Currently, thousands of adolescents travel to altitude to participate in recreational activities throughout the year (9,27). Many in this population are young athletes involved in skiing sport camps designed to improve skills and race performances. Sojourns to higher altitudes of just 6–12 hours are known to induce altitude illness, including acute mountain sickness (AMS), which can progress to high altitude cerebral edema and high altitude pulmonary edema (2). The severity and incidence of AMS is related to the altitude attained, length of stay, and speed of ascent (2). Young lowlander athletes exhibit a 20% rate of AMS in Summit County, Colorado, which has been shown to be similar to adults (9). The Lake Louise AMS questionnaire (AMSQ) is a short set of simple questions that are sensitive in quantifying levels of altitude illness and has been used to monitor lowlanders during altitude acclimatization (9,41). The underlying mechanism that causes AMS is hypoxia that induces hypoxemia and subsequent perturbations to the capillary beds, which results in fluid shifts from blood plasma to the intracellular compartment (54). The hypoxic stress of the central nervous system has shown to perturb perceptual-motor performances, and the fluid shifts are thought to cause headache, gastrointestinal, fatigue or weakness, dizziness or lightheadedness, sleep disturbances, reduction in overall effects on activities, changes in mental status, ataxia, and peripheral edema (8,9,11,41,54).
High-altitude youth sport camps can be expensive, thus, providing an incentive for the coaches, and families want to push for as much hill time and skiing as possible while in camp residence. Interestingly, the effects of AMS while participating in sport training has not been studied in youth athletes. Additionally, such initial data are dramatically needed to better understand and make recommendations for optimizing the practice time and safety during these high-altitude youth sport ski camps. A typical elite alpine ski racer in the United States will participate in one 2- to 4-week summer ski camp and one fall (October–November) on glaciers at high altitude in the northern hemisphere or travel to ski areas in the southern hemisphere, some of which are at high altitude. Importantly, many of these athletes are considered “lowlanders” and spend the majority of the year below 450 m (1,500 ft) of elevation. Rapid exposure to and ski practices at high altitude with lodging just below 3,000 m still put skiers at risk for developing AMS.
At high altitude, among the first cells thought to be affected by hypoxemia are Perkinje cells in the cerebellar cortex, which are known to reduce physical performance variables related to sport performance (8,11,31,54). Of these, balance and motor reaction time are critical to strategic aspects (such as line choice) and technique of alpine ski racing, which are highly related to competition outcome (51). Any decrement in these measures may hinder sport performance and quality of training and is associated with increased risk of injury (31). Thus, one might hypothesize that performance variables related to these mechanisms may well be affected. Field measurements of both of these variables have been shown to be valid and reliable. The use of Y-balance tests has been shown to be sensitive to predict lower extremity injury risk for combined boy and girl high school basketball players (43), and the Quickboard React Drill (QRD) are both sensitive to changes in reaction time after 4 weeks of speed agility and quickness training (22). Still, it is not clear how physical training through the altitude acclimatization period would affect a battery of performance tests commonly used to assess physical performance in young athletes (10,25,48).
Dehydration can compound the decrements of performance induced by hypoxia. Several studies have shown that because of the drier air and hyperventilation at high altitude, dehydration over several days of mountaineering can become significant (2). One study examined the effect of ad libitum fluid ingestion during a day of alpine skiing in 7 healthy, experienced, adult skiers (control group, no fluid intake) at an altitude of 2,438–3,200 m (47). It was shown that 1.6% (1.1 ± 0.2 kg) and 1.2% (0.8 ± 0.3 kg) in body mass (BM) was lost in a morning and afternoon, respectively, when ski sessions lasted 2.75 hours with a 1.5-hour rest break were performed, during which ad libitum fluid intake were allowed. In another study, examining the hydration levels in men across 12 days, climbing to 4,325 m, body mass loss was >3.5–4.0 kg (7.7–8.8 lbs) with approximately 50% accounted for by fluid loss. Not all this fluid loss may be detrimental, as a decrease of plasma volume increases the per-unit-volume carrying capacity of oxygen diminishing the hypoxic stress and subsequent altitude illness. This change in hematocrit concentrations is expected during the first 3–7 days of altitude exposure (2). Increases have been reported to be 14% in the first 3–4 days at 3,822 m and 17% after 12 days at 3,520 m (2). Given that blood volume contributes to about 87 ml·kg−1 of body mass (17), and approximately 55% of blood volume is plasma (49), 6.6–8.1 ml of plasma fluid per kilogram of body mass is lost during acute altitude acclimatization. If this fluid was all excreted by the body, it would result in less than a 1% decrease in BM.
Dehydration and fluid balance can have impacts on multiple aspects of performance, strength, power, and high-intensity endurance with performance effects at 2% and significant effects between 3–4% decreased BM (30). Decrements in mood and concentration with increase in headache symptoms have been described in women who were lowlander college-age students with just dehydration of 1.36% decreased BM (4). Children have a greater risk for mild dehydration induced by voluntary dehydration, children's sensation is inhibited before adequate fluid is consumed to replace fluid losses during exercise, resulting in impaired performance involving visual-motor tracking, psychomotor skills, perceptual discrimination, and short-term memory (14). Therefore, we speculated that there was a need to monitor daily hydration of each subject, as a control, by using body weight changes, urine color, and urine specific gravity (USG), which have been shown to be valid noninvasive markers of hydration (3).
The primary purpose of this investigation was to examine the effects of acute high-altitude exposure on performance variables in a week-long alpine skiing training camp at some of the highest altitudes that alpine ski racers regularly encounter (Summit County, Colorado). A secondary purpose was to assess the effect of high altitude on performance and learning curves during a weeklong preseason athletic training camp, with a moderate hydration control intervention. Because hypoxic environmental exposure and subsequent body fluid shifts may exacerbate both acute and chronic perturbation of sport-related motor tasks, we hypothesized that performance quality and balance would suffer with acute altitude exposure but then after several days of altitude acclimatization would improve.
Experimental Approach to the Problem
A junior alpine ski racing team from Hanover, New Hampshire (160 m), was selected for tracking of performance and hydration variables before and during their annual fall ski-racing camp in Summit County, Colorado (2,828.5 m). This group represents a typical group of athletes that travel to altitude to improve both sport skills and sport-specific fitness when snow is not available for training at their home training center. Independent descriptive variables included training volume, altitude of home town and training site, temperature, and humidity of training site, countermovement vertical jump without arms, Lake Louise AMSQ, and hydration status, which was monitored with urine color, USG, and change in body weight. This was monitored twice a day to provide feedback to each subject about his or her hydration status. Dependent variables chosen were split into daily tests: (a) Y-Balance test, QRD and CMJ and (b) a battery of performance tests: countermovement jump with arms, T-agility test, 1-minute sit-up and push-up tests, and the multistage fitness test (MSFT). In addition, we used the Pubertal Maturation Observational Scale (PMOS), which was found to be a validated and reliable (24) tool to address biological and chronological age disparities in adolescent athletes (19). Baseline data were collected at sea level one week before travel to the camp. The daily tests were performed twice a day for 6 consecutive days while at altitude to assess the effect of altitude and to provide a stimulus for learning and performance improvements in the young skiers. The battery of performance tests were performed a second time after ski training on the last day (i.e., day 6) of the camp.
All procedures were approved by the Internal Review Board at the University of Connecticut for human subjects in research. All subjects and parents or guardians were informed about the risks and benefits before giving written consent before participating in the study. All subjects filled out a medical clearance form based on the exercise screening recommended for maximal exercise by the American College of Sports Medicine's Guidelines for Exercise Testing and Prescription 8th Edition (52), which was reviewed by the medical monitor to screen for possible medical complications that might confound the results of this study.
Eleven subjects (4 boys and 7 girls) volunteered, and there were no differences in the characteristics presented in Table 1. The subjects were considered late in their pubertal maturation, 6.09 ± 1.3, on a scale of 1–8, and were 91.6 ± 1.8% of the average height of their biological parents. Alpine skiing was the sport with most years of experience, followed by soccer, and subjects were actively participating, or participated, in 4.3 ± 1.8 competitive sports for one season or more. All subjects where familiar and had one leg balance drills incorporated into a 4-week preseason off snow conditioning program before the ski camp trip.
All subjects participated in school sports and were members of a club ski team. Subjects filled out a baseline questionnaire and the PMOS (24) to determine their relative biological age. The questionnaire consists of 8 questions that are answered yes or no. The more questions answered “yes,” the later the subjects were in maturation, which was treated as interval-like data. A second questionnaire asked for the biological mother's and father's heights and for a list of sports that the subject had previously participated in, with approximate start and end dates.
Height was measured with a wall-mounted tape measure. Leg length (from iliac crest to medial malleolus) on the dominant leg was recorded with a standard fiberglass tailor tape measure. Body mass was recorded with a digital floor scale with t-shirt, shorts, and socks on (Health-o-meter, Sunbeam Products, Inc., Baco Raton, FL, USA).
The testing was broken up into 2 sections: (a) the daily tests and (b) the battery of performance tests. The order, timing, and altitude of the tests are shown in Table 2. Baseline tests were performed at 12:00 AM on the Saturday the week before departure to the altitude camp, where the subjects were taught how to perform each of the tests and how to fill out the questionnaires. The daily tests at the camp were performed at 7:00 AM and 4:30 PM after at least a 30-minute rest period from arriving back at the lodging. An additional AMSQ was also administered for after skiing in the base lodge of the ski resort (about 2:30 PM). An exception occurred on the last day when the afternoon tests were done at 3:00 PM followed by the second battery of performance tests.
The Lake Louise Scoring System for AMS was used to measure signs and symptoms of AMS (9,41). The Lake Louise Scoring System for AMS is a series of 6 questions that each subject answered on a small paper, on a scale from 0 to 3. These questions were used to measure signs and symptoms of AMS by asking the subject to rate his or her headache, gastrointestinal, fatigue or weakness, dizziness or lightheadedness, sleep, and overall effects on activities. In addition, the investigator evaluated each subject on 3 additional questions that are part of the Lake Louise Scoring System: (a) changes in mental status, (b) ataxia, walk heal-toe, and (c) an evaluation for peripheral edema.
Then subject's body mass was recorded, and urine was analyzed for urine color (2) and USG with a handheld refractometer (Model A300CL, Spartan Refractometer, Tokyo, Japan) (3). On a second visit, before ascending to altitude, subjects provided a urine sample and body weight for the calculations of a standard baseline hydration.
The Y-balance test (43), QRD (The Quick Board, LLC Memphis, TN) (22), and a countermovement vertical jump with hands on hips (CMJNH), a Just Jump System (Probotics Inc., Huntsville, AL, USA) were performed with the best of 3 trials used in the analysis of performances of each test.
Dynamic balance ability was assessed with the Y-balance tests, also known as the Star Excursion Balance Test, using the dominant leg, defined as the side preferred for one-ski skiing. The Y-balance test involves reaching for maximal distance with one leg in three defined directions while balancing their dominant leg and wearing athletic sneakers. The subjects started with one foot in the center of the “Y” and their hands on their hips. The balancing foot had to remain fully on the ground and in the same position with heel and toes on the ground at all times. For each trial, the investigator recorded the furthest distance reached by the free leg—the heel for the anterior reach and the big toe for the posterolateral and posteromedial reaches. The best of 3 trials of each reach direction was chosen, then the 3 directions where summed and divided by leg length (43).
The React Drill on the Quickboard were assessed using eye and foot coordination and reaction time. This included a set of 5 light-emitting diode (LED) lights on a small plate placed in front of the subject that correspond with 5 yellow touch pads on board that the subject stands on. The LED lights and touch sensors are in the formation similar to that seen on the side of a dice with 5 dots on it. The Quickboard randomly illuminates one LED on the display, and the subject uses their foot to touch the corresponding touch sensors on the Quickboard floor pad. The reaction times for each sensor and total successful and incorrect touches for a 10-second period were recorded. The best average mean reaction time of 3 trials was used for reporting and statistical analysis (22).
The countermovement jump was performed on a timing pad (Just Jump System). Internal reliability for the Just Jump system was determined to be acceptable (r = 0.91), for jump and reach height measured with the Vertec (Sports Imports, Hilliard, OH, USA), with 10 subjects performing 3 jumps each. It was also found to be acceptable when compared with a force plate (AccuPower; Athletic Republic, Fargo, ND, USA), with a sampling rate of 200 Hz for the variables peak watts relative to body mass (r = 0.97) and jump height (r = 0.95). This agrees with other findings (33). The subject was instructed to stand on the pad and to perform a countermovement jump as high as possible with the subject’s hands on their hips (CMJNH). The highest of 3 trials was used. For the CMJ trials, arm swinging was permitted (33).
The Battery of Performance Tests
The battery of performances after a standardized warm-up consisted of 5 minutes of light cardiovascular activities, which included jogging, skipping, side jacks, lateral cross-over walks, high knees, butt kicks, and 10 repetitions of dynamic stretches. The dynamic stretches were arm circles, spine twists, lateral spine flexion, hip circles, leg swings, knee hugs, foot-to-butt, cradles, and lunges. The first test performed was the CMJ as described above. All running and agility tests where done on asphalt with appropriate sport shoe footwear.
For the T-agility test, a course on a level paved surface was set up with 5 cones in the shape of a “T” (Figure 1). While facing in one direction subjects sprinted out 10 yards and touch the middle cone of the “T,” lateral shuffled 5 yards, without crossing their feet to one side, and touch a second cone. Then lateral shuffled 10 yards in the opposite direction to a third cone, followed by laterally shuffling back to the middle cone 5 yards, and finally, back pedaled 10 yards to the start or finish line. The fastest of 3 trials was used for analysis. Times were measured with an electric eye to start and stop (Track & Speed, Brower Timing System, Draper, Utah, USA) (48).
Sit and reach was measured using the best of 3 trials on a sit-and-reach box with legs fully extended, feet 15- to 20-cm apart and hands overlapped. Subjects kept their knees down and reached as far as possible while breathing out slowly (35).
All subjects performed as many standard push-ups in 1 minute as possible: toes and hands on the ground, with a straight line from the heels to the shoulders. The bottom of the push-ups was defined as when subject's chin touched the investigator's or partner's fist, placed on the ground in a neutral position, and the top of the push-up was defined as full extension of the subject's elbow.
Subjects performed as many sit-ups in 1 minute as possible, while the investigator or partner held the subject's feet. The subject kept a 90° angle at the knee joint. On the way up, the subject held their shirt collar with both hands and arms crossed. Once the elbows touch the thighs or knees, the subject lowered their torso to the ground such that their shoulder could touch the ground.
The MSFT was made up of a 20-meter (22-yard) course designated by cones. The test consisted of a digital audio recording with 23 stages of approximately 1 minute each. Each stage is comprised of a series of 20-m shuttles, where the starting speed is 8.5 km·h−1 and increases by 0.5 km·h−1 each stage. The standardized recording played a single beep to indicate the start of a shuttle and 3 beeps indicates the start of the next stage. The subject placed one foot on or beyond the 20-m markers at the end of each shuttle and could not start the next shuttle until the beep. The test ended when the subject failed to reach the end of the shuttle before the beep. The subject was allowed 2 further shuttles to attempt to regain the required pace before being withdrawn. The subject's score is the last level successfully completed (reach the line before the beep occurs), which can be converted to a relative V[Combining Dot Above]O2max (milliliter per kilogram per minute) score (10,34,45).
Sport Coaches' Perceptions of Athletes
During the preseason camp at altitude training, the sport coaches assessed each athlete's participation in training. Using a 1–5 Likert scale, the coaches rated from strongly agree to strongly disagree on each of the following questions: “Was the athlete's mood at training happy and positive” and “Did the athlete have a high-quality day of training?” (36). A third question asked the coach to record the number of chairlift rides that each athlete took during training that day for each chairlift at the resort, which was used to measure the vertical drop in meters skied by each subject. A comments section for the coach was provided to record information about a subject that the coach felt was important to the athlete's participation. An additional section on the investigators recording sheet was provided to record locally reported weather conditions, temperature, humidity, wind, cloud cover, and precipitation.
The primary data was analyzed with a one-way ANOVA (day) and two-way ANOVA (time × day) with repeated measures and a Fishers LSD post hoc test to determine mean pairwise differences. If the assumption of sphericity was not met, a Greenhouse-Geisser correction was used. To check for the influence of sex, maturation, and AMS, a one-way or two-way (time × day) analysis of covariance was used to determine differences. The AMS questionnaires did not allow for 2 groups to be created that had sufficient sample size for statistical analysis and descriptive impressions are only allowed for the entire group across time. The data are presented as mean ± SD. Significance in this investigation was set at p ≤ 0.05.
Environmental conditions for baseline testing, altitude testing, and training sessions are shown in Table 3 along with training volumes, the number of runs, and vertical meters skied each day. There was a main effect for days of skiing (F[2.164, 25] = 4.812, p = 0.030) and an effect for maturation, (F[1, 5] = 2.759, p = 0.041) where athletes with a higher maturity score skied more vertical meters. All days had significantly different volumes except between the following days: 1 and 2, 2 and 6, and 3 and 6. Skiable altitude is provided along with mountain resorts for each day of training along with baseline and lodging altitudes where testing occurred. Testing was performed in environments with similar temperatures.
The AMS scores are reported as sum of scores for the Lake Louise questionnaire for each subject, and a scatter plot is shown in Figure 2. At baseline, one subject reported a score of 4 because of poor sleep and fatigue or weakness. Two of the 3 subjects with scores of 4 or greater were girls. The three subjects reported a headache for all but one data point above the cut off for AMS. On day 1, subjects reported having AMS immediately after skiing with score of 5, 6, and 7 (boy, then the 2 girls, respectively), which decreased to 2, 4, and 6, respectively, at 4:30 PM. On the morning of the second day, those 3 subjects reported scores of 2, 0, 5, which increased to 2, 4, 5 after skiing, and all reduced to below the cut off for AMS at 4:30 PM. There where 9 reports, individual time points, during the first 3 days, of subjects having a headache (scores of 1 or 2) but did not have total scores of 4 or more. There where no reports of a headache after the third day. After 4:30 PM on day 3, no subject reported a score above 2, and after skiing on day 5, no subjects reported a score above 0. The most common reported symptom was fatigue or weakness, followed by sleep, overall effect on activity, headache, dizziness or lightheadedness, and gastrointestinal distress. The only sign of AMS observed for a change in mental status was a score of 1, meaning “Lethargic.” No effect of AMS scores on dependent variables exist at any time point. As this was a preseason athletic training camp, a reported answer of 1 for several of these questions were expected during recovery from sport practice.
No subject reported taking medications known to affect AMS, which includes acetaxolamide, dexamethasone, and nonsteroidal anti-inflammatory agents.
Results from hydration monitoring, percent change in body mass, and standard measures of USG and urine color are displayed in Figures 3, 4, and 5, respectively. And Table 4 contains mean values for the duration of the camp for the three hydration markers for two groups separated by the difference in the subject's self reported drive to drink. There was a main effect for the loss of body mass (F[6, 60] = 10.159, p < 0.000), from day 1 through day 6 and the 95% confidence interval was −1.27 to −0.57 kg (−2.97, −1.26 lbs). Body mass on days 3 and 4 were significantly lower than baseline and days 5 and 6 were significantly lower than all previous days. But days 5 and 6 were not significantly different from each other (p = 0.055 and p = 0.051, for first AM and PM time points). There were no significant changes observed for the AM versus PM across days for changes in body mass. Between AM time point comparisons, first morning body weight after voiding the bladder trended to be greater on days 3 and 4, but 5 and 6 were similar.
An order 4 main effect for both USG and urine color across days was observed (F[1, 10] = 25.569, p < 0.000; F[1,10] = 10.925, p < 0.008). The USG on day 3 was significantly greater than days 1 and 6. The same pattern occurred in urine color with day 3 being significantly darker than days 1, 4, and 5 (Figure 5). There were no AM versus PM time-point significant changes for USG or urine color.
The Y-balance test improved on days 3 through 6 (Figure 6), with a main effect between days (F[6, 60] = 34.798, p < 0.000) and from AM to PM time points (F[1, 10] = 10.980, p = 0.008). Only 1 of the 3 subjects who had AMS had a decrease in her Y-balance score of 8.7% and 4.5% at time points in day 2 AM and PM from baseline, however, at these time points, the subject reported an AMS score of 2 for AM (1 for sleep and overall effect on activity) and 3 for PM (1 for headache, fatigue, and sleep). But on the previous day, this subject had a score of 6 and 7 for AMS after skiing at 2:30 and 4:30 PM.
Performance on the QRD was mixed (Figure 7). A main effect for days was detected (F[5, 20] = 5.679, p = 0.005) for mean reaction time (QRD). There was an effect of maturation on reaction time (F[5, 20] = 4.572, p = 0.002). Post hoc tests showed that subjects with lower maturation had faster reactions times for the following time points: AM and PM on day 1 and PM on day 6 (p < 0.05). No main effects were observed for percent correct touches (F[5, 50] = 2.105, p = 0.080) or AM versus PM time points for both variables—reaction time and percent correct touches. Only 1 of the 3 subjects with AMS had decreased scores from baseline for mean reaction time of 5.8% for the AM time point on day 1, when she experienced AMS after skiing, with scores of 6 and 7 for AMS at 2:30 and 4:30 PM But, by the time point day 3 AM, her mean reaction time improved 34.9% from baseline values.
A main effect for between days and AM versus PM was observed for CMJNH (F[6, 60] = 5.876, F[1, 10] = 31.699, p < 0.000). Scores increased significantly from baseline on day 1 of the training camp and remained unchanged (Figure 8) with no effect for gender or maturation. On days 2, 5, and 6, jumps height increased from AM to PM.
The coach's perceptions of athletes mood while training decreased from day 1 through day 3 during the camp and improved on days 4 through 6 (Figure 9). The coaches' perception remained similar with 3 athletes who scored above 1 on days 2 and 3 but improved to all athletes perceived, to have the highest quality of training on days 5 and 6 (Figure 9).
Baseline and day 6 testing for performance variables can be seen in Table 5. CMJ increased significantly, with a significant gender effect at the end of the camp, the boys jumped 55.0 ± 5.6 cm as compared with the girls who jumped 47.0 ± 4.6 cm. T-agility test, sit-and-reach, and 1-minute sit-up and push-up tests, all increased significantly with the exceptions of the sit-up test that had a p = 0.055. All subjects experienced a significant decrease of their MSFT performance with a within subject mean estimated V[Combining Dot Above]O2max decrease of −8.9 ± 4.0 ml·kg−1·min−1.
The primary findings of this study were that the Y-Balance and QRD did not have a decrement in performance during acute high-altitude exposure and that both tests improve after 3 days of acclimatization. Therefore, these data reject the hypothesis that acute altitude exposure initially impaired performance at high altitude but support the hypothesis that performance data improves over the course of the week at altitude. In general, these data support the ability for youth athletes to adapt to physical and perceptual-motor training while acclimatizing to an overnight lodging of 2,828.5 m and training between 3,328 and 3,802 m.
The altitude of the testing and overnight lodging was just below the levels known to cause perturbation in balance, reaction time, and vision (3,048 m, 10,000 ft), but all skiing activities were above this threshold altitude (20). Because alpine ski racing is a sport where one commonly travels to moderate to high altitude for both training and competition, usually not above 3,650 m (12,000 ft), future research is obviously warranted to further explore effects of performance for on-snow training altitudes.
Three of 11 subjects (27%) experienced AMS, which is consistent with other observations of approximately 20% in children skiing in Summit County, Colorado (9,27,42). However, rates of AMS in youth at slightly higher altitudes, similar to those reached during on-snow training in this study, have been reported to be higher during an overnight stay at 3,500 m (641.5 m, higher than this study) and reported an incidence rate of 50% of adolescents (n = 10, 15.4 ± 1.5 years) (42). A rate of 91.7% was reported in 12 (7 boys and 5 girls, 15–18 years) hikers over a 21-day trip to Machu Picchu and the peak of Ausengate (2,500–5,500 m) (27). Despite the incidence of AMS observed, there were no effects demonstrated between AMS scores on dependent performance variables measured in this study at any time point. These findings indicate that youth athletes experiencing moderate levels of altitude illness, with short exposures above 3,000 m can acclimatize while participating in training and have benefits from participating in that training.
As AMS scores improved throughout the week, markers of hydration had a delayed response. Dehydration as measured by change in body mass from baseline slowly increased throughout the week. However, because USG was higher on day 3 than days 1 and 6 (p < 0.05) and urine color was higher on day 3 than days 1 and 5 (p < 0.05), it indicates that hydration decreased significantly on day 3 then returned to normal levels on day 5 and day 6. Also second morning body weight did not increase on day 6, indicating that body weight losses 6 days into acclimatization and training may not be because of fluid deficit and might be body mass loss from lean or adipose tissue. Son et al. (50) observed similar changes in body mass during acclimatization to moderate altitude and interpreted this as lean body mass loss in youth alpine skiers using the bio-impedance method of body composition analysis.
The order 4 effect in USG and urine color paralleled improvements in AMS scores, coach's perception's quality of training, and QRD observed in this study. Arginine vasopressin (AVP), which controls whole-body fluid balance by regulating plasma osmolality, by retaining water in the renal collecting ducts of the kidney, responds to high plasma osmolality (dehydration). The AVP threshold for plasma osmolality increased significantly with 2 days and 20 days of high altitude (4,300 m) acclimatization in 7 men (22 ± 1 years) (38). After about 3–4 days of acclimatization, the regulation of fluid balance of the body most likely was altered, resulting in better oxygen delivery and reducing the hypoxic stress allowing for improvements in neuromotor performance and the quality of training. Therefore, an adaptation of AVP may be one of the underlying mechanisms that help to explain the changes in performance observed in this study.
Interestingly, the afternoon time point was equal or slightly more hydrated than morning time points for the 3 hydration markers, indicating that ad libitum fluid consumption during and after training was sufficient to maintain or improve hydration. This was similar to a study examining the effects of a back mounted bladder hydration system for ad libitum fluid intake during alpine skiing for 2.75 hour (3,853 ± 430 m of vertical drop) versus no fluid intake in adult (23–35 years) experienced skiers at 2,438–3,200 m. The subjects who consumed no fluids during skiing replaced 71% of fluid loss, where a group that used the back mounted water bladder replaced 100% of their fluid loss during skiing and after skiing (47).
In this study all but 2 subjects reported that the motivations to drink was to diminish the feeling of an oncoming headache. The other 2 subjects reported drinking 1–2 extra liters of water per day than they would normally perceive to have done, to prevent the onset of a headache. Interestingly, these subjects consistently had markers of urine indices of hydration at or better than the mean of the rest of the group. These subjects also reported that they would add flavor to the fluid or cut fruit juices with water to make drinking the extra fluid more palatable. One study of Everest Base Camp Trekkers found that high fluid drinkers (5 L·d−1) had a lower incidence of AMS with an odds ratio of 1.54 (6). However, the only controlled experimental trial to investigate the effect of hydration on AMS showed no effect of increased daily drinking on the incidence of AMS (1).
The data from this study indicate that the altitude exposure experienced over a 6-day training period, at some of the highest ski resorts in the world, did not prevent improvements of performance on dynamic balance scores in these young skiers. The altitude tested in this study (2,828 m) was below the threshold of 3,000 m for increased observations of general performance decrements for testing (5), but altitudes for sport activity in this study were above this threshold (3,328–3,802 m). Tests performed over acclimatization period to altitude showed similar improvements in performance to this prior study. Wobble board tests improved in one study from baseline during the first 2 tests at 1,345 m and 1,660 m, respectively, then remained unchanged at altitudes of 3,300, 4,650, and 5,005 m in 20 adults (25–46 years, 16 men and 4 women) with each ascent to a higher altitude 2–3 days apart (28). This study concluded that the wobble board test maybe a useful adjunct in quantifying ataxia (28). This research group in a larger study had showed that during staged acclimatization (8 days per stage) at high altitude, decrements of the Sharpened Romberg Test (ability to stand still for 60 seconds with arms crossed against the chest and eyes closed) had a sensitivity of 71% at 3,610 m to predict AMS and 60% at 5,260 m and the specificity to increase from 69% at 3,610 m to 89% at 5,260 m (29).
However, studies looking into the mechanism of perturbation of balance at altitude have shown it to be sensitive to hypoxia and not to correlate with AMS scores. Fraser et al. (21) showed postural control mechanisms, as measured by 3 minutes of eye closed postural sway on a force plate, are very sensitive to even acute mild hypobaric hypoxia—30 minutes at 1,524 m and several studies have shown that decrements in balance performances do not correlate with AMS (7,8,13). Cymerman et al. (13) when investigating postural stability showed that decreases in balance did not correlated with AMS after 24 hours of simulated altitude exposure at 4,300 m and Baumgartner et al. (8) in 22 healthy subjects (17 men and 5 women, 42 ± 10 years) during a 3-day sojourn to 4,559 m showed postural sway decrements not to correlate with AMS scores. However, in a separate article, after a 24-hour ascent to 4,559 m and then 10 minutes of oxygen supplementation (3 L·min−1) had no effect for returning postural sway to baseline levels (8). This also indicated that a hypoxia-triggered mechanism separate from AMS, such as selective sensitivity of Purkinje cell of the cerebellar cortex to hypoxia, may be related to decrements in balance (8). Thus, decrements in balance performance are most likely because of hypoxic stress on the neurons and are not because of the fluid shifts that are thought to cause AMS.
Choice reaction time (CRT) as tested with the QRD improved over the course of the week, indicating that the lodging altitude was not high enough to induce reaction time performance decrements. The altitude threshold (ascent rate of 1,000 m per day) for decrements in performance of reaction time as tested by pressing a single button, with a finger, after an LED light randomly lights up, was found to be between 4 and 5 thousand meters, approximately 1,500 m higher than this study (37). However, in a CRT test designed to determine the threshold for impairments of perceptual-motor performance with 6 acute (within minutes) altitudes exposures, where altitude was measured by blood oxygen saturation (SaO2) and ranged from 76% to 86% in increments of 2%, found the threshold to be SaO2 of 82% equivalent to 3,048 m in 6 adult subjects (3 men and 3 women) (20). In this study, there was a linear relationship between altitudes from 3,048 to 3,475 m with decrements in reaction time, supporting this hypothesis that sensory motor task decrements are related to hypoxic stress (20). Other work showed that visual sensitivity decreased by 17% as low as 2,500 m and 33% at 3,500 m (53). Thus conclusions from this study and those mentioned above should be limited to the altitude tested (2,828.5 m) and the impact of visual CRT for on-snow training altitudes (∼3,500 m) still needs to be investigated.
Investigations into the mechanism for decrements of CRT from altitude exposure show that these are most likely again caused by the hypoxia rather than fluid shifts. Experiments using event related potential recording during surface cranial electroencephalography have examined the effects of acute hypoxia on P300 latancy (53), which is considered “an index of cognitive activity involved in stimulus evaluation, discrimination, and categorization” (23). Hayashi et al. (23) showed that after just 2 hours of exposure to 4,500 m (hypobaric hypoxic chamber), an increase of P300 latency occurred, which could explain increased CRT (23). This has been replicated in several other experiments (53). It is not clear what the exact cause of P300 latency is, but a decrease in the cognitive processing speed or in the sensitivity of the auditory input or cortex brain stem-neurons has been proposed as potential mechanisms that may mediate such an effect (23).
The use of changes in CMJNH can be used in assessing strength and power performance of individuals, specifically, the relative fatigue of connective tissue and contractile muscle tissue. CMJNH remained constant throughout the training camp. Improvements in explosive power were expected between morning and afternoon time points because circadian rhythms of peak rectal temperature and circulating hormones levels, such as melatonin, have direct effects (46). On days 1, 3, and 4, where training volume were elevated as compared with other days and prior training, afternoon vertical jump performances did not differ from morning performances. This indicated that significant lower body fatigue was induced on those training days, but the subjects where able to recover day-to-day during the camp. Additionally, all subjects with AMS had improvements in their vertical jump from baseline on the first 3 days, demonstrating that power and muscular skeletal adaptation may not be affected by AMS and altitude exposure experienced in youth alpine ski racers.
The perceptual data collected from the coaches questionnaire on the mood state and quality of training for each subject, matched trends found in AMS, Y-balance test, CMJNH, and QRT: scores improved on or after day 3 of the camp. Interestingly, coaches did not score any subject above 2 (agree), suggesting that all subjects had quality days of on-snow training during the camp. The male subject with AMS had reported mood scores of 2 for the first 3 days and a score of 2 for the quality of training on day 1. However, the other 2 subjects with AMS, girls, had no score above 1 for either question at any time point. This finding and the observed improvements in CMJNH, Y-balance test, and QRT over the week, indicate that a reasonable volume of quality training can occur on immediate ascent to high altitudes.
Performance tests at the end of the camp indicate that these subjects, despite the stress of altitude and travel, where able to sufficiently improve physical performance of flexibility, vertical jump, quickness, speed, and local muscular endurance.
Flexibility improved from baseline levels to a degree similar to youth athletes' involved in several weeks of participation in soccer training (12). In addition, the vibration stress from alpine skiing may have caused an increase in the compliance of tendons and ligaments, which would contribute to the flexibility, however, the timeline for these adaptations has not yet been investigated (16).
Improvements seen in CMJ increased throughout the week may have been because of other factors than a decreased tendon compliance as previously reported (44). However, because of the eccentric load stress from alpine skiing (26) and a decrease in body weight from baseline could contribute to the explanation of the improvements seen in vertical jump performance during the camp (18).
The increased flexibility and decreased body weight could also provide preliminary explanation for the improvement in the time required to complete the T-agility course. In addition to these changes, lateral agility and strength is fundamental to the movement pattern of making carved ski turns (51). Thus, sport skill improvements and physiological adaptations of muscle and tendons, and the decrease in body weight could have been transferred to the performance of the T-agility test.
The changes in the number of sit-ups that can be performed in a minute increased with a p value of 0.055. Only 3 of the 11 subjects had a decrease in the sit-up test, all were girls, and 2 had AMS during the camp. As a group, given that the baseline scores where at 38.8 ± 3.7 indicate that there is little room for improvement (25). Being able to measure change in this performance variable, with only a small range for improvements and low N size of 11, makes conclusions from this data set difficult to interpret. It is clear that core stability and upper body bracing are important in maintaining stability throughout a carved turn (31,39,40), which was seen in the number of push-ups performed in 1 minute.
Push-ups increased despite no upper body off-snow conditioning between the baseline and the end of camp time points (2 weeks). Unlike sit up, the starting push-up scores where 20.2 ± 8.9, indicating that there was a large range for possible improvement (10–30 more push-ups) (25). Douris et al. (15) showed the greatest balance deficit to be after a fatiguing aerobic upper body trial as compared with a lower body aerobic or anaerobic fatiguing trial. Considering the high force levels generated by a carved ski turn (1–2.5 G) (32), the importance of upper-body strength endurance to maintain balance and improvements seen in this study from 1 week of preseason on-snow training, provides preliminary evidence for the importance of upper body fitness among elite youth alpine ski racers.
Changes in MSFT were similar to those reported in a review for elite winter sport athletes, which found a 7.7% decrease for every 1,000 m of altitude, based on data from 11 studies on unacclimatized men with a mean V[Combining Dot Above]O2max of greater than 60 ml·kg−1·min−1 (11). Although this regression is based on fit men, using this linear relationship, the calculated decrement in aerobic capacity at the altitude encountered during our study is 21.75%, which was nearly identical to the observed 20.34% decrease in performance seen in this study with mixed gender youth athletes. Similarly, Son et al. (50) investigated the effects of moderate altitude exposure (lodging at 2,100 m and 2,700 m for on snow training) in adolescent youth alpine skiers and found an immediate increase of RBC concentration of 6% and a 13% increase after 5 weeks but no change in anaerobic cycling power in pre-post Wingate tests. Thus during a high-altitude youth athlete sport camp, aerobic capabilities will substantially diminish, but anaerobic supported activities should not be affected in youth.
One can gain some insights from a specific case report. Subjects with AMS had mixed changes in scores. Only 1 of the 3 subjects who had AMS on day 1, with AMS scores of 6 and 7 for the 2 postskiing time points, had decreased Y-balance scores of 8.7% and 4.5% on day 2. On the last day, her scores increased 10.4% from baseline. This subject on the first day did have elevated or stagnant scores for mean reaction time, but these quickly improved by day 3 AM by >30%, indicating that mechanisms of AMS could limit reaction times, but are probably not clinically significant for total AMS scores of 7 or less where a subject reports a 1 or 2 for specific questions on the Lake Louise AMSQ. Coaches' perceptions of this subject indicated that the subject had high-quality training and remained in a good mood throughout the camp.
All of the 3 subjects with AMS improved on the countermovement jump (6.1%, 2.7%, and 6.4%), 2 improved on the T-test (5.7%, −1.1%, and 6.6%), 2 improved on flexibility (6.9%, −5.3%, and 5.4%), 2 on push-ups (14.5%, 114.3%, and 0.0%), and 1 improved his sit-up test (7.5%, −13.2%, and −8.6%). The sit-up test was the only test in which these subjects had a decrease in scores, which pushed them below 1 standard deviation from the mean. And no post scores that decreased on any test where >2 standard deviations from the mean of the group. In general, a qualitative analysis of subject with and without AMS showed that pattern in their variability was not different. This pattern could be because of many factors related to the schedule of the camp, demands of travel, the process of team cohesion, nutrition, and the environment.
In summary, young ski athletes traveling to high altitude for athletic ski camps may expect improvements in balance, reaction time, quickness, strength endurance, and flexibility 3–6 days into acclimatization and training, despite having signs and symptoms of mild AMS.
The participation of young skiers in high-altitude ski camps seems to be relatively safe. Coaches and athletes should expect at least 20% of youth lowlander athletes to have signs and symptoms of AMS during the first 3 days of altitude exposure for alpine lift access sports at altitudes <3,800 m. Athletes should expect improvements in balance and reaction time 3–6 days into acclimatization. Physical performance changes might be variable dependent on prior training status, body mass changes, and altitude sickness symptoms. Training volumes should increase gradually during the first 3 days and overnight lodging should be below 3,000 m, to help reduce the prevalence of AMS in youth athletes. All athletes should be monitored daily for altitude illness, and hydration should be encouraged throughout the time at the ski camp.
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