Muscular Endurance Training: What Does Pump Mean?
One of the more challenging things to accurately measure for endurance adaptations is climbing itself.
The diversity of handholds, move distance, wall angle, time under tension, and a climber's morphology change the intensity of each move, making it difficult to measure muscular capacity. To remedy this, research has used a tread wall or campus board (feet on) with a mandatory fixed hold size and time per hand move. However, in the non-research context, we tell people to climb four boulder problems, perform repeaters on a fingerboard, and climb up and down to failure. Because of the aforementioned variation, most of these methods (except the fingerboard) lack enough consistency to measure physiology precisely. To understand the muscular and cardiorespiratory adaptations to training, we need training and testing that is simpler, more reproducible, and not reliant on the technical skills necessary for climbing performance.
Over the last many years, I've invested much time and effort in understanding the adaptations of finger strength training for climbing.
My goal was to understand better how and if the fingerboard was an accurate measure of muscle force. If you need to become more familiar with what I'm referring to, I suggest you watch my channel's YouTube videos and check out the Climbing Magazine articles published in January and March 2023. There are also multiple podcast episodes on the topic here. I’d suggest checking out the last one with Steven from The Nugget Climbing.
In the abovementioned examples, I demonstrated that a supra-maximal load (130-150% of a muscular 1RM) is necessary on a fingerboard (the same is true when lifting something off the ground) to gain changes in recruitment. I theorize that the fingerboard method uses an eccentric-like muscle contraction (yielding isometric) type, which makes each fiber tolerant of more external load (30-50% more) and is more reflective of the upper body muscle cross-sectional area than literal finger strength. Because each fiber tolerates more load in this way, we use less of them. That is, until the loads get very heavy, which adds some risk to the joints of the fingers.
Additionally, tolerating more load in this fashion should be questioned regarding translating to the climbing wall. The broader exercise science literature has demonstrated that the specific adaptations we gain from strength training programs are load-dependent (muscular recruitment) and skill-dependent (coordination). Because of this, we should not expect that same response once the external load is removed and the feet are on the wall. The load will never be that high, and thus, the coordination (force direction, center of mass, finger joint angles, etc.) will vary.
Here's a more straightforward example of what I'm referring to.
Think about the last time you performed your max-weighted pull-up or pull-ups to failure test. The goal is to pull up (concentric or shortening muscle contraction) with as much weight as possible or for as many reps as possible at a given intensity (40-60%). In this scenario, getting the chin over the bar (upward motion) is typically a slow/steady struggle for the one rep or the last few reps until failure. Now, think about how easy it was to lower back down to the starting position on every rep, even the hardest one. Why is it so hard to lift the chin over the bar and not that hard to lower back down? That difference in load tolerance is what I'm referring to above. On the way down, we use around 30-50% fewer muscle fibers than when going up unless the load is supra-maximal (eccentric overload in which we cannot go back up). When we stretch a muscle under load, we gain efficiency and capacity for each fiber by loading the stiff portion of a connective tissue structure called titin at the end of each muscle fiber.
This passive tissue response can be useful for building tissue tolerance, but for muscular endurance training, it's an obstacle to accessing muscular adaptations. By stressing them more intentionally, we add capacity (metabolic) to the muscles.
At the muscular level, each contraction type creates and handles metabolites (the leftovers of muscle metabolism) differently. At the same intensity, eccentric contractions are more fatigue-resistant because they rely on those passive structures. They still create fatigue (stretching does attach and detach muscle fibers), but they won’t be as negatively influenced by it. Conversely, concentric contractions create fatigue and are also heavily influenced by it. The metabolite accumulation will reduce shortening velocity and thus coordination first. This fatigue is why getting pumped on a route quickly reduces power (the ability to grab holds), and the pull-up endurance test fails on the upward motion (concentric).
The primary limiting factors with muscular endurance training are metabolite accumulation and changes in pH. It's a waste clearance problem (capillarization), not a lack of fuel problem. You are not falling off a route because you run out of ATP because you never will. You fall off a route because your muscle fibers can no longer shorten quickly, making difficult climbing sections less possible. So, to sum up, muscular endurance training aims to stress the muscle right up to failure, rest until it's recovered (although as minimally as possible), and repeat (although each set will reduce in intensity and duration) for multiple sets until we no longer get the appropriate stimulus.
Consequently, stressing the muscles up to failure should build a more robust energy production and waste management system (capillary network). The goal, but also the tricky part, is finding the right intensity and duration to stimulate the muscle fibers because, as discussed above, the typical contraction type used with finger training (fingerboard, climbing wall, campus board) is less muscular.
What my initial investigation demonstrated.
When I compare the same relative intensity (% maximum) lifting something off the ground (yielding isometric) or curling the fingers into an edge fixed to an immovable object (overcoming isometric) while measuring muscle oxygen desaturation (SmO2), the overcoming style isometric produces more muscle stress (O2 desaturation) and, thus, fatigue in the finger flexors.
In this first example, I demonstrate a 40-50% intensity repeater (5-6 seconds on 1-2 seconds off to failure) on different arms, curling (overcoming isometric) and lifting (yielding isometric) upwards while measuring oxygen desaturation (muscles using oxygen) and resaturation (muscles recovering). It has been predictable for the 6 (including myself) athletes I've measured in this way to have more FDS (flexor digitorum superficialis) muscle stress when performing the overcoming style (curling) isometric.
When comparing the upward standing position to the arms overhead position (more like the climbing position), the results are also the same (another six athletes, including myself). What I’m finding is that at the same relative fixed load for each contraction type, doing repeaters at 40-50%, 50-60%, or 60-70% of an athlete 1-repetition max, the overcoming style isometric stressed the muscle more than the yielding style isometric did. One important note when comparing the two positions is the increase in muscle desaturation in the overhead position, compared to the lifting position, with the yielding style isometric. It would be easy to confuse this as demonstrating increased muscle activity when the arm is overhead, but I don’t think that’s the case. Instead, it is likely due to the reduced cardiac output and oxygen availability during the exercise because the arms are overheard. In this scenario, the compression in the capillary beds with muscle contraction, connective tissue stretching, and the "uphill" force placed on the blood flow will produce less overall blood flow to the capillary beds, showing a more “normal” decline in SmO2.
One of the most interesting findings with these two testing protocols is that all participants noted more pump and difficulty completing the endurance task with the yielding style isometric, regardless of the position.
I hypothesize that because the external load is higher with the yielding style isometric, the muscle and connective tissue stretch at a higher relative intensity (30% higher in most participants), creating more ischemia (lack of blood flow) to the working muscles. So, in this context, getting pumped did not equate to more muscle fibers being fatigued; the opposite seems to be true. In addition, when exercises increase the perception of effort, the evidence shows that it further reduces muscular recruitment. And neither of these are the goals of muscular endurance training.
If we look at the climbing endurance research, it suggests these four tests.
Peak force, or maximum voluntary contraction for a single repetition (1-3 seconds in length).
Anaerobic power, or a 30-second all-out force test measuring peak, average, and force force loss.
Anaerobic capacity, or a 60% MVIC force for duration test measuring the sustainability of the anaerobic system.
The Aerobic capacity test with an intermittent or a 50-70% repeater test to a force deficit.
(Research: Climbing-Specific Exercise Tests: Energy System Contributions and Relationships With Sport Performance January 2022 | Volume 12 | Article 787902. Frontiers in Physiology)
I've compared all these tests with the positions and contraction types mentioned above, and all the evidence I see points toward my suggestion that intentionally applying force to the edge by curling the fingers (overcoming isometric while isolating the finger flexors) provides more muscle stress than hanging from a fingerboard or lifting something from the ground (yielding style isometric in which we use the entire upper extremity and rely on more passive tension).
So, if the fingerboard or yielding style loading at a given intensity creates more pump with less muscle activity, I'm suggesting that we modify the intention of our muscular endurance training protocols to be less about hanging from or lifting an edge and more about actively applying force (up to the % target) onto that same edge. This new intention could be done on the fingerboard (now called a no-hang) and by applying force upward (standing position) in which the working muscle has a greater blood flow, which may increase capitalization due to the hand being below the heart and receiving more direct blood flow. Even though the latter is less like the climbing position, that should not matter if the goal is to stress the local muscular for adaptation.
Training is about pushing the physiological needle, not mimicking the technicality of a sport.
If you want to test your athlete's physiology with the Tindeq Progressor, check out the online course in my store. There’s also a ton of detailed physiologic information on our Patreon account. Feel free to send me a dm as well @c4hp if you have any questions.
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