The Physiology of Climbing
As a sports scientist, I love getting to take concepts from research and applying them in practice to see what the outcome is for an individual. If I'm trying to solve a specific problem, I'll sift through research for solutions, then put them to the test and observe the results. Often clear trends emerge during this process, and the fruits of labor triple down into the programs I write for athletes I coach. Other times the responses are so variable between individuals that it’s difficult to parse out why something did/didn’t lead to the desired outcome. Recently i’ve been interested in understanding the physiological predictors of climbing performance. My hope is that this leads to better KPIs for physiologists, more targeted needs analysis for coaches, and more surgical training protocols for athletes.Â
What makes climbing so unique from a physiological standpoint is that it’s essentially a sport of sustained and intermittent isometric muscle contractions. This creates a unique demand on the cardiovascular system compared to other sports. The most significant difference in the cardiovascular response to static exercise versus dynamic exercise resides in their respective effects on active muscle blood flow. During an isometric contraction, blood flow decreases in response to the swelling and stiffening of active muscle fibers. The stiffening of active muscle fibers also leads to an increase in intramuscular pressure, which causes a mechanical constriction on the blood vessels. This happens during dynamic exercise as well, but the rhythmic alternation between contraction and relaxation, like during running, allows for blood flow to remain stable due to the skeletal muscle pump.Â
As such, the hallmark of isometric or static exercise is a failure to ensure adequate blood flow to the working muscles when force production exceeds the percentage of an individual's maximum voluntary contraction where they begin to restrict venous outflow (i.e., venous occlusion occurs). In these scenarios, task failure occurs when an individual can no longer supply oxygenated blood to the working muscle to keep up with the oxygen demand. This is particularly important in sports like climbing, where sustained isometric contractions with short relaxation periods are interspersed. To improve performance in climbing, we need to:
Increase maximal strength and recruitment of the finger flexors, among other muscle groups;Â
Increase the percentage of maximum voluntary contraction where one occludes and therefore cannot get oxygenated blood into the muscle and waste products out of the muscle;Â
Increase the speed at which oxygen can be re-supplied to the working muscle between contractions; andÂ
Improve intramuscular coordination to relax the muscle quickly between contractions to allow for improved venous outflow.
In a paper by Christine Merimer and colleagues titled, Physiological and anthropometric determinants of sport climbing performance, 44 climbers of various skill levels were studied to try and determine the greatest predictors of performance. Using multiple regression analysis, the investigators found that ~60% of climbing performance can be explained by trainable qualities, like those listed above. In contrast, anthropometric markers only explained 0.3% of the total variance in performance. Among the trainable qualities accounting for much of the inter-individual variation in performance, we can separate them into a handful of categories.
(1) Finger flexor strength endurance / maximal strength - Fatigue resistance of the finger flexor muscles is frequently cited as one of the most essential factors for climbing performance along with maximal force production of the finger flexors. In David Giles and colleagues' 2020 paper titled, An All-Out Test to Determine Finger Flexor Critical Force in Rock Climbers, the investigators sought to test whether a single all-out assessment of finger flexor critical force predicts climbing ability. Their results showed a strong association between finger flexor critical force and climbing ability, defined as an individual's max red-point grade. When critical force was expressed as a percentage of body weight, the association strengthened further, depicted in the image below.
(2) Finger Flexor Maximal Deoxygenation - In a study by Simon Fryer and colleagues titled, Forearm oxygenation and blood flow kinetics during a sustained contraction in multiple ability groups of rock climbers, the investigators aimed to determine the relationship between forearm flexor muscle blood flow, oxidative capacity, and climbing performance. Their results showed that intermediate, advanced, and elite climbers deoxygenated the flexor digitorum profundus and flexor carpi radialis muscles significantly more than novice climbers, and that both the rate and magnitude of desaturation correlated with climbing ability such that the elite climbers had a greater rate and magnitude of desaturation than the advanced climbers, the advanced climbers had a greater rate and magnitude of desaturation than intermediate climbers, etcetera.
(3) Finger Flexor Maximal Reoxygenation - In a study by Simon Fryer and colleagues titled, Hemodynamic and Cardiorespiratory Predictors of Sport Rock Climbing Performance, the investigators sought to determine the relationship between various hemodynamic parameters and climbing performance. In essence, they aimed to understand whether finger and forearm flexor reoxygenation rates predict climbing performance by examine the association between ‘oxygenation half time to recovery’ (O2HTR) and red point climbing grade. Using a linear regression analysis the investigators found that O2HTR showed a strong inverse association with highest self reported red point grade which is depicted in the image below.
(4) Treadwall VO2peak- In edition to establishing O2HTR as a strong predictor of climbing performance Simon Fryer and colleagues also demonstrated that treadmill VO2peak is strongly associated with self reported repoint performance in their paper titled, Hemodynamic and Cardiorespiratory Predictors of Sport Rock Climbing Performance. This makes sense given that an individuals ability to deliver and utilize oxygen in the primary working muscles are both strong predictors of climbing performance (VO2peak = Blood flow * Oxygen Consumption). However, it’s important to recognize the difference between VO2peak and VO2max. VO2max applies strictly to the highest attainable VO2 value for the whole body. VO2peak on the other hand is contextual. Your VO2peak during small muscle mass exercise is much lower than VO2max, whereas your VO2peak during full body all out exercise is equal to your VO2max. Since climbing uses a relatively small percent of total muscle mass, compared to rowing for example, an individuals VO2peak during climbing is typically much lower than their VO2max. As a result, VO2max is only a moderate predictor of climbing performance.
(5) While it hasn’t been established in the literature it’s also worth considering how maximal vasodilator capacity of the skeletal muscle will influence climbing performance. In my lab we recently ran a small scale pilot study aiming to investigate this topic. Over a handful of visits we had participants undergo a reactive hyperemia test involving a two-minute occlusive period with a pneumatic cuff restricting brachial artery blood flow followed by a two-minute perfusion period. The image below depicts a subjects muscle oxygenation response to this procedure:
Then, over four other visits, we had the subjects establish a critical power output on a custom-made gripping device. This small-scale study identified a linear correlation between these individuals' reactive hyperemia repercussion slope (calculated as the rate of change of muscle oxygen saturation during repercussion) and critical power (derived from the power-duration curve across 4 TTE trials). We also established a strong relationship between the % of critical power and the rate of change of muscle oxygen saturation during TTE trails, as depicted in the image below:
Interestingly, a similar concept can be applied when looking at the relationship between muscle oxygen saturation rate of change and bouldering grade. The image below shows muscle oxygen saturation rate of change (ΔSmO2) plotted on the Y-axis against bouldering grade (V-Scale) on the X-axis. Note that as the bouldering grade increases, ΔSmO2 becomes progressively more negative, indicating the oxygen utilization is outstripping supply at a greater rate.
We know that finger flexor maximal force, critical force, maximal deoxygenation rate, and maximal reoxygenation rate are key performance indicators for climbers. The question now becomes where climbers' training time is best spent. This will be highly individualized for each climber, and by identifying where they have the greatest room for improvement, they can dial in their training. Recently I had the pleasure of working with an experienced climber to assist in this process. Over two days, we performed assessments to identify:
Finger flexor critical force in the half crimp position;
Maximal deoxygenation (SmO2min) and maximal deoxygenation Rate (ΔSmO2min) of the Forearm flexors;
Maximal reoxygenation rate (ΔSmO2max) and half time to reoxygenation (O2HTR) of the forearm flexors;
Maximal skeletal muscle vasodilation capacity of all limbs (FMID test); and
Rate limiting factors for VO2peak and VO2max.
Through our analysis, we found that this climber's two most significant are of improvement are their ability to supply oxygenated blood to the working muscles, which will help them sustain high-intensity efforts and their maximal finger flexor strength. To address these issues while continuing to work on their sport, we’re going to use a limiter-bridge-performance style approach where limiter training is used to drive adaptations that are specific to this individual's priorities (raise the ceiling for performance), bridge training ties the limiter and performance protocols together (ie, bridges the gap between limiter based training and sport demands), and performance training is used to develop the physiological and psychological qualities needed to maximize sports performance. At any given point in time, will be training all of these qualities in some capacity, whether that means building or maintaining. In a future article for subscribers, i’ll discuss specific training protocols that fit within each of these specific phases and some case studies with climbers of various performance levels.
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