The athletes of the GJNTC were smaller, slimmer and had a lower BMI than age matched population distributions as reflected by the negative z-scores. Watts et al.  recorded comparable values for height in a cohort of 13 year old male climbers (mean 162.5 cm) to our sample but higher values for weight, BMI, and body fat. Therefore, our data supports the assumption that elite climbers tend to be of a smaller stature with low body fat, BMI and body weight  but there were no signs of pathological eating habits.
The finding that junior athletes had been climbing for an average of 8 years was unexpected as it meant that a large proportion of the athletes had commenced their climbing career aged 3 – 5 years. Less than half of the participants reported engaging in general endurance training to improve their cardiopulmonary exercise capacity.
When evaluating the CPET data from the 47 athletes who were seen on one occasion, the values of the boys (41.3 mL kg-1 min-1) and girls (39.8 mL kg-1 min-1) were comparable to a previous study which studied adult climbers on a cycle ergometer (45 .5 mL kg-1 min-1) . The highest values of are achieved by young elite (national team members) endurance athletes (60 mL kg-1 min-1) . Adolescent sprint- and power-related athletes range between 46 mL kg-1 min-1 for girls and 52 mL kg-1 min-1 for boys . Aerobic capacity has been estimated to be one of the most important predictors for good results in combat disciplines and they range between 55 mL kg-1 min-1 for male and 46 mL kg-1 min-1 for female adolescents  and even higher in elite junior judo athletes and boxers who achieved values as high as 53 – 66 mL kg-1 min-1 . Team sports achieve values ranging between 47 mL kg-1 min-1  and 59 mL kg-1 min-1 . All these values were achieved during treadmill testing during which higher - values can be achieved than when the testing is performed on a cycle ergometer. Considering this, the climbers probably compare to sprint- and power-related athletes and those in combat or team sports. It is unclear whether a higher could improve their climbing as observed in combat sports because this has not been studied yet. However, if climbers reach arm-specific during hard climbs, as suggested previously , improving their maximum oxygen uptake could possibly imply an improvement in the difficulty of climbing.
The adaptation of a particular aspect of the cardiopulmonary system, like an increase of the O2pulse, suggesting a higher cardiac output, or an improved minute ventilation could not be observed in the group of elite climbers studied during the cross-sectional approach.
Interestingly, although the climbers stated muscular fatigue as the reason for terminating the CPET, a mean RER of 1.1 and a peak lactate of 8.1 in girls and 9.0 in boys as well as a mean heart rate of over 180 beats min-1 point towards maximal exertion. Even though the climbers in our study climbed at a comparably high level and were of comparable age they also achieved poorer maximum workloads during the cycle test with 3.2 W kg-1 (boys) and 2.7 W kg-1 (girls) in comparison to 4.2 W kg-1  and a poorer mean RER (1.1 in comparison to 1.24). One explanation could be that the climbers in our study did not push themselves enough and could have gone higher. Another explanation is the different exercise protocol for cycle ergometry. Whereas we used an incremental step test, a ramp test was used in the other study .
The longitudinal approach of 14 athletes of whom two exercise tests spaced 2 years apart could be compared the nordic skiers achieved significantly higher CPET parameters except for peak blood lactate. The values of were comparable to the data from previous studies for endurance athletes  and taking into consideration the fact that they were obtained during a cycle ergometry and not on a treadmill, even higher. This finding reflects the very high endurance level of elite nordic skiers. It also allows for the clear differentiation between the nature of climbing and nordic skiing. Interestingly no significant changes occurred over the time frame of two years in both groups. For the nordic skiers this could be a consequence of their already highly trained status at the moment of the first examination, which could not further be improved in the timeframe of two years. Although the climbers increased their climbing training significantly, the time spent on classical endurance training like running or cycling did not change. The fact that there was no change in after two years of climbing on the GJNTC even though the time spent training for climbing increased significantly, suggests that climbing probably does not elicit cardiopulmonary changes seen in endurance sports. A surprising finding was the relatively low heart rate of the 14 male climbers on both occasions especially in comparison with their nordic skiing counterparts. As the RER was higher in the group of climbers and peak lactate values were comparable between both groups, it cannot be suspected that the nordic skiers just pushed themselves harder than the climbers. However, the high standard deviation of the peak heart rate, not observed in the group of nordic skiers suggests a big interindividual variability and indeed varied for the climbers between 153 and 200 beats min-1.
Whereas some adaptation to the endurance nature of nordic skiing could be seen in the increase of the cardiac ouput (O2pulse) as well as the minute ventilation (, though not significantly, such adaptations did not occur in the group of elite climbers. As both groups were comparable to age, size, and gender, the cardiopulmonary effects of climbing may not be important enough to elicit any adaptations. However, the question remains whether an endurance training targeted to increase could improve the overall climbing ability. Prospective studies are needed to evaluate this effect.
An important reason to perform cardiopulmonary exercise testing during the yearly medical examination of elite athletes is for preventing sudden cardiac death. The use of CPET in combination with an electrocardiogram allows for detection of channelopathies, dangerous arrhythmias, arrhythmogenic ventricular cardiomyopathy and for differentiation between athlete’s heart and hypertrophic cardiomyopathy in which O2pulse and the ventilatory threshold are taken into consideration. There were no pathological findings in the team members of the GJNTC during the investigated time-frame. However, since the SCD of a young Canadian athlete in the fall of 2019, the need for regular cardiac check-ups and a clear understanding of the impact of the sport on the cardiac system is essential and more knowledge especially with regards to young elite athletes is needed for a better prevention of SCD.
Our study has several limitations. First of all, the design of the study is retrospective which is a limitation in and of itself. The collective is rather inhomogeneous and presents young athletes over a large age-span. This is based on the fact that the study entry is defined by acceptance to the German Junior National Team of Climbing which is solely based on their climbing ability. For the longitudinal design the number of athletes is comparably small. As we only wanted to include high-level climbers and compare them to high-level nordic skiers we limited our evaluation to the members of the German Junior National Team in both sports, thus the number we were able to follow for the required timeframe was comparably low. Also there was no age-matched control group of sedentary subjects which is why literature data and z-scores were used for comparison.