Exercise Tubing and Bands (cont.)
Green, Yellow, Blue, Red, Purple, Black: How Much Weight Am I Lifting?
One of the difficulties in identifying the amount of resistance is that tension in rubber changes as you stretch it. For instance, the tension in an exercise tube when you first start to pull on it during a biceps curl is less than when you fully stretch it. In fact, some research shows that tension is not constant in the tube until it is stretched beyond 50% of its starting length, while other research shows that tension may not be constant until the elastic is stretched more than two and a half times its original length. The mechanical stretch properties of elastic vary based on thickness, age of the rubber, how much it is used, how quickly it is stretched, and other factors, and so it's difficult to quantify with certainty the "weight" of each tube or band that you stretch.
However, in one well-executed study, researchers were able to quantify the weight-equivalent of tubing and bands using sophisticated strain gauges. They measured tubing and bands from the Thera-Band Company (yellow, red, green, blue, black, and sliver tubing; yellow, green, and black bands) and stretched them under many different conditions. They found the following when the elastic was stretched to twice (or 100% of) its starting length:
Green: 5.6 pounds
Black: 8.1 pounds
Red: 3.0 pounds
Green: 4.7 pounds
Blue: 6.5 pounds
Black: 7.2 pounds
Silver: 10.5 pounds
Stretching each tube and band another 100% in this study yielded about one and a half times more tension, so when the green tube was stretched to 200% of its original length, the weight equivalent was approximately seven pounds. Keep in mind that not all manufacturers use the same color or quality of rubber, so these values are specific only to the tubes and bands used in the study. Also keep in mind that rubber loses its elasticity after many uses. One study showed that tension started to decrease slightly after just 50 full (100%) stretches, while in another study it took 500 stretches to reduce the tension in the bands and tubes by 12% and 6%, respectively. Whether you will notice the difference is hard to say, and so you should pay attention to the resistance over time. You can purchase new tubes or bands if you notice the elasticity decreasing, or alternatively, increase the tension by wrapping them around your hands a few times and shortening them. Shortening the elastic increases the tension (another benefit of tubes and bands).