Obesity is a serious social issue worldwide. In 2005, the World Health Organization announced that approximately 1.6 billion adults are overweight by the age of fifteen, and of this population, at least 400 million adults are obese. The World Health Organization predicted that the number of overweight adults and obese adults will be approximately 2.3 billion and 700 million, respectively, by the end of 2015 (World Health Organization, 2010).

Obesity is a major risk factor of cardiac disease, cancer, diabetes, and mortality. Also, obesity can aggravate chronic diseases, such as hypertension, arthritis, cholelithiasis, and hypercholesterolemia. For these reasons, numerous efforts are necessary to prevent obesity (Wadden and Stunkard, 2002).

In general, obese adults have lower fitness levels compared to the normal population (Wei et al., 1999). In addition to risk factors that prevent physical activity, a lower level of physical fitness is an independent risk factor, which increases the risk of developing chronic diseases (e.g., cardiovascular diseases) and raises mortality rates due to all etiological factors (Adamu et al., 2006). Accordingly, in addition to decreasing physical fitness level, the risk of causing prevalence and mortality due to chronic diseases increases in obese adults.

Principles of physical education subdivide fitness into health-related physical fitness and motor-related physical fitness. Health-related physical fitness consists of cardiorespiratory endurance, muscular strength, muscular endurance, and flexibility. Motor-related physical fitness consists of power, agility, and balance (Vivian, 2006). Although there are numerous, detailed fitness categories, current researchers predominantly choose cardiorespiratory endurance when assessing fitness level (Blair et al., 2001).

Cardiorespiratory endurance (VO₂max) is indubitably a gold standard for assessing physical fitness; however, supplementary research is needed to characterize the relationship between various physical fitness measures and obesity for establishing principles physical education.

Therefore, this study sought to confirm the relationships between physical fitness variables and obesity in grown men according to age group and to emphasize the importance of physical fitness level for preventing obesity. In addition, we explored measures of cardiovascular function, which can be used to evaluate physical performance indirectly.

Subjects were 2013 Korean male adults over the age of 20. Subjects visited a health promotion center at Yang-Cheon Gu, Seoul and took a comprehensive medical and fitness test between 01-01-2006 and 12-31-2009. Subjects who consumed drugs or had a history of stroke, cancer, heart failure, angina, or myocardial infarction were excluded from the study.

Subjects' height and weight was measured, and body mass index (BMI) was calculated from these results. The study used the WHO's Asia-Pacific standard of obesity: BMI<23 = normal, 23≤BMI<25 = overweight, BMI≥25 = obese (WHO/IASO/IOTF, 2000).

Fitness assessment of cardiorespiratory endurance, muscular strength, muscular endurance, flexibility, power, agility, and balance were evaluated by VO₂max (ml·kg^-1·min^-1), grip strength (kg), sit-ups (reps/min), sit and reach (cm), vertical jump (cm), side steps (reps/30s), and standing on one leg with eyes closed (sec), respectively.

The maximal oxygen consumption (VO₂max) was obtained from YMCA submaximal test using a cycle erogometer (Helmas SH-9600K, Korea). Through gradual increase of the exercise intensity which was started 150kgm for 3min and increased via YMCA protocol, the maximal oxygen consumption (VO₂max) was estimated (Golding, 2000). Also, the heart rate of each subject was monitored using Polar HR monitor system (Polar S610, Finland).

Grip strength was evaluated by recording the average (of three measurements) full-strength power (kg) generated by subjects using a grip strength dynamometer (Helmas SH-9600D, Korea), which was adjusted to the second knuckle of their fingers.

The number of sit-ups performed in a 60 second period was recorded for subjects lying on a sit-up board (Helmas SH-9600N, Korea), using their upper body only with their knees bent at right angles and both hands held behind their necks.

For the sit and reach test, subjects sat on a flexibility measuring instrument (Helmas SH-9600G, Korea) with their heels positioned at the edge and their knees pointed upwards, and they bent forward at the waist with their hands outstretched to push the measuring instrument; the test was administered three times, and the average value was recorded.

Subjects performed a vertical jump three times on a vertical jump board (Hermas SH-9600F, Korea), and we recorded the average value in cm.

The side step was measured as follows. Subjects stood on a board (Helmas SH-9600J, Korea) with a midline (white) in the center of the board. On either side of the midline was a parallel line (white) 100 cm from the midline. Initially, subjects stood with both feet on the midline. They stepped rightwards until their right foot crossed the right line. Next, they stepped leftwards until their leftfoot crossed over the midline, and they returned to the original posture on the midline. Next, they stepped leftwards until their left foot crossed the left line. To complete the maneuver, they returned to the midline. They repeated this maneuver for 30 s, and the total frequency of repeated maneuvers was determined.

To assess the ability to stand on one leg with eyes closed, subjects closed their eyes and stood on one leg on a balance measuring instrument (Helmas SH-9600H, Korea); we administered the test three times and calculated the average time (s) until the second foot touched the ground.

For cardiovascular function, we evaluated systolic blood pressure (SBP), diastolic blood pressure (DBP), resting heart rate (RHR), double product (DP), and vital capacity.

After subjects rested comfortably for at least 10 minutes, a nurse practitioner measured SBP and DBP using a sphygmomanometer (Alpk, Japan) at the right brachial artery. These values were measured three times, and the average values were determined. Resting heart rate was determined by attaching a heart rate sensor (Polar S610, Finland) to a subject’s chest for one minute. DP was determined by SBP X HR. A vital capacity measuring instrument (Helmas SH-9600C, Korea) was attached to subject’s mouth, and the maximum exhalation value was determined after a deep breath.

All results from this study are shown as the average and standard deviation. To determine the difference in fitness and cardiovascular function between BMI groups (normal group, overweight group, and obese group), we used one-way ANOVA and administered a post-hoc test to determine noted differences related to groups. All analyses were performed using SPSS version 12.0 software (SPSS, Chicago, IL, USA). Statistical significance levels were calculated: p < 0.05, p < 0.01 and p < 0.001.

Subject characteristics are shown in Table 1. The average age of the subjects was 47.3 ± 14.3 years, ranging from 20 to 83 years; the average height was 1.69 ± 0.06 m, ranging from 1.48 to 1.91 m; the average weight was 69.6 ± 9.3 kg, ranging from 40.0 to 116.0 kg; and the average BMI was 124.43 ± 12.82 kg·m^-2 (16.46- 34.45). According to their BMIs, 623 subjects (30.9%) were of normal weight, 578 (28.7%) were overweight, and 812 (40.3%) were obese.

The relationship between BMI and health-related physical fitness is shown in Table 2. The VO₂max level decreased significantly in the obese group, except for those over 70 (p < 0.01). When calculated over the entire age range, VO₂max levels decreased in the obese group (p < 0.001). The muscular strength level increased significantly in the obese group, except for subjects in their 20s or 60s or for those over 70 (p < 0.05). Also, muscular strength increased in the obese group (calculated over the entire age range) (p < 0.001). The muscular endurance level increased in the obese group for subjects in their 30s and 40s (p < 0.05). However, averaged over all age groups, muscle endurance levels did not show statistical increases in muscular endurance of the obese group (p > 0.05). The flexibility level did not vary between age groups, but averaging across age groups showed that the flexibility of the obese group decreased (p < 0.05). However, the post-hoc test did not show any statistical difference in flexibility level between the groups (p > 0.05).

The relationship between BMI and motor-related physical fitness is shown in Table 3. The power level decreased as BMI increased for all ages except for subjects in their 40s and 60s (p < 0.05). Also the power level decreased significantly in the obese group when averaged over all ages (p < 0.001). Agility level did not demonstrate a difference as BMI increased except for subjects in their over 70 (p > 0.05). Averaging over all age groups, there was no difference in agility level (p > 0.05). The balance level decreased as BMI increased for subjects in their 20s and 30s (p < 0.01), and the balance score of the total group decreased significantly with an increase in BMI (p < 0.001).

The relationship between BMI and cardiovascular function is shown in Table 4. The SBP and DBP increased with increasing BMI for all age groups (p < 0.01). And averaging over all age groups showed that SBP and DBP increased significantly with BMI (p < 0.001). The RHR did not show a statistical difference for the obese group except for subjects in their 20s (p > 0.05). There was no difference when values were averaged across all age groups (p > 0.05). The DP increased with increasing BMI for all age groups except for subjects in their 40s (p < 0.05). Averaged over all ages, DP increased significantly with BMI (p < 0.001). Overall p-value shows that vital capacity in the obese group decreased for all ages except for subjects in their 30s and 60s (p < 0.05). All age groups, vital capacity decreased significantly as BMI increased (p < 0.01).

TAs a person becomes more obese, the body becomes less sensitive, further limiting the scope of everyday activities. This physical inactivity in turn leads to the habit of remaining seated while working. Thus, it is natural to expect that an obese person would have a lower fitness level. However, most of the existing studies restricted the key evaluation parameters of fitness level to VO₂max, which is an indicator of cardio-respiratory endurance (Meyers et al., 1991; Wei et al., 1999). Due to this limitation of previous studies, the current study evaluated other fitness parameters, in addition to VO₂max, to analyze the fitness level differences between obese and average subjects.

Among health-related physical fitness parameters, cardio-respiratory endurance was low for the obese group at almost every age, which agrees with results from previous studies (Meyers et al., 1991; Wei et al., 1999). This is likely related to the higher heart disease prevalence in obese populations. Obesity overloads the heart through increases of triglycerides and low-density lipoprotein (LDL) levels and decreases in high-density lipoprotein (HDL) levels. An overloaded heart disturbs heart function or induces heart failure (Bray, 1996). This can be interpreted as a decrease in cardio-respiratory endurance. Jette et al. (1990) demonstrated that as a person becomes increasingly obese, their cardio-respiratory endurance and muscular endurance decrease and their muscular strength rather increase. This suggests that a higher level of obesity affects everyday life, which leads to increased muscular strength. This study also supports the theory that people of higher obesity levels maintain higher levels of muscular strength. Although muscular endurance and flexibility of an obese person do not differ substantially from those of an average person, it was demonstrated that an obese person tends to exhibit lower cardio-respiratory endurance and higher muscular strength.

Of the motor-related physical fitness parameters, power and balance were shown to be lower for the obese group compared to the normal group. However, there was no statistically significant difference in agility. Since power is defined as force multiplied by speed (Vivian, 2006), we can infer that this phenomenon develops because increased weight adversely affects speed, consequently decreasing power. In addition, obesity decreases balance levels because an obese person has greater difficulty balancing his body on only one leg than a normal person. This result is further supported by the findings of Coakley et al., 1998, who tested elderly subjects. Consequently, it is demonstrated that the findings of this study are consistent with previous studies in other age groups.

Obesity stimulates the sympathetic nervous system as hyper-insulinemia develops and sodium accrues. This stimulated sympathetic nervous system increases the risk of hypertension (Mikhail et al., 1999). This implies that obesity plays a crucial role in both the initiation and development of hypertension. In line with this implication, this study also implies that obese people in every age group suffer from higher SBP and DBP than normal people. Although there was no significant difference in resting heart rate between the two groups, the burden to the myocardium (DP) appears lower for the obese group. This observation helped us to confirm the correlation between obesity and blood pressure. In addition, the obese group had a lower level of vital capacity, which implies weaker cardiovascular function.

Obesity stimulates the sympathetic nervous system as hyper-insulinemia develops and sodium accrues. This stimulated sympathetic nervous system increases the risk of hypertension (Mikhail et al., 1999). This implies that obesity plays a crucial role in both the initiation and development of hypertension. In line with this implication, this study also implies that obese people in every age group suffer from higher SBP and DBP than normal people. Although there was no significant difference in resting heart rate between the two groups, the burden to the myocardium (DP) appears lower for the obese group. This observation helped us to confirm the correlation between obesity and blood pressure. In addition, the obese group had a lower level of vital capacity, which implies weaker cardiovascular function.

The limitation of this study is rooted in the use of cross-sectional methodology. The study therefore only clarifies the correlation between obesity and physical fitness; it does not demonstrate a causal relationship between the two. Also, the data are not representative of all Korean men since the participants only resided in Seoul. However, the large number of subjects (2,000) is a primary merit of this study compared to others. When extended to a cohort study, this study may provide a solid base for more in-depth research investigating the correlation between obesity, physical fitness, and cardiovascular function for Koreans and other Asians.

The obese group had a lower fitness level, including cardiorespiratory endurance, power, and balance, but the obese group demonstrated an increase in muscular strength. In addition, we found that the obese group had higher blood pressure and weaker cardiovascular function, including DP and vital capacity, than the normal group.