SCIENTIFIC DEVELOPMENT AND EVALUATION OF THE POLAR OWNZONE® FEATURE
Sports Science and R&D/Research, Polar Electro Oy
The OwnZone determination in Polar heart rate monitors and training computers is based on heart rate variability (R-R-interval) measurement during exercise and it is a result of an extensive research co-operation between Polar Electro Oy and international research groups. Heart rate variability (HRV) has traditionally been referred only in medical research in patients. Polar got interested in HRV in the beginning of 1990 when a Russian scientist presented his findings to the Polar R&D department. In 1993 Polar started research co-operation with the Merikoski Rehabilitation and Research Center, Oulu, Finland, to find out if HRV could be useful also in healthy subjects at rest and during exercise.
The first study projects were done with sedentary subjects and with top athletes at rest. The athletes had higher HRV at rest than the sedentary subjects (unpublished). Preliminary research was also done during acute stress and anxiety on adults. Even though HRV was related to stress, no notable results for the use of Polar Electro were found. HRV was further investigated in athletes before and after resting (2 months) and training (16 weeks) periods (Mäkikallio et al. 1996). In this phase of co-operation, the division of Cardiology at the University of Oulu joined the project to ensure experienced medical advice.
The next research project was a 3 months training study with relatively sedentary subjects. The results did not show any changes in the resting HRV after training (unpublished). However, in this project the systematic repeatability in the HRV decrease during graded exercise was found. A quantitative Poincaré plot analysis method for HRV analysis was adopted (Huikuri et al. 1996). A large bicycle exercise study with 110 men started (Tulppo et al. 1996a,b). An additional trial with atropine medication (parasympathetic blockade) was performed. It was shown that the Poincaré plot method can be used as a reliable analysis method of HRV during exercise (Tulppo et al. 1996a,b). On the average, the HRV "plateau" (Poincaré plot, SD1) was found at 50-55% of maximal aerobic power (VO2max) or at about 61-65% of the maximum heart rate (HRmax). In this phase Polar and Merikoski started co-operation with the Cooper Institute for Aerobics Research in Dallas, Texas, USA. Another large sample of 120 adult men and women was studied during treadmill exercise to ensure the previous finding of HRV plateau during exercise (Tulppo et al. 1996c, Wilkinson et al. 1996a,b, 1997). The plateau occurred at somewhat higher percentage of the maximal aerobic power on the least fit subjects (57%) compared to the most fit ones (53%) (Wilkinson et al. 1996c). The HRV measures were shown to be independent of the absolute heart rate (Thompson et al. 1997). Because all aforementioned studies concluded that the HRV measures could serve as reliable markers of exercise intensity, Polar adopted the method for technical development. This resulted in the OwnZone function.
After the basic research described above, several other study projects have been carried out in co-operation with the Merikoski Center from 1997 on. A large sample of 110 males was further analyzed and age was shown to explain the HRV at rest and physical fitness during exercise (Tulppo et al. 1997a,b, 1998a). One study has been conducted on the repeatability of the HRV measures. In this work every subject was measured on four consecutive days (two days between each) to detect possible day-to-day variation in HRV during exercise (Tulppo et. al. 1998a). Another study has been done on bicycle and on treadmill both at steady-state and during interval exercise to detect possible differences between exercise modes. The results showed that the HRV plateau, as expressed in percentages of maximal aerobic power, is well repeatable, and the changes in the autonomic modulation of HR were comparable during arm and leg exercise (Tulppo et al. 1999) Three of the aforementioned studies (Tulppo et al. 1996b, 1998a, 1999) have been discussed also in the doctoral thesis of Mikko Tulppo (Tulppo 1998b).
In the early phase of the OwnZone development, a controlled trial with a SmartEdge™ heart rate monitor simulator was done in the laboratory. The OwnZone determination developed was consistent (unpublished). SmartEdge™ prototypes were used in a field validation study on 50 adults to study if the field determination of the OwnZone done by slow to fast walking-jogging warm-up protocol is consistent with the HRV plateau measured in the laboratory. The lower and the upper OwnZone target heart rate limits determined by SmartEdge™ were (mean±SD) 121±8 and 154±9 bpm and corresponded to 64±4% and 82±5% of maximal heart rate, respectively (Laukkanen et al. 1998).
In a field study on ten adults, the OwnZone determination test (incremental warm-up) was done twice a day for a month (unpublished). In this group 90% of the subjects achieved the HRV-based OZ determination (OZV) with an individual variation of 5-10 bpm. The OZ values tended to be 3-5 bpm lower when the test was done in the morning (within 2 hours from waking up) than those determined in the evening (after 6 p.m.). The lowest HR limits were obtained in cycling, and the highest in cross-country skiing. The values in walking-jogging were in between. A resting period (several days without physical activity) as well as long-duration, low-intensity recovery-type exercise seemed to increase the OZ heart rates slightly, whereas bad sleep and stress feelings tended to decrease the heart rates.
The reproducibility of individual training heart rate determined by Polar SmartEdge™ HR monitor has proven to be good (Kinnunen et al. 1998). In this study on healthy males the OwnZone determinations were repeated four times with four days of recovery in between. In a study on 50 obese men and women (mean BMI 37 kg/m2) the lower and upper OwnZone HR limits determined by the SmartEdge™ corresponded to 118 bpm (68% HRpeak) and 150 bpm (86% HRpeak) on the average (Byrne et al. 1999). On 50 non-medicated hypertensive males and females (mean age 45 years) the lower and upper HR limits determined by the SmartEdge™ corresponded to 113 bpm (66% HRpeak) and 147 bpm (85% HRpeak) on the average (Byrne et al., submitted). On 58 keep-fit middle-aged marathon runners, men and women, the OwnZone lower limit corresponded to 117 bpm (65% HRmax) and the uppr limit to 147 bpm (83% HRmax) on the average (Virtanen et al. 2000).
In 2001 Calvani et al. published data in which the Polar OwnZone was assessed on different types of cardiovascular equipments. The developed test protocol for seven different cardiovascular training machines did define OwnZone successfully in 94% of the repeated measurement on 22 healthy adults. The mean lower target HR limit for the group was 120 bpm (mean age 36 years) corresponding to 65% HRmax and 46% of VO2max. The results did show that OZ is successful in Technogym cardiovascular training equipment.
Polar OwnZone was further developed and studied using Polar M52 and M61 heart rate monitors by Kivelä et al. (2003). In this work 17 (males and females) subjects performed two different OwnZone protocols after the laboratory testing. The results, based on randomized testing order, did show that Ownzone can be reliable detected during 5 min incremental protocol from walking to jogging with 1 min speed increments. The HR limits are the same as those detected from the 10 min (5 times 2 min increment) protocol.
Further, the Polar OwnZone has been developed for weight management purposes. The HR training thresholds were studied in 40 overweight (males and females, mean age 37 years and BMI 29 m/kg2) adults (Hills et al., unpublished 2003). This study showed that Polar OwnZone for weight loss purposes did define the training thresholds at 63 and 77 % HRmax compared to those for general aerobic training and weight management being defined at 66 and 83 % HRmax.
A Swiss study (Schweizer et al. 2004) investigated the relationship between blood lactates and OwnZone heart rate limits in healthy adults. The study group consisted of 63 men (mean age 35 yrs) and 38 women (mean age 34 yrs). Subjects performed graded OwnZone test on a treadmill and on a stationary bike . Blood lactates were measured from fingertip blood samples at the end of each test step. OwnZone was determined using Polar M51™ heart rate monitor. The OwnZone heart rate limits were determined in 5-7 minutes. The average OwnZone lower and upper heart rate limits in a treadmill test were 122 and 151 bpm in men and 126 and 154 bpm in women and the mean blood lactates 1.18 and 1.94 and 1.44 and 2.36 mmol/l, respectively. The average OwnZone lower and upper heart rate limits in a bike test were 114 and 143 bpm in men and 120 and 150 bpm in women and the mean blood lactates 1.54 and 2.90 and 1.48 and 2.97 mmol/l, respectively. OwnZone heart rates were slightly higher in a treadmill test than in a bike tests in both genders. Heart rates and blood lactates were same in men and in women, even the corresponding work loads (speed and Watts) were less in women. Blood lactates both at the lower and at the upper limits of OwnZone heart rate indicate aerobic working levels in both genders in both test modes.
Kappes and Simon (19xx) did study Polar Ownzone and lactate controlled endurance training in recreational runners in 8 weeks training study with laboratory measurements. They concluded that Ownzone-controlled training is economically suitable and useful alternative compared to lactate-controlled training.
Recent studies have shown that HRV has value in individual responsiveness of cardiorespiratory training and exercise prescription (Bouchard et al.1999, Hautala et al. 2003, Tulppo et al. 2003, Kiviniemi et al. 2010). Higher vagally mediated HRV has been associated with larger improvements in cardiorespiratory fitness and HRV guided training results better fitness improvements compared to regular non-HRV-guided training in both genders (Hautala et al. 2003,Hedelin et al. 2001, Kiviniemi et al. 2007,2010).
The position stand of American College of Sports Medicine (ACSM 1998) for the recommended quantity and quality of exercise for developing and maintaining cardiorespiratory fitness in healthy adults recommends 55/65-90 % of maximum heart rate for the intensity of training. The results obtained on Polar OwnZone indicate that it can be used for feasible target heart rate zone determination in adults.
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