Short-distance sprint performances in different techniques [DP (50 m), free-technique (F 50 m), and leg skating (L 50 m)] were measured through 50-m sprint tests on skating skis. The tests were conducted on a flat, straight XC skiing track. Participants completed three trials for each technique, with the testing order and recovery time between the tests controlled by bib numbers starting from one. The results of the best trial for each technique were used for analysis. The starting position was standardized by positioning the ski with the binding 50 cm before the starting line and placing the poles on the ground. Time measurement started when the athlete passed the first light sensor at the starting line and ended when they passed the 50-m mark.

The athletes were required to complete an uphill distance of 30-m DP (30 m) and the asymmetrical uphill 40-m V1 skating (XC skiers have a dominant and a nondominant side) with a slight incline of 0–1° for the first 5 m and an incline of 4°–5° for the remaining distance.

Athletes started (individual start intervals of 30 s) at the lowest point of the track avoiding one longer downhill passage at the beginning of the track. Getting to the start accompanied by a team of coaches was used as a further specific warm-up and getting used to the “grip waxed” skis. After an uphill climb of 400 m, an intermediate time was taken.

The agility course contained several demanding sections passed by all athletes. In between the agility parts, athletes had to use appropriate skating techniques adapted to the terrain for some longer passages also including uphill sections. After the individual start (start intervals of 30 s), each competitor had to skate a marked eight followed by slipping under several skiing gates, passing three waves and a slalom as well as a small jump and four giant slalom gates. The overall course (1,500 m) had to be passed twice.

The overall skiing performance index (P_XC) was calculated by normalizing the skiing times of both races (3,000 m skating including parcours and 1,160-m classic) using z-standardization [by using equation (xi−x¯)/s] and then taking the average of the two resulting z-values, which represents P_XC. The two competitions selected were chosen based on consistent weather and snow conditions, individual start intervals, and the full cooperation of the participants.

To evaluate the maximal force of the upper body (target muscles: latissimus dorsi, trapezius pars ascendens, rhomboideus minor et major, teres major, and supporting muscles like erector spinae, biceps brachii, brachialis, and brachioradialis) 5 days prior to the XC skiing sprints, a one-repetition maximum (1RM) lat pull-down test was performed using a machine with a seated position and support across the top of the quadriceps. Participants began with a 10-repetition warm-up using a weight of 30%–50% of their estimated 1RM. For the 1RM test, the seat was adjusted to ensure full arm extension during the eccentric phase of the exercise, and the seat height was adjusted to allow the participants to start the lift with their arms fully extended. A pronated wide overhand grip (hands slightly wider than shoulder width, palms facing away from the body) was used throughout the test.

For the attempt to be counted, the bar had to be pulled down to the participant's chin while maintaining an upright posture. The motion should be smooth; sudden jerks, hunching, or swinging the body was not allowed. Participants were able to select their starting weight based on past experience. If the attempt was successful, the weight was increased by 1.0–2.5 kg, depending on how easily they could complete a single repetition. If the attempt was unsuccessful, the weight was reduced, and another attempt was given. A minimum of 5 min of recovery was given between attempts. This process was repeated until a complete repetition was not possible (28, 29). This testing method has been found to have a high level of reliability, with ICCs ranging from 0.979*** (male) to 0.998*** (female) to 0.995* (total) (30).

Anthropometric data including body stature, body mass, inseam leg length, and sitting height were collected. In addition, the sum of skinfold (mm) was calculated by the four-site caliper skinfold method: triceps, biceps, subscapular, and suprailiac (31).

To account for any potential effects of maturation, age from peak height velocity (PHV) and the maturity offset were calculated using chronological age, body height, sitting height, and body mass according to the method described by Mirwald et al. (32).

The study found that short-duration maximal speed in various forms of XC skiing, such as V1 40-m uphill, DP 30-m (uphill), and DP 50-m (flat), and free-and leg skating, were related to P_XC for both young boys and girls. For boys, this connection was found even when maturity offset was used to account for the effects of maturation, except for DP 30-m (uphill r = 0.69 ns). This result aligns with previous studies on adult skiers (18–19, 21, 33–36). When accounting for maturation in girls by using maturity offset, most short-duration tests still had high correlations with P_XC, except for leg skating 50-m. Furthermore, the study findings regarding 50-m sprints align with the youth roller skiing study of Stöggl et al. (11), revealing that short-duration maximal roller skiing speed over 50 m in DP, V2 skating, and leg skating was related to P_XC for both young girls and boys, which is consistent with several studies on adult XC skiers (18–19, 21, 33–36).

Previous research by Stöggl et al. (18, 19) has shown that short-duration maximal speed in DP (treadmill) can predict performance in a DP sprint over a 1,000-m race distance in elite adult XC skiers. Additionally, short-duration maximal speed in DP and diagonal stride were found to have a strong correlation with performance in a classical-style sprint simulation on a treadmill over 1,100 m (18). Sandbakk et al. (21) found that peak speed during a short-duration incremental test was higher in male world-class sprint skiers compared to that in the national level ones using the V2 technique, but no differences were found in peak acceleration (30-m skating sprint) and maximal strength. Andersson et al. (18) found that maximal speed in DP and V2 skating was positively related to the percentage of racing time using the V2 technique during a sprint race. Similarly to the results found in elite XC skiers, the study finds that short-duration on-snow maximal speed is a time-efficient and highly predictive test of P_XC in young XC skiers, independent of age and sex. This result also highlights the importance of focusing on developing maximal speed abilities in youth XC skiers.

The current study found that DP skiing performances over short distances were among the highest predictors of P_XC in youth XC skiers, independent of sex. This result aligns with a previous study on roller skiing and P_XC by Stöggl et al. (11). Mikkola et al. (20) examined the factors that predict performance in a simulated XC skiing sprint competition (4 m × 850 m) in elite male skiers on roller skis using the V2 skating technique on an indoor track and a 2-km × 2-km DP test. The study found that the 2-km × 2-km DP test was the best single performance predictor for sprint performance, indicating that sprint skiers should focus on sport-specific upper body training and training skiing economy at high speeds. Fabre et al. (37) found that peak speed during an incremental DP test in female elite XC skiers (4% grade test duration of 7–8 min) was related to competition performance (Italian Ski Federation Points). Moreover, Stöggl et al. (11) found that the girls' and boys' DP225-m uphill performances were also strongly related to P_XC.

The current study found that only girls' 1RM lat pull-down test had a low correlation with XC skiing performance. This finding is not in line with previous research on the association between strength and XC skiing performance in adult elite athletes. For example, Mikkola et al. (20) found that faster XC skiers had higher maximum and explosive force in a bench press test, a conclusion that aligns with a study by Stöggl et al. (38), which showed that power output during submaximal bench pressing and pulling was related to classical-style maximum speeds. Additionally, Losnegard et al. (39) found a strong correlation between one-repetition maximum on a seated pull-down exercise, simulating a DP pull and performance on a DP ergometer, time trial performance over 1.1-km double poling, and 1.3-km uphill skating performance.

Our research group recently found that a push-up test was related to XC skiing performance for both boys and girls. Additionally, boys' pull-up performance had an acceptable correlation with XC skiing performance. It is worth noting here that both tests measured muscular endurance power (strength perseverance) more than the maximal power (10) measured in the present 1RM lat pull-down test. So, it can be assumed that the crucial determinant of youth P_XC is not maximal power, but, instead, it is the skills necessary for cross-country skiing, which includes utilizing poles correctly, maintaining balance and posture, and maneuvering through different types of terrain.