You know the feeling. Twenty moves into the route, your forearms turn to concrete, your grip starts to fail, and the send slips away. That's the pump. And no amount of raw finger strength fixes it.
What fixes it is endurance. Specifically, the kind built by the ARC protocol: Aerobic Restoration and Capillarity. ARC trains your forearms to keep blood flowing and stay powered up far longer before they flood with the pump. It's one of the most proven ways to extend your climbing endurance, and the Force Board makes it something you can actually dial in by the pound instead of guessing.
Here's how to run it.
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What ARC actually does
ARC builds capillary density and aerobic capacity in your forearms. More capillaries means more blood, more oxygen, and more time before the pump shuts you down. The catch is that the adaptation only happens in a narrow zone: hard enough to drive change, never hard enough to actually pump out.
That zone is the whole game, and it's exactly where most climbers get ARC wrong. Go too easy and nothing happens. Go too hard and you build a pump instead of clearing one. On the Force Board, the live force trace turns "stay under threshold" into a number you can hold to in real time. No more training by feel and hoping.
Step 1: Find your Critical Force
Your Critical Force (CF) is the hardest pull you can sustain in a steady aerobic state. It's your ceiling for ARC, and everything else builds off it.
Run the Force Board 4-minute all-out test: repeated max pulls on a 7-seconds-on, 3-seconds-off cadence, one hand. The force your pulls settle into by the end is your CF. Record it for the edge you plan to train on.
No time for the test? Use about 40 percent of your max pull (MVC) as a starting point and refine by feel from there.
Step 2: Set your target force
During ARC you'll hold 55 to 70 percent of your CF on each pull. Because you're alternating hands, each forearm gets generous recovery between pulls, so you can hold slightly more force than you would on standard repeaters and still stay well under threshold.
The math is simple: target equals CF times 0.55 to 0.70. It works in pounds, kilograms, or newtons, as long as you keep your units consistent with the CF test.
A couple of examples:
- A 90 lb CF puts your target band at roughly 50 to 63 lb.
- A 120 lb CF puts it at roughly 66 to 84 lb.
Punch your own CF into the app and let the target band guide every pull.
Step 3: Run the protocol with split reps
ARC on the Force Board runs on what we call split reps: left hand pulls, right hand pulls, back and forth in a steady rhythm with no deliberate rest between. Each hand works about 40 percent of the time, so recovery comes free while the other side pulls and as you switch.
Here's the structure:
- Cadence: 5 seconds left, 5 seconds right, alternating. No counting, just keep flowing.
- Set length: 20 to 30 minutes of continuous split reps. Run a timer.
- Sets: 2 to 3, with 3 to 5 minutes of easy rest between them.
- Frequency: 2 to 3 times per week, on rest or easy days. Never before a hard session.
If you're new to ARC, start at 2 sets of 15 minutes and build from there. And warm up thoroughly every time: light pulls, then progressively heavier short hangs before you start the clock.
How to know you're in the zone
This is where the Force Board earns its keep. You're doing it right when:
- Your pull force holds steady rep to rep. The peaks don't drift down over the set.
- You feel only a light pump that levels off and never keeps climbing.
- You could hold a conversation. Effort sits around 3 to 4 out of 10.
Back off the moment your pulls start sagging below target or the pump keeps building. That means you've crossed your threshold and tipped out of the aerobic zone. Drop your target by about 5 percent, or end the set. Watching the force trace makes the call obvious instead of leaving it to guesswork.
Why split reps work
This rhythm isn't arbitrary. It mirrors real climbing, where one hand holds while the other moves. Each forearm loads briefly, then recovers, over and over.
That alternating pattern keeps blood flowing through the muscle, which is exactly what drives capillary growth. A long continuous hold does the opposite: it clamps off blood flow and chokes the adaptation you're after. By giving each forearm about 60 percent recovery time, split reps keep you in the aerobic zone for the full set, right where the gains live.
How to progress
ARC rewards patience. Build it in this order:
- Duration first. Work each set up toward 30 minutes before you change anything else.
- Then add a set. Move from 2 sets to 3.
- Then nudge intensity. As your CF rises, your target band rises with it. If a set ever feels like nothing, drift toward the top of the band.
Retest your CF every 4 to 6 weeks and reset your numbers. Your endurance ceiling moves, and your training should move with it.
Train it like you mean it
ARC is the difference between flaming out mid-route and still pulling hard on the last move. It's not flashy, but it's the work that lets you climb longer, recover faster, and stay committed through all six pitches.
The Force Board turns that work into something you can measure, hold to, and beat week after week. Every pull, every rep, every gain, tracked. That's how you stop guessing and start building endurance you can count on.
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