Assessment of Maximal Aerobic Capacity in Ski Mountaineering: A Laboratory-Based Study

his study aims to evaluate the agreement in maximum oxygen consumption ( . V O 2max) be- tween a running protocol and a ski mountaineering (SKIMO) protocol. Eighteen (eleven males, seven females) ski mountaineers (age: 25 3 years) participated in the study. . V O 2max, maximum heart rate (HRmax), and maximum blood lactate concentration (BLAmax) were determined in an incremental uphill running test and an incremental SKIMO-equipment-speci c test. . V O 2max did not differ be- tween the SKIMO and uphill running protocols (p= 0.927; mean difference–0.07 3.3 mL/min/kg) , nor did HRmax (p= 0.587, mean difference –0.7 5.1 bpm). A signi cant correlation was found between . V O 2max SKIMO and . V O 2max running (p 0.001; ICC = 0.862 (95% CI: 0.670 0.946)). The coef cient of variation was 4.4% (95% CI: 3.3 6.5). BLAmax was signi cantly lower for SKIMO compared to running (12.0 14.1%;p= 0.002). This study demonstrates that . V O 2max determined with a traditional uphill running protocol demonstrates good agreement with an equipment-speci c SKIMO protocol. Keywords: ski mountaineering; sport-speci c exercise test; maximum oxygen consumption; perfor- mance; SKIMO 1. Introduction In the European Alps and other

3.3 6.5). BLAmax was signi cantly lower for SKIMO compared to running (12.0 14.1%;p= 0.002). This study demonstrates that . V O 2max determined with a traditional uphill running protocol demonstrates good agreement with an equipment-speci c SKIMO protocol. Keywords: ski mountaineering; sport-speci c exercise test; maximum oxygen consumption; perfor- mance; SKIMO 1. Introduction In the European Alps and other alpine countries, ski mountaineering (SKIMO) has developed into a fast-growing winter sport and leisure activity [1]. Several national and international competitions, including World Cups and Youth Olympic Games, have been arranged in SKIMO (ISMF 2019;, accessed on 4 June 2019). SKIMO competitions contain three major disciplines: single race, team race, and vertical race. Typically, SKIMO single races last between 1.5 and 2.5 h for the fastest racers, where most of the time (>80% of total race time) is spent on the ascent [2]. SKIMO competitions are usually held at altitudes around 2000 m above sea level and have been recognized as one of the most demanding endurance disciplines [2,3]. The high physiological demand is mirrored in exercise intensity during SKIMO competitions, which has been reported to be close to the respiratory compensation point [2,4]. Despite its growing popularity, only a few studies have been carried out on the physiological aspects of SKIMO. The energy cost of SKIMO was investigated by few stud- ies [2,5–7], demonstrating that SKIMO is more energy demanding than cross-country skiing or snowshoe walking [2]. This is partly due to the extensive equipment(8 2 kg) [1] necessary for SKIMO [3]. Moreover, SKIMO racing performance was reported to signif- icantly correlate with maximum oxygen uptake ( . V O2max), body mass of the athlete [3], rst ventilatory threshold (VT1), and respiratory compensation threshold (RCT) [2]. As demonstrated in previous studies, factors such as exercise modality and test protocol, including test duration and stage length, signi cantly affect the . V O2max attained during an exercise test [8–10]. Indeed, the concept that athletes should be tested sport-speci cally Int. J. Environ. Res. Public Health2021,18, 7002.

previous studies, factors such as exercise modality and test protocol, including test duration and stage length, signi cantly affect the . V O2max attained during an exercise test [8–10]. Indeed, the concept that athletes should be tested sport-speci cally Int. J. Environ. Res. Public Health2021,18, 7002.

Int. J. Environ. Res. Public Health2021,18, 7002 2 of 9 is supported by the results of Pinna et al. [11]. They demonstrated that predicting . V O2max in trained swimmers from non-speci c exercise tests such as cycling or arm cranking does not provide data similar to those obtained from swimming. Therefore, traditional laboratory . V O2max tests (e.g., cycling, level grade treadmill running) may provide less precise information on the physiological demands of exercising with SKIMO equipment when differences between SKIMO and traditional . V O2max tests are considered. Speci cally, SKIMO involves uphill moving, the use of more muscle mass due to the active involvement of both the trunk and upper body [2], as well as the additional equipment carried [3], compared to traditional . V O2max tests. Hence, as SKIMO places these speci c physiological demands, athletes might bene t from a SKIMO-equipment- speci c . V O2max test in terms of robust training planning and performance diagnosis. However, a SKIMO-equipment-speci c . VO2max test needs to ful ll the criterion of being a valid test. While several studies [3–5] have used traditional but unspeci c running exercises to assess . V O2max in ski mountaineers, others [2,12] have evaluated . V O2max in an incremental SKIMO eld test on a groomed snowy Alpine track using acoustic signals to match the required speed. Another approach in a more controlled laboratory environment is the use of roller skis [6,13,14] on large motorized roller-skiing treadmills, which most closely resembles SKIMO exercise. However, the friction coef cient between roller skis and SKIMO skis ( tted with adhesive skins) and, in particular, the dimensions of the skis are different, which limits the use of roller skis in terms of a sport-speci c context. To the best of our knowledge, to date, only one study has used a SKIMO-speci c incremental step protocol to evaluate . V O2max in eight elite SKIMO athletes [15] in a laboratory environment and compared it to a standardized cycle test, exhibiting inconsistency between cycling and SKIMO . VO2max. As existing methods to assess . V O2max

c context. To the best of our knowledge, to date, only one study has used a SKIMO-speci c incremental step protocol to evaluate . V O2max in eight elite SKIMO athletes [15] in a laboratory environment and compared it to a standardized cycle test, exhibiting inconsistency between cycling and SKIMO . VO2max. As existing methods to assess . V O2max in SKIMO are non-sport- and equipment- speci c, complex to conduct, or do not take into account muscle activity for uphill move- ments, the present study aims at evaluating a standardized maximal ramp protocol for laboratory SKIMO testing on a commercially available treadmill. Hence, the overall aim of the study is to evaluate the agreement in . V O2max between a running protocol and a SKIMO-speci c protocol. 2. Materials and Methods 2.1. Participants Study participants were recruited via personal contacts and social media between March and April 2019. Eighteen healthy (eleven males, seven females) and experienced ski- mountaineers (34 15 SKIMO tours per season) were included in the study. Prior to the rst exercise test (either running or SKIMO), participants underwent routine pre-participation screening by answering an adapted physical activity readiness questionnaire (PAR-Q) [16]. Exclusion criteria were pre-existing acute or chronic diseases, pregnancy, and lactation period. Before providing their verbal and written informed consent to participate in the study, participants were provided detailed information about the procedure and potential risks of the study. The study met the ethical standards set by the Declaration of Helsinki, and the procedures of the study were approved by the local Board for Ethical Questions in Science. A sensitivity analysis for the present sample was conducted using G*Power 3.1 (University of Düsseldorf, Düsseldorf, Germany). Based on the assumptions ofalpha = 0.05, power = 0.80, nonsphericity correction = 1, and r among repeatedmeasures = 0.5and using a repeated-measures ANOVA as the statistical analysis, an effect size of partial etaˆ2 > 0.11 was revealed as signi cant with the present sample size of 18 participants. Participants' demographic and anthropometric characteristics are shown in Table.

nonsphericity correction = 1, and r among repeatedmeasures = 0.5and using a repeated-measures ANOVA as the statistical analysis, an effect size of partial etaˆ2 > 0.11 was revealed as signi cant with the present sample size of 18 participants. Participants' demographic and anthropometric characteristics are shown in Table.

Int. J. Environ. Res. Public Health2021,18, 7002 3 of 9 Table 1. Demographic and anthropometric characteristics of the study group. Values are means SD. Variables Males (n = 11) Females (n = 7) Total (n = 18) Age [years] 25 3 26 3 25 3 Weight [kg] 78.1 6.5 58.4 4.8 70.4 11.4 Height [cm] 182 6 166 7 176 10 BMI [m 2 /kg] 23.5 0.8 21.1 0.9 22.6 1.4 Exercise [h/week] 10 7 10 3 10 5 SKIMO [tours/season] 38 18 29 8 34 15 2.2. Design This randomized crossover study consisted of an incremental uphill running test and an incremental SKIMO-equipment-speci c test, separated by at least seven days (maximum 14 days). Participants were advised to refrain from intense exercise and alcohol 24 h before each exercise test. 2.3. Exercise Testing The running test was conducted on a conveyer belt treadmill (h/p/cosmos pulsar®, h/p/cosmos Sports and Medical, Nussdorf, Germany). The participants wore a harness attached to the safety arch to prevent potential falls. The SKIMO test was performed on a treadmill with a slat belt surface (Woodway, Waukesha, WI, USA) without a safety arch. To provide adequate safety for the participants, two assistants spotted the participants in the last few stages of the test. Cardiorespiratory parameters were measured continuously using an open spirometric system (Oxycon mobile, CareFusion, Baesweiler, Germany) that was calibrated according to the manufacturer's guidelines before each test. First and second ventilatory thresholds (VT1 and VT2, respectively) were later determined by visual inspection from two experienced researchers. For determining VT1, the V-slope plot ( . V CO2vs. . V O2) as well as the increase in . V E/ . V O2, with no concomitant increase in . V E/ . V CO2, were considered for evaluation. For determining VT2, the second disproportional increase in . V E vs. . V CO2and the increase in . V E/ . V CO2were visually inspected. Heart rate (HR) was determined by a chest belt (Wear Link, Polar, Kempele, Finland) and transmitted to the spirometric device. The non-SKIMO-equipment-speci c exercise test was an uphill running protocol that was

for evaluation. For determining VT2, the second disproportional increase in . V E vs. . V CO2and the increase in . V E/ . V CO2were visually inspected. Heart rate (HR) was determined by a chest belt (Wear Link, Polar, Kempele, Finland) and transmitted to the spirometric device. The non-SKIMO-equipment-speci c exercise test was an uphill running protocol that was previously used in several studies in trained participants [17,18], described in detail in Table. Brie y, exercise started at 5.0 km/h and 5% inclination for two minutes; then, the inclination was set at 10% for another two minutes. Subsequently, the speed was increased to 6.0 km/h, and inclination was augmented by 2% every minute until 20%. Then, the running speed was increased by 1.0 km/h per minute while the inclination was kept constant at 20%. The SKIMO protocol was designed in conformity with the previously described uphill running protocol and preceding SKIMO studies [2,12,15]. Starting at 3.0 km/hand an inclination of 10%, the inclination was increased after two minutes to 20% for another two minutes. Then, speed was augmented to 3.5 km/h at an inclination of 20%. Hereafter, speed was kept constant at 3.5 km/h, whereas inclination was increased each minute by 2% until 30% was reached. Finally, speed was increased by 0.5 km/h each minute, while inclination was kept at 30% (Table). Tests were completed when participants reached volitional exhaustion. A test was considered maximal when three of the following criteria were ful lled: (1) . V O2peak plateau at peak exercise; (2) respiratory exchange ratio 1.10; (3) peak HR 90% of the theoretical maximal HR (220—age); (4) indication of maximal exhaustion by the athlete [19]. Maximum oxygen consumption was de ned as the highest 30-second average during the test. Directly after terminating the treadmill test, a capillary blood sample was collected from the earlobe to assess the maximal blood lactate concentration (BLAmax; Biosen C line, EKF Diagnostics, Barleben, Germany), and the ratings of perceived exertion (RPEmax; separately for breathing and lower limb muscles) according to the Borg scale [20] were recorded. Female and male

test. Directly after terminating the treadmill test, a capillary blood sample was collected from the earlobe to assess the maximal blood lactate concentration (BLAmax; Biosen C line, EKF Diagnostics, Barleben, Germany), and the ratings of perceived exertion (RPEmax; separately for breathing and lower limb muscles) according to the Borg scale [20] were recorded. Female and male

Int. J. Environ. Res. Public Health2021,18, 7002 4 of 9 participants performed the SKIMO test on 158 and 174 cm SKIMO skis, respectively (Tour 88 Ski, Dyna t, Aschheim, Germany). The skis were equipped with SKIMO skins (Speed Fell Tour 88, Dyna t, Aschheim, Germany) and SKIMO bindings (ST Radical, Dyna t, Aschheim, Germany) on the medium heel raiser. Participants wore a sex-speci c SKIMO boot model (HOJI PX W and HOJI PX, Dyna t, Aschheim, Germany, for females and males, respectively) in their individual shoe size. Moreover, extendable ski poles equipped with rubber stoppers, adjusted to individual body heights, were used for the test, resulting in a total added SKIMO gear weight of 3900 g for female participants and 4200 g for male participants. Table 2.Schematic of the uphill running protocol. Time Inclination (%) Speed (km/h) 2 5 5.0 4 10 5.0 5 10 6.0 6 12 6.0 7 14 6.0 8 16 6.0 9 18 6.0 10 20 6.0 11 20 7.0 12 20 8.5 13 20 9.0 14 20 10.0 15 20 11.0 16 20 +1.0 Table 3.Schematic of the SKIMO protocol. Time (min) Inclination (%) Speed (km/h) 2 10 3.0 4 20 3.0 5 20 3.5 6 22 3.5 7 24 3.5 8 26 3.5 9 28 3.5 10 30 3.5 11 30 4.0 12 30 4.5 13 30 5.0 14 30 5.5 15 30 6.0 16 30 +0.5 2.4. Statistical Analyses Statistical analyses were conducted using IBM SPSS Statistics for Windows, version 25 (IBM Corp., Armonk, NY, USA). Values are presented as mean SD. The data were tested for normal distribution with the Shapiro–Wilk test. The primary outcome parameter was the attained . V O2max (mL/min/kg) during the running and SKIMO exercise tests. The identical units in both conditions allowed a reliability approach, following Hopkins [21] and Weir [22]. A repeated-measures analysis of variance (ANOVA) with one within-subject factor (type of test: running, SKIMO) was used to determine the differences between run- ning and SKIMO exercise tests. In addition, an intraclass correlation coef cient (ICC(3,1); two-way mixed consistency) was calculated between running and SKIMO .

units in both conditions allowed a reliability approach, following Hopkins [21] and Weir [22]. A repeated-measures analysis of variance (ANOVA) with one within-subject factor (type of test: running, SKIMO) was used to determine the differences between run- ning and SKIMO exercise tests. In addition, an intraclass correlation coef cient (ICC(3,1); two-way mixed consistency) was calculated between running and SKIMO . V O2max [22]. The typical error (TE), including 95% con dence intervals (95% CIs), were calculated using

Int. J. Environ. Res. Public Health2021,18, 7002 5 of 9 the standard deviation of differences between running and SKIMO divided by p 2 [21]. The coef cient of variation (CV), including 95% con dence intervals, were calculated using the TE divided by the average . VO2max (running; SKIMO) multiplied by 100 [21]. Both a Bland-Altman plot and a scatterplot of . V O2max (running versus SKIMO) were created. The Bland-Altman plot consisted of the difference between . V O2max running and SKIMO and the average . V O2max (running; SKIMO), including 95% con dence intervals of the average difference [23]. The 95% con dence intervals were referred to as the limits of agreement. A simple linear regression analysis was conducted with average . V O2max as the independent variable and difference in . V O2max as the dependent variable to analyze proportional bias (e.g., higher measurement error in higher . V O2max values).p-values < 0.05 (two-tailed) were considered to indicate statistical signi cance. 3. Results All participants ful lled the criteria for a maximal test according to Cunha et al. [19] for the running test, and all but one participant (ful lled only two criteria) ful lled the criteria for the SKIMO test. No harmful incident was observed during all tests. Maximum oxygen uptake (mL/min/kg) values obtained during the running test did not signi cantly differ from the SKIMO-equipment-speci c test. There was a signi cant correlation between SKIMO and running for . V O2max (mL/min/kg) (p< 0.001; ICC [95% CI] = 0.862 [0.670 0.946]). The TE for the relative . V O2max was 2.3 mL/min/kg [95% CI: 1.7 3.4] and for the absolute . V O2max, 164 mL/min [95% CI: 123 241]. The coef cient of variation (CV) was 4.4% [95% CI: 3.3 6.5] for relative and absolute . V O2max values. The Bland–Altman plot shows that all values were within the limits of agreement (Figure).Int. J. Environ. Res. Public Health 2021, 18, x 5 of 10 V 6O 2max [22]. The typical error (TE), including 95% confidence intervals (95% CIs), were calculated using the standard deviation of differences

The study compares oxygen consumption in ski mountaineering and running protocols.