the stack.

The second hole on each weighted bar is much smaller. It is generally located on the broadest of the rectangle’s sides. This hole may reach halfway into the bar, meeting up with the first hole that goes from top to bottom. On some models, this smaller hole reaches all the way through the bar.

This vertical metal stake has a series of holes drilled into it. A selector pin can then be used by inserting it into the smaller, second hole on a bar. This selector pin locks into place in the vertical stake. The weight bar with the selector pin in it, along with every weight bar in the weight stack on top of that one, is now connected to the vertical stake.

Using the selector pin in this way, one can choose the amount of weight he would like to use from the weight stack when performing a particular exercise. For instance, many weight stacks come with approximately 10 to 15 bars at 10 pounds (4.5 kg) each. An individual may choose any number of bars from the stack that, together, total the specific weight desired. Furthermore, an individual could choose not to use the weight stack at all and, instead, perform the exercise without added resistance.

Most of the time, each weighted bar will be labeled in some way to help guide a user. A typical weight stack found in a gym may be labeled so that each bar tells the total amount of that bar plus the bars above it. Sometimes, each bar is simply labeled as one, two, three and so on.

A weight stack can be beneficial for those who incorporate strength training into their workout routines. Knowing how much weight an individual can handle without injury is important. A typical goal of weight training is to improve gradually over time, and a weight stack can help to determine one’s progress. With the ability to quickly and easily change the weight on any machine, gym-goers at different levels of fitness may all use the same equipment safely.