Adolescent Cross-country Skiers Research Articles

Effects of aerobic capacity on DNA telomere length in adolescent cross-country skiers

Effects of aerobic capacity on DNA telomere length in adolescent cross-country skiers

The effect of strength training on aerobic and anaerobic parameters in adolescent cross-country skiers

The effect of strength training on aerobic and anaerobic parameters in adolescent cross-country skiers

Cardiac remodelling in adolescent athletes – sex differences progress through adolescence

Abstract Background Cardiac remodelling beyond reference values is well-known in adult athlete's heart. Male endurance athletes are more prone to develop cardiac chambers and wall thickness above reference values. Cardiac remodelling is also described in adolescent athletes, but considered to be moderate compared to adults. However, few studies evaluate adolescent athlete's heart by paediatric echocardiographic reference values. Current paediatric reference values are sex-unspecific and do not include exercise data. The impact of sex and exercise on remodelling in adolescent athlete's heart remains unclear. Purpose We aimed to study the development of cardiac remodelling and potential sex differences in adolescent athletes. We hypothesized that male adolescent athletes would display greater degree of remodelling compared to female adolescent athletes. Methods Male (M) and female (F) adolescent cross-country skiers were recruited in a longitudinal cohort study. They were examined with echocardiography at age 12, 15 and 18. Data on exercise was collected at all examinations. We evaluated echocardiographic parameters by paediatric reference values (Z-score: number of standard deviations above estimated mean in the given body surface area). Echocardiographic measures were considered above upper reference value if Z-score was ≥2. Results Seventy-six athletes were examined at age 12 (48 M, 28 F), 48 at age 15 (34 M, 14 F) and 34 at age 18 (23 M, 11 F). Although Z-scores were within reference values at age 12 (Table 1), a subset of athletes displayed Z-scores ≥2 for end-diastolic intraventricular septum diameter (IVSd, M 13/48=27%, F 5/28=18%) and left ventricular posterior wall thickness (LVPWd, M 6/48=13%, F 2/28=14%). The male group demonstrated enlarged left ventricular mass (LVM) from age 15 (Figure 1). Males had greater left ventricular end-diastolic volume (LV EDV) from age 12. Additional sex differences were evident from age 15 for IVSd, LVPWd and LVM (Table 1). There was no sex difference in exercise hours. Both groups had normal myocardial function through the study period. Conclusion Cardiac remodelling beyond reference values was observed in athletes of both sexes from early adolescent age. Sex differences were evident from age 12 with further progression. Pathological values for LVM were more frequent in males. These findings suggest that sex differences in exercise-induced cardiac remodelling is more prominent in adolescents than previously reported. Sex and exercise history should be considered in questions of pathology. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): The South-Eastern Norway Regional Health AuthorityCentre for Children and Youth Sport, Norwegian School of Sport Sciences

Anthropometrical and Physiological Determinants of Laboratory and on-Snow Performance in Competitive Adolescent Cross-Country Skiers.

Purpose: To explore the anthropometrical and physiological determinants of laboratory and on-snow performance in competitive adolescent cross-country skiers. Methods: Fifty-two adolescent (25 girls) (14.8 ± 0.6 years) skiers performed an uphill treadmill rollerski session using the G2 ski skating technique. Gross efficiency (GE) was calculated from a submaximal work bout (∼84% of peak oxygen uptake; V̇O2peak) while V̇O2peak, accumulated oxygen deficit (ΣO2def) and laboratory performance were determined from a 3-min time trial (TT3min) before upper- and lower-body maximum strength were tested. Pearson’s product moment correlations and multiple regression analysis explored the relationship with anthropometrical and physiological determinations of laboratory and on-snow performance in sprint (∼1 km, ∼2.5–3 min) and distance races (5–7.5 km, ∼12–20 min) from the national championship for this age-group. Results: A large correlation was found between on-snow sprint and distance performance (boys r = 0.61, girls r = 0.76, both p < 0.01) and for on-snow distance performance with TT 3min (r = 0.51 to 0.56, p < 0.05). V̇O2peak, ΣO2def and GE explained ∼80% of variations in performance in the TT3min, but substantial lower on-snow skiing performance (∼20–30%). For the TT3min performance, V̇O2peak showed a very large and large correlation for boys and girls (r = 0.76 and 0.65 respectively, both p < 0.01), ΣO2def showed a large correlation for boys and girls (r = 0.53 and 0.55 respectively, both p < 0.01) and age showed a large correlation for boys (r = 0.56, p < 0.01), with no significant correlation for girls (r = -0.19). For on-snow distance performance, V̇O2peak showed a large correlation for boys (r = 0.53, p < 0.01) and girls (r = 0.50, p < 0.05). For on-snow sprint performance, upper-body strength (r = 0.55, both sexes p < 0.01) and body mass index (BMI) showed a large correlation for boys (r = 0.53, p < 0.01) and girls (r = 0.51, p < 0.05). Conclusion: V̇O2peak is an important determinant for overall XC skiing performance in competitive male and female adolescent skiers. However, upper-body strength and BMI correlate the most with sprint performance. While laboratory performance can to a large extent be explained by physiological factors, on-snow-performance for adolescents is based more on multivariate factors (tactics, equipment’s, technique, racecourse etc.), implying the need for a holistic approach to understanding the sport-specific demands in such age-groups.

The Effect of Different Periodization and Modes of Concurrent Strength and Endurance Training on Double Poling Performance and Body Composition in Adolescent Cross-Country Skiers.

The aim of the study was to compare the effects of different types and periodization of strength training on body composition and maximal aerobic performance in 10-week training period in adolescent XC skiers. Twenty-eight adolescent competitive cross-country skiers, including 10 females (age 17.9 ± 1.8 years; body mass 69.6 ± 9.7 kg; height 1.77 ± 0.1 m; training experience 8.6 ± 3.2 years) took part in this study. Pre-and post-intervention performance was measured with the incremental exercise test (Pmax) on a double poling ski ergometer. Changes in body composition were measured with DXA. In addition to regular endurance training, experimental group one (EXP1) performed maximal and explosive strength training two times per week, experimental group two (EXP2) performed maximal and explosive strength training 1–3 times per week, and the traditional (TRAD) group performed low intensity–high volume strength training 2 times per week. Increases in arm, trunk, and overall lean mass were found in TRAD (p < 0.05). Increases in arm lean-mass was found in EXP1 (p < 0.05), while no changes in body composition occurred in EXP2 (p ≥ 0.05). Pmax improved significantly in all groups (p < 0.05). Changes in body mass, overall and arm lean mass was related to changes in absolute performance (W; p < 0.05), while no relationships were found between changes in body composition parameters and relative performance (W/kg; p ≥ 0.05). In conclusion, different periodization of strength training led to similar improvements in double poling ergometer performance, but resulted in different changes in body composition (lean mass) in adolescent cross-country skiers.

Observational vs coaching feedback on non-dominant whole-body motor skill performance - application to technique training.

We studied the effect of peer- and self-observational feedback versus coaching feedback during technique training on performance in competitive adolescent cross-country skiers. Fifty-four skiers (14.3±0.6years) were divided into a control group and three intervention groups (dyad practice, video, or coaching feedback), which practiced in the asymmetrical uphill sub-technique G2 on one side (non-dominant side), but not the other (dominant side) for 6×30min over a 5weeks period, on roller skis outdoors. High-speed performance and skiing economy were assessed on a roller ski treadmill before and after the intervention, and a questionnaire was answered post-intervention. The video feedback (p=.025, d=.65) and coaching feedback (p=.007, d=.89) groups improved high-speed performance during the intervention and an ANCOVA showed a tendency for different change scores between interventions (F3,49 =2.5, p=.068, =.134), with a difference between the coaching feedback and dyad practice (p=.05). No change was seen in skiing economy in any group. Coaching feedback ranked higher on enjoyment compared with dyad practice (p<.001) and led to higher self-perception of improved technique compared with the control group (p=.038). Overall, feedback from a competent coach seems better than observation for improving performance in young athletes, although self-observation through video with attentional cues seems a promising tool for increasing individual feedback when coaching large groups.

Spinal alignment, mobility of the hip and thoracic spine and prevalence of low back pain in young elite cross-country skiers.

This study investigated the association between spinal alignment, mobility of the hips and the thoracic spine and low back pain in adolescent cross-country skiers. Cohort of 51 elite cross-country skiers from a cross-country skiing high school in Sweden participated in the study. Sagittal spinal alignment, active range of motion in flexion, extension and rotation of the thoracic spine as well as passive and active extension of the hips were measured. The participants also completed a questionnaire regarding training, competition, skiing technique and occurrence of low back pain. A simple linear regression was calculated to predict pain score based on thoraco-lumbar relation, with a significant (P<0.05) regression equation of y=−0.069x+2.280 (standard error of estimate, 0.034). Participants with greater lordosis than kyphosis were more likely to suffer from low back pain than subjects without this offset. Thoracic mobility and passive or active hip extension showed no correlation with low back pain. Sagittal spinal alignment seems to be related with low back pain among young elite cross-country skiers. This study shows that range of motion of the thoracic spine and hips do not have an effect on the prevalence of low back pain in this population.

Usefulness of training camps at high altitude for well-trained adolescents

Objective: Opinions on the suitability of sports training at altitudes of 1800-2200 m above sea level (ASL) for increasing performance in youth are not unanimous. The objective of this study was to test the influence of a ten day altitude training camp on performance in well-trained adolescent cross-country skiers. Methods: A running test of 3 × 2 km (aerobic, anaerobic and critical intensity) was used with a rest interval of 10 minutes. The test was performed 4 times - an initial test at a lowland (900 m ASL) prior to departure for altitude, two tests at altitude (1850 m ASL), a final test ten days after returning to lower altitudes. The aerobic, anaerobic and critical load intensities were set by graded a load test. For all individual tests, the participants maintained the same heart rate individually defined for the various segments using a heart rate monitor. Changes in speed between the tests were compared. The body's internal response was also monitored by the concentration of lactate (2 and 8 minutes after each exertion). Participants: Well-trained adolescent cross-country skiers (N = 11, age: 14.4 ± 1.2 years, weight: 54.4 ± 8.6 kg, height: 170 ± 7 cm, fat: 13 ± 2.6%). Results: The average times attained in the first altitude test for aerobic and anaerobic load were higher (p .05). The dynamics of the cool-down monitored via the lactate value at the eighth minute after completing the relevant segment showed that at altitude the adolescents cooled down significantly (p < .05) slower rate following the aerobic and anaerobic intensity than at low altitude. For critical intensity there was no statistically significant (p < .05) change in the kinetics of cooling down measured by lactate concentration between altitude and the low altitudes. Conclusions: In the model we were testing, the ten day altitude camp was to verify a positive effect on adolescents in acute improvement of their performance ten days after their return to low altitude. Thus it is physiologically suitable for adolescents, as with adults, to include altitude training with the objective of a subsequent rise in performance at low altitude. In accordance with the principles of a long-term approach to sports training corresponding to development, however, we believe that the use of higher altitudes is unnecessary for adolescents.

Non-invasive ultrasonic cardiac output monitoring in exercise testing

Background The purpose of this study was to evaluate the relationship of breath-by-breath oxygen uptake (VO 2) and CO, cardiac index (CI), stroke volume (SV) and heart rate (HR) determined by a non-invasive continuous wave (CW) Doppler-based system (USCOM) in healthy adolescent and adult athletes during exercise treadmill testing. Methods Twenty athletes were enrolled for a standardized ramp treadmill test including transthoracic echocardiography at rest, incremental breath-by-breath spiroergometry, lactate kinetics and CW Doppler. Results VO 2 max was 51 ± 11 ml/min/kg in the adolescent cross country skiers (CI 8.2 ± 1.2 l/min/m 2) and 50 ± 12 ml/min/kg in adult soccer referees (CI 7.1 ± 1.2 l/min/m 2). CW Doppler hemodynamic variables showed significant correlation with VO 2 ( p < 0.01, n = 95) across the total of measures, with excellent correlation demonstrated for CO and CI (0.904 and 0.897), while HR and SV showed good to very good correlation with r values of 0.842 and 0.766, respectively. Correlation of the variables at peak exercise and 1 and 3 min after recovery, demonstrate that CO and SV show superior correlation with peak oxygen consumption (VO 2 max). The regression equation for VO 2 and CO USCOM was VO 2 = 4.43CO USCOM–10.3. Conclusion CW Doppler measurement of cardiac output is feasible as a measure of cardiac performance during standardized treadmill testing in adolescent and adult athletes.

Young elite cross-country skiers and low back pain—A 5-year study

Objectives To evaluate possible changes in spinal curvature over a period of 5 years of an elite cross-country skiing squad, and to study whether there are any differences in this respect between individuals who report low back pain and those how do not. Participants Fifteen young cross-country skiers (M age=13.6±0.9) participated voluntarily throughout the entire study period. Main outcome measures Debrunner's kyphometer was used for measuring the difference between thoracic kyphosis and lumbar lordosis of the spine. All subjects also answered a questionnaire including questions about ski-related low back pain, the amount of ski training, and participation in other sports. Results The results at the end of the 5-year period comprise data from 15 skiers (M age=18.5±0.9 years). The relationship between thoracic kyphosis and lumbar lordosis increased from 3.5° to 13.1°, respectively ( p = 0.0001 ). Of the 15 elite cross-country skiers, seven reported low back pain at the 5-year examination. At the 5-year follow-up, skiers with low back pain showed significantly higher relationship between thoracic kyphosis and lumbar lordosis than did those skiers without low back pain, 18.2° and 10.5°, respectively ( p = 0.035 ). Of the eight elite cross-country skiers without low back pain, seven were also involved in other sports ( p = 0.005 ). Conclusions Based on these findings, our advice is that adolescent cross-country skiers also should participate in other physical activities besides cross-country skiing.

DEVELOPMENT OF UPPER BODY POWER IN JUNIOR CROSS-COUNTRY SKIERS

With the advent of the ski-skating technique, upper body power has increasingly been shown to be a major factor in cross-country skiing success. The purpose of this study was to evaluate 4 commonly used training methods (weight, circuit, rollerboard, and ski-specific training) for the development of upper body power (UBP) in junior cross-country skiers. Fifty-eight adolescent cross-country skiers (Boys: n = 29, age = 16.0 ± 1.2 y and Girls: n = 29, age = 15.5 ± 1.5 y) were assigned to one of the UBP training methods for a 10-week training program. Fourteen cross-country runners served as controls (boys: n = 7, age = 15.8 ± 1.7 y; girls: n = 7, age = 14.9 ± 1.3 y). Skiers were evaluated pre- and post-training for upper body strength (UBS) using a 10 repetition maximum (RM) rollerboard test, for UBP using a double-poling ergometer and for upper body endurance (UBE) with a 3-km, arms-only, rollerski endurance time trial. Competitive race results were collected during the winters before and after training as were all training data. Only the rollerboard training group improved significantly greater than the control group (p < 0.05) in UBP and UBS. Improvements in UBP, UPS, and UBE were significantly related (r = 0.545, 0.303, and 0.407, respectively) to improvements in competitive performance. These data suggest that training using a rollerboard with 5–12RM and explosive speed is more effective in developing UBP than other common training methods for adolescent cross-country skiers. The practical importance of these data was verified by the significant relationships between improvements in UBP, UBS, and UBE related to improvements in competitive race performance.

Pre- and post-season heart rate variability in adolescent cross-country skiers.

To investigate the effects on cardiac autonomic control after a competitive cross-country skiing season, 9 females and 8 males, 16-19 years old, performed tilt-table heart rate variability (HRV) recordings and incremental treadmill tests before (August), and after (April the following year) the most intensive period of training and competition. Spectral analysis of HRV showed increased total variability at rest and reduced low frequency variability in the tilted position (LFtilt) at the second test (P<0.05). The female subgroup showed consistently higher high frequency (HF) and total heart rate variability than males. Total run time (RunT) increased from 18.5+/-1.9 min to 19.4+/-1.7 min (mean+/-SD) in the entire group (P<0.05), while VO2max only showed a non-significant increase (0.05<P<0.10). Submaximal heart rates (HRsubm) were reduced by an average of 4 beats (P<0.01) but maximal HR was unchanged. Performance data suggest a positive training effect. Following training, the increased total HRV the reduced LFtilt (both at rest), and the lower submaximal heart rates indicate an altered control of heart rate both at rest and during exercise. The consistently higher HF and total variability in the females indicate an increased parasympathetic activity in females compared with males.

Dietary intake and body physique in adolescent cross-country skiers.

Sixteen adolescent cross-country skiers (6 males, 10 females) were assessed during a period of preparation carried out in the school year (period I) and during a period of training in the mountains before competition (period II). Body mass index (BMI), body composition (calculated from skinfolds) and dietary intake were ascertained over a 1 week period. The boys had the highest BMI and the lowest percentage of body fat when compared to controls and other athletic boys of comparable age. Their energy and protein intake (especially during period II) were also above the recommended dietary allowance (RDA) and above that of controls and other athletic boys of comparable age. The girls had a lower body fat percentage and BMI than untrained girls, and also elevated energy and protein intakes when compared to the RDA. The intake of energy, protein, fat, carbohydrate and micronutrients increased significantly during period II as compared to period I. An adequate energy balance was assumed as BMI and body fat did not change significantly during period II. Greater calcium intake during periods I and II, and a lower intake of iron during period I, when compared to the RDA, were observed in the girls. Thus, with the exception of micronutrients, which ought to be carefully monitored, the spontaneously regulated food intake was assumed to be adequate during changes in the intensity of training and climate in adolescent cross-country skiers.