Discrepancy between cardiorespiratory system and skeletal muscle in elite cyclists after hypoxic training
- Ryotaro Kime1, 2Email author,
- Trine Karlsen3,
- Shoko Nioka1,
- Gwen Lech1,
- Ørjan Madsen3,
- Rolf Sæterdal^,
- Joohee Im1,
- Britton Chance1 and
- James Stray-Gundersen3, 4
© Kime et al; licensee BioMed Central Ltd. 2003
Received: 07 February 2003
Accepted: 22 August 2003
Published: 22 August 2003
The purpose of this study was to determine the effects of hypoxic training on the cardiorespiratory system and skeletal muscle among well-trained endurance athletes in a randomized cross-over design.
Eight junior national level competitive cyclists were separated into two groups; Group A trained under normoxic condition (21% O2) for 2 hours/day, 3 days/week for 3 weeks while Group B used the same training protocol under hypoxic condition (15% O2). After 3 weeks of each initial training condition, five weeks of self-training under usual field conditions intervened before the training condition was switched from NT to HT in Group A, from HT to NT in Group B. The subjects were tested at sea level before and after each training period. O2 uptake ( O2), blood samples, and muscle deoxygenation were measured during bicycle exercise test.
Results and Discussion
No changes in maximal workload, arterial O2 content, O2 at lactate threshold and O2max were observed before or after each training period. In contrast, deoxygenation change during submaximal exercise in the vastus lateralis was significantly higher at HT than NT (p < 0.01). In addition, half time of oxygenation recovery was significantly faster after HT (13.2 ± 2.6 sec) than NT (18.8 ± 2.7 sec) (p < 0.001).
Three weeks of HT may not give an additional performance benefit at sea level for elite competitive cyclists, even though HT may induce some physiological adaptations on muscle tissue level.
KeywordsHypoxia Training Athletes NIRS Muscle oxygenation
High altitude training (HAT) is used by many athletes for the purpose of enhancing performance. The scientific theory behind HAT is related to the fact that exposure to high altitude produces an increase in red blood cell (RBC) mass and hemoglobin (Hb) concentration, thereby enhancing the blood's oxygen transport capacity [1, 2]. In addition, HAT has been shown to increase skeletal muscle capillarization[3, 4]. A number of favorable physiological changes have also been observed within the skeletal muscle microstructure as a result of HAT. These changes include increased concentration of myoglobin (Mb) , increased mitochondrial oxidative enzyme activity , and a greater number of mitochondria .
In contrast, however, some studies have reported that endurance performance was not much improved by HAT compared with sea level training [6, 7]. Moreover, Levine and Stray-Gundersen insisted that HAT would lead to down regulation of muscle structure and function associated with reduced power output and reduced O2 flux . The reasons for these divergent results may include the differences in exercise type, training intensity, training period and training altitude. Also, the subjects of HAT studies are usually divided into groups and then compared as to the effects of hypoxic training and normoxic training. Therefore, substantial interindividual variability in the adaptive response to HAT is involved in these studies . To our knowledge, there is no formal study that reported the effects of HAT among identical subjects in athletes.
Recently, near infrared continuous wave spectroscopy (NIRcws) technology has been updated and widely applied for the evaluation of muscle tissue oxygenation [9, 10]. Muscle oxygenation as observed by NIRcws is considered to reflect the balance between O2 consumption and O2 supply, as demonstrated by its gradual decrease during incremental exercise, and by its dramatic increase after whole body exercise [9, 11, 12]. If the HAT improves muscle capillarization and/or mitochondrial oxidative capacity, muscle oxygenation during and after exercise should be modified by HAT. The purpose of this study was to determine the effects of hypoxic training on the cardiorespiratory system and skeletal muscle among well-trained endurance athletes in a randomized cross-over design.
The subjects for this study were eight junior national level competitive young cyclists in Norway. The group included one female and seven male athletes (age: 17 ± 1 year, height: 180 ± 5 cm, weight: 70.6 ± 7.8 kg). Subjects gave their informed consent after obtaining all the information they requested concerning this study. To avoid acclimatization in hypoxic condition, the subjects lived at sea level and trained under normoxic and simulated hypoxic conditions. It is reported that some competitive athletes have a serum ferritin level that is suggestive of reduced bone marrow stores [17, 18]. When such athletes attempt hypoxic training, they often do not thrive, and clearly do not increase erythrocyte volume or O2max. Therefore, all the subjects took iron supplement during the study. The subjects took liquid iron supplementation during the study.
We simulated HC in the training room by replacing O2 gas in the room air with N2 gas. HT was performed in the room at ambient fractional O2 concentration of 15 % (corresponding to an altitude of approximately 2500 m). O2 concentration in the room was maintained by the system's feed back mechanism which activated a fan that brought in fresh air from the outside whenever the O2 concentration in the room was lower than the O2 set point in the system. CO2 gas in the room was also monitored and the CO2 built up in the room was reduced by using CO2 scrubber. Several air conditioning systems ensured that there were no changes in room temperature and humidity during the training session. The complete set up for simulating normobaric hypoxia in the room was evaluated and approved for use with humans by a Norwegian governmental safety organization.
Bicycle exercise test was performed at sea level within one week before and after each training period for evaluating training effects. Subjects had a brachial arterial line and then rested for one hour prior to exercise. After the resting blood samples were taken, subjects moved on to the stationary bike (Lode, Netherlands).
Expired gas was collected into Douglas bags. Gas fractions from the Douglas bag were measured by mass spectrometer (Ametec process & analytic instruments Division, USA). [La] was analyzed from arterial blood samples immediately following each exercise stage. A heart rate monitor was fitted around the chest of each subject for the biotelemetry of the heart rate. Arterial oxygen saturation was measured by pulseoximetry. Muscle oxygenation of vastus lateralis (VL) was monitored using NIRcws. The muscle oxygenation was measured after each training period but not before each training period.
Plasma volume was measured by using the Evans blue dye indicator-dilution technique. After the subject rested in a supine position for 30 min, a baseline blood sample was drawn and a known quantity of Evans blue dye was injected. Venous blood was drawn 10, 20 and 30 min after injection of the dye. Samples were spun and measurements of absorbance were taken at 620 and 740 nm by spectrophotometry (UV-1202, Shimadzu, Japan). Hematocrit was measured by averaging five runs on a Sysmex K-1000 total blood analyzer (TOA Medical Electronics, Japan). Blood volume was estimated by dividing plasma volume using one minus hematocrit; appropriate corrections were used for trapped plasma and peripheral sampling. Total red cell volume was defined as blood volume minus plasma volume. Hb concentration was measured from a 3 ml sample of venous blood in an EDTA-vacutainer, and it was measured with the same analyzer as hematocrit. Ferritin was measured on plasma samples taken before and after each training period by an immuno turbidimetric method (Modular P, Roche, Swiss).
Oxygenation of the vastus lateralis muscle was measured by NIRcws (HEO-100, OMRON, Japan). The basic principle of this NIRcws device has been discussed in detail in previous studies [9, 11, 13]. The NIRcws probe contains a light source and an optical detector, with a distance of 3.0 cm between the light source and the detector. Thus, the depth of penetration is evaluated to be ~1.5 cm, as extensively discussed previously [14, 15]. A pair of two-wavelength light emitting diodes, with wavelength of 760 and 850 nm, were used as the light source. A silicon photodiode was used as the photodetector. In this study, oxygenated Hb and/or Mb changes (ΔOxy-Hb/Mb) and total Hb changes (ΔTotal-Hb) were calculated using the algorithm reported previously . Also, deoxygenated Hb/Mb (Δ[Hb/Mb]), and muscle tissue deoxygenation (Δ[Deoxy]) were calculated by Δ[Total-Hb] - Δ[Oxy-Hb/Mb] and Δ[Hb/Mb] - Δ[Oxy-Hb/Mb], respectively.
In NIRcws measurements, the absolute O2 concentration or saturation determination is difficult because of unquantifiable biophysical quantities such as optical path length . In muscle oxygenation measurement, a subctaneous fat layer greatly affects the detected light intensity . As the fat layer thickness varies greatly in humans, optical densities of Δ[Total-Hb] and Δ[Oxy-Hb/Mb] cannot be compared between individuals. In this study, therefore, relative deoxygenation change at each stage during Submaximal (%d [Deoxy]) was normalized by the full deoxygenation during Vmax at each test. The %d [Deoxy] was evaluated during the last 30 sec of each stage. The muscle oxygenation recovery was taken from the maximal deoxygenation measured over the last few seconds of exercise and the minimum deoxygenation measured in the overshoot recovery. Half time reoxygenation (T1/2), the time to reach a value of half-maximal recovery, was determined after Submaximal. The probe was firmly attached to the skin overlying the lower one-third of VL muscle (~12 cm from the top of patella). No sliding was observed in any subjects.
Since Mb has similar absorption spectra to Hb, NIRS signal gives mixed information of both Hb and Mb. However, it is reported that Mb concentration is no greater than 25%  or 20% . Therefore, we can conclude that the signals are derived mainly from Hb. The specific probe position was recorded as the distance from the top of the patella in the first experiment in December, and the probe was placed at exactly the same location for each test after December.
The results are presented as mean value ± standard error (SE). The hematological assessments and measurements parameters during Vmax test were statistically analyzed with one-way ANOVA. The HR, [La] and %d [Deoxy] at Submaximal were compared by two-way ANOVA (time and training). The monitored parameters during each training and T1/2 after Submaximal were compared by paired t-test. Statistical significance was set at p < 0.05 for all comparisons.
Normoxic and hypoxic training
Measured parameters during each training
245 ± 15
206 ± 13*
96 ± 0.4
84 ± 1.2*
163 ± 3
160 ± 3
2.9 ± 0.1
3.2 ± 0.1
HB Concentration (g/dl)
14.4 ± 0.3
14.4 ± 0.3
14.3 ± 0.2
14.4 ± 0.2
Blood volume (ml/kg)
82.9 ± 1.7
86.0 ± 3.2
86.7 ± 2.1
83.1 ± 3.6
Plasma volume (ml/kg)
53.7 ± 1.7
55.7 ± 2.4
56.1 ± 1.6
54.0 ± 2.7
40.1 ± 1.1
39.3 ± 1.3
39.8 ± 0.7
39.4 ± 0.8
19.8 ± 0.4
19.7 ± 0.3
19.5 ± 0.3
19.7 ± 0.2
29.2 ± 0.5
30.4 ± 1.2
30.6 ± 0.6
29.1 ± 1.1
36.0 ± 3.5
35.8 ± 5.4
38.5 ± 4.9
44.7 ± 7.6
Systemic parameters measured during exercise test
Muscle tissue O2dynamics
The major finding of this study was that HT induced more deoxygenation and faster reoxygenation after Submaximal than NT. However, neither blood nor expired gas parameters were changed before and after each training period. These results suggested that three weeks HT may not give an additional performance benefit at sea level for elite competitive cyclists, even though HT may induce some physiological adaptations on muscle tissue level.
One of the most important adaptations in HT is considered to be an increase in Hb concentration and Hct, which increases the O2 delivery and improves aerobic capacity [1, 2, 8]. For this endogenous adaptation (i.e. Hb increase), serum ferritin concentration is decreased. However, the ferritin concentration did not decrease after HT (Table 2). Also, Hb concentration and Hct were not increased by HT either. These results suggest that only two hours of hypoxic exposure and/or training per day may not be sufficient to elicit erythropoiesis, thereby producing no improvements of Hb concentration and CaO2. This may be the main reason why the cardiorespiratory system (i.e. maximal O2 uptake) was not improved by HT.
The [La] during Submaximal was not significantly different between each training period even though %d [Deoxy] was significantly higher in HT than NT (Fig. 2). Brooks  already stated that [La] is determined by the size of the lactate pool in the blood such as its distribution throughout the body, its oxidation in the muscle, and its conversion to glycogen in the liver and muscle. In other words, [La] is reflected as the balance between blood lactate appearance and blood lactate clearance. Donovan and Brooks  found no significant effects of training on blood lactate appearance during exercise, but lower [La] was observed in trained subjects during exercise as a result of enhanced clearance capacity. In this study, training intensity was adjusted at LT level in each NT and HT, and [La] during training was very similar between each training period (Table 1). Therefore, as the training intensity was adjusted by [La], enhanced blood lactate clearance capacity (lactate turnover and oxidation) cannot be attributed to HT.
Effects of hypoxic training on muscle tissue level
In this study, higher muscle deoxygenation during the test and faster T1/2 after the test were found in post-HT than in post-NT (Fig. 4). One possibility may be due to down regulation of skeletal muscle structure and function by reduced absolute training workload in HT. Since relative exercise stress was the same in HT and NT, absolute workload was significantly lower in HT than NT (p < 0.01, Table 1). We expected to see that decreased work intensity might have resulted in the athletes being detrained when they returned to sea level, and thus may have adversely affected performance [1, 2, 8]. Although not significantly different, peak power during Vmax test in post-HT was 13 W less than pre-HT and post-NT (Table 3). If muscle atrophy happened after HT, reoxygenation time would be fast due to increase in capillary density and decrease in diffusion distance. Also, muscle atrophy may be related to relative deoxygenation change (%d [Deoxy]) during exercise. %d [Deoxy] was normalized by the full deoxygenation during Vmax at each test, and Submaximal was set at absolute same work intensity in all tests. Therefore, if peak power were to be slightly decreased, then the same workload would cause more deoxygenation. In other words, %d [Deoxy] during the same workload may be higher in post-HT than in post-NT if muscle atrophy happens.
Another possible explanation, quite different from the one above, may be due to up regulation of skeletal muscle structure and function by HT. In a number of studies an increased capillary network [3, 4, 21] and an elevated oxidative potential of skeletal muscles, including myoglobin content , mitochondrial content [3, 21], and oxidative enzyme activities , have been reported to accompany hypoxic training. Also, it is well known that endurance training improves muscle O2 extraction during submaximal exercise as demonstrated by a lower venous femoral PO2 [22, 23]. Therefore, it is suggested that O2 extraction may be improved in activating muscle during Submaximal caused by HT. In addition, we observed that T1/2 after Submaximal was significantly faster post-HT than post-NT (p < 0.001, Fig. 4). As we used bicycle exercise, which elicits a greater increase in cardiac output and blood flow to the working muscle, it is speculated that the T1/2 after this type of exercise may more reflect the "washing" of O2 supply than more than O2 consumption . Therefore, faster T1/2 seen after HT implies that O2 supply to the activating muscle may be much higher. Further NIRcws studies are needed to define the conclusions for up or down regulation of muscle function by HT.
Discrepancy between cardiorespiratory system and skeletal muscle after HT
We found that blood and expired gas parameters were not changed by HT even though HT may cause some adaptations on muscle tissue level. Some HT studies have also reported that HT did not improve cardiorespiratory system (maximal O2 uptake) but muscle oxidative capacity, which was determined by phosphocreatine resynthesis rate  and mitochondrial volume density and capillary length density . Although we cannot conclude whether or not HT caused up or down regulation on muscle function, three weeks of HT had no effect on the gain of cardiorespiratory system in either case.
Limitations of the study
It is important to note that the sample size (n = 8) was too small to apply our findings to a larger population. Certainly more data should be collected in order to generalize the findings obtained in this study.
Training effects evaluated by NIRcws were compared only for post-training in each subject because baseline data of muscle deoxygenation and reoxygenation were not measured in pre-training periods. However, all subjects trained in both HC and NC. Also, five weeks of self-training under usual field conditions was implemented as a washout period after each training period. Several studies have reported that any improvements due to HT diminish very rapidly upon due to acclimatization at sea level [1, 4, 5]. Furthermore, it is reported that cardiorespiratory and muscle oxidative functions are adapted to variable levels of energy demands within a few weeks [26, 27]. Hence, if the muscle oxidative capacity and capillarization were improved by each training, the improved muscle oxidative function may have been diminished by the time of another baseline test in January.
Three weeks of HT and NT did not improve performance, arterial O2 content, O2@LT or O2max in endurance athletes. In contrast, deoxygenation change during exercise in the vastus lateralis was higher after HT than NT. Furthermore, half time of reoxygenation was faster after HT than NT. These results suggest that three weeks HT may not give an additional performance benefit at sea level for elite competitive cyclists, even though HT may induce some physiological adaptations on muscle tissue level.
The authors are grateful to the experimental subjects for participating in this study. They also would like to acknowledge Yuanqing Lin for his expert technical assistance and Eric Sell for his invaluable comments.
- Stray-Gundersen J, Chapman RF, Levine BD: "Living high-training low" altitude training improves sea level performance in male and female elite runners. J Appl Physiol. 2001, 91: 1113-1120.PubMedGoogle Scholar
- Levine BD, Stray-Gundersen J: The effects of altitude training are mediated primarily by acclimatization, rather than by hypoxic exercise. Adv Exp Med Biol. 2001, 502: 75-87.PubMedView ArticleGoogle Scholar
- Desplanches D, Hoppeler H, Linossier MT, Denis C, Claassen H, Dormois D, Lacour JR, Geyssant A: Effects of training in normoxia and normobaric hypoxia on human muscle ultrastructure. Pflügers Arch. 1993, 425: 263-267.PubMedView ArticleGoogle Scholar
- Mizuno M, Juel C, Bro-Ramusen T, Schibye B, Rasmussen B, Saltin B: Limb skeletal muscle adaptation in athletes after training at altitude. J Appl Physiol. 1990, 68 (2): 496-502.PubMedGoogle Scholar
- Terrados N, Janson E, Sylven C, Kaijser L: Is hypoxia a stimulus for synthesis of oxidative enzyme and myoglobin?. J Appl Physiol. 1990, 68 (8): 2369-2372.PubMedGoogle Scholar
- Bailey DM, Davis B, Romer L, Castell L, Newsholme E, Candy G: Implication of moderate altitude training for sea-level endurance in elite distance runners. Eur J Appl Physiol. 1998, 78: 360-368. 10.1007/s004210050432.View ArticleGoogle Scholar
- Telford AD, Graham KS, Sutton JR, Hahn AG, Campbell DA, Creighton SW, Cunningham RB, Davis PG, Gore CJ, Smith JA: Medium altitude training and sea-level performance. Med Sci Sports Exerc. 1996, 28: S124-View ArticleGoogle Scholar
- Chapman RF, Stray-Gundersen J, Levine BD: Individual variation in response to altitude training. J Appl Physiol. 1998, 85 (4): 1448-1456.PubMedGoogle Scholar
- McCully KK, Hamaoka T: Near-infrared spectroscopy: What can it tell us about oxygen saturation in skeletal muscle?. Exer and Sport Sci Rev. 2000, 28 (3): 123-127.Google Scholar
- Boushel R, Piantadosi CA: Near-infrared spectroscopy for monitoring muscle oxygenation. Acta Physiol Scand. 2000, 168 (4): 615-622. 10.1046/j.1365-201x.2000.00713.x.PubMedView ArticleGoogle Scholar
- Chance B, Dait TM, Chang C, Hamaoka T, Hagerman F: Recovery from exercise induced desaturation in the quadriceps muscle of elite competitive rowers. Am J Physiol. 1992, 262: C766-C775.PubMedGoogle Scholar
- Hamaoka T, Albani C, Chance B, Iwane H: A new method for the evaluation of muscle aerobic capacity in relation to physical activity measured by near infrared spectroscopy. Med Sport Sci. 1992, 37: 421-429.View ArticleGoogle Scholar
- Shiga T, Yamamoto K, Tanabe K, Nakase Y, Chance B: Study of an algorithm based on model experiments and diffusion theory for a portable tissue oximeter. J Biomed Opt. 1997, 2 (2): 152-161.View ArticleGoogle Scholar
- Delpy DT, Cope M, van der Zee P, Arridge S, Wrary S, Wyatt J: Estimation of optical pathlength through tissue from direct time of flight measurement. Phys Med Biol. 1998, 33: 1422-1442.Google Scholar
- Matsushita K, Homma S, Okada E: Influence of adipose tissue on muscle oxygenation measurement with NIRS instrument. Proc SPIE. 1997, 3194: 159-165.View ArticleGoogle Scholar
- Mancini DM, Bolinger L, Li H, Kendrick K, Chance B, Wilson JR: Validation of near-infrared spectroscopy in human. J Appl Physiol. 1994, 77: 2740-2747.PubMedGoogle Scholar
- Stray-Gundersen J, Mordecai N, Levine BD: O2 transport response to altitude training in runners. Med Sci Sports Exer. 1995, 27: S202-View ArticleGoogle Scholar
- Stray-Gundersen J, Hochstein A, Levine BD: Effect of 4 weeks altitude exposure and training on red cell mass in trained runners. Med Sci Sports Exer. 1997, 29: S136-View ArticleGoogle Scholar
- Brooks GA: Current concepts in lactate exchange. Med Sci Sports Exerc. 1991, 23: 895-906.PubMedView ArticleGoogle Scholar
- Donovan CM, Brooks GA: Endurance training affects lactate clearance, not lactate production. Am J Physiol. 1983, 244 (7): E83-92.PubMedGoogle Scholar
- Geiser J, Vogt M, Billeter R, Zuleger C, Belforti F, Hoppeler H: Training high-living low: Changes of aerobic performance and muscle structure with training at stimulated altitude. Int J Sports Med. 2001, 22: 579-585. 10.1055/s-2001-18521.PubMedView ArticleGoogle Scholar
- Roca J, Agusti AGN, Alonso A, Poole DC, Viegas C, Barbera JA, Rodriguez-Roisin R, Ferrer A, Wagner PD: Effects of training on muscle O2 transport at O2max. J Appl Physiol. 1992, 73 (3): 1067-1076.PubMedGoogle Scholar
- Kiens B, Essen-Gustavsson B, Christensen NJ, Saltin B: Skeletal muscle substrate utilization during submaximal exercise in man: effect of endurance training. J Physiol (Lond). 1993, 469: 459-478.View ArticleGoogle Scholar
- McCully KK, lotti S, Kendrick K, Wang Z, Posner JD, Leigh J, Chance B: Simultaneous in vivo measurements of HbO2 saturation and PCr kinetics after exercise in normal humans. J Appl Physiol. 1994, 77 (1): 5-10.PubMedGoogle Scholar
- Kuno S, Inaki M, Tanaka K, Itai Y, Asano K: Muscle energetics in short-term training during hypoxia in elite combination skiers. Eur J Appl Physiol. 1994, 69: 301-304.View ArticleGoogle Scholar
- Mujika I, Padilla S: Cardiorespiratory and metabolic characteristics of detraining in humans. Med Sci Sports Exerc. 2001, 33 (3): 413-421.PubMedView ArticleGoogle Scholar
- Mujika I, Padilla S: Muscular characteristics of detraining in humans. Med Sci Sports Exerc. 2001, 33 (8): 1297-1303.PubMedView ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.