A 50/50 is a pulley system using gymnastic rings and a waist belt that essentially cuts the amount of strength required for many ring skills in half.
This makes it an excellent tool for training basic skills like muscle ups, making it possible to gradually build to unassisted versions, starting from where you are in terms of strength.
To explain why 50/50 machine works let’s start by looking at the above illustration of a trainee hanging from a bar.
If the trainee hangs from one arm, that arm is carrying 100% of his bodyweight. hanging by two arms reduces the load on the other arm by 50% and both arms supper 50% of the bodyweight. Now say you have two extra arms, yes you’re a magical 4 armed trainee! How much of your weight does each arm hold when hanging from a bar? 25%, that’s easy!
Now take a look at the illustration below. What the 50/50 does in essence is turn you in to a sort of 4-arm trainee. If you look at the cable in green you will see there are 4 ends, and each of them supports 25% of the bodyweight.
To make it a bit easier to visualise, let’s replace the trainee with bowling balls, big ones that altogether weigh as much as the trainee.
The two on the ends (R) weigh the same as the one in the middle (L). And since we know form our 4-armed man example that R (the force at the ring) = 25% Bodyweight, then L (the load being lifted) is twice that, so the load being lifted is 50% of the bodyweight, and the name 50/50 machine makes sense!
Right: Trainee hooked up to the 50/50 Left: Diagram of masses seen at rings and waist belt
Here’s a mathematical breakdown –
MB = Mass of Trainees Body
MR = Mass Supported by One Ring
ML= Load (Mass being Lifted)
MB = ML + 2MR (Trainees weight is distributed between belt and rings)
ML = 2MR In a static situation (The weight on the rings just balances out the weight on the belt)
Solving for ML gives –
ML = MB/2
I.e. The mass being lifted is equal to half of it’s total weight, the other half of the trainees weight is being applied to the the rings to counter balance the load. To move the load up, apply just a little more force to the rings.
The 50-50 is very easy to use, for example most people will be able to do a muscle up their first session with one. From there you’ll need to add weight to progressively load and build strength towards doing a full unassisted muscle up.
To add weight you can use a dipping belt, climbing slings or whatever else you can come up with.
How to Build a 50-50
What you need:
1 x Harness
2 x Rope
2 x Pulley
4 x Carabiner
2 x Aluminium Guy Line Tensioner
Most items can be found easily online or at your local climbing shop.
For rope I used 6mm accessory cord and think it’s the ideal balance between strength and flexibility. Too think a rope can be stiff and can add friction to the system. Too thin and it might not hold you. Another advantage of 6mm is it’s easy to knot, but also easy to unknot if you even need to undo a knot to readjust your system.
You’ll want two pieces of rope, they should be long enough to reach from where you’d like the rings to hang to your ceiling and back again, plus enough to knot both ends, and maybe a bit longer just in case. I added about a meter to the length of each rope.
You’ll also need two pulleys, if you buy from a climbing shop, make sure to get the large low resistance type and not the smaller, much less expensive ones. They have too much rolling friction and your 50-50 won’t feel right with them.
The whole set up ran me about €200 just so you know what you’re getting into.
Singing Rock Pole II Work Positioning Harness
Using the guy line tensioners, knot the end of the rope (In my case I have a little extra slack so used a loop knot). Leave a length of cord to form a loop and thread the remaining rope through. The loop will be used to attach to the harness.
Use a double half hitch knot with two to three loops to secure the other end of the rope to the ring.
Attaching the rope to the harness with a carabiner. You can forgo both the guy line tensioner and carabiner and just tie directly to the harness or use a slip knot to attach, but IMO this is much easier and nicer.
Singing Rock Pulley Extra. You need carabineers to attach to the ceiling. I have a concrete ceiling and used anchos with a eye bolts for the mounting.
The fully assembled 50-50. From here just attach the carabineers to your ceiling mount.