Abstract
(Deutsch)
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Perceived exertion, heart rate, blood lactate, oxygen consumption and ventilation in trained men during hiking at 430, 1500 and 2700m asl
Maillat Cédric, Clénin German, Mäder Urs, Mahn Holger, Marti Bernard
Institute of Sports Sciences, Federal Office of Sports, CH-2532 Magglingen
Introduction
Hiking at moderate altitude has become increasingly popular in central Europe. Moderate altitude influences cardiorespiratory and metabolic responses even during submaximal exercise. The overall aim of this study was to investigate the effects of moderate altitude on walking speed, heart rate (HR), blood lactate, oxygen uptake and ventilation. More specifically, we examined (i) whether a given perceived exertion (PE) can keep the physiological effort constant at different altitudes, both on even ground and climbing steeply uphill, (ii) whether rising from 430 to 1500m corresponds to rising from 1500 to 2700m and (iii) whether HR-monitoring could be helpful to select appropriate hiking pace at moderate altitude.
Methods
17 healthy subjects (age 35.1 ± 4 years, BMI 23.6 ± 2.2 kg/m2, V02max 59 ± 6 mlmin-1kg-1) performed an outdoor trial, consisting of 5 different submaximal hiking stages of 6 minutes each (even ''moderate'' and ''fast'', paced 7.4 km/h, uphill ''moderate'' and ''fast'') at 430, 1500 and 2700m asl. For ''moderate'' stages, the subjects had to choose a speed they believed they could maintain for 8 hours, for ''fast'' stages a speed that could be maintained for 30 minutes. The mean inclination of the uphill slope was 17.4% at each altitude. During the tests, HR (Accurex Plus, Polar Electro Oy, Kempele, Finland) and spirometry (Metamax 3B, Cortex Biophysik, Leipzig, Germany) were registered; after each stage capillary blood lactate (Lactate Pro, Arkray Inc., Kyoto, Japan), PE (Borg Scale) and walking speed were measured. Except for the stage ''even paced'', subjects had to walk each stage with the same PE at all 3 altitudes. Means were analysed using a one-way analysis of variance for repeated measurements across altitude; significant differences (p<0.05) were located by the t-test.
Results
On even ground, subjects were able to maintain PE with increasing altitude by reducing speed (5.4, 5.18, 5.02 km/h for moderate [n.s.] resp. 7.47, 7.22, 6.71 km/h for fast [p<0.001]), keeping nearly constant HR (99, 95, 96 resp. 125, 119, 119 bpm), blood lactate (1.2 resp. 1.6, 1.5, 1.4 mmol/L) and ventilation (33.2, 29.4, 33.2 resp. 53.6, 49.4, 55.6 L/min), but decreasing oxygen uptake for both moderate and fast stage (17.9, 15.5 and 15.7 mlmin-1kg-1 [p<0.001] resp. 28.9, 26.4 and 23.9 mlmin-1kg-1 [p<0.001]).
On uphill stages, subjects failed to maintain PE: at uphill moderate walking, PE rose (11.3 to 11.7, 12 Borg-units [p=0.01]), due to lack of speed reduction (3.96, 3.82, 3.93 km/h); thus blood lactate (1.3, 1.4, 1.7 mmol/L [p=0.01]), HR (124, 129, 138 bpm [p<0.001]) and ventilation (55, 57.6, 70.2 L/min [p<0.001]) rose, with oxygen uptake remaining nearly constant (30.7, 32.2 and 31.9 mlmin-1kg-1). At fast uphill walking, subjects reduced speed (6.13, 5.8, 5.58 km/h [p<0.001]), but PE (15.4, 16, 15.8 Borg-units [p=0.01]) rose, blood lactate (4.9, 4.9, 5.4 mmol/L [n.s.]) staying nearly constant and unchanged HR (171, 171, 170 bpm); however, ventilation rose clearly from 430 to 2700m (109.2, 112.6, 127.3 L/min [p<0.001]), without avoiding a significant fall in oxygen uptake (52, 50.5, 43.9 mlmin-1kg-1, [p<0.001]).
Walking on even ground with 7.4 km/h at 430 and 1500m showed almost identical results (HR 122 vs.121 bpm, lactate 1.4 vs.1.5 mmol/L, PE 12.1 vs. 12.1 Borg-units, oxygen uptake 27.4 vs. 27.3 mlmin-1kg-1, ventilation 51.9 vs. 51.4 L/min). However, the ascent to 2700m asl increased HR (128 bpm, [p=0.01]), lactate (1.8 mmol/L [p=0.01]), PE (12.6 Borg-units [p=0.05]) and ventilation (64.4 L/min [p<0.001]), causing a constant oxygen uptake (27 mlmin-1kg-1).
Discussion and Conclusion
Hikers can control PE at moderate altitude on even ground fairly well by reducing speed and thus keep the physiological strain constant. However, during uphill walking PE tends to be greater than anticipated, especially at moderate speed where HR and ventilation increase significantly with higher altitude. At fast speed, HR remains noticeably constant but ventilation increases significantly. Thus the inclination of steep slopes seems to multiplicate the effects of altitude.
The ascent from 430 to 1500m affects physiological responses to even walking with 7.4 km/h less than the one from 1500 to 2700m. Moreover, ventilation shows the strongest reaction to altitude.
This study shows a largely parallel pattern of HR and PE; therefore HR-monitoring is a suitable approach for selecting appropriate hiking pace also at moderate altitude, especially when steep slopes are involved at the very beginning of the effort.
Acknowledgement
This study was supported by Polar Electro Oy, Kempele, Finland
Field evaluation of energy expenditure using heart rate during acute exposure to moderate and high altitude
Mäder Urs, Maillat Cédric, Clénin German, Mahn Holger, Marti Bernard
Institute of Sports Sciences, Federal Office of Sports, 2532 Magglingen, Switzerland
Introduction
It is well known that acute exposure to moderate and high altitude modulates heart rate (HR) during exercise. Polar (Polar Electro Oy, Finland) developed a method (AXN) to estimate energy expenditure (EE) by HR taking into account the influence of altitude during acute exposure and especially after acclimatization. The objective of this study was to determine the accuracy of AXN-estimates during acute exposure to moderate (430 and 1500 m) and high (2700 m above sea level) altitude.
Methods
17 healthy men (age 35.1 ± 4 years, BMI 23.6 ± 2.2 kg/m2, V02max 59 ± 6 ml/min/kg) performed an outdoor trial, consisting of 5 different submaximal hiking stages of 6 min each; even ''moderate'', ''fast'' and "paced"
(7.4 km/h), uphill ''moderate'' and ''fast'' at 430, 1500 and 2700 m above sea level. For ''moderate'' stages, the subjects had to choose a speed they believed they could maintain for 8 h and for ''fast'' stages a speed that could be maintained for 30 min. Except for the stage ''even paced'', subjects had to walk each stage with the same perceived exertion at all 3 altitudes. The mean inclination of the uphill slope was 17.4% at each altitude. During the tests, HR (Polar Accurex+, Polar Electro Oy, Kempele, Finland), oxygen uptake and carbon dioxide production (MetaMax3B, Cortex Biophysik, Leipzig, Germany) were registered. Intraclass correlations were calculated for pooled values of each altitude to assess the strength of the relationship of the two methods. Paired sample t-tests were performed to test for significant differences between EE calculated by AXN-formula and EE measured by indirect calorimetry for each activity. Bland-Altman plots were used to assess agreement of the two measures. Accepted level of significance was set at p < 0.05.
Results
Correlations between the two measures of EE were high; r = 0.94, 0.93, and 0.95 for all activities at 430, 1500 and 2700 m above sea level, respectively. In-group mean values of EE determined by both methods were similar for all activities at both levels of moderate altitude except at 430 m for uphill fast (mean difference: 0.77 kcal/min, p = 0.04). Significant differences were found at high altitude (2700 m) for even moderate (1.11 kcal/min, p = 0.019), even paced (-0.65 kcal/min, p = 0.047), uphill moderate (-0.92 kcal/min, p = 0.01), and uphill fast (-0.89 kcal/min, p = 0.03). Bland-Altman technique shows agreement between the two methods (Fig. 1).
Fig. 1: Bland-Altman plots depicting error scores for energy expenditure for all 3 different levels of moderate altitude.
Discussion and Conclusion
Average values indicated that using the AXN-formula is a reliable method to determine EE at acute exposure to moderate altitude. However, EE estimated by AXN-formula and measured by indirect calorimetry may differ substantially for a few individuals during hiking at various levels of intensity. At high altitude, AXN-formula slightly underestimated EE during moderate activity, while estimates during vigorous activities were slightly higher compared to values of indirect calorimetry.
It can be concluded that during acute exposure to moderate altitude the accuracy of AXN-estimates for EE is good. At high altitude, using AXN-formula before acclimatization might be less accurate in some individuals.
Acknowledgements
This study was supported by Polar Electro Oy, Kempele, Finland
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