Ask the Expert
By Steven J. Fleck, PhD

Q: I have been seeing some advertisements for rubber cords that you are supposed to use in conjunction with a free-weight bar while performing exercises. You attach one end of the rubber cord to the floor and the other end to a free-weight bar. To keep the bar balanced, you attach one rubber cord to each end of the bar. The advertisements claim that using the rubber cords will increase your one-repetition maximum (1 RM) more so than doing an exercise in the normal way with just a free-weight bar. I am like many weight trainers and really do want to increase my 1 RM in certain exercises like the bench press and back squat. And like many weight trainers, I am constantly looking for any training edge that will help me increase my 1 RM. Is there any sports science research on the use of rubber cords to increase your 1 RM?

A: The use of rubber cords while doing weight-training exercises with free-weight bars like you describe has been around for several years. The rubber cords are normally used for only certain exercises with a strength curve called an ascending strength curve. This means that as you lift the weight or do the positive motion of a repetition, you get stronger and stronger. Two exercises with an ascending strength curve are bench presses and back squats. With these two exercises, if you only did a quarter or half-repetition you could actually lift more weight compared to doing a full repetition, or the exercise’s full range of motion. An ascending strength curve means that as you lift the weight you become stronger and stronger. Therefore, you can lift more weight during the upper part of a normal repetition.

Usually, one would attach the rubber cords to the floor and bar so that the cords are only stretched slightly when you are at the lowest point in a repetition. The lowest point in the bench press would be the “chest touch” position and lowest point in the back squat would be where your knees and hips are bent the most. As you lift the weight from the lowest point in a repetition, the cords stretch more and more, making the resistance you are lifting appear to become heavier and heavier— until it is the heaviest at the top or highest point of a repetition.
The major idea of using rubber cords is to make the weight you are lifting heavier and heavier, so that the resistance you are lifting matches your increase in strength as you perform the positive or “lifting” portion of a repetition. Advocates of rubber cord use believe you will recruit or use more of your muscle fibers through a greater portion of a repetition. The idea of recruiting more muscle fibers through a greater range of motion is that by doing so, you will increase strength to a greater extent.

Unfortunately, very little research in sports science journals has been published concerning the use of rubber cords. However, a training study using rubber cords while performing bench presses and back squats was recently published. The study lasted seven weeks and compared performing bench presses and back squats in a normal fashion to performing the exercises using rubber cords. The people participating in the training had, on average, 3.6 years of weight training experience, but no training experience with the use of rubber cords. Because subjects participating in the study had a relatively long history of weight training, the results of the study should be applicable to experienced lifters.

Training consisted of performing the following upper body exercises: bench presses, one-arm rows, triceps extensions, lat pulldowns and external shoulder rotations during one training session. The second training session consisted of the following (mostly lower body) exercises: back squats, power shoulder shrugs, Romanian deadlifts, walking lunges, dumbbell arm curls and shoulder press combos. These two training sessions were performed alternately three times per week. Three to 6 sets of each exercise for 2-10 repetitions per set were performed per training session in a periodized manner, where the number of repetitions and number of sets were changed as the seven-week training program progressed. The group training with rubber cords only used the rubber cords during the bench presses and squats.
So what happened? As you would probably expect, weight training with or without rubber cords did significantly increase bench press and squat 1 RM. However, the group using rubber cords showed significantly greater gains in 1 RM compared to the group that did not use rubber cords. In the bench press, 1 RM of the rubber cord group increased, on average, 8.0 percent; the group not using rubber cords, on average, improved only 4.0 percent. In the back squat, 1 RM of the rubber cord group increased, on average, 16 percent; the group not using rubber cords increased, on average, 6.0 percent.

On average, with bench presses, the use of rubber cords resulted in approximately two times greater gain in 1 RM and almost three times greater gain, on average, with back squats. This study clearly indicates that when doing the same training program, the use of rubber cords when doing bench presses and back squats results in significantly greater gains in 1 RM compared to not using rubber cords. It is important to note that this study lasted only seven weeks, so the conclusion of this study that rubber cords increase 1 RM more than not using rubber cords must be limited to relatively short training periods. This means that long-term effects of using rubber cords is still not known, but that short-term use of rubber cords should increase your 1 RM.
The authors speculated that the use of rubber cords caused greater 1 RM gains due to greater recruitment of muscle fibers throughout the range of motion in bench presses and squats. They also speculated that in particular, the use of rubber cords resulted in greater muscle fiber recruitment during the sticking point of each these exercises. If you can get through the sticking point of bench presses and back squats with a 1 RM weight most of the time, you can then complete the repetition. Which means that your 1 RM will increase.
So what's the bottom line? This study indicates that the use of rubber cords when performing bench presses and back squats will increase your 1 RM more so than performing the same training program without rubber cords. It is important to note that the conclusions of this study need to be limited to exercises with an ascending strength curve, like back squats and bench presses. Exercises that do not have an ascending strength curve like arm curls, upright rows and knee curls may not show increases in 1 RM with the use of rubber cords. Luckily, most people are primarily interested in increasing their 1 RM in bench presses and squats more so than other exercises. From a practical perspective, this means give rubber cord training a try if your training goal is to increase 1 RM in back squats and bench presses.

Reference:
Anderson, CE, Sforzo, GA and Sigg, JA. The effects of combining elastic and freeweight resistance on strength and power in athletes. Journal of Strength and Conditioning Research, 22:567-574, 2008.