BrJ SportsMed 1997;31:224-228

Energy expenditure and physiological responses

during indoor rock climbing

Christine M Mermier, Robert A Robergs, Susie M McMinn, Vivian H Heyward

AbstractObjectives-To report the physiologicalresponses ofindoor rock climbing.Methods-Fourteen experienced climbers(nine men, five women) performed threeclimbing trials on an indoor climbingwall. Subjects performed three trials ofincreasing difficulty: (a) an easy 900 verti-cal wall, (b) a moderately difficult nega-tively angled wall (1060), and (c) a difficulthorizontal overhang (1510). At least 15minutes separated each trial. Expired airwas collected in a Douglas bag after fourminutes of climbing and heart rate (HR)was recorded continuously using a tele-metry unit. Arterialised blood sampleswere obtained from a hyperaemised earlobe at rest and one or two minutes aftereach trial for measurement of bloodlactate.Results-Significant differences werefound between trials for HR, lactate,oxygen consumption (Vo,), and energyexpenditure, but not for respiratory ex-change ratio. Analysis of the HR and Vo,responses indicated that rock climbingdoes not elicit the traditional linear HR-Vo, relationship characteristic of tread-mill and cycle ergometry exercise. Duringthe three trials, HR increased to 74-85% ofpredicted maximal values and energyexpenditure was similar to that reportedfor running at a moderate pace (8-11 min-utes per mile).Conclusions-These data indicate thatindoor rock climbing is a good activity toincrease cardiorespiratory fitness andmuscular endurance. In addition, thetraditional HR-Vo, relationship shouldnot be used in the analysis ofthis sport, orfor prescribing exercise intensity forclimbing.(BrJ Sports Med 1997;31:224-228)

Center for Exerciseand Applied HumanPhysiology, UniversityofNew Mexico,Albuquerque, NM87131, USAC M MermierR A RobergsS M McMinnV H Heyward

Correspondence to:Dr Mermier.

Accepted for publication26 February 1997

Keywords: rock climbing; caloric expenditure; heartrate; oxygen consumption

Rock climbing has experienced rapid growth as

a recreational activity and an internationalcompetitive sport in the past decade. Althoughthere is a lack of accurate statistics on thenumber of climbers, Smoot' estimated thatthere may be more than 4 million in the UnitedStates alone.Much of the current growth in the sport is

due to increased participation in climbing on

short rock walls and indoor climbing, employ-ing strenuous gymnastic type movements.

Traditionally, rock climbing was one aspect ofmountaineering. Mountaineering usually in-volves multiday summit attempts of highmountains that combines hiking, scrambling,and technical climbing on rock and ice whilecarrying all necessary gear in a pack.There is now an international circuit of

climbing competitions that take place onindoor climbing walls. Many indoor climbinggymnasiums have been constructed in theUnited States and Europe using speciallyfabricated modular holds which enable climb-ers to train regardless of the season. Climbingwalls are set up to accommodate varying skilllevels by modifying wall angles and hold size.

Despite the rising popularity of this sport, todate there are few studies reporting physiologi-cal responses during rock climbing. Much ofthe research on mountaineering has focused onphysiological changes at high altitude.' Inaddition, some studies have measured physi-ological responses during exercise using eithera Versaclimber"6 or climbing treadmill 8 tosimulate climbing. Although Williams et a?reported heart rate (HR) and plasma catechol-amine responses during ascents of short rockfaces, the angle of the ascent and difficulty ofthe climbs were not specified. One recent studyby Billat et al'0 examined the change in wholebody oxidative metabolism during climbing onmodular walls. They used four experiencedclimbers to compare Vo~max measured duringrunning and upper body pulling with thatmeasured while climbing two difficult climbingcourses.Thus the purpose of the present study was to

measure physiological responses to indoor rockclimbing during easy, moderately difficult, anddifficult climbs. Knowledge of metabolic andcardiovascular responses to various activities isuseful for exercise prescription, to evaluate thesafety of activities for various populations, tocode more precisely for activity self-reports,and to assess nutritional needs and trainingmethods. In addition, we sought to provide abase of descriptive measures that can beutilised to generate more complex physiologi-cal questions for the sport in future researchstudies. We hypothesised that there would besignificant differences in the HR, oxygenconsumption (Vo,), blood lactate, energyexpenditure (EE), and respiratory exchangeratio (RER) for the three levels of climbing dif-ficulty.

MethodsFourteen climbers (nine men, five women)volunteered for the study. Subjects responded

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to recruitment posters placed at a local indoorclimbing facility. They were experienced climb-ers who were able to complete three rockclimbing courses of increasing difficulty takingfive minutes each.

Volunteers reported to the climbing facilitywith their climbing harness, shoes, and chalkbag. All subjects refrained from exercising atleast 12 hours before testing, and eating at leasttwo hours before testing. Comprehensivehealth history questionnaires showed that allsubjects were free from injury and disease.Informed consent was obtained from each par-ticipant before testing.

Subjects were weighed in shorts and T-shirtswithout shoes on a calibrated medical balancebeam scale (Health-o-meter, Bridgeview, IL,USA) to the nearest 0.1 kg. Gear weight(climbing shoes, harness, chalk bag, and datacollection instrumentation) was measured onthe same medical balance beam scale, andaveraged 3.1 kg with less than 0.5 kg variationbetween subjects. Total weight was calculatedby adding gear weight to body weight (sincethis is the weight that was supported duringclimbing). Height was measured to the nearest0.5 cm.

All trials for each subject were performed onthe same day. Before any data collection,subjects were allowed to practice climbingwhile wearing the data collection apparatus.The preparatory time was also used to ensurethat all apparatus was properly and securelyfitted. Before each trial, subjects performed astandardised timed five minute warm upincluding stretching and easy climbing. Sub-jects then performed three climbs of increasingdifficulty on 6.35 m walls, each lasting fiveminutes. Difficulty was increased by settingclimbs on walls with steeper angles and withsmaller and fewer handholds and footholds.Arrangements were made with the climbinggym staff to refrain from moving any holds onthe three courses until the study was com-pleted. Subjects were inactive for 15 to 20 min-utes between each climbing trial. To ensurethat a true resting baseline condition wasachieved, succeeding trials did not begin untilHR returned to resting pre-exercise values.The three climbs were performed in ascend-

ing order of difficulty according to theYosemite decimal system." The first climb wasan easy 900 vertical wall, rated 5.6. The secondclimb was a moderately difficult negativelyangled wall (1060), rated 5.9. The last climbwas a difficult horizontal overhang of 1510,rated 5.11+. Top ropes were used for safetyreasons; however, subjects climbed up anddown the walls continuously without aid fromany rope tension. Subjects who lost their gripand were forced to momentarily fall on therope were allowed to continue, but were notallowed to rest. Two female rock climbers wereunable to finish the most difficult climbwithout rest. None of their data were includedin any analyses. Subjects were instructed toclimb at their normal pace but were told tominimise isometric holding. There were asimilar number of ascents and descents for allsubjects (no more than two laps difference).

Expired air was collected during the lastminute of each climbing trial using a Douglasbag attached to the climbing harness. A facemask (M 1410, Hans Rudolph, Kansas City,MO, USA) covering the nose and mouth wasattached to 1 m of low resistance tubingconnected to a 200 litre capacity Douglas bag.Subjects wore this apparatus throughout eachclimb. A two way valve was opened during thelast minute of each trial to collect expired airinto the Douglas bag. The valve was opened asthe subject approached the lowest footholds,and the gas sample was obtained withoutdelaying the progress of the climber. The valvewas closed immediately after the subjectreturned to ground. The total collection timewas recorded for the calculation of volume ofexpired air (VE).VE was measured using a flow meter (Singer,

Philadelphia, PA, USA). Fractions of oxygenand carbon dioxide were measured withparamagnetic and infrared analysers respec-tively (Erich Jaeger, Hoechberg, Germany),which were calibrated with gases of known per-centages. Vo, Vco,, and RER were calculatedand EE was calculated using the non-proteinRER kJ equivalents. All gas samples were ana-lysed within one hour of data collection. HRwas measured continuously and stored inmemory using a small telemetry unit (CICHeartwatch, Hempstead, NY, USA). Thetransmitter was placed on the chest andattached to two standard electrocardiographelectrodes. Electrodes were used in place of thechest strap provided by the manufacturer toprevent constriction of the chest which mayhave restricted breathing. The receiver wasattached to the subject's wrist and was angledso that researchers could easily read the digitaldisplay to ensure that the telemetry unit wasfunctioning properly during the trials. Theaverage HR from the final minute of each trialwas used for analysis.Blood samples from the ear lobe were

obtained before the first climbing trial, andafter each climbing trial to determine restingand exercising blood lactate concentrations.Before any other data collection, a topical heat-ing agent (Balsem Gosok, Tangerang, Indone-sia) was rubbed on to both ear lobes to stimu-late blood flow to the area. After 15 minutes ofseated rest, a sterile lancet was used to make asmall incision into the base of one ear lobe, and30 gl arterialised blood was collected into aheparinised capillary tube. The blood was thentransferred to a tube prepared with 100 pl 7%perchloric acid. Only one resting blood samplewas taken to lessen the number of earpunctures required. Post-exercise blood sam-ples were drawn one or two minutes after eachclimbing trial to allow time for the subject toremove the apparatus and sit down after climb-ing. Research shows that during these initialminutes of recovery, lactate concentrations aremaximal or remain elevated for this type ofexercise."-4 Lactate was analysed by anenzymic spectrophotometric technique. Allsamples were assayed in duplicate.Each subject was hydrostatically weighed'5 at

residual volume' using standard procedures

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Table 1 Descriptive characteristics of rock climbers. Data are means (SD)

Group Age (years) Weight (kg) Height (cm) Bodyfat (%1)

Men (n=9) 26.7 (7.8) 66.3 (6.1) 175.5 (5.6) 6.8 (2.6)Women (n=5) 32.4 (9.7) 54.5 (3.9) 164.7 (5.6) 14.6 (2.3)Combined 28.4 (8.6) 62.3 (8.3) 170.7 (8.7) 10.2 (4.6)

within a week of the climbing trials. Body den-sity was converted to percentage body fat usingthe equation of Brozek et al."Independent t tests were used to determine

whether or not there were gender differencesfor each of the dependent variables (HR, Vo2,lactate, EE, VE, VcoV, and RER). No significantdifferences (P>0.05) were found. Thereforedata for the men and women were pooled forall subsequent analyses. One way analysis ofvariance with repeated measures was used tocompare the HR, Vo, lactate, EE, VE, VCo,,and RER responses across the three climbingtrials. Scheff& post hoc tests identified whichmeans differed significantly from each other.P<0.05 was used to define statistical signifi-cance.

ResultsTable 1 summarises the physical characteristicsof the subjects. Table 2 gives the average valuesfor HR, lactate, VE, Vco2, and EE for eachclimbing trial. The main effect of the trials wassignificant for HR (F(2,26) = 37.43, P =0.0001), lactate (F(3,39) = 44.242, P =0.0001), VE (F(2,26) = 3.657, P = 0.0399),VCo2 (F(2,26) = 4.801, P = 0.0168), and EE(F(2,26) = 3.947, P = 0.0318). ScheffMcomparisons for HR and lactate indicated thatthe average HR and post-exercise lactate for alltrials differed significantly from each other.Vo,, VE, Vco,, and lactate values for thedifficult trial were significantly larger than forthe easy trial. Also, the average resting lactatediffered significantly from the post-exerciselactate levels for all three climbing trials. Theaverage EE for the easy trial (0.622 kJ/kg permin or 38.9 kJ/min) was significantly less thanthat for the difficult trial (0.844 kJ/kg per minor 52.7 kJ/min). There was no significantdifference for RER across the trials.

DiscussionHEART RATE RESPONSESMean HR during three climbing trials in-creased to 142, 155, and 163 beats/min for theeasy, moderate, and difficult trials respectively.The means correspond to 74-85% ofpredicted

Table 2 Comparison of the physiological variables for easy, moderate, and difficultclimbing trials (n=14). Data are means (SD)

Variable Easy (5.6) Moderate (5.9) Difficult (5. 11 +)

HR (beats/min) 142 (19)*t 155 (15)*t 163 (15)j#Vo, (ml/kg per min) 20.7 (8.1) 21.9 (5.3) 24.9 (4.9)tRER (CO,/02) 0.81 (0.06) 0.84 (0.09) 0.86 (0.11)EE (kJ/kg per min) 0.622 (0.393) 0.665 (0.318) 0.844 (0.309)tVE (litres/min) 32.6 (16.4) 39.8 (14.5) 44.3 (14.5)tVco, (ml/kg per min) 17.4 (6.2) 19.2 (4.8) 22.3 (4.2)t*Lactate (mmoln) 1.64 (0.63)*t 2.40 (0.68)** 3.20 (0.97)11

HR = heart rate; Vo2 = oxygen consumption; RER = respiratory exchange rate; EE = energyexpenditure; Vco, = carbon dioxide production.* P < 0.05 v difficult.t P < 0.05 v moderate.* P < 0.05 v easy.

maximal HR (220 - age). These results weresimilar in range to, but different in degree ofchange across trials from, those reported byWatts et at8 for five climbing trials ranging from80 to 1020 angles using a Treadwall (BrewersLedge, Jamaica Plain, MA, USA) climbingtreadmill. A direct comparison between climb-ing trials for these two studies is difficult sincea rating system such as the Yosemite decimalsystem was not used by Watts et al.' However,an adequate comparison can be made usingangles of the climbing trials. In their study, theaverage HR increased from 156 beats/min (800angle) to 171 beats/min (910 angle) butplateaued between 91 and 1020 (171-173beats/min). The failure of the HR to increaseacross the last three trials could be attributed tothe small difference in angle between the trials.In their study, there was an average of 60increase in angle with each successive trial.This may not have been a large enough changeto observe a HR difference, especially at thesteeper angles.

Billat et al'0 measured HR during two climbsrated 7b (French rating system), which roughlycorresponded in difficulty to the 5.1 1 +(Yosemite decimal system) trial. Average HRwas 176 and 159 beats/min for the first andsecond trials respectively, which correspondedto an average of 85.5 and 77% of the subjects'running maximal HR measured during atreadmill test.

Regardless of angle or difficulty of climbingtrials, the results from the present study and theother studies8 1O show relatively high HRresponses during climbing exercise. This in-crease in HR during rock climbing can beexplained in part by the use of intermittent iso-metric muscular contractions (37% of totalascent duration)'0 and the reliance on the armsas a major muscle group during more difficultclimbing trials.

Research has shown that isometric contrac-tions produce a disproportionate increase inHR relative to Vo2 at any level of work.'120 Ithas also been shown that the magnitude of thecardiovascular response to isometric contrac-tion is directly influenced by the size of thecontracting muscle mass.' Another factor thatmay be important in the understanding ofHRresponses during rock climbing is arm position.During rock climbing, the arms are often heldabove the level of the heart. Astrand et at'reported greater increases in lactate, HR, andblood pressure for carpenters nailing with thearms in a vertical position above the head com-pared with nailing at waist level. Although theposition of the arms may be anywhere fromlevel with the feet to fully extended overheadduring rock climbing, much of the time thearms are above the level of the heart.

Psychological stress may also be a considera-tion in the understanding of HR responsesduring rock climbing. Williams et al' measuredHR and plasma catecholamine responsesduring rock climbing. Subjects undertook twoclimbs on the same day. The first trial was car-ried out after the ingestion of a placebo tablet,and the second after ingesting oxprenolol (a [blocker). HR rose during both trials, with mean

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(SD) maximum HR of 166 (20) beats/minduring the placebo trial, and 120 (10) beats/min for the oxprenolol trial. Plasma catechol-amine levels rose only during the placebo trial.Based on these physiological measures, theauthors concluded that increases in HR are duemore to anxiety or fear of falling than to physi-cal exertion during difficult rock climbing onsmall cliffs. Billat et al'0 also addressed this issueby allowing their four subjects to trainextensively on the routes before the trials tominimise psychological stress during climbing.During the present study, psychological

stress was not measured, but is assumed to belimited somewhat by testing experiencedclimbers and by the use of safety ropes duringclimbing trials. Nevertheless, owing to theobservation that some fear of heights seems tobe common, the comments of Williams et alcannot be discounted.

Vo2 RESPONSESThe results of the present study show a markedincrease in HR without a concomitant increasein Vo2 across the trials. Vo, values were 20, 22,and 25 ml/kg per min for the easy (5.6), mod-erate (5.9), and difficult (5.11+) trials respec-tively. Billat et al'o reported average Vo, valuesof 25.9 and 20.6 ml/kg per min (46 and 37.5%of subjects' measured running Vomax)for twoclimbs rated 7b. Watts et al also reported lowVo, values compared with corresponding HRvalues during Treadwall climbing. The Vo,values were slightly higher (20.9-31.7 ml/kgper min) compared with those observed in thepresent study.Data from these three studies show relatively

low Vo, values compared with correspondingHR levels. These data indicate that therelationship between HR and Vo, appears to benon-linear during rock climbing. Although HRincreased progressively as a function of diffi-culty, Vo, remained constant across the trials.This response to rock climbing differs from thetypical linear HR-Vo, relationship demon-strated for exercise modes such as running andcycling.7 22

Isometric work elicits a disproportionate risein HR in relation to Vo2. Although care wastaken in the present study to instruct subjectsto minimise isometric holding during theclimbing trials, isometric work could not beeliminated. Climbing requires combined armand leg work, characterised by dynamic moves,interspersed with periods of isometric muscu-lar contractions. This pattern alternates be-tween the legs and arms, usually allowing twoto three points of contact on the holds for sup-port while moving. In general, on easier climbs,the legs do more of the work, similar to climb-ing a ladder. However, as climbs become moredifficult, the importance of arm work andisometric contraction increases. Although theamount of isometric work was not measured inthis study, it was observed that climbing speedslowed and isometric holding increased withthe difficulty of the climbing trial.As mentioned previously, Billat et alf' noted

that isometric work represented more than onethird of the total climbing time for two difficult

climbing routes, as determined by video analy-sis of the four subjects on the climbing routes.Thus the disproportionate use of the smallerupper body musculature combined with inter-mittent isometric work during difficult climbsmay explain why Vo, did not increase inproportion to HR during the more difficultclimbing trials.

LACTATE RESPONSESThe post-exercise lactate concentrations in-creased significantly across the climbing trialsfrom 1.28 mmol/l at rest to 1.64, 2.40, and3.20 mmol/l for the easy, moderate, anddifficult climbing trials respectively. Thesedata, along with increased RER from 0.81 to0.86, reflect the increased physiological de-mands of the moderate and difficult climbs ascompared with the easy climb, as well as anincreased reliance on glycolytic metabolism asthe climbing trials increased in difficulty.

Post-exercise lactate concentrations meas-ured during the present study were lower thanthose reported for simulated climbing,8 armplus leg ergometry," overhead nailing,2' climb-ing modular walls,'0 and treadmill running.7Subjects reported forearm fatigue withoutconcomitant leg fatigue after the moderate anddifficult climbing trials. During the trials onsteeper terrain, most of the lactate productionmay have been in the forearm, a relatively smallmuscle mass.Given the high HR values during the three

trials, lactate concentrations were lower thanexpected. Two possible explanations as to whypost-exercise lactate did not increase as ex-pected during the three climbing trials are theeffects of dilution caused by the large centralvenous blood volume and impaired lactateclearance during isometric contraction. Uptakeof circulating lactate by non-exercising musclemay be a factor as well. This point is addressedin a study by Richter et al4 in which lactateconcentration was measured during kneeextension exercise, with and without accompa-nying arm cranking. The authors concludedthat both exercising and non-exercising muscleis capable of lactate uptake and removal fromthe circulation.Lower lactate concentrations were measured

during the present study compared with valuesduring Treadwall climbing and climbing onhigh-angled artificial walls. Billat et al'0 re-ported 5.75 and 4.3 mmol/l after climbing twodifficult (7b) routes, lasting an average of 3.45minutes. Also, Watts et al' observed meanlactate levels of 3.6 mmol/l for the lowest angleto 5.9 mmol/l for the steepest angle.

ENERGY EXPENDITUREIn the present study, the mean EE values forthe three climbing trials were 0.622,0.665, and0.844 kJ/min per kg (38.9, 41.4, and 52.7kJ/min) respectively, for a mean body weight of62.3 kg. These values reflect energy expendi-tures similar to those for running on a horizon-tal surface at speeds of 10:30, 10:15, and 8:00minutes per mile respectively.25

Watts et al' reported average EE rangingfrom 43.5 to 46.8 kJ/min for five climbing trials

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on the Treadwall, with the highest EE attainedat the 860 angle. Although they found nosignificant differences in EE with increasingclimbing angle, our data show the average EEduring the easy trial was significantly less thanduring the difficult trial. Again, this disparitymay be explained by differences in angle anddifficulty of the climbing trials between the twostudies. The larger average difference in anglesbetween successive trials in the present studymay explain why the EE increased across trials,while it remained constant during the Tread-wall study. Although the average increase inRER was not significant in the present studyacross trials, there was a tendency for RER torise as the climbing trials increased in difficulty.

ConclusionsIndoor rock climbing expends energy at a rela-tively high rate. The increase in Vo2 for thisactivity was similar to moderate paced walking,and mean HR increased to 74-85% of age pre-dicted maximal values. Our data indicate thatindoor rock climbing requires moderate levelsof physical exertion and therefore may be agood activity for increasing cardiorespiratoryfitness and muscular endurance, especially in apreviously sedentary population.Data collected during three climbing trials

showed significant increases in HR and lactatebut only modest increases in Vo2. Given thatisometric muscular contraction and raising thearms above the level of the heart are often nec-essary during climbing, the traditional HR-Vo,relationship should not be used in the analysisof this sport or for prescribing exercise intensityfor climbing activities. Also, the significant dif-ferences in HR and lactate between threeincreasingly difficult climbing trials (and sig-nificant difference between the easy anddifficult trials for Vo,, Vco,, VE, and EE) indi-cate that the ratings system currently used byclimbers discriminates well between easy,moderate, and more difficult climbs.

Additional research is needed to assess theamount of isometric and dynamic movementduring climbing, the relative use of aerobic andanaerobic metabolic pathways for energy pro-duction during climbing, as well as the contri-bution of muscle strength and endurance torock climbing performance.

The authors would like to thank Craig Keaty for his invaluableassistance in subject recruitment, data collection, and access tothe climbing wall facility. We would also like to thank SharonGriffin and Jim Milani for their help in preparing themanuscript.

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