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Responses to training in cross-country skiers

GASKILL, STEVEN E.; SERFASS, ROBERT C.; BACHARACH, DAVID W.; KELLY, JOHN M.

Medicine & Science in Sports & Exercise: August 1999 - Volume 31 - Issue 8 - p 1211-1217
Applied Sciences: Physical Fitness And Performance
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Responses to training in cross-country skiers. Med. Sci. Sports Exerc., Vol. 31, No. 8, pp. 1211-1217, 1999.

Purpose: This study evaluated whether cross-country skiers who did not respond positively to a training program consisting of high volume and low intensity would improve if high-intensity training volume was doubled during a subsequent training year.

Methods: During the first year of the study, cross-country skiers (N = 14) were evaluated for O2max, O2threshold, lactate response, max arm power, and competitive results after a standard training program. During the second year, the athletes were divided into a control group (athletes who had responded well to the training) and a treatment group (athletes who had responded poorly to the training). The control group (N = 7) repeated the previous year's training program. The treatment group (N = 7) was given a modified training program which increased high-intensity training time as a percentage of total training from < 17% to > 35% and decreased low-intensity training volume 22%.

Results: The treatment group, using the high-intensity training program, demonstrated significantly improved O2max, O2threshold, max arm power, and competitive results (P < 0.05).

Conclusions: Increased volume of high-intensity training may improve competitive results in cross-country skiers who fail to respond to increased volume of low-intensity training.

University of Montana, Department of Health and Human Performance, Missoula, MT 59812; University of Minnesota, Department of Kinesiology and Leisure Studies, Minneapolis, MN 55455; and St. Cloud State University, Exercise Science Laboratory, St. Cloud, MN 56301

Submitted for publication April 1996.

Accepted for publication December 1998.

Address for correspondence: Steven E. Gaskill, Ph.D., Department of Health & Human Performance, McGill Hall, The University of Montana, Missoula, MT 59812.

Ingjer (12) studied data on many years of test results from elite Norwegian cross-country skiers, including many who had won Olympic and World Championship medals. His conclusions were that the best cross-country ski athletes have the greatest yearly variations in maximal oxygen uptake (O2max) and anaerobic threshold oxygen uptake (O2threshold) with the highest values being reached in the competitive season and the lowest values being reached in the spring. Ingjer (12) also noted that athletes who do not periodize their training during the year, including a post-competitive detraining period, seldom reached the same level of competitive results as athletes who periodized their training and demonstrated wider swings in O2 over the yearly cycle. One goal of the current research was to verify if current training programs with cross-country skiers would show similar variations in O2 that could also be related to competitive results.

Rusko (15) documented that up until about age 20 there is an increase in O2max and O2threshold with increases in the volume of low-intensity training. Rusko (16) also demonstrated that after age 20 O2max often plateaus but elite skiers are able to further increase O2max by increasing both the volume and intensive of training. Acevedo and Goldfarb (1) further demonstrated that previously trained runners who increased their training intensity for 8 wk improved endurance performance by lowering lactate at the intensity at which they trained despite no changes in O2max and O2threshold.

A paradigm of cross-country ski training that has developed over the past decade has been to build a base with high volumes of training during the off-season, add speed during the precompetition period, and engage in higher intensity intervals and training in the final preparation for competition with a final taper into the most important events (3,10,11,18,21). Athletes have continually added greater volumes with increases of about 5-10% annually being accepted as the best range for optimal annual improvements (16). Training plans for cross-country skiing have been published by several coaches and physiologists (3,10,18,21). All of these programs embrace the high volume-low intensity paradigm. Training material from major cross-country ski countries around the world show that the high volume-low intensity concept is promoted for most top skiers. Training programs reported at international cross-country skiing coaches seminars held at the Olympic Training Center, Lake Placid, NY, in 1992 and 1993 and at Thunder Bay, Ontario, during the cross-country world championships contained less than 10-20% of total time at or above the maximum steady state lactate threshold (LT) during a year of training and competition. Many elite athletes on these low intensity-high volume programs have reached very high levels of performance including Olympic and World Championship medals.

Despite this overwhelming focus on high volume programs, there is a body of anecdotal evidence of successful results achieved used low volume - high intensity programs. One example is Bill Koch who during the year before winning the 1981 World Cup, reportedly trained using a low volume-high intensity program.

Ingjer and other researchers (3,8,12,16,18,24) have also observed that many athletes seem to reach performance plateaus concurrent with plateaus in O2max, O2threshold, and other physiological parameters. The reasons for these performance plateaus are not known, but it may be speculated, at least for some athletes, that major changes in their training stimuli may be necessary in order to further improve performance. For some athletes, further improvement may not be possible.

Upper body power and endurance are also known to play major roles in the performance of cross-country skiing. Rundell and Bacharach (14) showed a positive correlation (r > 0.80) between upper body power and competitive results in U.S. Biathlon Team members as well as a strong relationship (r = −0.79) between a 1-km uphill double-pole test and racing ski time. Bilodeau et al. (2) showed that increasing arm O2peak as a percentage of leg O2max was a powerful predictor of competitive success for Nordic skiers. Watts et al. (25) reported that upper body aerobic power in cross-country ski racers during double poling averages 77% of total body aerobic power during diagonal stride technique. These large upper body O2 values, along with the efficient transfer of upper body work via the poles during skiing, result in a large advantage to skiers who can develop and maintain high levels of power with their arms and torso during ski racing. Other research (6,14,22,23) has demonstrated the importance of upper body power and endurance for cross-country skiers. During the 2 years of this study, we monitored strength training methods, intensity, and volume as well as testing for upper body power.

Bouchard, Simoneau, and others (4,5,9,19,20) have determined that the response to training may have a genetic component and that about 45% of the variance in fiber types may be accounted for by genetic factors. These authors have observed that individual athletes on similar programs respond differently. Genetics may play a part in this individual response and further research with elite athletes may someday establish the link between genetics and the necessary load and intensity to optimize individual stimulus.

It was a goal of the current study to determine if skiers who appear to have reached a competitive and physiological plateau can stimulate higher O2 values and improved performance via increased high-intensity training volumes. Based on the hypothesis that different athletes require individualized stimuli, this research was designed to test whether athletes who did not seem to respond to a high volume-low intensity program would demonstrate better performance and improved O2 values with a program repeating the prior year's total energy expenditure but using increased high-intensity training and decreased low-intensity volume.

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METHODS

A 2-yr project was designed to study a group of 14 cross-country skiers, all working with the same club, who were willing to have their training monitored and manipulated for a 2-yr period. During the first year, all 14 athletes used similar programs based on the current paradigm of high volume and low intensity. Training averaged 660 h·yr−1 with 16% of the training at high intensity (LT or higher). All athletes used similar strength programs and the periodization of training cycles was well structured and similar for the entire group. Each athlete had his/her own individual plan based on their needs within the basic training structure. Athletes recorded training under the guidance of the researcher and coach.

Selected characteristics of the subjects are shown in Table 1. Each subject reviewed and signed consent forms approved by the Human Subjects Committee at St. Cloud State University. This statement conformed to the policy statement regarding human subjects as published by Medicine and Science in Sports and Exercise.

TABLE 1

TABLE 1

Training data were collected monthly. Weekly meetings were held between the researcher, coach, and athletes. Testing was done to correspond with the major changes in training periods. Mid-summer testing corresponded with basic endurance training. Mid-December testing was done half-way through the precompetition period. Testing during the competition period was done during late February. Data collected included O2max, O2threshold (as estimated by the breakaway blood lactate point occurring at 3-5mM·L−1 blood lactate) (17), max arm power, and competitive results.

Values for O2max and O2threshold are expressed using the units of mL·kg−2/3·min−1. These units are used as they are better predictors of cross-country skiing performance (7) than mL·kg−1·min−1. For purposes of comparison and clarity both values are given in Table 6.

TABLE 6

TABLE 6

Subjects tested six times over the 2 yr corresponding to the training periods. The tests included a O2max ski walk test and an upper body power test. The ski walk test was completed similar to testing by Rundell (14) at 4.5 miles·h−1 for male and female subjects while simulating ski poling on an arm ergometer, alternating arms. Every 3 min the treadmill grade was increased 2.5% with the arm resistance for the first test self-selected to match the perceived output of the legs. Each subsequent test was performed at the arm and leg settings of the baseline test. Finger stick blood samples were taken every 3 min at the end of each stage and during recovery. Blood samples were immediately analyzed for lactate concentration using two Yellow Springs Instruments (Yellow Springs, OH) 23-L analyzers and duplicate samples to check for reliability. Heart rates were monitored using Polar Electro OY, (Kempele, Finland) Vantage HR monitors. Ventilation and respiratory gases (CO2 and O2) were monitored continuously using a Rayfield (Waitsfield, VT) open spirometry system with Ametek (Cambridge, UK) freestanding O2 and CO2 analyzers. In addition, expired gas was periodically collected in meteorological bags to verify results of the Rayfield system.

The max arm power test used an SMI, Inc., (St. Cloud, MN) upper body arm ergometer with a protocol modified from Rundell and Bacharach (14). Athletes performed a double-pole motion, pulling with both arms at the same time. After a 5-min warm-up, the initial resistance was set at 1 kg for women and 1.2 kg for men. The athletes maintained a constant RPM of 375 for the women and 400 for the men. Every 20 s the resistance was increased 0.2 kg until the athlete was no longer able to maintain the flywheel speed within 25 RPM of the target speed for three stages. Max W were recorded and W·kg−1 body weight were calculated.

Training data were recorded by the athletes using a five-level intensity scale as described in Table 2. After each test, athletes were given updated target heart rate zones for training and recording purposes. Hours, repetition maximum (RM), and intensity of strength training was also monitored.

TABLE 2

TABLE 2

The training data were separated into three training periods for each year. 1) Basic endurance period: this period consisted of 23 wk from May through October during which an aerobic base was developed. 2) Precompetition period: this included the 10 wk period of November through mid January between the end of the basic endurance period through the start of the major competitions and including the early season preliminary competitions. During precompetition the focus was on increased intensity, maintained volume, and greater emphasis on LT intervals and race simulation. The volume was held high initially and then slowly decreased. 3) Competition period: a 10-wk period from mid January through March. This period included reduced-volume, high-intensity intervals, and racing with planned recovery periods between races.

The competitive goal of athletes in this study was to perform optimally during the competition period and to maintain a competitive plateau throughout the period. Race results were collected far all competitions in which the athletes competed during the winter. Primary performance ranking criteria used were: 1) the United States Ski Association (USSA) Points List and 2) the highest place achieved by each athlete at the United States Senior National Cross-Country Championships.

At the end of the first year the athletes were separated into two groups. The control group (N = 7) was designated as those athletes that met the following improvement criteria the previous year: 1) O2max (increase > 7%); 2) O2Threshold (increase > 10%); and 3) USSA points (increase > 10%). The control athletes maintained similar training for the following year. The remaining skiers who did not meet the improvement criteria (N = 7) were then started on a modified training program of doubled high-intensity hours, reduced low-intensity volume, and slightly (nonsignificant) reduced total training hours and are hence forth referred to as the treatment group. Details of the training are listed in Table 3. The athletes in both groups were very motivated to have their training be effective and were diligent in following prescribed training plans.

TABLE 3

TABLE 3

Statistics. A 2 × 5 design, repeated measures ANOVA (α = 0.05) was run on each dependent variable to determine differences between means for each test. Contrasts were used to evaluate the significance of the change between year 1 and 2 for the basic endurance, precompetition, and competition periods. Fischer's LSD paired t-tests were performed for the control and treatment groups for each of the five dependent variables tested. The dependent variables included O2max, O2Threshold, arm power, competitive results at U.S. nationals, and national (USSA) points ranking.

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RESULTS

The results demonstrated significant (P < 0.05) differences for the treatment group for all five dependent variables and no significant differences for the control group from year 1 to year 2. Contrasts for each of the five dependent variables demonstrated that the treatment group improved significantly (P < 0.05) from year 1 to year 2 during the competition period.

Table 4 shows a significant difference in hours of both low-intensity and high-intensity training between groups during the second year. Training plan details are listed in Tables 3, 4, and 5. No significant difference was noted between the strength training hours from year 1 to year 2 within or between groups.

TABLE 4

TABLE 4

TABLE 5

TABLE 5

Table 6 demonstrates significant improvements in the control group in O2max and O2threshold within each of the 2 yr during the precompetition and competition periods when compared with the basic endurance period. Using a high volume-low intensity program, the control group improved max arm power from basic endurance levels to the competitive season both years. This is in contrast with the treatment group that, with the same low-intensity training during year 1, did not show any significant changes throughout the year in O2max, O2threshold, or max arm power. During the first year, the treatment group preformed significantly (P < 0.05) lower in competition results than the control group despite both groups finishing the prior year with similar competitive results and starting the study with similar respiratory gas values.

During the second year of training, the control group repeated the previous year's training program with an average 6% increase in volume, which follows current training paradigms (16). No significant improvements in O2max, O2threshold, max arm power, and both measures of competitive results were seen in the control group from first year data.

Pretreatment laboratory data demonstrated significantly (P < 0.05) lower O2max, O2threshold, and max arm power values during the first competitive season for the treatment group than for the control group. The treatment group then significantly changed their training during year 2 by reducing low-intensity volume (from 443 to 283 h) and increasing high-intensity volume (from 100 h to 236) with no significant change in total training volume. During the second competitive season, the treatment group showed significant improvements in all dependent variables over the prior competition period (Table 6). The ventilatory and power data showed that the treatment group significantly improved O2max (263 mL·kg−2/3·min−1 to 286 mL·kg−2/3·min−1, P < 0.01), O2threshold (212 mL·kg−2/3·min−1 to 241 mL/km−2/3/min, P < 0.001), and max arm power (3.1 W·kg−1 to 3.8 W·kg−1 body weight, P < 0.01). The treatment group's test values improved to a level equal to the control group during the second year.

The competitive results (Table 7) follow the same pattern as the laboratory test data. USSA points and competitive results showed the control group to be significantly better than the treatment group during the first competitive season. The competitive results for the second year showed no significant changes from the prior year in the control group whereas the treatment group significantly improved their USSA points and individual best placing at U.S. National Championships.

TABLE 7

TABLE 7

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DISCUSSION

This study demonstrates that some mature, high-level cross-country skiers may respond more positively to increases in high-intensity training volume than to increases in low-intensity training volume. This study is unique in that it is the first to manipulate and quantify training load over a competitive season. The treatment subjects appeared to have reached performance plateaus based on race data from the previous 3-yr and O2 data from the year before this study (data not shown). The treatment group's training was altered by decreasing low-intensity volume and increasing high-intensity volume while maintaining total volume of the previous year. The treatment group significantly improved in all five dependent variables (O2max, O2threshold, max arm power, and two competitive results measures) posttreatment. The control group followed essentially the same program as the previous year's training and did not significantly change O2max, O2threshold, max arm power, or competitive results over the 2 yr of the study.

Our results supported those of Ingjer (12), who looked at the annual fluctuations of O2max and O2threshold. Those athletes who did not significantly vary their O2 values during the year (high O2max and O2threshold values during the competitive season and lower values during the spring) had the poorest overall race results within our study group.

The control group spent 16-17% of their total training time training at high intensities (at or above LT) both years. This is higher than suggested in some current training programs (10,18,21) but not inconsistent with material handed out during recent international cross-country coaching symposiums (1992-1995). The control group's training program was consistent with members of the U.S. National Ski Team. During the period of this 2-yr study, the control group did not significantly change their training other than an average 6% overall volume increase, consistent with annual volume increases seen in elite athletic programs of top cross-country ski countries (3,10,18,21). The control group's competitive results did not significantly improve over the 2-yr study. Training hours of the control group were about 15-25% less than the total annual hours reported for international elite athletes, with reported high-intensity training time for the control group about 5-10% less than that of elite world-class athletes.

The treatment group increased the percentage of time at high intensity by 136% over pretreatment from 15% (100 h) of total training time the first year to 37% (236 h) the second year. The treatment group also reduced their low-intensity training volume by 36% (443 to 283 h). This modified training program resulted in improvements by the treatment group in both competitive measures and laboratory testing for O2max, O2threshold, and max arm power during the competitive season. Compared with international elite skiers, who average 650 h of low-intensity training and 75 h of high-intensity training annually, the treatment group during the second year trained only 40% of the international elite low-intensity hours but over 150% of the international elite's average high-intensity hours.

Our performance results support the findings of Acevedo and Goldfarb (1) in showing that previously trained endurance athletes can improve performance through increased intensity training. Our data differed, however, in that they found no improvements in O2max and O2threshold but rather a decrease in blood lactate at the intensity at which the athletes had trained. Our blood lactate data (not reported) support this finding by Acevedo and Goldfarb. The difference in respiratory data between the two studies may be due to the length of the two studies, with 8 wk not being sufficient time in trained athletes to see measurable O2max and O2threshold improvements.

During the first year, both groups had similar O2 and max arm power data during the basic endurance training program of high volume-low intensity. During the precompetition period of the first year, the intensity training was increased from about 6% of total time during basic training to about 25% of total time with a resultant significant improvement in all outcome variables by the control group. The treatment group, during year 1, failed to show any changes in their respiratory gas values or max arm power over the three test periods. During the second year, after a 50% increase in high-intensity training during the precompetition period, the treatment group improved on an equal basis with the control group, and both groups had similar competitive results. This would suggest that the treatment group required a much greater volume of high-intensity training to elicit physiological responses similar to the control group.

The max arm power data may provide an insight into effective arm power training for cross-country skiing. Both groups maintained similar strength programs throughout the 2-yr period. However, during the precompetitive period of the second year, the treatment group spent three sessions a week working at a resistance of 15-30 repetitions to fatigue while moving as fast as possible. The control group used slightly lighter weights and worked at higher (> 35 repetitions to fatigue) repetitions for only two session each week. The total strength hours for both groups were similar. The treatment group showed no changes during the first year in maximal arm power, but showed a significant improvement in maximal arm power during the precompetitive and competitive periods during the second year. Whether the increased arm power is a result of the increase in overall high-intensity training or the lower RM resistance program cannot be determined. Increased speed training, high-intensity poling, and other arm work such as increased endurance double poling workouts done by the treatment group could also have contributed to the improved arm power.

In this study, the reduction in total hours of training for the treatment group was not significant, whereas the increase in high-intensity hours and the decrease in low-intensity hours was significant (P < 0.01). Thus, the improved results of the treatment group cannot be attributed to a reduced annual volume but may be attributed to the greater volume of high-intensity training.

A model for evaluating the overall training load, using an arbitrary training unit called a TRIMP, has been developed by Morton et al. (13). This model factors a training load based on volume and intensity, where high-intensity training is weighted using an exponential scale matching a standard blood lactate response curve.

The total training load of the groups in this study was determined using the TRIMPS model. Pretreatment (year 1) demonstrated no difference in the annual training load in TRIMPS between the two groups (control = 87,326 ± 2,345 and treatment = 88,278 ± 2,635; P > 0.05). For year 2, the control group showed no increase in TRIMPS whereas the treatment group increased significantly (P < 0.01). The increase in training load by the treatment group as determined via TRIMPS was a result of the increased high-intensity training hours and resulted in similar training loads to those estimated for elite world-class skiers. The increased training load imposed on the treatment group probably resulted in the observed physiological and competitive improvements. However, this study does not answer the question of whether the improvements were due solely to increased high-intensity training, the increased total training load, or to other motivational factors. The increase in high-intensity hours and the improved competitive results would seem to indicate a link between intensity training hours with performance. However, the possibility that any equivalent increase in total training load via either increased volume or intensity training hours would have resulted in similar improvements cannot be ruled out.

Of interest was the lack of improvement by the control group during year 2 even thought they increased their training to an average of 688 h annually, which parallels the recommendations made by the Norwegian national program for this age group. This 6% increase in volume, added entirely to low-intensity training with no increase in high-intensity training did not appear to stimulate improvements in competitive performance. The control group didn't increase their training load measured in TRIMP units as much as the treatment group (4,287 vs 13,745). These results suggest a need for large training load increases to yield improved performance.

When one reviews the year 2 data for the competition period found in Table 3, it is apparent that low-intensity training for the treatment group was less than that of the control group. Race zone (level 4) training hours were similar, but speed work (level 5) was three times greater for the treatment group. With speed work comes the need for increased recovery time. It is difficult to determine what influence speed work, recovery, or less low-intensity training had on performance; however, the combination of the three was effective for the treatment group.

An important training variable not adequately measured or recorded during this study was the quality of recovery for the two groups. During the second year, the treatment group was encouraged to be very careful about recovery between training sessions while on the high-intensity program. Although data entries on recovery routines and diet were incomplete from training logs, available data and athlete interviews suggest a better recovery program for the treatment group than for the control athletes.

Further longitudinal training research is necessary in order to adequately look at the effects of training volume and intensity manipulation. Multiple-year training program methodology must be carefully evaluated to account for individual response to training load.

This research provides some evidence that cross-country skiers may benefit from a program including a greater dose of high-intensity training than most current training paradigms. It is our belief that more research needs to be done to evaluate and understand the individual response to training in order to better target training recommendations for endurance athletes.

In any long-term training study, there are many variables that might affect the results. An attempt was made to control health, technique, equipment, motivational, and coaching variables by having all members coached within the same club and by giving all athletes equal attention. We believe the training was controlled as well as possible given the long-term nature of the study and the high-level performance of the athletes.

Cross-country skiers not responding to a traditional low intensity-high volume training program showed improvements in competitive and lab results when placed on an annual training program of decreased low-intensity volume (283 h vs 443 h), increased high-intensity volume (236 h vs 100 h), and an upper body power program incorporating 15-30 RM resistance training three times a week.

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REFERENCES

1. Acevedo, E. O. and A. H. Goldfarb. Increased training intensity effects on plasma lactate, ventilatory threshold, and endurance. Med. Sci. Sports Exerc. 21:563-568, 1989.
2. Bilodeau, B., B. Roy, and M. R. Boulay. Upper body testing of cross-country skiers. Med. Sci. Sports Exerc. 27:1557-1567, 1995.
3. Bompa, T. O. Theory and Methodology of Training: The Key to Athletic Performance. Dubuque, IA: Kendall/Hunt Publishing, 1983, pp. 63, 76, 132-140, 188-193.
4. Bouchard, C. Genetics of aerobic and anaerobic performance. Exerc. Sports Sci. Rev. 20:27-58, 1992.
5. Bouchard, C., M. Chagnon, M. C. Thibault, et al. Muscle genetic variants and relationship with performance and trainability. Med. Sci. Sports Exerc. 21:71-77, 1989.
6. Burgh, U., I-L. Kanstrup, and B. Ekblom. Maximal oxygen uptake during exercise with various combinations of arm and leg work. J. Appl. Physiol. 41:191-196, 1976.
7. Burgh, U., B. Sjodin, A. Forsberg, and J. Svedenhag. The relationship between body mass and oxygen uptake during running in humans. Med. Sci. Sports Exerc. 23:205-211, 1991.
8. Denis, C., and R. Fouquet. Effects of 40 weeks of endurance training on the anaerobic threshold. Int. J. Sports Med. 3:208-214, 1982.
9. Dionne, F. T., L. Turcotte, M. C. Thibault, M. R. Boulay, J. S. Skinner, and C. Bouchard. Mitochondrial DNA sequence polymorphism, VO2max, and response to endurance training. Med. Sci. Sports Exerc. 25:766-774, 1993.
10. Gaskill, S. E. Fitness Cross-Country Skiing. Champaign, IL: Human Kinetics Publishers, 1998, pp. 53-165.
11. Fleck, S. J., and W. Kraemer. Designing Resistance Training Programs, 2nd Edition. Champaign, IL: Human Kinetics Publishers, 1997, pp. 66-73.
12. Ingjer, F. Maximal oxygen uptake as a predictor of performance ability in women and men elite cross-country skiers. Scand J. Med. Sci. Sports 1:25-30, 1991.
13. Morton, R. H., J. R. Fitz-Clarke, and E. W. Bannister. Modeling human performance in running. J. Appl. Physiol. 69:1171-1177, 1990.
14. Rundell, K. W., and D. W. Bacharach. Physiological characteristics and performance of top U.S. biathletes. Med. Sci. Sports Exerc. 27:1302-1310, 1995.
15. Rusko, H. K. The effects of training on aerobic power characteristics of young cross-country skiers. J. Sports Sci. 5:273-286, 1987.
16. Rusko, H. K. Development of aerobic power in relation to age and training in cross- country skiers. Med. Sci. Sports Exerc. 24:1040-1047, 1992.
17. Rusko, H., P. Luthaned, P. Rahkila, J. Viitasalo, S. Rehunen, and M. Harkonen. Muscle metabolism, blood lactate and oxygen uptake in steady state exercise at aerobic and anaerobic thresholds. Eur. J. Appl. Physiol. 55:181-186, 1986.
18. Sharkey, B. Training for Cross-country Ski Racing. Champaign, IL: Human Kinetics Publishers, 1986, pp. 61-68, 123-126.
19. Simoneau, J. A., C. Bouchard. Genetic determinism of fiber type proportion in human skeletal muscle. FASEB J. 9:1091-1095, 1995.
20. Simoneau, J. A. and C. Bouchard. Human variations in skeletal muscle fiber-type proportion and enzyme activities. Am. J. Physiol. 257(4 Pt 1):E567-572, 1989.
21. Sleamaker, R. Serious Training for Serious Athletes. Champaign, IL: Leisure Press, 1989, pp. 24-26, 33, 38.
22. Street, G. M. and E. C. Frederick. Measurement of skier-generated forces during roller-ski skating. J. Appl. Biomech. 11:245-256, 1995.
23. Stromme, S. B., F. Ingjer, and H. D. Meen. Assessment of maximal aerobic power in specifically trained athletes. J. Appl. Physiol. 42:833-837, 1977.
24. Tanaka, K., and Y. Matsuura. A longitudinal assessment of anaerobic threshold and distance running performance. Med. Sci. Sports Exerc. 16:278-282, 1955.
25. Watts, P. B., M. D. Hoffman, J. E. Sulentic, et al. Physiological response to specific maximal exercise tests for cross-country skiing. Can. J. Appl. Physiol. 18:359-65, 1993.
Keywords:

OXYGEN UPTAKE; ANAEROBIC THRESHOLD; ARM POWER; LACTATE THRESHOLD

© 1999 Lippincott Williams & Wilkins, Inc.