Dr.Biol., Professor S.I. Loginov
PhD A.S. Kintyukhin
Associate Professor, PhD M.N. Mal'kov
Postgraduate student S.G. Sagadeeva
Surgut State University, Surgut

Keywords: rated walking, treadmill, HR, oxygen demand, ventilatory equivalent, linear regression equations, students.

Background. It was around half a century ago that R.-O. Astrand and B. Saltin [3] found that ventilator equivalent Ve logically grows with the physical loads and, hence, may be used as an indirect indicator of energy cost (EC) of physical loads [8]. Actually Ve is known to correlate with oxygen demand VО₂ as described by the formula: VО₂ = Ve × inO₂, – exO₂, with inO₂ meaning the inspiratory O₂ rate and exO₂ – meaning the expiratory O₂ rate [8]. In case of moderate-intensity loads with the ventilatory equivalent rate varying under 50 l/ min, the VO₂ is known to keep in linear correlation with the ventilatory equivalent rate [5]. These regularities are still valid albeit some qualitative adjustments are needed to provide for the environmental conditions, lifestyles and the dramatic sag in the human physical activity [1, 2].

Objective of the study was to find effects of the variable-speed walking practices on the cardiorespiratory system performance rates in the young people (students) residing in the Yugra North area.

Methods and structure of the study. Subject to the study were students and masters (n=25) of Surgut State University aged 22.1±2.6, including 12 men and 13 women. Neither of the subjects was diagnosed with contraindications for the physical tests, and every subject gave his/ her informed consent for the tests. The subjects were tested with the interval (5 min) Torneo treadmill walking tests at 2, 3, 4, 5, 6 and 7 km/h walking speeds to assess the load effects on the cardiorespiratory system performance rates, the test sessions taking 30 min on the whole. СOSMED (Italy-made) Fitmate Pro metabolimeter was used to test the respiratory system performance and basal metabolism. The tests were used to obtain the respiratory rate (RR, exp/min) oxygen demand (VO₂, ml/min) rate, ventilatory equivalent (Ve, l/min), expiratory oxygen rate (exO₂, %) and heart rate (HR, bpm). The VO₂, Ve and HR data were averaged every 15 seconds, downloaded to computer for presentation and stored in the database for further detailed analysis. Prior to the tests, anthropometric data of the subjects were obtained, including leg length (cm), body height (cm) and body mass (kg). The data arrays were processed using the standard statistical tools of Statistica v.10 software package (made by StatSoft, USA), followed by preliminary normality assessments and calculations of the mean arithmetic value (Х), mean square deviation (SD), 0.95-level confidence interval (±0,95 CI) and data correlation and regression analyses. A two-way t-test of the correlated and non-correlated groups plus Wilcoxon matched pairs tests and Mann-Whitney tests were used to rate the significance of the data differences, with the difference rated significant at p≤0.05.

Study results and discussion. Men in the tested sample showed higher anthropometric measurements than the women and differed in age from the latter (see Table 1). The oxygen demand was found to significantly grow (t test, p <0.05) with the growth in the treadmill test starting from 3 km/h. At the speed of 4 km/h, the HR, Ve and VО₂ were on the rise, whilst the respiratory rate (RR) showed some growth starting from 5 km/h, with the expiratory oxygen rate exО₂ showing no significant variations (see Table 2).

Table 1. Anthropometric measurements of the tested students (n=25), X±SD

Table 2. Cardiorespiratory system performance variation with the walking speed in the treadmill test (n=25) X±SD

*Men vs. women data difference significant at p <0.05

The relative oxygen demand rate in the young men and women was found to correlate with the HR (r=0.7; p =0.0000). The VO₂ variation with the HR in the young men and women was described by the following equations for men and women, respectively: VО₂=-10.2 + 0.2HR; and VО₂=-3.04 + 0.2HR (r=0.7; p =0.0000) where the VО₂ means the relevant oxygen demand rate (in ml/ kg/ min) and -10,2 and 0,2 are the empirical ratios (see Figure 1). The study found the ventilatory equivalent rate Ve being in clear correlation with HR as described by the following regression equations for men and women, respectively: Ve = 4.272 + 0.2086HR; and Ve = 1.8346 + 0.2242 HR (r=0.5; p=0/0000), see Figure 2. And the oxygen demand rate VО₂ variation with the ventilatory equivalent rate Ve was described by the following equations: VО₂ = -12.9 + 40.3 Ve (r=0.98; p=0.0000) for men; and VО₂ = 116.3 + 34.7 Ve for women (r=0.97; p=0.0000), see Figure 3. On the whole, the test data given hereunder in Figures 2 and 3 clearly demonstrate the ventilatory equivalent rate Ve in the variable-speed treadmill walking tests of the Surgut University students being in a closer correlation with the VО₂ rates (r= 0.98; p=0.0000) than with the HR (r=0.5; p=0.0000).

Figure 1. Relative oxygen demand rate (VO₂, ml/kg/min) variation with heart rate (HR, bpm) in the 2-7 km/ h treadmill walking tests of men (А) and women (B)

Figure 2. Ventilatory equivalent rate (Ve, l/min) variation with heart rate (HR, bpm) in the 2-7 km/ h treadmill walking tests of men (А) and women (B)

Figure 3. Oxygen demand rate (VО₂, ml/min) variation with heart rate (HR, bpm) in the 2-7 km/ h treadmill walking tests of men (А) and women (B)

Physical activity dominated by contractions of skeletal muscles is known to claim the highest energy costs and be the most variable component of human bioenergetics [4, 5, 9]. Precise measurements of energy costs of physical activity are always challenging, particularly in cases of irregular activity [8]. To precisely rate energy costs of physical loads, one needs to know the oxygen demand per time unit per kilo of body mass. The ventilatory equivalent rate may be recommended as a much simpler measure for such rating tests since it is more closely connected with the oxygen demand variations than the HR under varied-intensity physical loads.

The above correlation is described by the following equations: VО₂ = -12.9 + 40.3 Ve (r=0.98; p=0.0000) for men; and VО₂ = 116.3 + 34.7 Ve for women (r=0.97; p=0.0000). It should be noted that the similar data were obtained by S. Gastinger et al. (2010) who used the 6 minute treadmill walking tests to find the VО₂ rates being in close correlation with the ventilatory equivalent rates Ve (r=0.94; p<0.001) as described by the following linear regression equation: VО₂=63.2+44.1 Ve where VО₂ means the oxygen demand rate (ml/min), Ve means the ventilatory equivalent rate (l/min), and 63,2 and 44,1 mean the empirical ratios [6, 7].

Conclusion. The regression equations obtained by the study could be applied to manage physical loads in the health-improvement trainings and academic physical practices of university students in the Yugra North areas. The test procedure may include dry spirometric tests to obtain the ventilator equivalent rate per minute followed by the above formula being applied to obtain the oxygen demand rate. Further studies are needed to define more exactly the empirical ratios with a broader sample of Northerners being tested with due account of the subjects’ age structure and body mass indices. 

References

1. Loginov S.I. Fizicheskaya aktivnost': metody ocenki i korrekcii. Surgut: SSU (SurGU) pub. h-se, 2005. 342 p.
2. Loginov S.I., Kozlova V.V., Gorlenko V.A., El'nikov A.V. Vliyanie fizicheskih uprazhnenij na parametry kardiorespiratornoj sistemy zhenshchin i muzhchin vtorogo zrelogo vozrasta v usloviyah HMAO-YUgry. // Teoriya i praktika fizicheskoy kultury. 2013. №11. P. 88-92.
3. Astrand P.-O., Saltin B. Maximal oxygen uptake and heart rate in various types of muscular activity. // J. Appl. Physiol. 1961. V. 16. P. 977-981.
4. DeLany J.P., Kelley D.E., Hames K.C., Jakicic J.M., Goodpaster B.H. Effect of physical activity on weight loss, energy expenditure, and energy intake during diet induced weight loss. // Obesity (Silver Spring). 2014. V. 22. N 2. P. 363-370. doi: 10.1002/oby.20525.
5. Fair A.M., Montgomery K. Energy balance, physical activity, and cancer risk. // Methods Mol. Biol. 2009. V. 472. P. 57-88. doi: 10.1007/978-1-60327-492-0_3.
6. Gastinger S., Nicolas G., Sorel A., Sefati H., Prioux J. Energy expenditure estimate by heart-rate monitor and a portable electromagnetic coils system. // Int. J. Sport Nutr. Exerc. Metab. 2012. V.22. N 2. P. 117-130.
7. Gastinger S., Sorel A., Nicolas G., Gratas-Delamarche A., Prioux J. A Comparison between Ventilation and Heart Rate as Indicator of Oxygen Uptake during Different Intensities of Exercise // J. Sports Sci. Med. 2010. V. 9, N 1. P. 110-118.
8. Saltin B., Astrand P.-O. Maximal oxygen uptake in athletes. J. Appl. Physiol. 1967. V. 23, N 3. P. 353-358.
9. Wasserman K., Beaver W.L., Whipp B.J. Gas exchange theory and the lactic acidosis (anaerobic) threshold. // Circulation. 1990. V. 81. P. 14-30.

Corresponding author: apokin_vv@mail.ru

Abstract         

Subject to the study were 12 male and 13 female students (n=25) aged 22.1±2.6 years who were tested with the interval (5 min) treadmill walking tests at 2-7 km/h walking speeds to rate the physical load effects on the cardiorespiratory system performance rates. СOSMED (Italy-made) Fitmate Pro metabolimeter and a heart rate (HR) test system were used to obtain the oxygen demand (VO₂, ml/min) rate, ventilatory equivalent (Ve, l/min), expiratory oxygen rate (exO₂, %) and heart rate (HR, bpm). The study found the subject rates growing with the rising walking speeds (time test, p <0.05) with the only exclusion for exO₂ rates that showed insignificant variations. The VO₂ variation with the HR was described by the following equations for men and women, respectively: VО₂=-10.2 + 0.2HR; and VО₂=-3.04 + 0.2HR (r=0.7; p =0.0000). The Ve variation with the HR was described by the following regression equations for men and women, respectively: Ve = 4.272 + 0.2086HR; and Ve = 1.8346 + 0.2242 HR (r=0.5; p=0/0000). And the VО₂ variation with the Ve was described by the following equations: VО₂ = -12.9 + 40.3 Ve (r=0.98; p=0.0000) for men; and VО₂ = 116.3 + 34.7 Ve for women (r=0.97; p=0.0000). Therefore, the Ve rates in the variable-speed treadmill walking tests were found to be in closer correlation with the VО₂ rates (r= 0.98; p=0.0000) than with the HR (r=0.5; p=0.0000) that gives us the grounds to recommend the VО₂ f (Ve) function as an energy cost measure in the student group practices.