4 May 2010

A review of strength and endurance in climbing

NB: This article used to live in the articles section of my old site. I’ve reposted it here since it was really popular. Note that it’s nearly ten years old now! 
Sport climbing is the branch of rock climbing involving routes protected by pre-placed anchor bolts. The explosion in popularity of sport climbing and organised competitions have prompted a significant rise in participation and standards in recent decades. The focus of this new discipline is the athletic and competitive aspects of movement on rock (Jones, 1991). Coupled with this has been the development of structured and sport specific training techniques among professional and amateur climbers alike (Goddard and Neumann, 1993; Morstad, 2000). Climbing is a physical activity involving repeated movements of the body against gravity by producing forces on the holds on the wall surface via the upper and lower limbs. A considerable movement technique and psychological performance element is also universally recognised in the climbing related literature. The rise in participation, training and organised competitions in climbing and well documented increases in the occurrence of climbing related soft tissue injuries underlines the importance of research which evaluates the physiology of climbing.
The aim of this review is to critically evaluate the current literature concerning the physiological demands and determinants of performance in sport climbing. Particular focus will be given to the forearm, specifically the finger flexors, and the physiological characteristics and adaptations occurring in trained climbers, which confer increased forearm strength and endurance. Future research objectives will also be outlined within this specific area.
Physiological demands of climbing
Rock climbing involves moving over the wall surface supported by four limbs, described by Quaine et al. (1997) as “vertical quadrupedia” (Fig. 1). Early attempts by climbers to identify key aspects of performance on which to focus their training recognised that the centre of acute fatigue during climbing lay invariably in the upper limbs, especially the forearms (Hurn and Ingle, 1988; Goddard and Neumann, 1993). It was observed that in general, the difficulty of the climbing becomes greater when the wall angle becomes steeper and the holds (particularly handholds) become smaller and further apart. The apparent limitation of the forearm in climbing makes physiological sense given its comparatively small muscle mass, not anatomically designed to support forces comparable with body mass (or exceeding it to produce accelerations against gravity). Morstad (2000) (citing unpublished quantitative analyses) argued that even at wall angles 45 degrees beyond vertical, where the lower limb cannot support much of the body mass in the vertical direction, successful movements must be initiated using the lower limb and trunk in order to reduce peak forces required at the hand holds. Although there are few reports in the climbing related literature of significant lower body fatigue, there is anecdotal evidence that lower limb strength is an advantage on certain types of moves, particularly to maintain contact on the footholds on very overhanging rock (Morstad, 2000). 
Unfortunately, no studies have examined lower limb or core strength in trained climbers.
Bouts of sport climbing last for several minutes with sustained periods of intermittent isometric contraction in the finger flexors. Schadle-Schardt (1998) observed mean climbing times of 4.5 minutes during indoor competition climbing. Thus, sport rock climbing must be considered an endurance event. Few studies have attempted to analyse the movement patterns associated with climbing. Billat et al. (1995) observed that upward movement during indoor climbing occurs intermittently. Video analysis revealed that 63% of the total climbing time was spent ascending (vertical displacement of the hips) and 37% was spent maintaining an ‘immobilized’ position (static equilibrium). In climbing, static equilibrium must be maintained at certain times in order to clip the rope into protection bolts, rest individual fatigued limbs and scan and reach for the next holds (Goddard and Neumann, 1993; Sagar, 2001). Schadle-Schardt (1998) measured mean contact times for the fingers on each hold in competition climbing of 10 seconds with 2.4 second rest periods in between holds (presumably spent reaching the next hold and replacing chalk on the hands).
The angle of the wall surface has been shown to be an important influence on the physiological demand placed on the body due to climbing. Noé et al. (2001) examined the biomechanical constraints of static climbing positions at different angles (vertical and 10 degrees overhanging). When vertical and overhanging quadrupedia were compared there was a large shift in the distribution of the supporting forces to the upper limbs, from 43% to 62% of body weight supported by the upper limbs in the vertical and overhanging positions respectively. Given that rock climbs can feature angles of up to 90 degrees beyond vertical, this magnitude of shift appears remarkable and certainly explains the physiological findings (described below) of performance studies which showed much greater energy expenditure and lactate production with only small increases in angle beyond vertical (Watts et al., 1998).  Unfortunately this is the only study to compare supporting force distribution at different angles. Further studies examining a greater range of wall angles would give further insight into the dependence on the upper limbs for support at overhanging angles.
Finger flexor strength has been extensively measured in trained climbers by a number of studies. The conclusion of these studies appears to be that trained climbers have higher finger strength compared to controls, although methodological differences have provided varying results (Sheel, 2004). An early study by Watts et al. (1993) observed no differences in absolute values of hand-grip strength measured by hand-grip dynamometry in world class climbers and controls. It was suggested that climbers may not need high grip strength per se. Rather, strength to mass ratio was thought to be a more important variable and this was significantly higher in climbers (due to low body mass). Several later studies have measured hand-grip strength, some observing no differences in absolute forces between elite climbers and recreational or non-climbers (Ferguson and Brown, 1997; Watts et al., 2003) and others observing that climbers have higher grip strength (Bollen and Cutts, 1993; Grant et al., 1996, 2001). Grant et al. (1996) recognised that grip strength dynamometry might not provide an accurate assessment of the type of strength required in rock climbing, and developed a climbing specific device for measuring finger strength that simulated more closely the grip styles used on climbing holds (Schweizer, 2001) (Fig. 1, 2). All subsequent studies using this type of grip specific measurement have recorded higher finger strength in trained climbers (Grant et al., 1996, 2001, 2003; Quaine et al., 2003; MacLeod et al., unpublished data; Reid et al., unpublished data). Although climbing moves often involve hanging or moving underneath horizontally aligned finger edges, the types of moves and positions experienced in climbing are extremely varied and it seems likely that some may involve a force requirement greater than that needed to support the body in the vertical direction (such as using ‘undercut’ holds) (Goddard and Neumann, 1993; Sagar, 2001). This view would challenge Watts’ suggestion that climbers do not need to produce large absolute forces. Unfortunately no biomechanical analysis has been carried out on a range of climbing positions/movements to date, in order to determine the supporting force requirements of climbing positions.
Anthropometric characteristics of climbers
Several studies have measured anthropometric data in various populations of climbers. Watts et al. (1993) studied a highly homogenous group of climbers; semi-finalists in a sport climbing world cup event. This study observed that this group were characterised by low stature and very low percentage body fat values (4-14% for men, 10-20% for women).  This finding has been supported by several subsequent studies of trained climbers (Binney and Cochrane, 1999; MacLeod et al., unpublished data; Mermier et al., 2000; Sheel et al., 2003; Watts et al., 1996, 2000, 2003) and percentage body fat has been proposed as a key predictor of sport climbing performance. Grant et al. (1996, 2001, 2003) failed to observe any differences in percent body fat between trained climbers and controls or other athletic groups. However, the absence of significant differences might be attributable to the comparatively low ability of the climbers compared to the studies mentioned above and/or different equations used to estimate body fat percentage..
It is logical that a large body mass or any excess body fat would be disadvantageous in elite level climbing as body mass must be repeatedly moved against gravity. However, it is well known that climbers have long considered excess body fat to be a disadvantage and control it strictly. It is also considered advantageous to avoid hypertrophy training of lower body muscle groups. Hence, the question remains whether body mass and body fat percentage are important determinants of climbing performance or merely a feature of climber’s training patterns (Farrington, 1999). It is conceivable that any performance advantage conferred by maintaining very low body fat may be offset by problems with consumption of sufficient caloric energy to support a rigorous training regime. Longitudinal study of the effect of manipulation of percentage body fat on climbing performance would yield more meaningful data on the subject (Sheel, 2004). Low stature might be an advantage in climbing due to volume-mass ratios. However, any advantage may be offset to some degree by a reach limitation in shorter climbers (Sagar, 2001).
Reach is universally recognised as a common limitation on climbing moves among rock climbers. This has led to ‘ape Index’, a measure of reach relative to height, (arm span/height) being proposed as a performance predictor. Watts et al. (2003) measured ape index in adolescent competitive climbers and found small but significant differences relative to age matched controls. There was no relationship between climbing ability and ape index. Watts suggests this may be due to the lack of variability between climbers. Grant et al. (1996, 2001) found no differences between trained climbers and controls for leg or arm length. The significance of these findings is limited due to the small sample sizes and ability level of the climbing groups. It is not possible to make any conclusions about these variables from the available data.
Given that climbers perform repeated contractions of the forearm muscles and appear to possess greater finger strength than controls, it has been hypothesised that climbers will develop greater forearm muscle mass. Muscle force is highly correlated to muscle mass, whereas no consensus has been reached on whether force per unit muscle mass is influenced by training (Fukunaga et al., 2001). Only three studies have attempted to measure forearm muscle mass in trained climbers and controls. MacLeod et al. (unpublished data) measured forearm circumference is 12 elite climbers and found significantly higher forearm circumference to body mass ratios in climbers. The absence of significant differences in absolute values is explained by the difference in body mass between the subject groups. This finding agrees with those of Watts et al. (2003) who observed similar forearm volumes in competitive climbers and controls, despite the climber’s lower stature and body mass. Reid et al. (unpublished data) measured forearm circumference in height and body mass matched trained climbers and controls. Climbers had higher forearm circumference although the difference was not significant. Again, the low variability in this anthropometric measure calls for further study using larger subject groups and more sensitive methods of measurement.
Mermier et al. (2000) attempted to quantify the relative contributions of anthropometric variables (Height, mass, leg length, percentage body fat), hip flexibility and training variables (grip, shoulder and leg strength, grip and hang endurance, lower body anaerobic power) in a study of 44 trained climbers of varying standard. It was concluded that trainable variables were much more important predictors of climbing ability and that anthropometric and hip flexibility variables were very poor predictors of ability. It was concluded that climbers do no need to possess particular anthropometric characteristics to be successful sport climbers.
Body flexibility is another variable which is thought to be relevant in climbing performance as the ability to reach distant holds and maintain positions at extreme joint angles can provide a clear advantage on certain climbing moves (Goddard and Neumann, 1993; Sagar, 2001). Grant et al. (1996, 2001) measured hip flexibility in trained climbers and controls but observed no significant differences. However, issues with the standard of the climbing group discussed above may have affected the validity of the comparison. An intervention study into the effect of flexibility in competitive climbers would yield more useful information.
Fatigue factors in climbing
To successfully complete a sport route, climbers must maintain the ability to make high force, intermittent isometric contractions of the finger flexors. Indeed, competition routes are designed to have progressively more difficult individual movements (the purpose being to separate out climbers of different abilities). Failure to produce the required finger force, coupled with burning, stiff and painful sensations in the forearm (known as ‘pump’) are recognised as being the dominant symptom of fatigue associated with failure to complete a climb, resulting in a fall (Goddard and Neumann, 1993). Finger endurance has been identified as a key attribute of elite level climbers by several studies (Binney and Cochrane, 1999; Ferguson and Brown, 1997; MacLeod et al., unpublished data; Quaine et al., 2003; Reid et al., unpublished data).  Grant et al. (2003) demonstrated that intermediate level climbers do not differ from other athletic groups with respect to finger endurance.
The intermittent isometric contractions seen in climbing are unusual in sport generally (Spurway, 1999). The nature of isometric exercise has several important consequences for the development of muscular fatigue with repeated contractions. Asmussen (1981) characterised this type of contraction as causing significant increases in intramuscular pressure. This change causes blood to be squeezed out of intramuscular blood vessels and hinders or even completely stops blood flow through the muscle. Blood flow can only resume when the contraction ends. The magnitude of increases in intramuscular pressure, and hence blood flow occlusion, is dependent on the intensity (that is, the percentage of MVC) of the contraction. It is thought that contractions below 10-25% of MVC receive adequate blood flow and can be maintained without muscle fatigue (Asmussen, 1981). Above 45-75% MVC, blood flow is completely occluded in the forearm and fatigue patterns mimic those where artificial occlusion is present (Barnes, 1980; Heyward, 1980; Serfass et al., 1979). Between these values, blood flow is reduced and fatigue occurs, but at a slower rate. There is considerable variability in the extent of occlusion in a given subject and muscle due to the following factors: the prevalent muscle fibre type, the size and structure of the muscle. MacLeod et al. (unpublished data) measured finger endurance using a climbing specific protocol (a ‘crimp’ grip with 10/3sec contraction/relaxation ratio) in trained climbers and controls. The intensity was 40% MVC and times to failure in the climbers were similar to the total climbing times observed in a world cup climbing event (Schadle-Schardt, 1998). The authors suggested that 40% MVC may be representative of the average MVC percentage required from the finger flexors in climbing.
Carlson and McGraw (1971) observed lower isometric endurance in subjects with higher MVC and hypothesised a negative relationship between these variables. Based on these findings, it would be anticipated that the climbers would have shorter endurance times as they exhibit higher MVCs than non-climbers. The literature has demonstrated that this is not the case and it is thought that adaptations present in trained climbers appear to offset any disadvantage due to higher force production (MacLeod et al., unpublished data). Quaine et al. (2003) demonstrated that muscle fatigue, measured by the decline in median frequency of surface electromyogram (EMG) in the active forearm muscles, in a climbing specific finger endurance task was delayed in elite climbers compared to non-climbers. The rate of fatigue in climbers was twice as slow as controls at 80% MVC. The authors concluded that this delay was due to climber’s enhanced ability to recover between contractions, speculating that enhanced vasodilation during rest periods accounted for the climber’s advantage. Reid et al. (unpublished data) also observed EMG fatigue using a similar protocol to MacLeod et al.. Trained climbers and controls had similar times to fatigue and decline in EMG median frequency. However, the climbing group had higher MVC and hence produced significantly higher force for a given test period. Watts et al. (1996) measured maximum hand-grip force before and immediately after a climbing task to exhaustion. Hand-grip MVC decreased 22% after the climbing task and remained depressed for 20 minutes post-exercise. However, later work by Watts et al. (2000, 2003b), which also measured maximum hand-grip and finger strength before and after a fatiguing climbing task showed no drop in ability to exert maximum force. Watts et al. (2003b) showed no change in root mean squared EMG values pre and post climb. However, change in median frequency was not measured. It seems possible that the results of Watts et al. (1996, 2000, 2003b) may be affected by the delay in measuring MVC after the climbing bout ended. It is noted that the measurements were taken within one minute of failure on the climb. However, Quaine et al. (2003) points out that the difference in endurance capacity between climbers and non climbers is due to an ability to recover significantly in the short (5 seconds in this case) rest periods between contractions. Future study employing continuous EMG data during a climbing or climbing specific task is required to fully establish whether loss of finger strength occurs during strenuous climbing.
MacLeod et al. (unpublished data) pointed out that loss of fine muscular control may be an additional causative factor for failure to complete a climbing task. Climbing movements require precise timing of force development, as well as extremely rapid and complex movements of the body. Indeed, it is often necessary to lunge for handholds which require precise placement of the fingers in the most advantageous position on the hold to provide adequate support (Goddard and Neumann, 1993; Sagar, 2001). It seems plausible that falls could be caused even by small decrements in force production on such precise holds, or by loss of coordination due to the effects of muscle fatigue on muscular control. Bourdin et al. (1998, 1999) observed a hierarchical organisation of reaching movements between climbing holds (measured on a climbing ergometer). It was noted that reaching duration was shortened by increased postural constraints, regardless of the destination hold size (and therefore accuracy requirements). This factor appeared to override the speed/accuracy trade-off seen with seated or standing reaching movements. Postural constraints are greater in vertical than overhanging climbing, however, overhanging positions are characterised by greater force requirements from the fingers to support body weight (Noé et al., 2001). It seems plausible that this factor would produce an additional demand for shorter reaching durations. This hypothesis has anecdotal support in the climbing literature (Morstad, 2000). Future studies using a similar protocol to that of Bourdin et al., comparing the organisation of reaching and grasping movements at different wall angles would help resolve this question. Such a study has not been undertaken to date.
Physiological responses and adaptations to climbing
Climbing involves whole body movement against gravity for sustained periods. It appears that the upper body is the primary centre of fatigue in climbing, but the role of the lower body in climbing movements has yet to be quantified (Sheel, 2004). Several studies have measured whole body VO2 during climbing on an indoor wall or climbing treadmill. These studies have shown that VO2 rises during climbing to a moderate proportion of running VO2 max (Billat et al., 1995; Watts et al, 2000). VO2 values are markedly variable between studies, but this can be explained by differences in testing protocol and subject groups. It appears that average VO2 during difficult sport climbing is about 25 ml.kg.-1 min-1 (Sheel, 2004). However, values of 43.8 ml.kg.-1 min-1 were recorded in a maximal treadmill climbing task to exhaustion (Booth et al., 1999). Sheel et al. (2003) showed that climbing VO2 was related to climbing difficulty, with VO2 values reaching 45% and 51% of cycle ergometer VO2max for an ‘easier’ and ‘harder’ climb respectively. However, Watts et al. (1998) observed no increases in climbing treadmill VO2 as treadmill angle increased (four minute climbing bouts at angles between 80 and 102 degrees). It is suggested that arm specific peak VO2 may have been reached, rendering further increases impossible when climbing angle became steeper. In addition, the active muscles may be completely blocked from general circulation during contractions, limiting large increases in VO2 (Asmussen, 1981).
Several studies have measured blood lactate concentration after a climbing bout (Booth et al., 1999; Billat et al., 1995; Grant et al. 2003; Mermier et al., 1997; Watts, et al., 1996, 1998, 2000). The values for blood lactate following strenuous climbing range from 2.4 to 6.1 mmol/l. This large variation is likely to be attributable to different modes of climbing (wall, treadmill or simulated climbing), different subject groups and different intensities of the climbing bouts. Watts et al. (1998) demonstrated that lactate production is related to climbing angle. This finding is supported by Mermier et al. (1997) who observed that lactate production is related to climbing difficulty. Large increases in blood lactate may be surprising given that climbers report that muscular pain and fatigue lies predominantly in the forearm. The small muscle mass of the forearm would not be expected to produce large amounts of lactic acid. However, as mentioned above, the relative contributions of different muscle groups to movement on rock have not been quantified to date. Given that such increases in lactate are observed, and that blood flow may be partly or wholly occluded in the forearm during intermittent exercise at high intensities, it seems likely that lactate may accumulate to high concentrations within the forearm muscles during climbing. No studies have compared lactate production in elite and novice climbers in order to establish whether there is any adaptation in trained climbers which affects metabolite build up during climbing (see section below on blood flow). Grant et al. (2003) observed greater increases in blood lactate during a climbing specific forearm endurance task. It is possible that greater blood lactate could be an indicator of increased lactate clearance from the exercising forearm due to increased blood flow.
It has been suggested above that climber’s superior finger endurance may result from an increased ability to recover from isometric contractions. Ferguson and Brown (1997) measured forearm blood flow by venous occlusion plethysmography after intermittent isometric contractions of 40% MVC. Trained climbers had significantly higher vascular conductance following the exercise bout. The authors concluded that climbers demonstrate enhanced vasodilator capacity, which is attributed to adaptations of the local vascular bed, including increased capillary density, capillary cross-sectional area or alterations in local dilator function related to endothelial change (Delp, 1995; Smolander, 1994; Sinoway et al., 1986; Snell et al., 1987).  MacLeod et al. (unpublished data) monitored changes in forearm blood oxygenation continuously during a climbing specific endurance test using near infra-red spectroscopy (Fig. 3).  Oxyhaemoglobin levels in trained climbers were significantly lower during contraction phases (attributable to higher force production) than controls, but recovered to a significantly greater extent during 3 second rest phases. It was concluded that ability to restore forearm oxygenation (by increased blood flow) was an important predictor of success in an endurance test of this type.
The pressor response to isometric exercise has also been identified as a variable of interest. Isometric exercise causes increases in both systolic and diastolic blood pressure (BP) greater that would be expected for equivalent dynamic exercise, reaching a peak at the point of fatigue (Asmussen, 1981). The large increases are caused both by rises in intramuscular pressure, exceeding systolic pressure and blocking blood flow into the active muscles, and sympathetic vasoconstriction in other tissues in order to re-direct blood flow to working muscles. Increased sympathetic activity is triggered by the muscle metaboreflex and a central command component. Significant rises in systolic and diastolic BP have been observed during a climbing specific task (Ferguson and Brown, 1997; MacLeod et al., unpublished data). Increasing central arterial BP has been shown to enhance force production during isometric contraction (Wright et al., 2000). MacLeod et al. hypothesised that an increased pressor response would confer a performance advantage in the endurance tests by opposing occlusion caused by the muscular contraction, thus permitting increased intramuscular blood flow. No differences were found between BP responses for trained climbers and controls during a climbing specific task. Ferguson and Brown (1997) observed an attenuated BP response in trained climbers, an adaptation known to occur following endurance training. The authors hypothesised that the reduction in muscle sympathetic nerve activity could be caused either by reduced chemosensitivity in of the metaborecetptors or reduced build up of metabolites in trained individuals. The latter possibility would seem to be contradicted by the evidence of MacLeod et al. who found significantly lower muscle oxygenation during climbing specific contractions, and by those of Mermier et al. (1997) who found that lactate production is related to climbing difficulty. However, further study is required in this area to fully elucidate the responses and adaptations of pressor response in trained climbers.
It is concluded from the available data that sport climbing relies on both aerobic and anaerobic energy pathways. It seems likely that increased climbing difficulty and/or angle causes more reliance on the anaerobic system. Further research is required, examining both central and peripheral adaptations and responses to climbing, in order to fully understand the physiological determinants of climbing performance.
Current understanding of the mechanical and physiological demands of sport rock climbing has revealed that performance is dependent on a wide array of physiological, anthropometric, movement technique and psychological factors. The centre of physiological fatigue and performance limitation lies predominantly in the forearm musculature. It appears that successful sport climbers have developed greater finger strength and endurance than other populations. As climbing difficulty increases there may be increased reliance on the anaerobic system, particularly in the forearm, coupled with increased lactate production and blood pressure. Enhanced climbing specific endurance may be the result of an increased forearm vasodilatory capacity allowing better recovery from intense contractions of the finger flexors.
Future research objectives have been noted in the text. Much of the research to date has focused on comparison between trained climbers and controls and is descriptive in nature. It seems likely that the results of several studies seeking to establish their physical characteristics have been weakened by problems with availability of subjects of appropriate training status (Sheel, 2004). The diverse nature of the sport of climbing, with its many disciplines compounds this problem. Future studies of this nature should seek to recruit subjects who participate in similar patterns of climbing activity, for example sport climbing competition teams.
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Anonymous said...

The authors concluded that this delay was due to climber’s enhanced ability to recover between contractions, speculating that enhanced vasodilation during rest periods accounted for the climber’s advantage. Reid et al. (unpublished data) also observed EMG fatigue using a similar protocol to MacLeod et al.

Hullo Dave. Thanks much for your work and for posting these studies! Given the mode of fatigue (blood flow occlusion) I'm curious about of potential of L-arginine supplementation for delaying fatigue. In sport generally, evidence for the efficacy of arginine supplementation doesn't appear so conclusive. But what I read here suggests supplementation may be useful for climbers. If supplementation increased delay to fatigue at a given level of intensity, then it could increase total training load. Could be an interesting study!

slack---line said...

Great review and write up, have you considered submitting it to a journal for publication?

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I do climbing but just for fun not like a sport to challenge, it's very nice i really like it, thanks for the article i will keep reading.

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