Self-tests consist of sets of physical tests for climbers to assess their specific strength and endurance. In many studies, both capacities have been associated with climbing performance (1-3). According to the current scientific evidence, self-testing is a valid and reliable way to value them (3-5). Each test is carried out by doing two-handed finger hangs by means of the R-Evolution App (the App from here on) and the R-Evolution Board. The App allows, among other features, to set rest times between repetitions that can be as low as 0.5 seconds, and to measure how accurately the finger hangs are done. The latter is possible as the R-Evolution Board slightly varies its position when one hangs on it, which the App is able to detect. Performing self-testing through finger hangs and controlling their accuracy, are two key elements in terms of validity and reliability. How the strength and endurance indicators are obtained, and which elements configure the tests that assess them is explained here below.
Self-testing is essentially centered on two abilities:
- the ability to grip the holds, which depends on two factors: 1) the strength of the finger flexors and 2) some anthropometric characteristics of the fingertips. The smaller the hold is, the more dependent on the latter this ability is (in fact, there is evidence thast this is the primary factor on hold sizes below 5,8 mm) (6). The edges used in self-testing are adapted in size to the strength of each climber, with a minimum of 8 mm in order to make the results of the tests mainly dependent on the maximum strength that can be exerted with the tip of the fingers. This is the reason behind calling the indicator of this ability maximum strength indicator (S). In practice, the test that assesses it consists on finding the maximum added weight allowing to perform a 5” finger hang on an edge adjusted to the proper size, which is the one where each climber is able to sustain its own body weight for 40”, and called the minimum edge depth for a 40” hang (MED_40). These factors (added weight, body weight and edge size) are used to calculate the “S” indicator (3). See the example below:
Data for this example: Body weight (BW): 70 kg; MED_40: 10 mm; Maximum added weight (MAW) for a 5” hang in the MED_40: 30 kg.
“S”= (((BW + MAW) / BW) / (MED_40)) x 100) = (((70 + 30) / 70) / 10) x 100) = 14,28
- the ability to sustain an intermittent effort under controlled hemodynamic conditions, assessed by two different tests, each one of them consisting of intermittent finger hangs performed on the same MED_40 and using the same grip positions than in the “S” indicator test. The work and rest times in each protocol are indicated by the App using visual and acoustic signals. Both tests must be performed to the point of muscular failure, which is when during a repetition, there is a clear incapacity to maintain the grip on the indicated edge. This should be done by strictly following the pace marked by the effort:rest ratio, which is different for each one of them. This has been considered essential in this kind of measurements (7) since variations of more than a half or full second, depending on the ratio, could significantly alter the muscular oxygenation dynamic (8), making the results of the test inaccurate and less valid, as explained later. In this sense, for each test, at the end of it, the App shows information on how accurately it has been done, that can be compared to the value indicated as acceptable in its description, to know if it should be performed again. In both tests, the intermittent finger hangs are made at the same intensity, which may vary between climbers. This intensity is the lowest at which vascular occlusion happens inside the muscles mainly involved in the action, the finger flexors, and is known as occlusion threshold (OT). Its value is approximated during the initial self-test. The two indicators of specific endurance obtained are:
- the indicator of the anaerobic component of endurance (ANAE), obtained by means of intermittent finger hangs with an effort:rest ratio of 8”:0.5”. This manifestation of the endurance is related to the ability to pass the most intense sections in any kind of climb. This ratio is based on observations made on boulder climbers (9). Therefore, this indicator may be more specific for this modality in which rest times of only 0.5” between contractions have been evinced.
- the indicator of the aerobic component of endurance (AE), obtained by means of intermittent finger hangs with an effort:rest ratio of 10”:3”. This manifestation of the endurance is related to the ability to recover as fast as possible when the hand moves from a hold to the next one, allowing a longer climbing time on sections of sub-maximum intensity, and possibly a faster recovery on the rest spots. Therefore, this indicator may seem more essential for sport climbing (10). This ratio is so far the most used in climbing-related research to assess the specific endurance (11-13) as it is similar to the effort dynamic that occurs in real conditions.
To construct both indicators of specific endurance (ANAE and AE), the maximum time reached in each test and the level of strength applied are taken into account (4). The product of these two variables allows to obtain the force-time integral variable (FTI) which is considered the most appropriate indicator to assess the specific endurance in climbing (SEC) (11), although it isn’t clear yet if it allows a separation between the different modalities of this sport (13). This will be discussed later. In addition, since the intensity depends on the OT (a personal parameter) and is not fixed, a standardizing factor for the intensity (if) is applied to allow a comparison of the FTIs obtained at different intensities. This factor comes from the theoretical isometric effort times reached at different intensities in accordance to the model proposed by Rohmert (14,15) (see the table below).
It follows that the specific endurance indicators (ANAE and AE) would be calculated as this:
FTI = S x if x T x tf
With: S = S indicator
if = standardizing factor for the intensity, which depends on the intensity used in the OT test
T = the time obtained in the test
tf = standardizing factor or adjustment for the time, equal to 8/8,5 for the ANAE indicator and 10/13 for the AE.
Example of the ANAE and AE indicators calculation:
Data for this example: “S” = 14,28 (see the previous example for that indicator); OT = 65%; T for AE = 180 seconds; T for ANAE = 85 seconds.
AE = 14,28 x (188,43 / 787,76e-4,087(65%)) x 180 x (10/13) = 6752,90
ANAE = 14,28 x (188,43 / 787,76e-4,087(65%)) x 85 x (8/8,5) = 3901,67
The features of the self-tests are explained next in detail.
SPECIFICITY IN THE APPLICATION OF THE FORCE AND VALIDITY OF THE ASSESSMENTS
Specificity is a basic element in any test and is relevant to its validity, as it constrains that test to measure only what it is intended to measure (16,17). In the field of physical capacities, specificity refers to the similarity between how the motor action is performed in the test environment and in the real world. In this sense, finger hangs have been shown as the exercise that better imitates the essential climbing motor action: gripping holds with the fingers of the hands. It has been observed, at an electromyographic level, that finger hangs generate an activation of the finger flexors similar to that produced by climbing (18), which didn’t occur with other kind of exercises as, for example, manual dynamometries. Besides, the position of the arm during a hang places the hand above the head, which is analogous to its position during a climb. This fact has shown to be incidental in the level of perifusion found in that extremity (19), which means it affects the blood flow reaching the finger flexors in this action, and, as a consequence of this, the specific endurance they can manifest (20). This is explained later.
Still in relation to specificity, self-testing is performed on edge shaped holds, which are the most common in climbing (21), and typical, in their smallest versions, of the hardest parts of the routes or boulders (6). In addition, they allow, independently of their depth, to perform the tests in a safer way as four fingers can almost always be used on them, distributing the tension that is generated on the soft tissues among all (22). As earlier explained, in self-testing the size of the edge is always adapted to the strength level of each climber (MED_40), since in a recent study (3) a high association has been found between different tests assessing the strength and sustained endurance by means of finger hangs. This suggests that the abilities that define them are very similar and that the results of their corresponding tests can be approached with precision through the results of the others. The App takes advantage of this to adjust, at the beginning of the initial self-test, the size of the edge in accordance to the strength level of each individual, to make it comply with the requiered conditions of specificity, reliability and safety. Reliability means that a test is able to reproduce the same results (or almost) each time it is repeated. In this sense, it has been observed that climbers with a higher level, who generally speaking, manifest more finger strength, exert force on small edges with more reliability (21). Therefore, only these climbers will have to adjust the edge to the smallest sizes for self-testing, while only those with the lowest levels will adjust it to the largest sizes: the soft tissues of their fingers may have produced fewer adaptations and the tension generated at their level will always be weaker on larger edges, since the lever arm created between the finger pulleys and the point where the force is exerted, will be smaller (23-25). This choice makes the tests to be safer.
As earlier said, the smallest edge size used for self-testing is 8 mm. This comes from the conclusions of Bourne et al. (2011) (6), who observed that the ability to grip an edge of less than 5.8 mm was more dependent on the skin characteristics of the fingertips (in particular, the thickness of its flesh), than on the maximum strength manifested on deeper edges. Therefore, it would seem that a 6 mm edge would be an appropriate minimum for self-testing, but on the R-Evolution Board 8 mm is used instead, since its edges have rounded corners with a 5 mm radius. This design intends to make the grip more comfortable to prevent the pain that is usually felt in the skin when doing finger hangs on sharp edges, which may be a limitation for the exercise (see the image below).
Rounded corner VS. Sharp edge
The grip positions to be used in self-testing, as indicated in the corresponding help texts, are the open crimp grip or the half crimp grip, avoiding for safety the full crimp grip which generates a heavier tension on the finger pulleys. This freedom of choice is supported by the conclusions of Amca et al. (2011) (26), who observed that the best grip position, in relation to the hold’s size, was determined in basis of a criterion of an efficient use of that hold’s surface. In addition, it seems logical that the size and proportions of the fingers may also be related to this. Therefore, depending on the size set for the edge, the size of the fingers, and which grip each climber is more used to, a position could be chosen over the other (27), which makes clear that forcing everyone to use the same grip would be a nonsense. However, once chosen, the same grip must be used along all the tests to maintain the same recruitment pattern. This pattern will always be prevalent, or at least important, for the flexor digitorum profundus (FDP) (24), a muscle considered as the most essential for climbing performance (13), since it is in charge of the flexion of the distal phalanx, which is the most involved when gripping small holds.
Another thing that should be highlighted is that the size of the edge used during self-testing will always be smaller or equal to the length of the middle finger’s distal phalanx of the dominant hand. This is based on observations made by Bergua on a study previous to the researches that substantiate self-testing (4), and on which various climbers performed finger hangs on an edge, at different relative intensities, to the point of muscle failure. For some of them the edge was smaller than the length of their distal phalanx, and for others it was bigger. The hanging times achieved by the latter were far from what the existing theoretical models predict for isometric efforts (14,15,28), which normally are exponential at the lowest intensities and linear at the highest (see the graph below).
Duration of isometric effort (s) vs. relative strength (%) according to Rohmert formula (14,15)..
This variation in the slope (from lineal to exponential) has been explained by the presence of blood flow at the lowest intensities inside the muscles involved in the effort (29,30). This is why blood flow is considered as the prevalent factor regarding the duration of isometric contractions (30-32). The endurance times observed on the climbers who used an edge bigger than the length of their distal phalanx may be explained by differences in the recruitment models due to performing the hangs on that size instead of using smaller edges, as the rest of the climbers did. This hypothesis is based on a study carried out with non-climber subjects (29) assessing the blood flow in their forearm muscles at different intensities of isometric contraction. Different circulation patterns were observed depending on the level of absolute strength of each subject. This may seem reflected in many endurance time vs intensity graphs (as shown below).
Blood flow patterns with one and two peaks in the forearms of non-climber subjects (with high and low strength levels) at different intensities of isometric contraction. [En Barnes (1980)] (28)
In conclusion, since different muscular recruitment models have been observed in the finger flexors depending on which grip position is used (half crimp vs open grip) (24,33), adopting the length of one phalanx as the maximum edge size has been considered a requirement to “force” the use of the open crimp or half crimp in self-testing. This should ensure a similar recruitment model for every climber.
BLOOD FLOW MEASUREMENT AND VALIDITY OF THE ENDURANCE ASSESSMENT
The specific endurance in climbing (SEC) is assessed at the local level, in the muscles that are responsible for the most important motor action in this sport, the finger flexors. The most specific way to do this is with intermittent contractions since a purely isometric assessment has been suggested not being able to reflect the effort dynamic of this activity (16). The SEC has been observed as greatly dependent on the magnitude and speed at which re-oxygenation occurs during the rest phases between the contractions of the intermittent effort (34,35). This is largely determined by the presence of blood flow during those phases (20), since during the contractions, which are of isometric nature, it may be very limited (11). Therefore, blood flow is a key element in terms of the magnitude of the recovery that can be achieved between efforts, thus, it is key for the SEC.
The presence of blood flow inside a muscle is determined by its occlusion threshold (OT) (29,36). Until now, only one study, carried out by Bergua et al., (2020) has approximated the OT in climbers (5), finding it to be around 65.59 (± 8.86%) of the maximum strength for those of advanced (7a+/12a to 8a/13b) and elite (8a+/13c to 8c+/14c) level. Since a study to assess the SEC on climbers under similar hemodynamic conditions would have required to previously know the OT, none has been done so far. As Staszkiewicz et al. (2002) (37) have noted, doing such tests without knowing the intensity of the blood flow during the isometric contractions, would make them have a low diagnostic value. Indeed, the presence of blood flow during the contractions: i) would cover up the effect of the local re-oxygenation during the rest phases of the intermittent efforts, and ii) would lead to dissimilar evaluations between subjects, impeding possible comparisons (5).
The intermittent protocols to assess the SEC used in most of the studies, have been performed by means of voluntary isometric efforts, exerting force at a previously defined intensity on a hold (11,12). To achieve this, the finger flexors were isolated from the rest of the body by having the subjects seated, leaning the corresponding elbow on a table, flexed, as well as the shoulder, at an angle of 90º. The force was applied on an edge with a sensor to measure its magnitude, placed just under the fingers. This procedure, required to assess such parameters as the oxygenation kinetics (35) or the hemodynamics (20), have allowed us to widen our knowledge on determinant elements of the SEC. However, they may have not provided a good control of the local blood flow and the hemodynamic conditions because of the (±10%) margin left, in terms of the intensity of the force that had to be applied, in relation to what was set. For example, when the intensity to assess the endurance was set at 60% of the maximum strength, it actually fluctuated between 50% and 70%.
To avoid these issues, self-testing evaluates the intensity at which blood flow becomes nonexistent, as it approximates the OT of each climber. On the other hand, since the protocols are performed by means of finger hangs, ensuring that a minimum intensity of force is applied, they don’t allow any oscillation going below the OT. This means that by using this procedure, a total occlusion of the blood flow always exits during the contraction phases, which makes possible a specific assessment of the ability to recover during the rest phases. This procedure then, is the one that has been suggested to be the most valid to evaluate the SEC (5), as it places the different climbers under the same hemodynamic conditions, allowing reliable comparisons between them.
REST TIMES AND METABOLIC DISTINCTION
The rest times between isometric contractions also affect the local blood flow (20,38,39), thus, the SEC (20). Demura et al. (2008) (8) have shown significant differences on the oxygenation dynamics between distinct isometric efforts, sustained and intermittent done at different work:rest ratios. These authors have suggested that re-oxygenation is almost nonexistent for rest times below 2 seconds, as they not be long enough to restore the blood flow. Since the protocols that assess the SEC are set at an intensity that supposes a total occlusion during the contraction phases (like the OT), the re-oxygenation of the muscle becomes totally dependent on the duration of the rest phases. The prevailing metabolism in the muscle is related to the oxygen bioavailability inside it (36), therefore, as a result of the protocols previously explained, like those used in self-testing, the SEC will manifest itself mainly through its aerobic or anaerobic components according to whether the rest times between repetitions are set above or below 2 seconds (8). In this sense, self-testing allows to obtain the indicators of the SEC (AE and ANAE), by means of two endurance tests, both performed at the OT intensity but with different effort:rest ratios.
This separation based on the possibilities of oxygen bioavailability inside the muscle (36) is substantiated on some studies looking for the existence of distinct adaptations on climbers of different modalities like bouldering and sport climbing (13,40). That a discipline mostly implying short efforts of high intensity, like bouldering, may not generate the same adaptations as one implying longer efforts, even if those may also be intense, like sport climbing, seems logical. However, some studies measuring the expression of the SEC using the FTI, haven’t found significant differences between climbers of both modalities (13,40). There could be many reasons for this: i) most of the subjects on the study had an advanced climbing level (from 7a+/12a to 8a/13b), and the development of their specific adaptations was possibly limited, ii) the tests were done without controlling the hemodynamic conditions (37), making their validity questionable, iii) the tests were done at low intensities, making them not be specific (which may be related to the previous point). For example, Fryer et al. (2017) (13) have assessed the SEC by means of a 10”:3” ratio intermittent test at 40% of the maximum strength, an intensity that is commonly used for this purpose on many studies of the same field (11-13), which has been criticized by other authors (7,41), since it would allow the presence of blood flow during the contraction phases. This would cover up the assessment of the target capacity, expressed by the magnitude of the re-oxygenation during the rest phases between contractions, which would make it have a low validity (37), and the comparison between subjects impossible (5). This wouldn’t happen with the use of self-tests, as explained before.
One last element to consider is the precision achieved in relation to the rest times of the intermittent protocols. Balas et al., (2015) (7) have observed a delay on the exertion of the force on a hold equipped with a sensor, when it was expressed voluntarily. This procedure has been used in most of the studies that have measured the SEC (as explained before) (11-13), and possibly none of them has considered the precision of the contraction and the rest times in their protocols. But this element seems very important to assess the SEC since this capacity has been associated with the magnitude and speed of the re-oxygenation that can occur at the local level during very short rest times. Indeed, Fryer et al., (2016) (34) have shown that 1 second of difference in the speed at which re-oxygenation reached a certain level inside the flexors (half of the maximum deoxygenation level previously suffered), supposed a difference of one grade in the climbing level of the subjects. This is anonther reason that make the R-Evolution Training App an essential tool to carry out valid and reliable assessments of the SEC, as it’s able to detect the real rest times between contractions during the intermittent protocols.
(1) Baláš J, Pecha O, Martin AJ, Cochrane D. Hand–arm strength and endurance as predictors of climbing performance. European Journal of Sport Science 2012;12(1):16-25.
(2) Magiera A, Roczniok R, Maszczyk A, Czuba M, Kantyka J, Kurek P. The structure of performance of a sport rock climber. Journal of human kinetics 2013;36(1):107-117.
(3) Bergua P, Montero-Marin J, Gomez-Bruton A, Casajús JA. Hanging ability in climbing: an approach by finger hangs on adjusted depth edges in advanced and elite sport climbers. International Journal of Performance Analysis in Sport 2018;8(3):1-14.
(4) Bergua Gómez PV. Fuerza y resistencia específica en escalada: valoración mediante suspensiones. 2016.
(5) Bergua P, Montero-Marin J, Gomez-Bruton A, A. Casajús J. The finger flexors occlusion threshold in sport-climbers: an exploratory study on its indirect approximation. European Journal of Sport Science 2020:1-21.
(6) Bourne R, Halaki M, Vanwanseele B, Clarke J. Measuring lifting forces in rock climbing: effect of hold size and fingertip structure. Journal of applied biomechanics 2011 Feb;27(1):40-46.
(7) Baláš J, Michailov M, Giles D, Kodejška J, Panáčková M, Fryer S. Active recovery of the finger flexors enhances intermittent handgrip performance in rock climbers. European Journal of Sport Science 2016;16(7):764-772.
(8) Demura S, Nakada M, Yamaji S, Nagasawa Y. Relationships between force-time parameters and muscle oxygenation kinetics during maximal sustained isometric grip and maximal repeated rhythmic grip with different contraction frequencies. Journal of physiological anthropology 2008;27(3):161-168.
(9) White DJ, Olsen PD. A time motion analysis of bouldering style competitive rock climbing. Journal of strength and conditioning research / National Strength & Conditioning Association 2010 May;24(5):1356-1360.
(10) Warner A, Stone K, Sveen J, Draper N, Dickson T, España V, et al, editors. Forearm oxygenation kinetics, strength and endurance characteristics of boulderers and sport climbers. ; 30-Noviembre-2016; Nottingham: British Association of Sport and Exercise Sciences; 2016.
(11) MacLeod D, Sutherland DL, Buntin L, Whitaker A, Aitchison T, Watt I, et al. Physiological determinants of climbing-specific finger endurance and sport rock climbing performance. Journal of sports sciences 2007 Oct;25(12):1433-1443.
(12) Philippe M, Wegst D, Muller T, Raschner C, Burtscher M. Climbing-specific finger flexor performance and forearm muscle oxygenation in elite male and female sport climbers. European journal of applied physiology 2012;112(8):2839-2847.
(13) Fryer S, Stone KJ, Sveen J, Dickson T, España-Romero V, Giles D, et al. Differences in forearm strength, endurance, and hemodynamic kinetics between male boulderers and lead rock climbers. European Journal of Sport Science 2017 07/28:1-7.
(14) Rohmert W. Ermittlung von Erholungspausen für statische Arbeit des Menschen. European journal of applied physiology and occupational physiology 1960;18(2):123-164.
(15) Allison B, Desai A, Murphy R, Sarwary R. Human potential of applying static force as measured by grip strength: Validation of Rohmerts formula. 2004.
(16) Schoffl VR, Mockel F, Kostermeyer G, Roloff I, Kupper T. Development of a performance diagnosis of the anaerobic strength endurance of the forearm flexor muscles in sport climbing. Int J Sports Med 2006 Mar;27(3):205-211.
(17) Rodríguez F, Aragonés M. Valoración funcional de la capacidad de rendimiento físico. In: González Gallego J, editor. Fisiología de la actividad física y el deporte. Interamericana ed. Madrid: McGraw-Hill; 1992. p. 237-274.
(18) Watts P, Jensen R, Agena S, Majchrzak J, Schellinger R, Wubbels C. Changes in EMG and finger force with repeated hangs from the hands in rock climbers. International Journal Exercise Science 2008;1(2):62-70.
(19) Fitzpatrick R, Taylor JL, McCloskey D. Effects of arterial perfusion pressure on force production in working human hand muscles. The Journal of physiology 1996;495(3):885-891.
(20) Fryer S, Stoner L, Lucero A, Witter T, Scarrott C, Dickson T, et al. Haemodynamic kinetics and intermittent finger flexor performance in rock climbers. International Journal of Sports Medicine 2015;36(2):137-142.
(21) E. López Rivera. Efectos de diferentes métodos de entrenamiento de fuerza y resistencia de agarre en escaladores deportivos de distintos niveles. Toledo: Universidad de Castilla la Mancha; 2014.
(22) Morenas Martin J, Del Campo VL, Leyton Roman M, Gomez-Valades Horrillo JM, Gomez Navarrete JS. Description of the finger mechanical load of climbers of different levels during different hand grips in sport climbing. Journal of sports sciences 2013;31(15):1713-1721.
(23) Moor BK, Nagy L, Snedeker JG, Schweizer A. Friction between finger flexor tendons and the pulley system in the crimp grip position. Clinical Biomechanics 2009 1;24(1):20-25.
(24) Vigouroux L, Quaine F, Labarre-Vila A, Moutet F. Estimation of finger muscle tendon tensions and pulley forces during specific sport-climbing grip techniques. Journal of Biomechanics 2006;39(14):2583-2592.
(25) Schweizer A. Biomechanical properties of the crimp grip position in rock climbers. Journal of Biomechanics 2001;34(2):217-223.
(26) Amca AM, Vigouroux L, Aritan S, Berton E. Effect of hold depth and grip technique on maximal finger forces in rock climbing. Journal of sports sciences 2012;30(7):669-677.
(27) Westling G, Johansson R. Factors influencing the force control during precision grip. Experimental Brain Research 1984;53(2):277-284.
(28) Frey Law LA, Avin KG. Endurance time is joint-specific: a modelling and meta-analysis investigation. Ergonomics 2010;53(1):109-129.
(29) Barnes WS. The relationship between maximum isometric strength and intramuscular circulatory occlusion. Ergonomics 1980 Apr;23(4):351-357.
(30) Heyward VH. Influence of static strength and intramuscular occlusion on submaximal static muscular endurance. Research Quarterly 1975(46):393-402.
(31) Carlson BR, McCraw LW. Isometric strength and relative isometric endurance. Research Quarterly American Association for Health, Physical Education and Recreation 1971;42(3):244-250.
(32) Start K, Holmes R. Local muscle endurance with open and occluded intramuscular circulation. Journal of applied physiology 1963;18:804-807.
(33) Schweizer A, Hudek R. Kinetics of crimp and slope grip in rock climbing. Journal of applied biomechanics 2011;27(2):116-121.
(34) Fryer S, Stoner L, Stone K, Giles D, Sveen J, Garrido I, et al. Forearm muscle oxidative capacity index predicts sport rock-climbing performance. Eur J Appl Physiol 2016:1-6.
(35) Fryer SM, Stoner L, Dickson TG, Draper SB, McCluskey MJ, Hughes JD, et al. Oxygen recovery kinetics in the forearm flexors of multiple ability groups of rock climbers. Journal of strength and conditioning research / National Strength & Conditioning Association 2015 Jun;29(6):1633-1639.
(36) Yamaji S, Demura S, Nagasawa Y, Nakada M, Kitabayashi T. The effect of measurement time when evaluating static muscle endurance during sustained static maximal gripping. J Physiol Anthropol Appl Human Sci 2002;21(3):151-158.
(37) Staszkiewicz R, Ruchlewicz T, Szopa J. Handgrip strength and selected endurance variables. Journal of Human Kinetics 2002;7:29-42.
(38) Thompson EB, Farrow L, Hunt JE, Lewis MP, Ferguson RA. Brachial artery characteristics and micro-vascular filtration capacity in rock climbers. European journal of sport science 2015;15(4):296-304.
(39) Ferguson RA, Brown MD. Arterial blood pressure and forearm vascular conductance responses to sustained and rhythmic isometric exercise and arterial occlusion in trained rock climbers and untrained sedentary subjects. European journal of applied physiology and occupational physiology 1997;76(2):174-180.
(40) Stien N, Saeterbakken AH, Hermans E, Vereide VA, Olsen E, Andersen V. Comparison of climbing-specific strength and endurance between lead and boulder climbers. PloS one 2019;14(9):e0222529.
(41) Michailov ML, Baláš J, Tanev SK, Andonov HS, Kodejška J, Brown L. Reliability and Validity of Finger Strength and Endurance Measurements in Rock Climbing. Res Q Exerc Sport 2018:1-9.