Alpine Skiing as Winter-Time High-Intensity Training : Medicine & Science in Sports & Exercise (2024)

It has previously been shown that during winter months physical activity is reduced (²²), and this is associated with both lower total daily energy expenditure (EE) (^5,19) and decreases in maximal oxygen uptake (V˙O_2max) (⁹). Concomitantly, cardiovascular risk factors including blood pressure, blood glucose, blood lipids, inflammatory markers, arterial stiffness, and body mass index increase in all age groups and both sexes. In summary, this leads to an increasing risk of cardiovascular diseases and events (e.g., [^4,17,35,40]).

Physical inactivity is one of the main modifiable risk factors of cardiovascular diseases (²³) and has been reported to be as deleterious as tobacco smoking (¹⁸). Furthermore, physical fitness has been shown to be the strongest predictor of cardiovascular mortality, with physically fit healthy individuals and physically fit patients having the best prognosis (³⁸). Nonetheless, in industrialized nations including Austria, only one third of the population fulfills the World Health Organization recommendations for physical exercise of 150 min·wk⁻¹ spent on 3 to 7 d (Statistik Austria). There is an apparent need to identify modes of exercise and sports that are attractive to the general population (e.g., elderly, unfit, high risk) and possess the potential to maintain if not even increase physical fitness during winter. We hypothesized that alpine skiing (AS) might have the potential to fulfill these criteria.

High-intensity training (HIT) is a time-efficient alternative to traditional continuous endurance training (⁷), inducing similar or even superior changes in numerous physiological, performance, and health-related markers in both healthy and diseased populations (e.g., ^{6,7,29,32,34,39}). This receives special attention from a public health perspective, given that “lack of time” is one of the most commonly cited barriers to regular exercise training (^12,33). Finally, individual reports have suggested that HIT performed during cycling, running, and walking might be more enjoyable for some individuals than continuous endurance training (^1,16,31).

Alpine and Nordic sports have a longstanding tradition in mountainous regions, with AS being the most popular winter sport worldwide (³). Recent investigations by our and other groups have shown that AS is a suitable and safe recreational sport even for an elderly and/or sedentary population (^10,20,24,25). Furthermore, it was previously demonstrated by our group (^25–28) that AS intensity can be controlled by the choice of skiing styles (e.g., parallel ski steering, carving, short turn skiing). There is evidence that short-turn skiing is suitable for HIT efforts (^27,28). However, previous research on high-intensity AS was almost exclusively analyzed during racing in elite athletes (^8,11,36). Furthermore, Karlsson et al. (¹¹) doubted that recreational skiers would be able to reach high intensities during AS due to poor technique and lack of strength when compared with professional skiers. In this context, Stöggl et al. (²⁷) recently demonstrated that during AS and cross-country skiing (XCS) all participants in the male, fit and young groups were able to increase their EE and V˙O₂ more pronounced than participants in the female, unfit, and elderly groups.

Therefore, the aims of the current study were to 1) compare the metabolic and cardiorespiratory responses as well as rates of perceived exertion during AS and XCS during continuous HIT (HITc) and intermittent HIT (HITint) and to compare the outcome with indoor cycling (IC) as the criterion standard indoor exercise, 2) analyze if HIT during AS and XCS is feasible for various subpopulations (sex, age, fitness level), and 3) translate the duration of these two AS HIT protocols to isocaloric HIT training sessions of XCS and IC. The specific hypotheses were that a) HIT during AS will induce a lower metabolic and cardiovascular response as compared with XCS and IC, b) HIT during AS and XCS will not be feasible for unfit and elderly participants, and c) a HITint protocol over 10 min will lead to a greater mean EE and physiological responses, compared with 4-min HITc.

METHODS

Participants

Twenty-one volunteers were included in this study according to the following criteria: written informed consent, >30 yr; no abnormalities in the ECG, nonsmoker for at least 1 yr, proficiency in AS and XCS (>10 d of AS and XCS per season), no medical conditions which would conflict with participation in maximal indoor and outdoor exercise tests, no intake of anticoagulants including aspirin, no alcohol or drug abuse, and no severe obesity (BMI < 35). Participants’ characteristics are presented in Table 1. For statistical analysis, participants were grouped according to age (two age groups delineated by the median in age; young: n = 11, age, 38 ± 4 yr; old: n = 10, age = 60 ± 6 yr), fitness level (two levels according to relative V˙O_2max; fit: n = 11, age = 40 ± 7 yr, V˙O_2max = 49.2 ± 10.8 mL·kg⁻¹·min⁻¹; unfit: n = 10, age = 54 ± 12 yr, V˙O_2max = 29.3 ± 7.8 mL·kg⁻¹·min⁻¹) and sex (female: n = 8; male: n = 13) The study received approval from the Ethical Committee and was conducted in accordance with the Declaration of Helsinki. This study is registered and published at ClinicalTrials.gov: NCT02082106.

Overall design

The study was carried out from January to March 2014. After the recruiting process, every participant underwent a complete medical examination and a cycle ergometry ramp protocol until volitional exhaustion, all supervised by a physician. Those who met all inclusion criteria performed an AS, XCS, and IC session in randomized order on three separate days with a minimum of 48 h in between. During each session oxygen uptake (V˙O₂), HR, blood lactate, blood glucose, RPE (BORG scale,: 6–20) for the whole body (RPE_whole-body), legs only (RPE_legs) and arms only (RPE_arms), and kinematic data (speed, altitude) during AS and XCS were recorded. Each session commenced with a 10-min rest period, followed by a 15-min warm-up at low and moderate intensity, one 4-min stage of continuous high intensity exercise (HITc: HR = 90% HR_max or short turn skiing during AS) followed by a 10-min resting period (2 min active, 8 min passive) for determination of excess postexercise O₂ consumption (EPOC), a 10-min intermittent HIT protocol [HITint: 5 × 1 min high intensity (HR > 90%HR_max or short turn skiing during AS) interspersed by 1-min active rest (approximately 60% HR_max, or slow skiing)] and another 10-min EPOC period (2 min active, 8 min passive). For standardization purposes food intake was not permitted 4 h before testing and participants were instructed not to change their diet and amount of physical activity throughout the examination period.

Baseline medical examination and V˙O_2max ramp test

Baseline examinations (see Table 1) included completion of two questionnaires about physical activity (IPAQ) and training/competition history, routine blood analysis in a fasting state, determination of body mass, lung function testing (EasyOne, Medizintechnik, Switzerland), and an incremental cycling ergometry to volitional exhaustion (Ergoselect 200; Ergoline GmbH, Bitz, Germany) to assess maximal power output (P_max), V˙O_2max, HR_max and peak lactate. The testing protocol was adapted to sex and estimated physical fitness: for females, start: 50 W; increment: 15 W every 1 min; for unfit men, start: 50 W; increment: 20 W every 1 min; and for fit men, start: 50 W; increment: 25 W every 1 min (categorization for fit or unfit was based on the questionnaire data). HR (12-lead-ECG stress test system; Amedtec, Aue, Germany) and breath-by-breath spirometric data (MasterScreen CPX, Carl Reiner GmbH, Wien, Austria) were recorded continuously. The flow of the turbine was measured with the integrated automatic volume calibration program of the ergospirometry system. Gas calibration was performed with the automatic gas analyzer calibration procedure using standardized oxygen (16.00 vol%) and carbon dioxide (5.01 vol%) concentrations (rest volume, nitrogen). Both calibration procedures were performed directly before each test. Lactate as well as blood pressure was measured every 2 min, as well as three and 5 min after the completion of the test. For lactate analysis, a 20-μL blood sample from the earlobe was collected immediately after each second increment and quantified amperometric-enzymatically (Biosen S-Line Lab+; EKF-diagnostic GmbH, Magdeburg, Germany). The lactate sensor was calibrated before each test using a lactate standard sample of 12 mmol·L⁻¹. Results within a range of ±0.1 mmol·L⁻¹ were accepted.

Outdoor trials

Participants’ HR and GPS data (distance, skiing speed, vertical speed, altitude and number of turns) were recorded by telemetry (Suunto Ambit 2.0, Helsinki, Finland) sampling at 1-s intervals. For altitude calculations automated barometric measurements and GPS data were used. V˙O₂ was continuously recorded by a portable breath-by-breath spirometer (K4b2; Cosmed, Rome, Italy). For determination of lactate and blood glucose (see above) a sample was collected immediately after each intensity stage, as well as 3, 5, and 10 min after the completion of the HITc and HITint trials during the EPOC phase.

AS trials

AS trials were performed on a slope with sufficient width (~50 m) and hom*ogenous grade, allowing steady skiing of more than 4 min (~1.6 km with ~490 m altitude change, 17°–18° grade). Each trial was done in one separate descent and all skiers used their own skiing equipment (ski radius: 14 ± 1 m). The 4-min HITc trial and the 10-min HITint were performed on one single downhill each using short-turn skiing only which is characterized by short but highly frequent turns at low skiing radii and using high dynamic whole body motion (up–down motion of the center of mass partly leading to a jump in between swings). During HITint, to further increase the intensity the participants were instructed to perform as many short turns during each of the five 1-min periods. For standardization, all downhill trials were instructor paced, by a board certified Austrian AS instructor who adapted the skiing speeds to the skill level of the participant. The amount of skiing turns over each 1-min period was determined from video data (50 Hz) of another tester skiing behind the participant.

XCS trials

XCS sessions were performed on a 450-m loop with a total altitude change of 6 m. All participants used the classical technique (mainly the diagonal stride in the skiers with lower fitness level, and according to the track topography a mix of diagonal stride, kick double poling and double poling in the fit skiers) and their own equipment. After the 15-min warm-up, the HITc trial (90% HR_max), followed by the 10-min recovery phase and the 10-min HITint session (reaching >90% HR_max in all five intervals) were performed. HR was monitored by a Suunto Ambit 2.0 monitor in paired fashion (i.e., HR belt worn by participant; HR monitors worn both by the participant and examiner) and verbally communicated by the examiner who was skiing right next to the participant.

IC ergometry sessions

IC sessions were conducted on indoor cycle ergometers (Ergoselect 200, Ergoline) following the same protocol as in XCS regarding stage duration and HR controlled exercise intensity (target intensity for the 1-min stages during HITint was 100% P_max).

Parameter calculations

During the ramp test P_max was calculated by linear interpolation using the formula: P_max = P_f + ((t/60)ΔP), where P_f was the power output during the last workload completed, t the duration of this last workload (s) and ΔP the difference in power output during the last two workloads (¹⁵). The breath-by-breath values of the V˙O₂ measurements were converted into a 1-Hz signal by linear interpolation. Furthermore, all cardiorespiratory data were smoothed by application of a 15-s moving average. The EPOC phase after HITc and HITint consisted of 2 min low-intensity activity (cycling at 60% HR_max, or walking to the shelter with a seat during AS and XCS) and 8 min sitting in an upright position with no talking being allowed. The formula of Weir (³⁷) EE (kcal·d⁻¹) = (1440[3.9V˙O₂ + 1.1V˙CO₂]), approximating a caloric equivalent of 21.1 kJ·L⁻¹ O₂ was used. To get the EE values, the 1-Hz values (kcal·d⁻¹) were converted to kilocalories per second and then integrated over the respective phase (4-min HITc, 10-min EPOC after HITc, 10-min HITint, 10-min EPOC after HITint). For the sake of comparison between the three exercise modes and both HIT protocols, we assumed that the HITc or HITint trials were repeated (e.g., approximately four times and three times) with a 10-min rest in between each run (e.g., simulating standing in the queue and sitting in the chairlift during AS) for 1 h. Therefore, the mean EE per minute for 14-min HITc and 20-min HITint were calculated and extrapolated to 1 h (EE per minute). All these calculations were performed using the Ikemaster Software (IKE-Software Solutions, Salzburg, Austria).

Statistical analysis

All data exhibited a Gaussian distribution verified by the Shapiro–Wilk’s test and, accordingly, the values are presented as means (±SE). Repeated-measures ANOVA (with three exercise modes and two intensities as repeated measures, and two sex; two fitness level, two age groups as independent measures) were performed to test for main effects. Alpha level of significance was set to 0.05.

RESULTS

Patient characteristics

Of the 21 screened volunteers two had to be excluded during the initial medical examination: one woman because of uncontrolled type 2 diabetes mellitus and one man because of signs of myocardial ischemia during exercise stress testing (n = 19) (Table 1).

Characterization of AS and XCS trials

During HITc and HITint in AS, participants skied a distance of 1.26 ± 0.05 km and 2.20 ± 0.12 km (P < 0.001), with an altitude change of 350 ± 19 m and 556 ± 38 m (P < 0.001), a vertical speed of 87 ± 5 m·min⁻¹ and 60 ± 4 m·min⁻¹ (including the 1-min active recovery phases during HITint, P < 0.003) and a peak skiing speed of 28.5 ± 1.0 km·h⁻¹ and 31.3 ± 1.7 km·h⁻¹ (P = 0.052). During HITint skiers were able to perform 69 ± 4 single turns during each 1 min bout (range 38 to 93 turns) independent of sex (P = 0.051), age (P = 0.596) and fitness level (P = 0.293). Time for waiting in line and sitting on the chairlift was 11:36 ± 2:36 min. Active skiing time as a percent of total time was 42% ± 7%.

For XCS during the HITc and HITint trials, participants skied a distance of 0.73 ± 0.07 km and 1.50 ± 0.11 km (P < 0.001), with total vertical climb of 13 ± 2 m and 29 ± 3 m (P < 0.001) and a mean skiing speed of 11.0 ± 1.0 km·h⁻¹ and 10.8 ± 0.6 km·h⁻¹ (P = 0.604).

Cardiorespiratory and metabolic responses according to exercise mode and intensity

When data for HITc and HITint were pooled within each mode of exercise (i.e., AS, XCS, and IC), all variables demonstrated significant differences between AS, XCS, and IC (Table 2, main effect “mode”). XCS demonstrated greater values compared with AS and IC regarding HR, blood glucose, and RPE levels (whole body, arms, and legs) (all P < 0.01 to <0.001). Furthermore, blood lactate values and mean RER were greatest during XCS followed by IC and AS (P < 0.05 to <0.001). V˙O₂ values and EE were lower during AS compared with XCS and IC (P < 0.05 to 0.001).

Mean EE per minute for the 4-min HITc was greater compared with the 10-min HITint (11.6 ± 0.8 kcal·min⁻¹ vs 10.9 ± 0.8 kcal·min⁻¹; P = 0.001), whereas the mean EE per minute including the 10-min EPOC phase was greater for the 20-min HITint versus 14-min HITc trials (6.2 ± 0.4 kcal·min⁻¹ vs 7.5 ± 0.6 kcal·min⁻¹; P < 0.001). With XCS and IC a more pronounced increase in EE from HITc to HITint was demonstrated compared with AS (interaction effect mode × intensity P = 0.005). For both intensities and all three exercise modes, HR values >90% HR_max and V˙O₂ values >84% V˙O_2max were achieved. With the exception of V˙O₂ values, all measured metabolic and cardiorespiratory were greater during HITint compared with HITc (P = 0.002 to <0.001).

When considering a 10-min break (here: 2 min active and 8 min passive) in between repeated 4-min HITc or 10-min HITint series the estimated EE for 1 h exercising with HITc or HITint was 333 versus 387 kcal·h⁻¹ for AS, 389 versus 485 kcal·h⁻¹ for XCS and 396 versus 475 kcal·h⁻¹ for IC (Fig. 1), with greater values during HITint compared with HITc (pooled data over all exercise modes: 449 ± 34 kcal·h⁻¹ vs 373 ± 26 kcal·h⁻¹; P < 0.001). An AS duration of approximately 1:10 h:min (HITc), respectively 1:14 h:min (HITint), would be necessary to achieve comparable EE of 1:00 h:min of XCS or IC with the respective intensity (Fig. 2) with no difference between XCS and IC.

Effects of sex, age, and fitness level

Pooled data for HITc and HITint and the three exercise modes for sex, age, and fitness level are presented in Table 3. Male participants revealed higher RER, V˙O₂, and EE compared with females (P = 0.005 to <0.001). Furthermore, absolute HR was lower in men compared with women (P = 0.034) and old compared with young (P = 0.004) with no difference regarding relative peak HR (%HR_max). With the exception of lower V˙O_2peak values in the unfit participants (P < 0.001), no further differences with respect to fitness level were found. Young participants achieved a more pronounced increase in estimated EE per hour from HITc to HITint compared with old (ΔHITint-HITc: young = 100 kcal·h⁻¹ vs old = 49 kcal·h⁻¹, P = 0.047) participants with no effect of sex and fitness level. There was no effect of sex, age, or fitness level on RPE values.

DISCUSSION

The main findings of the current study are: 1) HIT during AS, XCS and IC induced >90% HR_max and >84% V˙O_2max in all subjects irrespective of sex, age, and fitness level; 2) EE is higher during HITint as compared with HITc during AS, XCS and IC; 3) to be isocaloric, exercise time has to be longer during HITc AS (10%) or HITint AS (14%) as compared to the respective training modes during XCS and IC; 4) young participants were able to achieve a more pronounced increase in EE from HITc to HITint compared with older participants; 5) fitness level had no effect on EE, metabolic response, and RPE; 6) RPE during HITc and HITint were not affected by sex, age, and fitness level.

EE

In the current study, V˙O₂ and EE were similar during XCS and IC, but significantly lower in AS which is in accordance with our previous results at low to high intensities with the same exercise modes (²⁷). In comparison with HITc, when using the HITint protocol in combination with a 10-min EPOC phase for both situations, across all exercise modes a further increase in mean EE was possible, which was slightly more pronounced in XCS and IC compared with AS. Therefore, even though HITint had the potential to further increase the physiological response during AS, the mix of static and dynamic muscle activity of the lower extremities (^14,21) with both moderate to high concentric and eccentric loading (³⁰) might be associated with the attenuated increase in cardiorespiratory output based on muscular limitations as compared with XCS and IC (²⁷).

In the studies by Stöggl et al. (^27,28), it was demonstrated that AS using low and moderate intensity has to be performed approximately 2.5 h to equalize the EE of 1 h of continuous XCS or IC. In the current study, when applying HITc or HITint interspersed with longer breaks of low intensity or passive recovery (e.g., 10 min to simulate the break during AS based on the chairlift time and standing in queue)—an AS duration of 1:10 or 1:15 is sufficient to equalize the EE during XCS and IC (using the same 10-min break in between each series). This assumption is plausible during AS based on the unavoidable approximately 10-min rest due to the transportation back to the top of the lift for the next descent. During XCS and IC, however, it might of course be possible to reduce the break in between the HITc and HITint (e.g., 2–3 min rest as during conventional interval training instead of 10 min). If doing so, the difference in EE per hour will rise up to 2 h AS to be isocaloric. However, on the other hand, it might not be feasible to perform approximately 10 times 4-min intervals with HITc using 2- to 3-min rest in between, or 30 times 1-min high-intensity/1-min low-intensity HITint over the duration of 1 h with XCS or IC. Therefore, the abovementioned assumptions can be seen as ecologically valid, being practical and feasible for a wide range of persons.

When applying AS with low (parallel ski steering: EE of 242 kcal·h⁻¹) or moderate (carving: EE 276 kcal·h⁻¹) intensity (^27,28), an AS duration of 1:24–1:36 h:min, respectively, 1:13–1:23 h:min will be necessary to be isocaloric with AS using HITint or HITc (22%–60% longer skiing time to be isocaloric). Within this calculation the assumed augmented EPOC after HITc or HITint after exercise was not considered.

Hence by applying interval type (HITc) or intermittent HIT (HITint) during AS, the duration to equalize EE when compared with classical endurance sports (e.g., XCS and IC) can be strongly reduced (almost divided in half). Therefore, for example, by applying three times 5 × 1 min/1 min HITint (e.g., three descents with HITint interspersed with lift time) almost the same EE as during similar HIT XCS and IC protocols can be achieved.

A further increase in EE during AS can be achieved by prolonging active skiing time, therefore either choosing longer descents and/or to minimize the duration of standing in the queue or sitting on the lift. Based on the steady developments in ski lift technology and the greatly increased transportation capacity—resulting in shorter waiting times and faster uphill transportation—the latter will be a realistic development/potential. Another aspect is to reduce passive skiing time by avoiding prolonged breaks during the active skiing phase to maintain the physiological response on a high level during a longer steady period of activity. When compared with the study of Müller et al. (²⁰) active skiing time was already increased from 33% up to 42% by using HITc and HITint skiing as in the current study.

Cardiorespiratory parameters

During all exercise modes, HR was >90% HR_max and V˙O₂ values >84% V˙O_2max (84%–96% V˙O_2max). Therefore, by using short turn skiing with 4-min HITc or 10-min HITint, distinctly higher physiological loading can be achieved than previously documented. Müller et al. (²⁰) reported mean HR values during the active skiing time of 73% HR_max and Scheiber et al. (²⁵) values of 62% to 82% using different skiing styles and slope conditions. As with HR values, percent V˙O_2max of >84% were distinctly higher compared to the study by Scheiber et al. (²⁵) who reported values of only 38% to 52%. Seifert et al. (²⁶) recently demonstrated that HR values in a broad group of skiers (stratified by sex, age and skill level) was 64%–74% during slow guided skiing, 67%–77% during fast guided skiing and 71%–85% during free skiing on flat and steep terrain. During AS racing, percent V˙O_2max were documented to be between 68% and 88% (^11,36). Therefore, in the current study sufficient physiological loading for high intensity exercise can be achieved comparable with AS racing. Based on that concept, AS might serve—besides a leisure activity—as a new HIT winter workout and greatly stress the physiological response (e.g., cardio skiing). Hence, high intensity workouts during wintertime using AS, XCS, or IC seem to be feasible for a broad population irrespective of sex, age, and fitness level.

Effects of sex, age, and fitness level

In the current study, even though V˙O₂ was higher in the fit group, no differences were found in physiological loading between fit and unfit. Therefore, based on these data, no matter if fitness level is high or low, equal physiological response is possible independent of the exercise mode. This finding is in line with a previous study in our group (²⁷). Furthermore, based on that RPE levels during HITc and HITint (RPE of 12–17) were unaffected by sex, age, and fitness level these exercise modes and intensities are well applicable over a broad population.

Recent investigations have shown that AS is a suitable and a safe recreational sport for an elderly and a sedentary population (^{10,20,24–26}). In the study of Stöggl et al. (²⁷), the younger participants demonstrated approximately 19% greater absolute V˙O₂, approximately 13% greater absolute HR values, 17% to 27% greater EE when applying low to high exercise intensities. In the current study, absolute HR (~ +13%), relative blood lactate (~ +20%) and trends for increased V˙O₂ and EE in the young versus the old were found. However, an interaction effect toward a less pronounced increase in EE from HITc to HITint was found in the elderly compared with young. Therefore, the potential for HIT in elderly seems to be limited. This might be based on the ability of young people to push themselves harder when exercise intensity is increased, a lower fear level (e.g., when skiing speed and dynamics are increasing), and a higher skill level and therefore less technical limitations when exercise intensity and speed gets high (²⁷).

To be mentioned that AS with moderate intensity leads to metabolic and cardiovascular loading that can be also tolerated by persons with slight cardiovascular disease. However, to increase the tolerable loading during exercise, it is advised to increase the fitness level before performing exercise (e.g., AS, XCS holiday) to decrease the cardiovascular risk (²). This statement is supported by Klug, et al. (¹³) who demonstrated that the most cardiac events occur within the first 2 d during an AS holiday, especially in persons with a low fitness level. This aspect should be especially considered when applying higher intensities as in the current study.

Limitations and perspectives

To allow comparisons between the three exercise modes, the EE per hour was extrapolated based on the results of one trial of 4-min HITc or 10-min HITint followed by 10 min active/passive rest. However, the exact EE per hour and the feasibility to perform 1 h with HITc or HITint within the single exercise modes need to be proven in a future study. Furthermore, as already stated above, the 10-min rest in between each 4-min HITc or 10-min HITint series is realistic since this is the approximate time to be transported back to the top of the lift. However, during XCS and IC a 10-min passive rest might be overly long and needs to be either shortened (e.g., 3–5 min rest) or performed actively at low intensity.

CONCLUSIONS

Within all analyzed exercise modes (AS, XCS, and IC), with both exercise intensities (HITc and HITint) and irrespective of sex, age and fitness level all participants were able to reach exercise intensities of >90% HR_max and >84% V˙O_2max. Therefore, all exercise modes and both training protocols were shown to be feasible for HIT in a broad population. When using repeated 10-min HITint followed by a 10-min rest compared with repeated 4-min HITc efforts with 10-min rest in between, the estimated EE per hour is higher in HITint compared with HITc in all exercise modes. Even though there were greater demands on the cardiorespiratory system during XCS and IC compared to AS, when applying the same loading and recovery pattern with the HITc or HITint protocol only approximately 1:15 h of AS are necessary to be isocaloric to 1:00 h of XCS, respectively, IC. This value is much lower as compared with previous studies, where a skiing duration of approximately 2:30 h at low to moderate exercise intensity was necessary to equalize the 1-h EE of XCS and IC. Therefore, EE during AS can be maximized by using only short or no breaks during the downhill phases, choosing a more dynamic skiing mode, that is, short turn skiing with a HITint protocol to prolong the duration of continuous high intensive loading during each descent. By using the HITc or HITint protocol during AS and if the terrain allows for steady skiing over a longer period, AS might provide sufficient stimulus for the cardiologic and metabolic system to enhance fitness and reduce cardiovascular risk. Consequently, besides being a popular leisure activity to experience nature and freedom in the winter months, AS might also serve as a high-intensity fitness workout.

We would like to thank Manuel Hirner, Kathrin Hirner, Stephanie Feuchter and Markus Förmer for their assistance during the measurements, the participants for their enthusiasm and cooperation and the ski resorts of Saalbach Hinterglemm and Flachau Winkel for granting us free access. The current study complies with Austrian ethical standards and laws. This study was supported in part by an unrestricted grant of the State of Salzburg. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Reporting of these findings does not constitute endorsem*nt by the American College of Sports Medicine. None of the authors had any personal or financial conflicts of interest.

REFERENCES