Eur J Appl Physiol (1992) 65:409-414 European Journal of
Applied
Physiology and Occupational Physiology © Springer-Verlag 1992
Reliability of measurement of oxygen uptake by a portable telemetric system Yasuo Kawakamil, Daichi Nozaki 2, Akifumi Matsuo 1, and Tetsuo Fukunaga 1 1 Department of Sports Sciences, College of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo, Japan 2 Laboratory for Sports Sciences, Faculty of Education, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, Japan Accepted June 29, 1992
Summary. The purpose of the present study was to check the reliability of measurements of oxygen uptake (lkO2) using a newly developed portable telemetry system. This system (K2) consisted of a face mask, a flow meter, a gas analyser with a transmitter, and a receiver. The total mass for the subject to carry was about 850 g. Three experiments were carried out, firstly to check the reliability and reproducibility of the flow meter and the K2 gas analyser, secondly to check the accuracy of K2 by comparing it with the Douglas bag method (DB), and thirdly to apply K2 to sports activities. In the first experiment, the flow meter was highly accurate up to 1801"min -1 with good reproducibility. The measurement error of the gas analyser was less than 2°7o. In the second experiment, there was no significant difference in the calculated ventilation between K2 and DB. The 1702 showed no significant difference between K2 and DB with some exceptions. In the third experiment, we succeeded in the measurement of 1202 during rowing on water. The measurement of IkO: during running and playing soccer was also possible. It would seem that the present system could well be a powerful tool in the field measurement of IkO2 during various sports activities.
Key words: Oxygen uptake - Telemetry - Rowing Running - Soccer
jected to exercise using special apparatus such as a cycle ergometer or a treadmill. Attempts have been made to reduce the monitoring apparaus in size and mass so that the subject can exercise freely, allowing measurement of his or her physical response to it. Riley (1972) has measured respiratory frequency using a thermister and a telemeter. Ikegemi et al. (1988) have succeeded in the measurement of VO2 during sports activities by connecting a portable 1202 measuring device (Ballal and MacDonald 1982) to a telemetric system. However, it had the drawback of poor reliability in its measurement of larger 1202, in addition to the problems of the size of the apparatus which weighed about 4 kg and the awkward design of the face mask connected to the tube. Recently, a new portable apparatus for measuring 1202 making use of telemetry has been developed. The apparatus has an analytical component for expired air and oxygen concentration which is very much reduced in size and mass, thereby allowing the measurement of 1202 in various physical activities. The purpose of the present study was to check the reliability of measurements obtained by this telemetric 1202 measuring apparatus. The second purpose was to study the feasibility of its application in actual sport, for example boat-racing and athletics.
Method Introduction Apparatus. The apparatus used in the present study was K2
Oxygen consumption (VO2) is often measured to determine the energy cost of physical movements. In general, IkO2 has been measured by the Douglas bag method (DB), which employs such bulky apparatus as to limit the movements of the subject, thereby making it very difficult to measure VO2 on the spot during sport and other physical exercise. For this reason, measurements are often made in a laboratory where the subject is sub-
Correspondence to: Y. Kawakami
(Cosmed, Italy; Dal Monte et al. 1989). The components of the K2 system are shown in Fig. 1. The K2 system consists of a face mask to sample expired air, a sensor to measure ventilation and oxygen concentration in the air and a transmitter, an electrode to pick up heart rate, a battery, and tubes and cables to connect them to each other, and a receiver. Figure 2 shows a subject equipped with the K2 system. Total mass which the subject carried was about 850 g. Figure 3 illustrates a block diagram of the K2 system. Expired air was conveyed through the face mask to a turbine-flow meter. A photo-detector measured the velocity of revolutions of the turbine and from the velocity flow volume was calculated. Ventilation (V~) at body temperature and pressure, staturated with water
410 •
On-line transmission
-~ ...... Off-line transmission
Face m~t, gas pickup
"~ ~
turbine flow m
I Receiver Ventilation Oxygen uptake Respiration frequency Heart rate
Fig. 3. Block diagram of the K2 system. Expired air is passed through the turbine flow meter and ventilation is calculated. A sample is taken through a pick-up tube to a sensor at the transmitter to measure oxygen concentration
Fig. 1. A telemetric system measuring oxygen uptake (K2) used in the present study. The K2 system consists of a face mask, a transmitter, a receiver, an electrode for heart rate recording, a battery, and connectors
er analysis by a personal computer. Intervals of the calculation could be set at 5, 15, 30, and 60 s. The telemetry covered a distance of about 100m, unless there were obstacles between the transmitter and the receiver.
Refability o f measurements Ventilation. A syringe (3 1, Vise Medical Co., Ltd., Japan) was attached to the turbine flow meter of the K2 system. Air was pumped into the flow meter by moving the syringe lever back and forth at specific rates; three conditions of once every 4 s, once every 2s, and once every second corresponding to flows of 45 1. min - 1, 901. rain - 1, and 1801. rain - 1, respectively. The K2 system was set up to analyse flow at 15-s intervals and four measurements obtained in a minute were averaged to give a mean per minute. To examine the reproducibility, measurements were obtained in duplicate for each test. The error of measurements was calculated by the following equation: Error(%)
(measured volume - a c t u a l flow volume). 100 actual flow volume
Oxygen concentration. A standard gas of a known concentration (16.3% 02) was introduced to the pick-up of the K2 system. Before the measurement, the pick-up was left in ambient air to correct the K2 system to the FrO2 which was found at that time to be 20.9°70. The measurement was performed twice at a 10-rain interval. The following equation was used to calculate the error on measurement: Fig. 2. The K2 equipment as worn by a subject. Total carrying mass is 850 g
vapor (BTPS) was determined at the transmitter. Part of the expired air was sampled from a pick-up located near the turbine and fed into the transmitter, where oxygen concentration of expired air (Fz02) was detected by polarographic oxygen sensor. Heart rate (]'c) was obtained from R-R intervals of the electrocardiograph detected by electrodes attached to the chest. The 1)'O2 at standard temperature and pressure, dry (STPD) was calculated from lYE and FzOz by the following formula: 1202 (STPD) = lYz"(FI02 - FEO2) (STPD) where F~O2 is fractional concentration of oxygen in inspired air and was assumed to be 20.9%. The 12E, 1202, ventilatory equivalent (12E/1202), respiration frequency (fR) and fc were calculated and displayed and/or printed by the receiver. These data were also stored in the receiver for lat-
Error (%) = (measured concentration- actual 02 concentration). 100 actual 02 concentration
Comparison with the Douglas bag method. The expired air was collected from eight subjects [one woman and seven men; mean age 31.3 (SD 8.3) years; mean height 169.9 (SD 9.2) cm; mean body mass 65.3 (SD 9.5) kg] exercising on a cycle ergometer and respiring through the K2 mask and the turbine into a DB. The expired air collected in the DB was passed through a flow meter (Max Planck Respiration Gasmeter, Max Planck Institute, Germany) and gas concentration analyser (1H21, NEC San-el, Japan) to calculate 12E and 1202 every minute by the conventional method (Dill 1966). Each subject exercised on the cycle ergometer to a state of exhaustion in accordance with the method of gradually increasing loads after 5 min of rest. The load was increased by 0.5 kp (4.9 N) per minute from an initial load of 0.5 kp (4.9 N). For one woman, the load increased in 0.25 kp (2.45 N) increments.
411
Application of K2 to sport activities. To study the feasibility of the application of K2 in actual sporting events, changes of 1202 during sport were examined using the K2 in rowing, running and soccer.
Rowing. The subject was a male university rower (21 years, 175 cm, 75 kg). He rowed in a single scull on the still water course for boats. The subject put on the K2 equipment prior to starting recording on commencing exercise. The IkE, 1202, and fc of the subject were measured every 15 s. The subject was asked to increase the boat speed in a stepwise manner. The tester was positioned on the opposite bank and measured the time taken for the boat to travel a certain distance to calculate the velocity.
200 ¢,- : ".~-
150
4)
E _=
100
O >
:3
so
m O 0
t
i
i
i
50
100
150
200
Test volume (/,rain -!)
Running. The subject (18 years, 179 cm, 59 kg) was a member of a university track club and a distance runner. After warming up, he ran on the 400-m track wearing the K2 equipment having been instructed to increase speed every lap of the track. At two points on the track, two testers were posted to measure the time every 200 m for calculation of his running speed. He ran six laps in total at full speed for the final test. Then, to compare 1)'O2at the sea level and at altitude, the subject ran on a 400-m track at 1000 m above sea level under the same condition as at sea level. The IkE, lkO2,fR, IkE"1202-~, and oxygen pulse (I702"f~-~) were determined.
Fig. 4. Results of the measurement of flow volume. Values of K2 measurement were in good agreement with the actual flow from the syringe. The measurements were highly reproducible (r=0.999). l , First measurement; ©, second measurement. I l y = - 0 . 9 0 + 1.01x, r = 1.000; © y=0.95 + 1.01x, r = 1.000
120 ~0'7
100
Soccer. A member of a club team in Japan (24 years, 165 cm, 75 kg) served as a subject. Wearing the K2 equipment, he practiced some basic exercises in soccer [e.g. dribbling (free and against defense), passing, kicking, passing against defense - 3 vs 1; 1 vs 1 -1 in series. The Ikr, lkO2, fR, and fo were continuously monitored during these exercises. In addition, a specially made foot switch was employed to measure the step frequency of the right leg of the subject. The signals obtained by the step meter were stored in a small data memory device (Vine Co., Ltd., Japan) for synchronization with the K2 data.
gZ ~ "
60 40 2O 0
mA
:c_
Statistical analysis. The IkE and
~rO 2 m e a s u r e m e n t s obtained by the K2 and DB methods were subjected to a paired Student's t-test for the statistical analysis of difference. In investigating relationships between respective items of measurement, a Pearson's correlation coefficient between two arbitrary items was calculated. The level of significance was set at P
Applied
Physiology and Occupational Physiology © Springer-Verlag 1992
Reliability of measurement of oxygen uptake by a portable telemetric system Yasuo Kawakamil, Daichi Nozaki 2, Akifumi Matsuo 1, and Tetsuo Fukunaga 1 1 Department of Sports Sciences, College of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo, Japan 2 Laboratory for Sports Sciences, Faculty of Education, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, Japan Accepted June 29, 1992
Summary. The purpose of the present study was to check the reliability of measurements of oxygen uptake (lkO2) using a newly developed portable telemetry system. This system (K2) consisted of a face mask, a flow meter, a gas analyser with a transmitter, and a receiver. The total mass for the subject to carry was about 850 g. Three experiments were carried out, firstly to check the reliability and reproducibility of the flow meter and the K2 gas analyser, secondly to check the accuracy of K2 by comparing it with the Douglas bag method (DB), and thirdly to apply K2 to sports activities. In the first experiment, the flow meter was highly accurate up to 1801"min -1 with good reproducibility. The measurement error of the gas analyser was less than 2°7o. In the second experiment, there was no significant difference in the calculated ventilation between K2 and DB. The 1702 showed no significant difference between K2 and DB with some exceptions. In the third experiment, we succeeded in the measurement of 1202 during rowing on water. The measurement of IkO: during running and playing soccer was also possible. It would seem that the present system could well be a powerful tool in the field measurement of IkO2 during various sports activities.
Key words: Oxygen uptake - Telemetry - Rowing Running - Soccer
jected to exercise using special apparatus such as a cycle ergometer or a treadmill. Attempts have been made to reduce the monitoring apparaus in size and mass so that the subject can exercise freely, allowing measurement of his or her physical response to it. Riley (1972) has measured respiratory frequency using a thermister and a telemeter. Ikegemi et al. (1988) have succeeded in the measurement of VO2 during sports activities by connecting a portable 1202 measuring device (Ballal and MacDonald 1982) to a telemetric system. However, it had the drawback of poor reliability in its measurement of larger 1202, in addition to the problems of the size of the apparatus which weighed about 4 kg and the awkward design of the face mask connected to the tube. Recently, a new portable apparatus for measuring 1202 making use of telemetry has been developed. The apparatus has an analytical component for expired air and oxygen concentration which is very much reduced in size and mass, thereby allowing the measurement of 1202 in various physical activities. The purpose of the present study was to check the reliability of measurements obtained by this telemetric 1202 measuring apparatus. The second purpose was to study the feasibility of its application in actual sport, for example boat-racing and athletics.
Method Introduction Apparatus. The apparatus used in the present study was K2
Oxygen consumption (VO2) is often measured to determine the energy cost of physical movements. In general, IkO2 has been measured by the Douglas bag method (DB), which employs such bulky apparatus as to limit the movements of the subject, thereby making it very difficult to measure VO2 on the spot during sport and other physical exercise. For this reason, measurements are often made in a laboratory where the subject is sub-
Correspondence to: Y. Kawakami
(Cosmed, Italy; Dal Monte et al. 1989). The components of the K2 system are shown in Fig. 1. The K2 system consists of a face mask to sample expired air, a sensor to measure ventilation and oxygen concentration in the air and a transmitter, an electrode to pick up heart rate, a battery, and tubes and cables to connect them to each other, and a receiver. Figure 2 shows a subject equipped with the K2 system. Total mass which the subject carried was about 850 g. Figure 3 illustrates a block diagram of the K2 system. Expired air was conveyed through the face mask to a turbine-flow meter. A photo-detector measured the velocity of revolutions of the turbine and from the velocity flow volume was calculated. Ventilation (V~) at body temperature and pressure, staturated with water
410 •
On-line transmission
-~ ...... Off-line transmission
Face m~t, gas pickup
"~ ~
turbine flow m
I Receiver Ventilation Oxygen uptake Respiration frequency Heart rate
Fig. 3. Block diagram of the K2 system. Expired air is passed through the turbine flow meter and ventilation is calculated. A sample is taken through a pick-up tube to a sensor at the transmitter to measure oxygen concentration
Fig. 1. A telemetric system measuring oxygen uptake (K2) used in the present study. The K2 system consists of a face mask, a transmitter, a receiver, an electrode for heart rate recording, a battery, and connectors
er analysis by a personal computer. Intervals of the calculation could be set at 5, 15, 30, and 60 s. The telemetry covered a distance of about 100m, unless there were obstacles between the transmitter and the receiver.
Refability o f measurements Ventilation. A syringe (3 1, Vise Medical Co., Ltd., Japan) was attached to the turbine flow meter of the K2 system. Air was pumped into the flow meter by moving the syringe lever back and forth at specific rates; three conditions of once every 4 s, once every 2s, and once every second corresponding to flows of 45 1. min - 1, 901. rain - 1, and 1801. rain - 1, respectively. The K2 system was set up to analyse flow at 15-s intervals and four measurements obtained in a minute were averaged to give a mean per minute. To examine the reproducibility, measurements were obtained in duplicate for each test. The error of measurements was calculated by the following equation: Error(%)
(measured volume - a c t u a l flow volume). 100 actual flow volume
Oxygen concentration. A standard gas of a known concentration (16.3% 02) was introduced to the pick-up of the K2 system. Before the measurement, the pick-up was left in ambient air to correct the K2 system to the FrO2 which was found at that time to be 20.9°70. The measurement was performed twice at a 10-rain interval. The following equation was used to calculate the error on measurement: Fig. 2. The K2 equipment as worn by a subject. Total carrying mass is 850 g
vapor (BTPS) was determined at the transmitter. Part of the expired air was sampled from a pick-up located near the turbine and fed into the transmitter, where oxygen concentration of expired air (Fz02) was detected by polarographic oxygen sensor. Heart rate (]'c) was obtained from R-R intervals of the electrocardiograph detected by electrodes attached to the chest. The 1)'O2 at standard temperature and pressure, dry (STPD) was calculated from lYE and FzOz by the following formula: 1202 (STPD) = lYz"(FI02 - FEO2) (STPD) where F~O2 is fractional concentration of oxygen in inspired air and was assumed to be 20.9%. The 12E, 1202, ventilatory equivalent (12E/1202), respiration frequency (fR) and fc were calculated and displayed and/or printed by the receiver. These data were also stored in the receiver for lat-
Error (%) = (measured concentration- actual 02 concentration). 100 actual 02 concentration
Comparison with the Douglas bag method. The expired air was collected from eight subjects [one woman and seven men; mean age 31.3 (SD 8.3) years; mean height 169.9 (SD 9.2) cm; mean body mass 65.3 (SD 9.5) kg] exercising on a cycle ergometer and respiring through the K2 mask and the turbine into a DB. The expired air collected in the DB was passed through a flow meter (Max Planck Respiration Gasmeter, Max Planck Institute, Germany) and gas concentration analyser (1H21, NEC San-el, Japan) to calculate 12E and 1202 every minute by the conventional method (Dill 1966). Each subject exercised on the cycle ergometer to a state of exhaustion in accordance with the method of gradually increasing loads after 5 min of rest. The load was increased by 0.5 kp (4.9 N) per minute from an initial load of 0.5 kp (4.9 N). For one woman, the load increased in 0.25 kp (2.45 N) increments.
411
Application of K2 to sport activities. To study the feasibility of the application of K2 in actual sporting events, changes of 1202 during sport were examined using the K2 in rowing, running and soccer.
Rowing. The subject was a male university rower (21 years, 175 cm, 75 kg). He rowed in a single scull on the still water course for boats. The subject put on the K2 equipment prior to starting recording on commencing exercise. The IkE, 1202, and fc of the subject were measured every 15 s. The subject was asked to increase the boat speed in a stepwise manner. The tester was positioned on the opposite bank and measured the time taken for the boat to travel a certain distance to calculate the velocity.
200 ¢,- : ".~-
150
4)
E _=
100
O >
:3
so
m O 0
t
i
i
i
50
100
150
200
Test volume (/,rain -!)
Running. The subject (18 years, 179 cm, 59 kg) was a member of a university track club and a distance runner. After warming up, he ran on the 400-m track wearing the K2 equipment having been instructed to increase speed every lap of the track. At two points on the track, two testers were posted to measure the time every 200 m for calculation of his running speed. He ran six laps in total at full speed for the final test. Then, to compare 1)'O2at the sea level and at altitude, the subject ran on a 400-m track at 1000 m above sea level under the same condition as at sea level. The IkE, lkO2,fR, IkE"1202-~, and oxygen pulse (I702"f~-~) were determined.
Fig. 4. Results of the measurement of flow volume. Values of K2 measurement were in good agreement with the actual flow from the syringe. The measurements were highly reproducible (r=0.999). l , First measurement; ©, second measurement. I l y = - 0 . 9 0 + 1.01x, r = 1.000; © y=0.95 + 1.01x, r = 1.000
120 ~0'7
100
Soccer. A member of a club team in Japan (24 years, 165 cm, 75 kg) served as a subject. Wearing the K2 equipment, he practiced some basic exercises in soccer [e.g. dribbling (free and against defense), passing, kicking, passing against defense - 3 vs 1; 1 vs 1 -1 in series. The Ikr, lkO2, fR, and fo were continuously monitored during these exercises. In addition, a specially made foot switch was employed to measure the step frequency of the right leg of the subject. The signals obtained by the step meter were stored in a small data memory device (Vine Co., Ltd., Japan) for synchronization with the K2 data.
gZ ~ "
60 40 2O 0
mA
:c_
Statistical analysis. The IkE and
~rO 2 m e a s u r e m e n t s obtained by the K2 and DB methods were subjected to a paired Student's t-test for the statistical analysis of difference. In investigating relationships between respective items of measurement, a Pearson's correlation coefficient between two arbitrary items was calculated. The level of significance was set at P
