Written and maintained by CASRAI Editorial Board
Last updated
General product information, not medical advice. For exercise selection or any health concern, ask a physician or physical therapist.
A resistance band works by stretching: the more it is stretched from its resting length, the harder it pulls back. The manufacturer’s instruction manual calls this “force-elongation”, and it is the one idea that explains how a band, a tube or a loop behaves in use.
How a resistance band works: force depends on percent stretch
According to the Thera-Band (The Hygenic Corporation) instruction manual, the resistance from elastic bands and tubing is based on how far the band is stretched, measured as a percentage of its resting length. Regardless of how long the band is before it is stretched, the force at its stretched length depends on the percent elongation.
Worked example from the manufacturer
The manual’s own example uses a 2 ft (60 cm) Green band. Stretched to 4 ft (120 cm), it is at 100% elongation and produces 4.6 lb of force. Stretched to 6 ft (180 cm), it is at 200% elongation and produces 6.7 lb. The manual also advises against bands that are too short, to avoid overly high pull forces.
Force at 100% and 200% elongation, by band color
| Thera-Band color | Force at 100% elongation (lb) | Force at 200% elongation (lb) |
|---|---|---|
| Tan | 2.4 | 3.4 |
| Yellow | 3.0 | 4.3 |
| Red | 3.7 | 5.5 |
| Green | 4.6 | 6.7 |
| Blue | 5.8 | 8.6 |
| Black | 7.3 | 10.2 |
| Silver | 10.2 | 15.3 |
Source: Thera-Band Resistance Band & Tubing Instruction Manual (rev. 5/12). For every color in the table, the force at 200% is higher than at 100%, so stretch distance matters as much as color. For the full level-by-level layout, see the TheraBand color chart.
The manual also describes elastic resistance as a distinct kind of resistance training compared with isotonic or isokinetic resistance.
What you need
- A band, tube or loop in good condition, long enough that the planned stretch does not exceed the limit below.
- A securely anchored, sturdy object if the exercise calls for an anchor.
- A latex-free version if anyone using it has a latex allergy or sensitivity; the manual states the standard bands are made of natural rubber latex and that latex-free versions exist (for the same material question in gloves, see what a latex glove is).
- Protective eyewear if the exercise could send the band toward the head.
Flat bands, tubing and loops
Performance Health, which sells Thera-Band products, says tubing is often used interchangeably with flat resistance bands. Premade loops remove the need to tie a band into a loop. The manual shows how to make a short loop by tying each end into a square knot, and notes that tubing handles are made by tying or looping the tubing.
Steps
- Inspect. Before use, look for small nicks, tears or punctures, and check connection points for wear. Discard and replace a band with flaws.
- Prepare. Remove rings and watch for long fingernails; keep the band away from sharp objects.
- Anchor. Attach to a sturdy object securely so the band cannot slip free.
- Stretch within the limit. Do not stretch a band or tube more than 3 times its resting length (the manual’s example: a 12 in / 30 cm band should not go past 36 in / 90 cm).
- Store. Keep out of direct sunlight and away from extreme temperatures (see the storage section).
What can go wrong
- Snap-back. A band can snap toward the head in some exercises; the manual advises avoiding such exercises or wearing protective eyewear.
- Overstretching or damage. Stretching beyond 3 times resting length, or using a nicked or torn band, risks failure. Performance Health also notes that bands may break if they have small tears.
- Latex reaction. People with latex allergies or sensitivities should use latex-free bands.
- Children. The manual states bands are not toys and children should be supervised.
How to store and care for resistance bands
Per the manufacturer’s manual: store all bands and tubing out of direct sunlight and away from extreme temperatures. After use in chlorinated water, rinse with tap water and dry flat (Performance Health says to rinse in tap water and hang to dry). If a band becomes sticky, clean it with mild soap and water, dry it flat, then dust with talcum powder, baby powder or corn starch. Performance Health says bands used frequently in clinics or exposed to extreme temperatures may need replacing every 1-2 months, and should be replaced on cracks, small tears or abrasions. For related equipment lists, see the physical therapy clinic supply checklist and athletic training room equipment guide, and for another elastic product, what an elastic bandage is.
When to get professional help
The manual advises consulting a physician before starting, and stopping and contacting a healthcare provider for sharp pain, shortness of breath, dizziness or lightheadedness.
FAQ
How does a resistance band work?
It pulls back harder the further it is stretched. The force depends on the percentage stretched from resting length (force-elongation), not on absolute length: a Green Thera-Band gives 4.6 lb at 100% elongation and 6.7 lb at 200%.
What is the difference between loop bands and tube bands?
Per Performance Health, tubing is often used interchangeably with flat bands, and premade loops save tying a loop yourself. The manual covers tying loops from bands and tubing.
How do you store resistance bands?
Out of direct sunlight and away from extreme temperatures, per the manufacturer. Rinse after chlorinated water and dry flat; inspect before each use.
How far can a resistance band be stretched?
The manual says not more than 3 times its resting length.
Sources
- Thera-Band Resistance Band & Tubing Instruction Manual, The Hygenic Corporation, rev. 5/12 (checked 2026-10-30).
- What TheraBand resistance band should I buy and more FAQ, Performance Health (checked 2026-10-30).
