STUDIES IN PHYSICAL CULTURE AND TOURISM

Vol. 12, No. 2, 2005

Physical activity practised regularly and with appropriate intensity brings positive changes in functioning of the body at the psychical, somatic and morphological levels. The following paper aims at a comparison of health-related effectiveness of various types of physical education classes on the cardio-respiratory system in accordance with four pre-determined heart rate reserve zones of intensity. The research was carried in 2003 in two junior high schools in Poznań, Poland. Four types of physical education classes were monitored: outdoor track and field, team sports, gymnastics and swimming, each lasting 45-minutes. Heart rates of randomly selected pupils aged 13-14 were recorded during one physical education lesson, with the use of S 601i Polar heart rate monitors. The most effective lessons in terms of stimulation of cardio-respiratory fitness appeared to be outdoor track and field and team sports lessons, which supports earlier findings of other studies [7, 14, 17].

As it has been reported in numerous studies [6, 12, 13, 20], there is a danger of growing overweight and obesity among children, associated with poor health-related fitness. With the decreasing time allowance for school physical education the matter seems to be worsening [8]. Insufficient intensity of physical education classes in school appears to play a major role in developing health-related problems in young people. Studies carried out in Poland [14, 15, 16, 21] and other countries [4, 7, 17] indicated this growing problem, pointing at relatively little effectiveness in supporting the development of cardio-respiratory fitness in children and adolescents.

Stratton’s [17] study concerning children aged 9-15 from British public schools shows that almost 80% of lesson time do not fulfil the National Public Health Service criteria of having 50% of total lesson time with intensity HR 150 beats/min. He also indicated that the amount of time with sufficient moderate-to-vigorous physical activity increased until the pupils’ age of 11-12, and then systematically decreased to 10% of lesson time with such intensity among the 15-year-olds. As a possible explanation of this fact Stratton suggested change of school at the age of 12 and negative change in quality of lessons provided in the later years of education. Burton [4] established that during physical education lessons the average heart rate for 9-13 year-old American pupils was 142 beats/min, and 45% of lesson time failed to achieve this level. According to the study carried out by Baquet et al. [3] children from French schools exercised with intensity lower than 50% HR max for almost 40% of lesson time. Only 25% of total lesson time they exercised with intensity above the level of 60% HR max, and 10% of lesson time with intensity above the 75% HR max.

Cabak and Woynarowska [5] have recently reported, on the basis of the results of a nationwide research program, that only 35% of Polish adolescents have met the criteria of recommended physical activity (moderate-to-vigorous activity, 5 days a week). This result places Poland in the middle of the list European countries, with Ireland and the Czech Republic at the top and Belgium and France at the bottom, where children attained the recommended level of physical activity. Findings of the abovementioned research enabled the authors to state that one-fifth of male and one-fourth of female adolescents in Poland were in the increased risk category because of exceedingly low physical activity, and that the percentage of them was increasing with age. In all categories boys appeared to be more active than girls. Some researchers [13, 14, 16, 17] indicate that only moderate-to-vigorous (over 140 b/min) and vigorous (over 160 b/min) physical activity can have a positive effect on the cardio-respiratory fitness and support biological development.

Therefore, the aim of the research was to establish the proper amount of exercising time with moderate-to-vigorous intensity during selected physical education lessons of 13-14-year-old pupils in Poland.

Over 300 physical education lessons were observed and monitored for intensity of the physical workloads, all of them carried out in accordance with the methodological organization of specific types of physical education lessons. The classes were conducted by fully qualified teachers in two junior high schools in Poznań. Selected boys under study fulfilled the optimal weight (49 ± 4 kg) and height (162 ± 3 cm) standards. Also in girls, the weight (47 ± 5 kg) and height (157 cm ± 5.5) developmental standard had to be reached according to 50^th percentile ± SD [after 19].

Intensity of physical education lessons was assessed using the Polar S 610i sport-testers heart rates monitors. The sport-testers were then processed and data was downloaded for statistical and graphical analysis. To establish the significance of the differences between boys participating in the same lessons, a one-way ANOVA analysis was performed. The same procedure was undertaken separately for girls who participated together in the same lesson. The level of significance was established at p < 0.05. From this data percentage of lesson time, mean values and time allocation of intensity in four pre-determined heart-rate reserve zones of intensity were calculated.

Swaim and Edwards [19] established five zones of intensity, according to the percentage of max HR and fuel usage. In our research those zones were adopted into four zones in accordance with the percentage of heart rate reserve. Using the resting and maximal heart rate (HR max) values the heart rate reserve (HRR) was calculated as a percent of the difference between the resting and maximal heart rates. Percentage of lesson time spent in four HRR intensity zones was calculated for every type of physical education lesson examined. To establish the maximal heart rate for this age category the Ball State University Formula [19] was used, where HR max for females = 209 – (0.7) (age), which gave an approximate figure of 197 beats/min for girls; and HR max for males = 214 – (0.8) (age), gave an approximate figure of 201 beats/min for boys. Zone 1 describes loads of intensity up to 50% HRR (up to 140 beats/min), with fuel usage of 10% carbohydrates, 50-75% fat, 5% protein, and energy expenditure approximately 5-8 calories per minute. Zone 2 describes loads of intensity between 51-65% HRR (141-160 beats/min), with fuel usage of 60% carbohydrates, 35% fat, 5% protein, energy expenditure approximately 8-10 calories per minute. Zone 3 describes loads of intensity between 66-85% HRR, with fuel usage of up to 80% carbohydrates, 15-45% fat, 5% fat, energy expenditure approximately 10-15 calories per minute. All loads elevating the heart rate above 85% HRR (above 180 beats/min) were designated to Zone 4, with fuel usage of 90% carbohydrates, 5% protein, 5% fat and energy expenditure approximately 15-20 calories per minute.

The analysis of four types of physical education lessons: track and field, team sports, gymnastics and swimming was carried out. The research was part of the Polish Science Committee Research Grant 3 PO5D 04623 and received approval of the Research Ethics Committee.

The highest average heart rate was observed in classes of team sports in boys and it equated 162 beats/min; however, the most intensive appeared to be the track and field classes in boys, with the average of 161 beats/min and a considerable amount of time with moderate-to-vigorous intensity.

The intensity curve presented in Figure 1 shows a relatively shallow ups and downs characteristic for the athletic interval endurance training. The heart rate values ranged from 125 to 190 beats per minute. Figure 2 shows that during a 45-minute lesson in an open-field area the 13-14-year-old boys under study spent almost 89% of total lesson time with intensity over 50% of HRR (over 140 beats per minute), considered to be sufficient for development of cardio-respiratory fitness. Maximum heart rate was recorded at 194 b/min. Exercising time with submaximal intensity (Zone 3) was 32.6% and with maximal intensity of Zone 4 amounted to 19.5%. The examined boys exercised with intensity lower than 140 beats/min, only 5% of the total lesson time, mainly in the final stage of the lesson. Average energy expenditure for the boys during outdoor track and field classes was 520 kcal (± 60 kcal).

Figure 1. Curves of average heart rate during an outdoor track and field lesson in 13-14-year-old boys (p=0.186)

A comparison of several physical education lessons, including team sports, shows differences in the curves of intensity. Lessons where playing small-sided games took place featured a characteristic curve with a few minutes of play resulting in high intensity, and a few minutes of rest time resulting in a drop of the intensity curve. This is represented in Figure 3 by the highest intensity curve. Lessons where technical and tactical skills were being developed had flatter curves of intensity. Figure 4 indicates that during physical education lessons, including team sports, the examined boys practiced with intensity supporting development of cardio-respiratory functions (intensity over 140 beats/min) for more than 50% of lesson time. Generally, in team sports classes the boys achieved the level of moderate-to-vigorous intensity and above for 32 minutes, which was approximately 70% of the overall time. The average heart rate was 162 beats/min, and the average energy expenditure in physical education lessons, including team sports, was 420 kcal (± 88 kcal). Interestingly, the least effective in promoting cardio-respiratory fitness were volleyball classes with the average heart rate for boys reaching 130 beats/min and for girls 136 beats/min (but not present in this study).

Gymnastics lessons usually require discipline and well-organized lesson structure to avoid injuries, especially while using professional gymnastic apparatus. However, this additional organizational obstacles affect the level of intensity. Figure 5 shows flat lines of intensity in gymnastics lessons (not including gymnastics jumps). In the skills practice lessons almost 80% of total lesson time was spent by the pupils listening, preparing and learning new gymnastic-specific movements, which explains not so high intensity during such lessons. In the research the examined boys exercised with intensity sufficient for cardio-respiratory fitness (over 50% HRR), only for about 10 minutes (21.4%) of total lesson time (Fig. 6). The average heart rate was 125 beats/min, reaching the maximum of 150-155 beats/min. The average caloric burn-out for boys was 274 kcal (± 60 kcal).

Figure 2. The percentage of lesson time spent with different intensity during an outdoor track and field lessons in 13-14-year-old boys [%]

Figure 3. Curves of average heart rate during a team sports lesson in 13-14-year-old boys (p=0.019)

Figure 4. The percentage of lesson time spent with different intensity during team sports lessons in 13-14-year-old boys [%]

Figure 5. Curves of average heart rate during gymnastics lessons in 13-14-year-old boys (p=0.011)

Figure 6. The percentage of lesson time spent with different intensity during gymnastics lessons in 13-14-year old boys [%]

Figure 7. Curves of average heart rate during swimming lessons in 13-year-old girls (p=0.01)

Figure 8. The percentage of lesson time spent with different intensity during swimming lessons in 13-year-old girls [%]

Figure 7 presents intensity curves characteristic of swimming lessons with a few lengths of swimming and a resting break system of organization. Interestingly, the swimming classes resulted in a very low caloric burn-out and low energy expenditure amounting on the average to 173 kcal (± 35 kcal). Also, the average heart rate over the duration of a 45-minute swimming lesson was low, not exceeding 140 beats/min, which has been shown in Figure 8. This was probably due to the specific environment – the cooling water in the pool slows down the heart beat, but also while swimming in the horizontal position, the heart rate response to physical efforts is often lower, compared to similar workloads undertaken in the vertical position. The average heart rate in the examined 13-year-old girls was 105 beats/min. It appeared that the least effective in achieving the 50% HRR criterion of cardio-respiratory time appeared to be the swimming classes, but certainly having other health-related benefits like, for example, reduced body weight in water enabling undertaking physical efforts of longer duration.

The research supports earlier findings of other authors [7, 16, 17, 21] on decreasing intensity of physical education in school, insufficient for maintaining biological development of growing children and adolescents. This, in the long term, may result in poor motor achievements, overweight or obesity, and other health-related problems in young generations. Health consequences related to reduced physical activity in adolescents concern many risk factors such as cardiovascular (dyslipidemia, elevated systolic and diastolic blood pressure), endocrine risk factors (insulin resistance, abnormal metabolism), life style factors (low fitness, low physical activity level, low movement competence), orthopaedic risk factors (accelerated, abnormal growth) and psychosocial factors (low self-esteem and socio-economic status). There are also strong indications of carrying obesity from the adolescent age into adulthood and elderly stages of life [for extended review of the evidence see Vouri 2004].

Improvements in cardio-respiratory fitness require activities with intensity sufficient for supporting delivery of oxygen to the working muscles, with the frequency, duration and level of intensity adequate to the age and general motor capacities. The most recent recommendation for achieving such level of intensity is associated with the criterion of 50% heart rate reserve [1, 9].

According to our findings (supported also in other works 7, 17, 11) invasion games such as basketball, football, handball, floorball and most likely other team games, including small-sided games (2 vs. 2, 3 vs. 3) are reasonably effective in promoting cardio-respiratory fitness. The explanation may be found in the amount of major muscle groups required in such sports due to the translocation (invasion into the opponents’ part of the field) and high level of general motor abilities required.

In the research the most intensive and effective in supporting cardio-respiratory fitness appeared to be track and field classes with an average of 161 beats/min, and invasion team games, with the average of 162 beats/min. It is also worth mentioning that the least effective were the volleyball classes or boys – 130 beats/min and for girls 136 beats/min (although not included in this presentation). Gymnastics lessons seemed to have a very low cardio-respiratory impact on one’s health too, with the average heart rate of 125 beats/min and relatively little time of exercising with intensity over 140 beats/min – 21%. The swimming classes did not seem to be intensive, and the average heart rate was low, only 105 beats/min; however, we have to be careful with drawing negative conclusions, as is has to be remembered that such results were due to the influence of other factors, such as physiological response of the body (heart) to the specific water environment and generally a relaxed state of psychological well-being in the water.

In consideration of all the results we must realize that there are some other factors influencing these results, such as individual somatic differences within the same age group or gender-depended relations of morphological parameters and motor abilities, increasing with the secular changes in the body mass and height. Therefore, only boys and girls within 50% ± SD in body mass and height were selected for the research. The ANOVA analysis of boys’ heart rates proved that there were no significant differences between consecutive team sports classes (p=0.019) and gymnastics classes (p=0.011) for boys and swimming classes for girls (=0.01). The difference in the case of the boys’ outdoor track and field classes was p=0.186.

Bar-Or [2] found that girls’ heart rates were approximately 20 beats/min higher than boys’ in the same intensity workloads. This finding can be also supported by the results of the research carried out by Lutosławska [10], who found that endurance among pubertal girls was significantly lower when compared with boys due to the lower haemoglobin level in the blood. As for the improvement in delivering of stimuli sufficient for development of cardio-respiratory functions, the findings of Mandigout et al. [11]can be very valuable. Mandigout et al. [11] found that only a programme with continuous activity organized on the basis of three sessions per week (but not on two), with 25-35 minutes, at an intensity higher than 80% of maximal heart rate during each session, enhances VO2 max in prepubertal boys and girls. However, this level of intensity is difficult to maintain in every physical education lesson, which was shown in our research. Intensity of physical education lessons in Poland seems to be insufficient (except for outdoor track and field and team sports) to promote development of cardio-respiratory functions, and therefore requires changes in quality and quantity of the provided workloads. Better class-room organization and management will certainly improve the quality and intensity of any lesson, even those considered less effective in stimulating aerobic fitness such as volleyball, gymnastics and net team games. Health-related effectiveness of the lesson depends on the aims and methods of realization and, therefore, the evaluation of its effectiveness should vary as well. It has to be reminded that cardio-respiratory fitness, although important as a health-related aim, is not the only goal of physical education, and that there are other equally important goals, like development of locomotor skills, movement competency, moral development or building up of intrinsic motivation towards physical activity for the entire life span. These goals should also be implemented during the same lessons of physical education or otherwise within school health-related education. Cardio-respiratory fitness can also be stimulated by several short bouts of activity during the day, which would accumulate in 20-25 minutes of activity, not necessarily during the PE classes themselves. An increase in the total amount of daily physical activity of required intensity could be achieved through quality health-related education, but to change pupils’ behaviour and attitude towards physical activity, school lessons need to be a source of inspiration for further self-development of every young person, considering their strengths, weaknesses, interests and other capacities.