Construction of a chest expander
A Chest Expander most common is made out of two handles and steel- or rubber springs that are attached to the handles. The springs can be removed to adjust the resistance.
This is the famos Deuser Band with a resistance of 12kg (26 lbs) at 100% stretch and 24kg (53 lbs) at 200% stretch. It’s perfect to learn the exercises and for warming up before a workout.
This 5*30kg Elastikon Expander (150kg = 330 lbs) from Schmidt Sport (German Manufacture) has rubber-springs. It’s the best choice for a beginner expander, because the handles are big enough (The Lifeline Chest Expander is the best you can get, but in Germany it is hard to get). The rubber strings of this Elastikon Expander are pretty long, so you should be around 5’9 heigh, or make knots on each string to adjust the length.
This 5*40kg Elastikon Expander (200kg = 440 lbs) from Schmidt Sport is from 1969 and has rubber strings.
This is the stretch-resistance-diagram, sent with the 5*40kg Elastikon Expander. It shows that the resistance (in this case 200kg) is only reached when fully stretched. This means the resistance is much lower at the beginning of the exercise and at its peak it’s big.
This self-made steel chest expander weighs about 7kg (15 lbs). It consists off 7 of the strongest produceable steel-springs (at this size) and two rotating handles. We don’t know the exact resistance but it feels way stronger than the 200 (440lbs) Elastikon Expander.