It is well known that obesity in young people has increased during the last 10 yr in Western countries (2). In particular, the prevalence of obesity has increased across all age and social groups during the last 20 yr (13). On the other hand, there is little scientific information available concerning changes in physical fitness of young people during the last few decades.
In the United States Army, physical fitness of recruits has not changed dramatically during the years 1978-1993 (21). Only body mass has increased significantly, whereas aerobic capacity, muscle strength, and fat-free mass have not changed (21). In young Norwegian men, the maximal oxygen uptake of entering conscripts has decreased and obesity has increased during the years 1980-2002 (7). This has also been a trend in Denmark and Sweden (19,23). In these studies, the subjects have been representatives of a selected sample of the population, and thus those results do not represent the whole population of a certain age group.
The Finnish national defense is based on compulsory military service. Every year, approximately 30,000 young men (about 95% of the age group) perform their military service. The purpose of present study was to examine the physical fitness profiles consisting of aerobic performance during the years 1975-2004, muscle fitness characteristics in the years 1982-2003, and anthropometric characteristics in the years 1993-2004 among Finnish conscripts. The sample of the present population-based study represents practically all the Finnish men aged 20 yr. The hypothesis of this study was that body weight of the conscripts has increased and that, at the same time, endurance performance and muscle fitness characteristics have decreased throughout the study period.
The data of the present study are based on the fitness test results of 387,088 young healthy men (mean age of 19.9 yr) for endurance performance, of 280,285 young healthy men for muscle fitness characteristics, and of 324,911 young healthy men for body anthropometric data. The subjects gave written informed consent to participate in the military service, which included the present tests after healthcare examinations by medical doctors. All subjects were fully informed of the procedures and possible risks of the experiment.
The data have been collected annually from several garrisons all over Finland. Thereafter, weighted means, normalized by the number of subjects in each garrison, have been collected and archived in the training division of defence staff. The running test data (N = 387,088) used for the measure of endurance performance were collected between the years 1975 and 2004. The sampling size varies from 5799 to 27,142 during the years 1975-1997 and from 16,168 to 26,761 during the years 1998-2004. Muscle fitness data (N = 280,285) were collected during the years 1982-2004, and the sampling size varies from 4515 to 26,771. The anthropometric data (N = 324,911) were collected beginning in 1993, and the range of sampling size varies between 20,689 and 30,659.
The fitness tests were conducted during the first 2 wk of military service in different garrisons all over Finland. Data were collected by local fitness officers educated according to the standards determined by the training division of the defense staff.
In the beginning of military service, body height and mass of the conscripts were measured during the healthcare examination. Body mass was measured using commercial scales with an accuracy of 100 g and with the conscripts wearing only shorts. Body height was recorded by tape measure, with an accuracy of 5 mm, with each conscript in a standing position without shoes.
Endurance performance was measured by the 12-min running test (6), performed mainly outdoors. In the winter, some garrisons had the option of conducting the tests under indoor conditions, which was recommended. Test timing and circumstances were standardized according to an expert supervisor. Conscripts were instructed to perform the 12-min run with a maximal effort and at progressively increasing running speed. Furthermore, they received safety instructions regarding their option of stopping voluntarily. The accuracy of the measurements was ± 10 m.
Muscle fitness tests consisted of sit-ups (27) and a back-muscle test to gauge endurance of abdominal, back, and hip-flexor muscles; push-ups (1) and pull-ups (22) to test physical performance of the upper extremities; and standing long jump (4) to test for explosive force production. Sit-ups, which measure performance of abdominal and hip-flexor muscles, were done with each subject lying on the floor with his hands behind the neck and directing his elbows forward. The knees were flexed at an angle of 90°, the legs were slightly abducted, and the assistant supported the ankles. During the movement, the each subjcet lifted his upper body and touched his elbows to the knees. The result of this test was expressed as the number of sit-ups completed in 60 s (27).
Push-ups, which measure performance of arm- and shoulder-extensor muscles, were started from the lowest face-down position. Each subject's hands were kept shoulder-wide and level. The fingers were directed forward, and the legs were kept parallel and close to each other. During the movement, the arms were fully extended and the torso was straightly tensed. In the second phase, the torso was lowered down to an elbow angle of 90°. The result of this test was expressed as the number of push-ups completed in 60 s (1).
Pull-ups, which measure performance of arm- and shoulder-flexor muscles, were started from the lowest position with each subject hanging straight and tightly gripping the horizontal bar. During the movement, the arms were flexed until the chin was above the bar. Thereafter, the body was lowered down to the starting position, and this movement was repeated continuously as many times as possible without stopping the movement. The result of this test was expressed as the number of pull-ups completed (22).
The back-muscle test (back-ups) measures performance of back and hip-extensor muscles. Each subject began face down in the lowest position with his hands behind the neck. The assistant supported the legs. During the movement, the upper body was lifted so that the scapulas were 30 cm higher than the shoulder level in the initial position (marked with elastic rope). Thereafter, the upper body was lowered down to the starting position. The result of this test was expressed as the number of back-ups completed in 60 s.
The standing long jump measures explosive force production of the lower limbs. The jumps, which were performed twice, started on the ground level, with the legs close to each other. Explosive bilateral takeoff was assisted by powerful swinging of the upper body and arms. The landing of each jump was performed bilaterally as well. The result of the best jump was expressed in meters as the shortest distance from the landing to the starting line (4).
The recovery time between each test was at least 5 min. Before testing, supervisors showed and taught a technically correct way to perform each test. Performance technique of each conscript was also controlled by the supervisors. The absolute results for each muscle fitness test were scored to corresponding fitness categories, from 0 (poor) to 3 (excellent). Thus, the total muscle fitness index (MFI) was the sum of five muscle fitness tests (Table 1).
Results are expressed as means of the weighted means, which were collected from all garrisons. Further statistical analyses were done using logistic regression (multinomial and cumulative logistic models). The explanatory variable was a year, which was used either as a continuous or a classified variable. The level "good" and the first studied year were used as reference categories when appropriate. The significance between physical fitness test class distributions has been analyzed by chi-square test. Correlation coefficients were calculated by the Spearman method. A P value less than 0.01 was determined as the significance level.
The mean body mass of the conscripts increased from 70.8 to 75.2 kg (P < 0.001) during the years 1993-2004 (Figure 1). Thus, the overall gain of body mass was 4.4 kg (5.9%). At the same time, the mean body height increased by 0.6 cm (0.3%).
12-min running test.
The mean distance of the conscripts in the 12-min running test increased from 2650 to 2760 m (4%) during the years 1975-1979 (Figure 2). Thereafter, it decreased by 12%, being 2434 m in 2004 (P < 0.001). The number of subjects who ran less than 2200 m decreased by 57% (P < 0.001) during the first study phase (1975-1979) but increased 5.6-fold thereafter (P < 0.001). During the same time period, the number of subjects who ran more than 3000 m first increased by 51%, but thereafter the decrease was 3.9-fold (P < 0.001). The mean running distance during the 12-min running test correlated inversely with the mean body mass (r = −0.89, P < 0.001).
The relative number of conscripts who achieved excellent and good MFI increased (P < 0.001) from 56.5 to 66.8% during the years 1982-1992. Thereafter, it decreased (P < 0.001) gradually to 41.2% in 2004 (Figure 3). Simultaneously, the number of subjects who had poor MFI showed an opposite pattern of change (from 16.5% in 1982 to 8.1% in 1992, and then to 25.2% in 2004, P < 0.001). No relationship between body mass and MFI was observed.
The sample of the present population-based study represents practically all Finnish men aged 20 yr. During the years 1975-2004, almost 95% of this age group initiated their compulsory military service. The present data indicate clearly that aerobic performance of Finnish young men has dramatically decreased during the last 15-20 yr. When this is calculated as changes in running distance during the 12-min run, the decrease in aerobic capacity has been 12%, corresponding to the calculated values from 50.4 to 43.2 mL·kg−1·min−1 (6). It must be emphasized that these values of maximal oxygen uptake (V˙O2max) are only estimations based on indirect, predictive technique, but they seem to be highly comparable with the direct determinations of V˙O2max (r = 0.897) (6). In addition, the estimated V˙O2max of 50 mL·kg−1·min−1 in the Finnish conscripts at the end of 1970s is almost the same as those of U.S. Army male recruits during the pre-initial entry training (51 mL·kg−1·min−1) (28) or Canadian (49 mL·kg−1·min−1) (15) or Japanese (51 mL·kg−1·min−1) (16) students at the same time period. On the other hand, Sharp et al. (21) have reported that the recruits entering basic training in the U.S. Army were as aerobically fit as those entering in 1993.
The primary finding of the present study, that of gradually lowered aerobic fitness from 1975 until 2004, is supported by the decreasing physical activity levels among Finnish adolescents (25). However, the reasons for the declines in physical fitness among adolescents are not distinct. Obviously, decreased hours of physical education in school do not counter this negative development in the physical fitness of children and adolescents in all social groups (24). These findings are supported by Trost et al. (26), who have reported rapidly declining physical activity among children and adolescents in a population-based study of Australian students. Furthermore, participation in continuous 20-min bouts of vigorous physical activity was low or nonexistent, and there was a clear trend for shorter 5- and 10-min bouts of moderate to vigorous physical activity. At the same time, adolescents spending more time watching television and playing computer games (9). In addition, the popularity of sporting events that develop endurance has decreased (24). Physical activity seems to decrease after the adolescent years. Fogelholm et al. (9) found that only 26% of 30-yr-old reservists have adequate physical activity to improve and maintain health-related fitness. Physical activity was also inversely associated with 12-min running test results during the military service and with the last school physical education grade. Thus, additional encouragement is necessary for more active lifestyles, to increase physical fitness and health among young and somewhat older people.
Another possible reason for the decline of endurance fitness might be the significant gain observed in body mass. During the years 1993-2004, the mean body mass of the conscripts increased by almost 5 kg, without a significant change [+ 0.6 cm] in body height. At the same time, body mass was inversely associated with endurance performance. The present results suggest, in line with earlier findings, that the prevalence of obesity has increased among adolescents (12) in Finland. In the present population-based study covering almost 30 yr, it has not been possible to measure body composition. Nevertheless, it has recently been reported that body weight was 12% and that fat-free mass was 8% greater in male volunteers recruited to the basic training in the U.S. Army in 1998 than in those entering the army in 1978 (21). There was also a 9% difference in body fat. However, the sample of Sharp et al. (21) does not represent the whole U.S. male population as comprehensively as the Finnish conscripts represent the whole Finnish male population. Therefore, comparison between these samples should be made with caution. Nevertheless, it can be suggested that the changes in endurance fitness and anthropometry could be explained by the Western lifestyle, which includes reductions in both the amount and intensity of physical activity and/or increased energy intake (13). More importantly, these lifestyle changes are occurring very early in childhood. The decreases in aerobic capacity were accompanied by a significant decrease in muscle fitness tests of the Finnish conscripts. Decrease in muscle fitness characteristics may result from a reduced amount of physical activities, but they might also be attributable to a decrease in the intensity of these activities.
Decreased muscle fitness characteristics and aerobic capacity and increased obesity have been shown to increase the risk factors for musculoskeletal injuries among conscripts (11). Furthermore, a fourfold-higher injury rate has been reported in previously untrained soldiers compared with well-trained soldiers (20). A slight increase in musculoskeletal injuries has also been observed among Finnish conscripts (5). One reason for this increase might be that conscripts" tasks such as loaded marching, which have both strength and aerobic components, may be negatively affected further by greater body mass.
The reasons for the decline in the overall physical fitness profile of adolescents are not distinct. It is obvious that the decreased hours of physical education in school curricula do not lead to improved physical fitness among pupils and adolescents (24). Therefore, if the decrease in physical fitness, combined with the increase in body mass, continues to progress among children and young adults, the incidence of several diseases will also increase. It has been demonstrated that a low level of physical activity increases the risk of coronary artery disease, hypertension, osteoporosis, certain cancers, and Type 2 diabetes (8). Obesity, inactivity, and hereditary have also been implicated as possible reasons for metabolic syndrome (17), which has been shown to be associated with poor cardiorespiratory fitness (14). Sedentary people with good fitness, on the other hand, seem to show less cardiovascular disease and a smaller risk of untimely mortality than people with poor fitness (3).
According to general recommendations to improve and maintain cardiorespiratory fitness, one has to exercise the large muscle groups for at least 20-60 min, three to five times a week, at an intensity of 60-90% maximal heart rate (18). However, the amount of activity necessary to improve fitness depends on baseline fitness. Sedentary people improve their fitness with much lower intensity and volume loads than active people. In Western countries, most people do not exercise enough in relation to their health behavior, and it is quite probable that untimely mortality caused by various cardiovascular diseases will increase in the future. Although the health-related lifestyle changes are occurring very early in the childhood years before enlistment in the army, the months spend in the service should be used to affect the health behavior of young people. Rosendahl et al. (20) have reported that the 12-wk standardized training includes 7 h of marching, 4 h of general conditioning (mostly running), and 9 h of military-specific training. Overall, the physical training consisted of aerobic, lower-extremity weight-bearing activities. Only 5-10% of the training intensity was over the anaerobic threshold. The training program led to a 16% improvement in the 12-min running test in previously untrained soldiers, but no change occurred in well-trained groups.
In conclusion, the main findings of this study revealed that physical fitness among young men has decreased and that body mass has increased during the last 15 yr in Finland. These negative phenomena may cause serious health problems among whole population in the future.
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